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Tel.X Ni-Cd batteries for telecom networks Technical manual
March 2013
3
Contents
1 Introduction .............................................................................................5
2 Electrochemical principles ..........................................................................5
3 Tel.X construction .....................................................................................6
3.1 Cells and modules ..................................................................6
3.2 Battery string ........................................................................7
4 Features and benefits ................................................................................8
4.1 Long life ...............................................................................8
4.2 Reliability ..............................................................................8
4.3 No watering maintenance ........................................................8
4.4 Resistance to electrical abuse ..................................................8
5 Cell voltages ............................................................................................9
6 Capacity and baseline performance ...........................................................10
7 Discharging ...........................................................................................11
7.1 Internal resistance ...............................................................12
7.2 Maximum inrush charge current ............................................12
8 Charging ...............................................................................................13
8.1 Constant voltage charging .....................................................13
8.2 Float operation ....................................................................14
8.3 Reconditioning charge...........................................................15
8.4 Reconditioning charge procedure ...........................................15
9 Effect of temperature on performance .......................................................16
10 Gassing .................................................................................................17
10.1 Ventilation practice ...............................................................17
11 Storage and shelf life ..............................................................................18
11.1 Charge retention ..................................................................18
12 Service life .............................................................................................20
12.1 Effect of temperature on calendar life ......................................20
13 Special operation ....................................................................................21
13.1 Cycling ...............................................................................21
13.2 Temperature shock ..............................................................21
13.3 Prolonged power outage and over discharging ..........................22
14 Abusive operation ...................................................................................24
14.1 Short circuit ........................................................................24
14.2 Thermal runaway .................................................................24
14.3 Mechanical abuse ................................................................25
14.4 Corrosion and carbonates .....................................................25
15 Paralleling with other battery string technologies .........................................26
16 Battery sizing .........................................................................................27
17 Appendix A – Parallel currents ..................................................................28
18 Glossary ................................................................................................29
4
5
In contrast, in the case of the lead-acid battery, the positive and negative active materials chemically react with the sulfuric acid electrolyte during the charge/discharge process. This results in an unavoidable aging and dilutes the acid solution when the battery is discharged. This is most significant in lead-acid batteries that use a limited amount of electrolyte such as AGM (Absorbed Glass Mat) type VRLAs. The lack of acid at the end of the discharge may limit the battery’s capacity.
In a Tel.X cell, the support structure of both electrodes includes materials such as nickel plated steel or pure nickel metal. These materials are relatively unaffected by the surrounding electrochemistry. Because of that, it will retain good conductive and mechanical characteristics throughout its useful life.
In the case of the lead-acid battery, the basic support structure of both plates is lead. Lead is susceptible to corrosion resulting in positive plate growth and a mechanical weakening of the structure which leads to a gradual loss of conductivity and available capacity. In extreme cases corrosion, in the lead-acid cell, can cause an open circuit and thus cause complete loss of battery string support. This cannot happen to a Tel.X battery since the support structure of both electrodes are relatively unaffected by the electrochemistry.
The charge/discharge reaction of a nickel-cadmium battery is given as follows.
During discharge, the positive electrode is the cathode. The nickel oxy-hydroxide active material is reduced to nickel hydroxide. Simultaneously, on the negative electrode, or the anode, the cadmium metal is oxidized to cadmium hydroxide. As the oxidation and reduction reaction continues, the voltage decreases. When most of the active material is consumed, the voltage declines more rapidly. Eventually the cut-off voltage is reached and the discharge stops.
During charge, the reverse reaction takes place. As the active material
Introduction and Electrochemical principles
1 Introduction
Saft Tel.X batteries are inherently safe to handle and operate. As long as Saft’s information and instructions are followed, they will last longer and function more reliably than other storage batteries.
To obtain optimum performance and operating life and to ensure safe handling and operation, Saft’s information and instructions must be followed. Other documents not included in this manual are:
■■ BIS (Battery Information Sheet)
■■ Tel.X Installation and Operation Manual and sheets
In addition, studying this Technical manual will give you a better understanding of Tel.X batteries. Tel.X batteries are designed for standby operation in telecom networks and are particularly suited for uncontrolled temperature environments.
2 Electrochemical principles
The Tel.X battery uses nickel hydroxide (NiOH) as active material in the positive electrodes, and cadmium hydroxide (CdOH) as active material in the negative electrodes. An aqueous solution of potassium hydroxide (KOH) is used for the electrolyte. The nature of the Tel.X electrochemistry promotes stable performance over its life, it exhibits fail safe behaviour under abuse and inhibits life limiting reactions like electrode corrosion.
The electrolyte in the Tel.X is not acidic as with lead-acid batteries. The electrolyte is an alkaline aqueous solution of about 24% KOH. Additionally, there are small added quantities of lithium hydroxide (LiOH) and sodium hydroxide (NaOH) to improve life and high temperature performance. The electrolyte is only used for ion transfer and is not chemically changed or degraded during the charge/discharge cycle. It is sometimes referred to as the “liquid wire”. Like other flooded nickel-cadmium batteries, in the Tel.X the amount of electrolyte does not restrict the available capacity.
re-charges the voltage increases. It continues to increase as active material accepts charge current. Eventually, the cell voltage rises to a level where hydrogen is evolved at the negative electrode and oxygen is evolved at the positive electrode. When this occurs, it is referred to as overcharging. Water is consumed in the electrolyte when gas exhausts from the cell. The battery maintains its state of charge by continuous float charging at the recommended set point voltage. By limiting the set point charge voltage as prescribed by the installation and operation manual, the eventual float charging current decreases and is maintained at low level. As a result, the water losses can be kept at a minimum. In this way, the Tel.X maintains a high state of charge and eliminates water topping over its useful life.
Referring to charge/discharge reaction above, note that the KOH, a component of the aqueous electrolyte, is not mentioned in the reaction formula. This is because it is neither consumed nor produced during charge or discharge. Its only function is ion transference. In other words, it is a “liquid wire” that continues to support the electrochemical reactions with the same level during the discharge or the charge process. This is one main reason why electrode corrosion in the Tel.X is eliminated.
According to the reaction, water (H2O) is produced during charge and consumed during discharge. With the flooded design of the Tel.X, the volume of electrolyte is large enough so that the change in its concentration is relatively small. The specific gravity is not affected in any significant way. With a relatively stable electrolyte concentration, a low internal resistance can be maintained even at the end of discharge. This results in the enhanced feature of the Tel.X to be fully discharged and utilize its active material well. This is a main reason why the Tel.X has the enhanced feature of only a minimal derating of discharge performance at very low temperature since the risk of freezing electrolyte is decreased.
Thus, through its electrochemistry, the Tel.X battery string has a very stable behavior, a long life, a high level of performance in a wide range of temperature and a much greater resistance to abuse conditions than lead-acid batteries.
2 NiOOH + 2 H20 + Cd ➞➞ 2 Ni(OH)2 + Cd(OH)2
Charged Discharged
6
3 Tel.X construction
3.1 Cells and modules
A Tel.X module (or battery block) is constructed using single cells connected in series. The completed module assembly utilizes handles, covers and a stainless steel cradle.
Tel.X construction
The width (W) and height (H) are fixed at 105 mm (4.125”) and 254 mm (10.0”), respectively, but the length (L) varies depending on how many cells are assembled in the module. See the Tel.X product data sheet for complete details.
■■ Handles provide two lifting points on each end of the module. Made of fabric, they can be positioned out of the way during installation.
■■ Module covers are held securely to the module providing complete protection from dirt, moisture and inadvertent short-circuiting.
■■ Intercell links complete the series connections of each cell in the module. They are nickel plated and NoOx is applied to each.
■■ Tabs carry the current from each plate (both positive and negative) to the terminals and are permanently welded to the terminals and the plates.
■■ Cell vent allows the cell to vent gases, maintains 2 psi internal pressure and prevents spilling of electrolyte.
■■ Terminals provide a connection surface to carry the current from the cell. They are secured to the cell top with a clamp ring and sealed using o-rings. It uses an M6x1 bolt and is compatible with a standard ¼" (6.4 mm) ring terminal.
■■ Separator system keeps the plates isolated from each other and makes electrolyte available, in its highly porous structure, between the plates.
■■ Negative plate uses cadmium active mass to provide useful capacity.
■■ Positive plate uses nickel active mass to provide useful capacity.
■■ Cradle mechanically finishes the battery module assembly (or battery block). It’s a welded construction of stainless steel.
H
L
W
7
3.2 Battery string
A Tel.X battery string is assembled using modules and various interconnection types. The assembly in Figure 3.2.1 shows a typical 48 V nominal battery string. There are 4 modules interconnected. With a total of 38 cells connected in series (for a normal 48 V system), three of the modules are 10-cell and one is an 8-cell and in this case they are placed adjacent to each other. The cables use 6 AWG (13.3 mm2) untinned copper with ¼" (6.4 mm) ring lugs that are nickel plated and crimped on each end. A heat shrink finishes each. The cables are normally routed from the back of one module to the front of another. This allows a “front accessible” connection point. In some cases, a back to back connection is used in order to finish the string with front connecting points for the power bus.
Another module connection method is shown in Figure 3.2.2. When modules are placed in line with each other, a strap link is used. It’s nickel plated metal and has an insulation sleeve.
Any variation of module sizes can be used for a string. When a 24 V nominal assembly is made, 19 cells are used.
Only use the same Tel.X type within a string assembly. However, connecting a Tel.X string on a power bus with other technologies and other size Tel.X can be considered. See the section Paralleling with other battery string technologies.
Figure 3.2.1. A typical 48 V nominal battery string is shown. It uses cable connections to allow front accessible connection points during field assembly.
Figure 3.2.2. When inline modules are placed, a strap link is used to interconnect.
(+) bus connection
(-) bus connection
6 AWG (13.3 mm2) cable, back to back connection
6 AWG (13.3 mm2) cable, back to front connection
M6x1 bolt and washer
8
4 Features and benefits
The Tel.X design provides long and reliable life in standby applications without requiring regular maintenance. These are the main factors that make its total cost of ownership the lowest.
4.1 Long life
Industrial nickel-cadmium batteries continue to demonstrate operating life in excess of 30 years on continuous float charge and in uncontrolled environments. For example, they have been used for nearly a century in outdoor rail signal applications where they have an excellent track record protecting life and valuable property.
There are many examples of 20 – 30 year old batteries capacity test results consistently higher than 90%.
4.2 Reliability
Nickel-cadmium batteries are the batteries of choice for the world’s airlines and rail transit systems, and are generally used when reliable power is required to protect people’s lives, valuable property or to avoid costly downtime.
Tel.X batteries are reliable because of their stable chemistry. They do not suddenly fail and the most common lead acid ailments such as corrosion, plate growth and sulfating are not present in this battery system.
Based on the long field history of nickel-cadmium batteries and using standard calculation techniques, the MTBF results indicate more than 1,000,000 hours.
4.3 No watering maintenance
When the Tel.X is operated as recommended (refer to Saft I/O manual) in a standby power application, no watering maintenance will be required. This is true for all environments of outside plant remote terminal applications. Several field test batteries and ongoing lab test results, operating at an average temperature of + 40°C (+ 104°F) were conducted. Results indicate that the battery could be left for over 20 years without a top up. Aside from normal power routines like checking bus voltage and
Features and benefits
visual inspection, no other regular maintenance is required.
4.4 Resistance to electrical abuse
Abusive conditions that will permanently damage lead-acid batteries will have little to no effect on Tel.X batteries. Occasional overcharging may result in more water usage but will have no effect on life. Undercharging or lack of charging during extended storage may lead to a temporary loss of capacity due to self discharge. This loss is reversible and full battery capacity will be restored after proper charging. The battery can be discharged completely and left with a load for days without damage. After inflicting the Tel.X with all the common abusive conditions it will re-charge, float charge and discharge normally. For more details, see sections “Special operation” and “Abusive operation”.
9
End of Discharge Voltage
Nominal Voltage
Average Discharge Voltage
Open Circuit Voltage
Float Voltage
Reconditioning Charging
48 V String Voltage (38 cells)
Cell Voltage
36
38
40
42
44
46
48
50
52
54
56
58
60
62
0.9
5
1.0
0
1.0
6
1.1
1
1.1
6
1.2
1
1.2
7
1.3
2
1.3
7
1.4
2
1.4
8
1.5
3
1.5
8
1.6
5
5 Cell voltages
The nominal voltage for the nickel cadmium couple is 1.20 V per cell. This value was originated by the normal mid-discharge level of voltage during a nominal discharge rate. It is characterized over a wide range of cell designs and over a wide range of applications. In this way, it is a generic value. It is mostly used where nominal estimations about some characteristic metrics are made like Wh or Wh/l.
In a more practical look, the actual cell voltage values can vary depending on the mode of operation. Figure 5.1 shows the typical voltage spectrum range of the Tel.X based on a few modes of operation giving cell values and string values scaled for a 48 V nominal system.
The average discharge voltage is in the range of 1.23 to 1.26 V per cell (46.7 V to 47.9 V) for discharge rates equal to 3 to 12 hours of runtime and after 24 hours of re-charge time. See Figure 7.1 in the section Discharging for typical discharge voltage curves.
There are two ranges for charging the Tel.X. The typical in service charging method uses a single set point voltage between 1.43 to 1.45 V per cell (54.6 V to 55.1 V). At this single set point, the string is re-charged following a discharge event as well as float charged during standby operation. However, in a special procedure of high voltage overcharging (for details see Reconditioning charge section), the cell voltage will be in the range of 1.65 V per cell when completing the charge.
Figure 5.1. Typical voltage spectrum of the Tel.X.
Cell voltages
10
Table 6.1. Definition of baseline performance of the Tel.X at 25°C (77°F).
6 Capacity and baseline performance
For telecommunication batteries like the Tel.X, capacity is commonly measured in ampere-hours (expressed using Ah). This corresponds to the quantity of electricity that can be supplied under specified conditions. On discharge, it is the amount of stored chemical energy delivered to a load. For a constant discharge current, it is equal to the value of current multiplied by the total time of discharge.
The symbol “C” is used for capacity. Under specific conditions of test, the value of C varies since the available capacity from a battery is dependent on the charging method used, the temperature of the battery and the rates of charge and discharge. For the Tel.X, two baseline values of C are defined based on different industry standards. Table 6.1 summarizes the test conditions that establish the baseline performance values for two industry references.
The industry reference of GR-3020 includes the generic requirements for nickel-cadmium batteries used in the outside plant telecom applications. The capacity evaluated in accordance with GR-3020 establishes a baseline level of performance. This value of capacity is indicative of the level of performance when used in telecom applications while using ideal test conditions. The symbol C8 is used to represent this value since the test conditions evaluate the level of capacity to provide 8 hours of runtime. The baseline performance is most useful for comparisons across product lines in order to contrast their relative performance differences. It is also used to establish standard discharge
Capacity and baseline performance
curves. The actual performance can deviate from this baseline value depending on the rate of discharge, conditions of charging (available current, voltage set-point and duration) and battery temperature.
In practical use, the C8 capacity is used as a baseline value. It is adjusted since the actual capacity varies due to the departure from standard conditions of test. For example, telecom applications are normally operating the battery in standby mode that includes long periods of charging (or float charging). This deviation from 24 hours of charging slightly reduces the available capacity due to the prolonged charging effect. As a result, published values of capacity are nominally lower than the baseline value. This value is referred to as the nominal capacity and uses the same symbol, C8. The nominal capacity is referenced as the 100% performance level of the Tel.X.
The industry reference of IEC 60623 is an industrial specification and includes the requirements for flooded nickel-cadmium batteries. This method of test establishes the C5 capacity. It represents the best available capacity of the Tel.X due to a constant current charging method with no upper voltage limit combined with a lower end of discharge voltage. The C5 capacity is referred to as the rated capacity. It is rarely used as a baseline performance reference with regards to telecom applications.
Charge Discharge
Industry Reference
Associated Symbol
Type Temp. Time Current (A)
Voltage limit*
Current (A)
EODV**
GR-3020 C8 Telecom 25°C (77°F) 24 h 0.15 C8 1.45 0.125 C8 1.10
IEC 60623 C5 General 20°C (68°F) 7-8 h 0.20 C5 none 0.20 C5 1.00
* Volts per cell ** End of discharge voltage per cell
11
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
1.45
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%Capacity (% of C8)
Ave
rage
Cel
l Vol
tage
34
36
38
40
42
44
46
48
49
51
53
55
48
V S
trin
g Vol
tage
0.083 C8A (C8/12)
0.125 C8A (C8/8)
0.25 C8A (C8/4)
0.50 C8A (C8/2)
1 C8A (C8/1)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
0 1 2 3 4 5 6 7 8 9 10 11
Hours of Runtime
Ava
ilabl
e Cap
acity
(% C
8)
1.14 V per cell1.10 V per cell1.05 V per cell1.00 V per cell
34
36
38
40
42
44
46
48
49
51
53
55
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
Capacity (% of C8)
48
V S
trin
g Vol
tage
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
1.45
Ave
rage
Cel
l Vol
tage
25°C (77°F)0°C (32°F)- 20°C (- 4°F)
Figure 7.1. The voltage characteristics of the Tel.X are shown with typical discharge curves at 25°C (77°F).
7 Discharging
The ability to utilize the charged capacity while discharging is a function of a few main factors when operating at + 25°C (+ 77°F).■■ Level of current; the higher the current the lower the available capacity.
■■ Level of cutoff voltage; the higher the cutoff voltage the lower the available capacity.
Based on standard conditions of test that establish the baseline performance, Figure 7.1 shows the typical discharge voltage characteristics at different rates of discharge. The Tel.X is designed and suited for long runtimes. This is apparent when comparing the 0.25 C8A curve with the 1 C8A curve, where in this range the Tel.X utilizes more than 95% of its stored capacity. Additionally, it utilizes more than 80% of its nominal capacity at the 0.5 C8A rate to an end voltage of 1.10 V per cell (42 V per string). That is equivalent to about 1.6 hours of runtime. When the current is increased to the 1 C8A rate, the available capacity decreases to approximately 20% to the same end voltage. That’s equivalent to approximately 12 minutes of runtime.
The available capacity is a function of discharge rate and end voltage. This is shown in Figure 7.2. It illustrates the available capacity (% of C8). It is shown that the charge capacity is utilized above 80% at 2 hour runtimes and higher for 1.10 V per cell.
Rate tables are used to summarize performance and provide useful values for sizing. Values of constant current and constant power are included. Refer to the Tel.X product data sheet for the published performance.
The available capacity is also a function of the battery temperature. As the temperature decreases below + 25°C (+ 77°F), the ability to utilize the charged capacity decreases. This is due to an increase in the cell’s internal resistance. Figure 7.3 shows several discharge curves at the 8-hour rate (0.125 C8A or C8/8A). The rate of decrease of available capacity increases faster as the temperature decreases below 0°C (32°F).
For further details about temperature and performance, see section Effect of temperature on performance.
Figure 7.2. The available capacity of the Tel.X as a function of discharge rate and end of discharge voltage is shown at 25°C (77°F).
Figure 7.3. The voltage characteristics of the Tel.X at the 0.125 C8A (8-hour rate) at different temperatures.
Discharging
Capacity (% of C8)
Capacity (% of C8)
Hours of Runtime
12
1.151.37
2.35
1.88
0.0
0.5
1.0
1.5
2.0
2.5
3.0
TLX 80 TLX 100 TLX 150 TLX 180
mill
i-Ohm
s pe
r ce
ll
Figure 7.1.1. The average internal resistance of the cell is labeled for each Tel.X type at 25°C (77°F) with inter-cell connections included. The maximum variation of ±8 % is indicated by the limit bars and includes the state of charge and mode of operation factors.
7.1 Internal resistance
The internal resistance defines how much voltage change will occur when a load is applied or a change of load is applied. The calculated product of the applied current, in amps, and value of internal resistance shown in Figure 7.1.1 estimates the cell voltage drop, in mV per cell, immediately after the application of the load.
The value of internal resistance depends on the type of Tel.X cell. As the capacity increases, the internal resistance decreases.
The internal resistance also varies with the state of charge and is non-linear when under a continuous load. It varies by approximately ±8 % in the useful capacity range of the Tel.X depending on the state of charge reached during the continuous mode of operation (discharge or charge).
Figure 7.1.1 gives the average internal resistance including the inter-cell connections of each Tel.X cell type. It indicates a ±8 % window of values.
For an example, to estimate the internal resistance of a 48 V nominal battery string, the average value of internal resistance multiplied by 38 cells is suitable.
7.2 Maximum inrush charge current
In the case where the rectifier current capacity or control does not limit the re-charge current, the Tel.X will accept charge current limited by its internal resistance. When powered on, the inrush charge current will have a maximum value over a few seconds and will decrease rapidly over a few minutes as charge continues. The value of this inrush charge current depends on the open circuit voltage of the battery string. The open circuit voltage varies depending on the state of charge of the battery string, i.e., delivered with standard discharged state or delivered with fully charged state. The state of charge will also depend on the period of time the string was in storage and at what temperature it was stored at. See Table 7.2.1 for a summary of maximum inrush charge currents at 20 to 25°C (68 to 77°F). The inrush values are given for the normal operation parameters of 1.43 Vpc charge set point (54.4 V on a 38-cell string) and maximum storage times (see Tel.X Installation and Operation Manual for more details).
Values are ±9% depending on normal variation of cell internal resistance.
Table 7.2.1. The maximum inrush currents for the Tel.X.
Type Delivered standard (10% SOC) Delivered charged (full SOC)
Less than 1 week storage
(Amps)
1 year of storage (Amps)
Less than 1 week storage
(Amps)
2 months of storage
(Amps)
TLX 80 72 123 38 64
TLX 100 90 154 48 80
TLX 150 124 212 66 109
TLX 180 148 252 78 130
13
0.00
0.05
0.10
0.15
0.20
0.25
50
51
52
53
54
55
56
1.32
1.34
1.37
1.39
1.42
1.45
1.47
A = (Rate Factor) x (C8)
0%
20%
40%
60%
80%
100%
120%
0 2 4 6 8 10 12 14 16 18 20 22 24Hours
0.20 C8 current limit
0.10 C8 current limit
0.00
0.05
0.10
0.15
0.20
0.25
50
51
52
53
54
55
56
1.32
1.34
1.37
1.39
1.42
1.45
1.47
A = (Rate Factor) x (C8)
0%
20%
40%
60%
80%
100%
120%
0 2 4 6 8 10 12 14 16 18 20 22 24Hours
0.20 C8 current limit
0.10 C8 current limit
0.00
0.05
0.10
0.15
0.20
0.25
50
51
52
53
54
55
56
1.32
1.34
1.37
1.39
1.42
1.45
1.47
A = (Rate Factor) x (C8)
0%
20%
40%
60%
80%
100%
120%
0 2 4 6 8 10 12 14 16 18 20 22 24Hours
0.20 C8 current limit
0.10 C8 current limit
8 Charging
Tel.X battery strings can be charged with constant voltage or constant current.
In telecom applications, constant voltage is the common method used. Single set point rectifiers are normally installed. In this case, the rectifiers share the DC output current by providing charge current to the battery strings and discharge power to the telecom load. Constant voltage charging methods are most appropriate when operating the Tel.X in a standby application where emergency power is provided infrequently.
Constant current is not commonly used with telecom applications. Considered as an optional way of charging, constant current is the best way to get the Tel.X battery string fully charged and in the shortest period of time. This method may require off-line charging or implementation of an auxiliary charging device while installed in the telecom application. Constant current charging methods are most adequate where frequent and deep discharge cycling may be encountered or a reconditioning charge is required. See Chapter 10 concerning Gassing and Table 8.1.1.
8.1 Constant voltage charging
For constant voltage charging, several rectifiers connected in parallel may be wired or plugged in to the main DC bus. Similarly, several battery strings may be connected to the same bus sharing the available re-charge current. This method employs a single set point voltage level and typically does not include current control.
Understanding that there is an operating tradeoff between water consumption and set point voltage is important. Maintaining the voltage as low as possible minimizes the amount of overcharge and as a result water consumption will be at a minimum. But, at low voltage set point, after a discharge it will take longer to bring the batteries back to full capacity. In this case, the batteries may, for some period, operate below 100% state of charge. If frequent discharge cycling is encountered, the available capacity may operate at below 100% state of charge for a longer period of time.
This will not reduce battery life, but full battery capacity may not always be available. The charging voltage should therefore be set according to the
Charging
Table 8.1.1. Single set point voltage for the Tel.X.
Cell 24 V nominal
48 V nominal
Number of Cells in series 1 19 38
Recommended set point 1.43 27.2 54.4
Maximum set point 1.45 27.6 55.1
Minimum available charging current for each battery string 0.10 C8A
Minimum re-charge time with minimum available current 24 h
Figure 8.1.1. Constant voltage re-charge characteristics of the Tel.X at 25°C (77°F).
recommended set point. This will obtain a high level of recharge in the shortest amount of time and keep the water consumption at a normal level. The Tel.X is designed to not require water additions over its useful life if operated within recommended limits.
Operating limits of the Tel.X are given in Table 8.1.1. Operating within the maximum and minimum limits allows the Tel.X to perform with little deviation from published performance while maintaining maintenance free operation.
Figure 8.1.1 shows the re-charge
48
V S
trin
g Vol
tage
Cel
l Vol
tage
Rat
e Fa
ctor
%C
8 A
vaila
ble
Cap
acity
Hours
14
characteristics for constant voltage set point of 1.45 V per cell and at 25°C (77°F).
As the charge continues the state of charge increases and eventually the current will decrease.
Temperature Compensated Voltage control (TCV)
Temperature compensated voltage control is not recommended. The Tel.X should have its set point voltage at one level no matter what the operating temperature. With the voltage set at one value, the current will vary as the battery temperature changes. This is normal and it is also beneficial since the changing current compensates appropriately to keep the battery string at a high state of charge.
If temperature compensated voltage control is active, it will not be detrimental to the Tel.X however the battery string may operate at less than 100% state of charge. This is because when temperature compensation is active, it reduces the set point voltage automatically when the temperature increases. When this happens, the current going into the battery string, during float charge, decreases. Since the Tel.X actually needs higher current at higher temperature during float charge, with a relatively lower current, the state of charge will eventually stabilize lower. As a result, at the same level of discharge power, the runtime will decrease.
If temperature compensated voltage is operated on the Tel.X, the reduced state of charge is reversible and can be recovered. A reconditioning charge method can be implemented to recover the capacity most efficiently.
Parallel connected strings and re-charging
Make sure to take care about parallel connected battery strings and the distribution of current, particularly when installing and powering battery strings with a low state of charge. See Appendix A – Parallel currents for more details.
Never connect and power battery strings in parallel with unknown or different states of charge. In this case, if connected, the strings will pass a high level of current until the voltages equilibrate.
Table 8.2.1. Typical float current values for the Tel.X.
TLX 80 TLX 100 TLX 150 TLX 180
Typical float current at 40°C (104°F) is normally less than 57 mA 73 mA 106 mA 130 mA
Battery requires action if the float current is persistently measured to exceed at any
temperature
380 mA 490 mA 700 mA 860 mA
8.2 Float operation
For standby operation in telecom applications, battery strings normally float charge over 99% of their useful life. The Tel.X was designed for this type of operation. When operated at the recommended set point voltage, it is optimized to have the best trade-off between re-charge time, state of charge and water consumption. The purpose of float charging is to maintain a high state of charge during standby operation. During float charging, the float current stabilizes to offset the self-discharge. Any excess float current is overcharging and consuming water. After a discharge event and following re-charge, the float current is, for all practical purposes, stabilized after 1 week.
A measurement of the float current is a good way to determine the Tel.X state of health. As it ages, the self discharge increases which, in turn, increases the float current. If the value exceeds the normal sanction, then further investigation is necessary. If the string is determined to have a poor state of health, the eventual replacement of the Tel.X battery string can be handled on a routine basis over a few months time as there is no risk of unsafe operation even when the string is unhealthy.
15
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.000 5 10 15 20 25 30
8.3 Reconditioning charge
A high voltage charging method is required to conduct a reconditioning charge. See section 8.4 concerning the procedure.
A reconditioning charge may be necessary for batteries that have been subjected to various forms of electrical abuse or irregular operating conditions such as:■■ long storage periods (more than 1 year)
■■ frequent deep discharges with limited constant voltage recharge
■■ cycling at high temperatures with insufficient recharge
As Tel.X batteries represent a relatively high initial investment, batteries that appear to have low capacity should not be discarded. A reconditioning charge may completely restore the battery to full capacity. If facilities for such work are not available within your company, call your Saft representative for advice.
Table 8.4.1. Charging current
TLX 80 TLX 100 TLX 150 TLX 180
Capacity C5 (Ah) 83 103 152 185
Current C5 (A) 16.6 20.6 30.4 37.0
Figure 8.4.1. High voltage charge
8.4 Reconditioning charge procedure
In case we need to check the IEC capacity (IEC 60623) the following procedure must be applied:
1. Make sure that the string is discharged fully to 1.00 V/cell with C/5A and each cell is at the same SOC.
2. Charge at constant voltage with a maximum voltage set point of 1.65 V per cell and current limit of C5/5A as mentioned in the Table 8.4.1.
3. Continue charging for a minimum of 30 hours (a maximum of 1 week). See Figure 8.4.1.
4. Maximum 30 minute pause is allowed.
5. Apply the load mentioned in the Table 8.4.1 and discharge to a cut-off of 1.0 V per cell (measured at the string terminals) and verify that the 5 hr of runtime are delivered.
V
C-rate
%C
16
30%
40%
50%
60%
70%
80%
90%
100%
-20 -15 -10 -5 0 5 10 15 20 25 30 35 40
Temperature (ºC)
% o
f Pub
lishe
d Per
form
ance
-4 5 14 23 32 41 50 59 68 77 86 95 104
Temperature (ºF)
Table 9.1. The main factors that impact the performance of the Tel.X with a change in temperature are summarized.
Charging factors
Float charging factors
Discharging factors
Less than 20°C (68°F)
Charge efficiency increases resulting in higher state of charge with the same
level of current
Charge acceptance decreases, due to an impedance increase, resulting in lower charge current at the same
voltage
Voltage decreases, due to an impedance increase, resulting in less utilized charged capacity to the same
end voltage
20°C to 25°C (68°F to 77°F) Baseline performance according to published values
Higher than 25°C (77°F)
Charge efficiency decreases resulting in lower state of charge with the same
level of current
Charge acceptance increases, due to an impedance decrease, resulting in higher
charge current at the same voltage
Voltage slightly increases, due to an impedance decrease,
resulting in slightly better utilized charged capacity to the same
end voltage
9 Effect of temperature on performance
As the temperature deviates from 25°C (77°F) the Tel.X’s ability to charge and discharge is affected. The impact of temperature on the performance is summarized in Table 9.1.
The overall result of the summarized factors is a deviation from the baseline performance. To estimate expected performance in an uncontrolled environment, a temperature derating factor should be used when sizing the capacity. Figure 9.1 gives the derating factors for the Tel.X in the range of - 20°C (- 4°F) to 40°C (104°F). The derating factors given in Figure 9.1 are estimated using Telcordia GR and IEEE test methods and are compiled in order to provide practical approach to estimating the Tel.X performance.
Effect of temperature on performance
Figure 9.1. The temperature derating factors for the Tel.X are shown. They can be applied for published discharge rates of 4 hours to 24 hours.
17
Table 10. Tel.X measured maximum gassing rates.
Operation type
Volts/cell
T (ºC / ºF) Cell type H2 per cell
(l/h)H2 per 38 cell
string (l/h)
Floa
ting
1.45
25 / 77
TLX 80 0.000018 0.00068
TLX 100 0.000023 0.00087
TLX 150 0.000033 0.00125
TLX 180 0.000040 0.00152
45 / 113
TLX 80 0.00095 0.03610
TLX 100 0.00122 0.04636
TLX 150 0.00176 0.06669
TLX 180 0.00216 0.08208
Rec
ondi
tioni
ng
1.65
25 / 77
TLX 80 0.04763 1.810
TLX 100 0.06124 2.327
TLX 150 0.08847 3.362
TLX 180 0.10888 4.137
45 / 113
TLX 80 0.56 21.2
TLX 100 0.72 27.4
TLX 150 1.04 39.5
TLX 180 1.28 48.6
Table 10.1.1. Forced ventilation for EN 50272-2.
Equation (1) Q = (0.05) x (n) x (Igas) x (Cn) x (10-3)[m3 / hour]
n = Number of cells operating either in parallel and/or series
Igas = See Table 10.1.2.
Cn = Tel.X Nominal Telecom Ah
10 Gassing
During normal operation, hydrogen gas, oxygen gas and water vapor are exhausted through the cell vent. When exhausted, the water is incrementally consumed from the electrolyte. Water vapor is a result of evaporation. Hydrogen and oxygen gas results from electrolysis during periods of overcharging. It should be noted that gassing from electrolysis only occurs during overcharging and float charging. It will not occur during battery storage, normal discharging and normal re-charging.
The Tel.X uses a low pressure valve in the cell vent. This valve maintains approximately 1 to 2 psig (0.07 to 0.14 bars gauge) of internal cell pressure. The valve regulates the exhaust and reduces water consumption by increasing the oxygen recombination. The slightly higher cell pressure also reduces the rate of water evaporation. The primary mechanism of water consumption is gassing through electrolysis.
During overcharging, electrolysis occurs with a fixed stoichiometry. That is, for every 3 Ah of overcharge, 1 cm3 of water is consumed and dissociated into gas. And for every 1 cm3 of water electrolyzed and exhausted, approximately 690 cm3 of oxygen and 1380 cm3 of hydrogen are generated on the positive and negative plates, respectively.
Not all the gas generated on the plates is exhausted. A part of the oxygen and hydrogen gas is recombined back into water. When this occurs, the net reaction replenishes some of the water that was initially consumed. The gasses that do not recombine will eventually exhaust from the cell. During float charging the current is very low, the recombination rate is in excess of 95 % and the proportion of the current that generates oxygen gas and recombines back to water is quite large.
The Tel.X operates as a standby battery and is float charging or overcharging at a low rate over most of its life. See Table 10 for maximum hydrogen gassing rates. The reported values were measured in accordance with GR-3020.
Gassing
10.1 Ventilation practice
A Tel.X battery should never be installed in a sealed space without any ventilation. Industry specifications associated to ventilation practice can be found in GR 487 and EN 50272-2. Additionally, the gas recombination level of the Tel.X was tested in accordance with NFC 58311. It has a recombination level higher that 95 %. For GR 487, the maximum hydrogen gassing rates are given in Table 10. For EN 50272-2, the ventilation equation is given in Table 10.1.1 and the Igas parameters are given in Table 10.1.2.
The following tables provide information needed by the ventilation standards most commonly used in different areas of the world.
Table 10.1.2. Tel.X parameters for EN 50272-2 ventilation calculation.
Operation type Voltage (V per cell)
Igas (mA/C8 Ah at 25ºC / 77ºF)
Floating 1.45 0.30
Reconditioning 1.65 2.30
18
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0 30 60 90 120 150 180 210 240 270 300 330 360
Days since 10% repolarization charge
Ope
n Cir
cuit V
olta
ge (V/ce
ll)
11 Storage and shelf life
Tel.X batteries are shipped at 10% state of charge. The state of charge is set by what’s commonly called a re-polarization charge. This low state of charge allows the Tel.X batteries to be stored for extended periods of time without maintenance. When stored at that level, the self discharge is very low. The maximum storage period, without maintenance, is 1 year if stored at - 20°C to 35°C (- 4°F to 95°F).
While being stored, the Tel.X cell self discharges. As the cell self discharges its voltage will decrease. Figure 11.1 represents the average open circuit voltage (OCV) evolution of a cell over a period of 1 year. Day zero represents the same day the re-polarization charge set the state of charge at 10%.
The self discharge rate will increase with higher temperature and decrease with lower temperature. As a result the measured OCV will vary compared to the values given in Figure 11.1.
It is not recommended to store the Tel.X in a fully charged state. The main problem with storing at a high state of charge is the positive electrode self discharges at a different rate than the negative electrode. If this is allowed to continue for too long, the difference in the electrodes’ state of charge will grow. These effects are bigger with higher temperature. As a consequence, the available capacity, after charging with a constant voltage set point, may result in a lower available capacity. In order to recover this difference in electrode state of charge and return to normal expected capacity, a reconditioning charge may be necessary. See section Charge retention for more information about the impact of long storage in the fully charged state.
11.1 Charge retention
Self discharge tests were conducted on the Tel.X in accordance with GR-3020. The performance level after storage was also evaluated and the Tel.X met the minimum required sanctions.
Self-discharge is mostly due to electrochemical side reactions in the cell and the rate of self discharge depends on the storage temperature.
Figure 11.1. The measured evolution of the open circuit voltage (OCV), of the Tel.X, during a 1 year stand at 25°C (77°F) is shown.
Table 11.1.1. Summary of charge retention results for Tel.X after 6 months of storage.
°C (°F) Retained Capacity (% of C8)
Actual Capacity (% of C8)
23 (73) 81% 101%
45 (113) 31% 89%
Storage and shelf life
19
Test 2007-02204/01/2008
Cycle 5
Confidential - SAFT PROPRIETARY 7/3/10 / Excel Graphs BW-2 SD.xls / Figure 11.1.2
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0 10 20 30 40 50 60 70 80 90 100Capacity (%C8)
Vol
tage
(V/ce
ll)
23°C 45°C
Test 2007-02203/01/2008
Cycle 4
Confidential - SAFT PROPRIETARY 7/3/10 / Excel Graphs BW-2 SD.xls / Figure 11.1.1
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
0 10 20 30 40 50 60 70 80 90 100Capacity (%C8)
Vol
tage
(V/ce
ll)
23°C 45°C
Figure 11.1.1. After a 6 month storage in the full charged state, the discharge voltage as a function of %C8 is shown at 23°C (73°F) and 45°C (113°F). These discharges determined the retained capacity after storage.
Figure 11.1.2. The first discharge cycle after the 6 month storage is shown. These discharges determined the actual capacity after storage.
With higher temperature, the self discharge rate increases.
Before storage, the battery was fully charged. After 6 months in storage and without re-charge, the battery was discharged at the 8-hour rate to a cut-off voltage of 1.10 V/cell. This was the retained capacity. After, the battery was re-charged at 1.45 V/cell for 24 hours and immediately discharged at the 8-hour rate to 1.10 V/cell. This was the actual capacity. Table 11.1.1 summarizes the results after storage at two temperatures for a new and unused battery.
At 23°C (73°F) storage temperature, the retained capacity was 81%. That means that approximately 19% was lost due to self-discharge. The actual capacity, after storage, was found to be 101% of nominal capacity.
At 45°C (113°F), the retained capacity was 31% or approximately 69% was lost due to self-discharge. In this case, the rate of chemical side reactions were increased with temperature, as expected. After a re-charge and discharge, the actual capacity was 89% of nominal capacity. This lower than nominal result suggests that storage, in the fully charged state, at high temperature should be avoided. Even so, the capacity is not irreversibly lost and can be recovered by performing a reconditioning charge.
Figures 11.1.1 and 11.1.2 show the discharge characteristics of the retained capacity and after re-charging for the actual capacity.
The results of this test demonstrated compliance to GR-3020:
■■ Charge retention after 6 months was 81% and well within the specified minimum of 50%.
For the 45°C (113°F) test, reconditioning charge cycles were done in order to demonstrate the ability to recover capacity. After reconditioning, the actual capacity was recovered from 89% to 100% of nominal capacity.
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70 80 90 100
Capacity (%C8)
23ºC (73ºF) 45ºC (113ºF)
Capacity (%C8)
23ºC (73ºF) 45ºC (113ºF)
20
VRLA VRLA with with ““sudden deathsudden death””
Tel.XTel.X experiences linear degradationexperiences linear degradation
Time in standby modeTime in standby mode
Available CapacityAvailable Capacity
80% End of Life80% End of Life
Service life
12 Service life
A battery’s useful life can be characterized by the amount of cycles it can perform, when mostly in cycling mode or the amount of time it can operate, when mostly in standby mode. Telecom applications can involve either mode, but in most cases, it’s normally more indicative of a standby mode. The expected calendar life normally limits the useful life of a Tel.X in telecom applications.
The end of life (EOL) is typically defined by a 20% loss of capacity. This irreversible capacity leaves only 80% of it’s beginning of life performance. For the Tel.X, as the aging and loss of capacity continues, it experiences linear degradation. This means that the Tel.X will continue to provide useful power in a predictable way over its useful life and beyond. For comparison, when VRLA’s have lost 20% of capacity, the available power may decrease very rapidly after. It can be unpredictable and the risk of a sudden death event may be eminent. Figure 12.1 compares the general trend of capacity loss over their useful life.
12.1 Effect of temperature on calendar life
Tel.X batteries are designed to last 20 to 30 years at 25°C (77°F). At higher operating temperatures, the battery’s life will be reduced. However, the temperature effect on life is much lower for the Tel.X than it is for a lead-acid battery. At lower temperature, the battery life is expected to be as long as the 25°C (77°F).
According to various independent organizations such as Eurobat, IEEE and Telcordia (Formerly Bellcore), for approximately every 10°C (18°F) increase in battery temperature above room temperature, the reduction in life for a lead-acid battery is 50%. The corresponding life reduction for the Tel.X battery is only 20%.
This reduction in lifetime for a Ni-Cd battery and, for comparison, VRLA battery is illustrated graphically in Figure 12.1.1. Figure 12.1.2 shows the lifetime of Tel.X and of a VRLA battery at different temperatures, as typically used in remote telecom applications.
Figure 12.1. The comparison of end of life characteristics of the Tel.X and VRLA.
Figure 12.1.1. The comparison of minimum calendar life as a percentage of 25°C (77°F) life at elevated temperature.
Figure 12.1.2. Years of lifetime comparison of a “10 year” design VRLA with Tel.X.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
25 30 35 40 45 50 55 60
Temperature (°C)
% o
f 2
5°C
(7
7°F
) Li
fe
77 86 95 104 113 122 131 140
Temperature (°F)
VRLA
Tel.X
0
2
4
6
8
10
12
14
16
18
20
25 30 35 40 45 50 55 60
Temperature (°C)
Year
s of
Life
77 86 95 104 113 122 131 140Temperature (°F)
VRLA
Tel.X
Temperature (ºC)
Temperature (ºC)
% o
f 2
5°C
(7
7°F
) Li
feYe
ars
of L
ife
Temperature (ºF)
Temperature (ºF)
⁓
⁓
⁓
⁓
21
Special operation
13 Special operation
13.1 Cycling
Batteries in telecom applications are generally on float charge and normally see very few deep discharges. The effect of cycling on the life of a Tel.X battery in a typical telecom application is therefore negligible.
The Tel.X is optimized for continuous float charging conditions. If it is operated in a frequent cycling application, it will be necessary to apply a higher charging voltage to maintain the battery at a high state of charge (the same applies to lead acid batteries). The required charging voltage and frequency to apply the higher charge voltage will depend on depth of discharge and frequency of discharge. The level of charge voltage required will often be higher than the normal voltage available in telecom applications. Offline charging or auxiliary charging devices may be necessary in this case.
Frequent deep cycling of batteries on float charge at 1.43 V per cell (54.4 V for a 38 cell battery) will gradually decrease their capacity. The decreased capacity is temporarily faded and is reversible. Full capacity can be restored with a reconditioning charge.
Likewise, repeated cycle testing (deep discharges) in the field of the same battery string with only float voltage recharge should be avoided. Each recharge will gradually return less capacity to the battery, particularly at high temperatures. If more than one deep discharge has been performed in succession, a reconditioning charge may be needed to bring the battery back to full capacity. Repeated cycle testing does not represent normal telecom operating conditions and should only be conducted in a lab or a workshop with appropriate reconditioning chargers.
13.2 Temperature shock
The Tel.X can withstand temperature extremes without compromising its performance. Two tests were conducted using Telcordia GR-63 as a guideline. Figure 13.2.1 compares the discharge voltage curves after temperature shock at + 70°C (+ 158°F) and - 40°C (- 40°F) with the baseline
Figure 13.2.1. The cell voltage as a function of discharge capacity is compared with its baseline performance after a temperature shock at both - 40°C (- 40°F) and 70°C (158°F). The performance difference is not noticeable.
performance before the shock. In both cases, the performance compared almost identically with the baseline. The actual capacity and mid-discharge voltage, in both cases, were the same as the baseline; 100% of C8 and 1.25 V/cell, respectively.
In another extreme test example, it was shown that the Tel.X could start operating after being dormant or cold soaked at - 40°C (- 40°F) for an extended period of time. The rationale behind this test is to demonstrate that the Tel.X is compatible in a few extreme operational scenarios. The scenarios include (a) initial installation in the winter after a cold storage and (b) restarting a system (or restoring
A/C power) after a power outage or disruption of service during the winter. In both cases, the equipment could begin charging the battery at a very cold temperature.
With the test conducted in accordance with GR-3108 Class 3 Equipment, the results showed that the battery can operate without a safety event, without sustaining damage and without any deterioration of functional performance. Figure 13.2.2 shows the behavior of the battery at startup. As charging continued, the environment temperature was allowed to increase to 20°C (68°F) over a period of 7 days. Approximately 126% of its nominal capacity was accepted in this period.
Figure 13.2.2. The first 6 hours after applying power to the TLX- 150 at - 40°C (- 40°F) are shown. It accepted a significant level of current at the cold temperature.
Test 2008-00108/02/2008
Cycle 6
Confidential - SAFT PROPRIETARY 7/3/10 / Excel Graphs BW-2 SD.xls / Figure 13.2.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3 4 5 6
Time (h)
Cur
rent
(A
)
-50
-40
-30
-20
-10
0
10
20
30Te
mpe
ratu
re (°C
)
Current
Temperature
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
%C8
Cel
l Vol
tage
Baseline After 70°C Shock After -40°C Shock Baseline After 70ºC (158ºF) Shock After - 40ºC (- 40ºF) Shock
22
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 110%
% C8 Ah
Cel
l Vol
tage
Baseline -40°C Cold Start
% C8Ah
At the end of 7 day test, the battery was discharged at the 8-hour rate to 1.10 V/cell. Figure 13.2.3 shows the discharge voltage as a function of % of nominal capacity. The performance after the cold start compared to the baseline performance.
It is safe to start-up and operate the Tel.X at very cold temperature without impacting its performance.
13.3 Prolonged power outage and over discharging
From time to time, grid power outages can last for many days. Back up power, in remote terminal telecom cabinets, is normally designed for about 4 to 8 hours of runtime. This raises the question of whether or not a low voltage disconnect is required in order to protect the battery from too deep of a discharge for too long of a time. For the Tel.X over discharging and prolonged power outages (up to 1 week) does not pose a problem.
A test procedure was conducted that simulated a prolonged power outage. The capacity was measured before and after the prolonged power outage. Table 13.3.1 summarizes the test results. Five test modules were used and each was designated S1 through S5. During step 4 in the sequence and including all applied load durations of 1 to 7 days, the battery cells were discharged fully and the measured cell voltage was 0.0 V per cell before removing the resistor. When comparing the baseline results with
the post results it’s evident that the capacity change was insignificant since the variations are within the expected variation limits of normal testing.
An insignificant loss of capacity was noticed from the results in Table 13.3.1.
Figures 13.3.1 and 13.3.2 show the discharge voltage for the baseline and post performance. The average cell voltage is shown and is plotted against the % of capacity from the Baseline performance. The voltage characteristics were unchanged.
With up to 1 week of applied discharge
load, equal to a 1 week grid power outage, the Tel.X was completely discharged. With the applied load constant for the duration, the capacity loss was insignificant and the battery operated normally after 1, 2, 3 and 7 days of power outage. The discharge voltage characteristics were also unchanged. The results were the same for 23°C (73°F) and 40°C (104°F). The use of LVD’s in this case is not required.
The Tel.X operates normally and without performance degradation after a prolonged power outage up to 1 week and at a high environment temperature.
Table 13.3.1. Summary of test results and comparison of discharge (DChg) capacity change are shown after long time power outage at 23°C (73°F) and 40°C (104°F).
Sequence S2 S4 S3 S1 S5
1. Baseline Telecom Discharge 100%
2. Baseline IEC Discharge 100%
3. Application Charge ➞■Resistor Discharge time at different temperatures
1 day @ 23°C (73°F)
2 days @ 23°C (73°F)
3 days @ 23°C (73°F)
7 days @ 23°C (73°F)
3 days @ 40°C (104°F)
4. Post Telecom Discharge (% of Baseline) 98.6% 100.4% 99.9% 99.3% 100.6%
5. Post IEC Discharge (% of Baseline) 100.0% 98.8% 99.2% 99.3% 99.1%
% Change Telecom Discharge - 1.4 + 0.4 - 0.1 - 0.7 + 0.6
% Change IEC Discharge 0.0 - 1.2 - 0.8 - 0.7 - 0.9
Figure 13.2.3. After applying power at - 40°C (- 40°F) and continuing charge for 7 days while the temperature equilibrated to 20°C (68°F), the discharge after compared closely to the baseline performance before.
Baseline - 40ºC (- 40ºF) Cold Start
23
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Telecom Baseline
Ave
rage
Cel
l V
Telecom Post S1
Telecom Post S2
Telecom Post S3
Telecom Post S4
Telecom Post S5
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
% IEC Baseline
Ave
rage
Cel
l V
IEC Post S1
IEC Post S2
IEC Post S3
IEC Post S4
IEC Post S5
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% Telecom Baseline
Ave
rage
Cel
l V
Telecom Baseline S1
Telecom Baseline S2
Telecom Baseline S3
Telecom Baseline S4
Telecom Baseline S5
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
1.30
1.35
1.40
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
% IEC Baseline
Ave
rage
Cel
l V
IEC Baseline S1
IEC Baseline S2
IEC Baseline S3
IEC Baseline S4
IEC Baseline S5
Figure 13.3.1. A comparison of the telecom discharge voltage is shown for all 5 modules (S1 through S5). No significant change was noticed after the deep discharge.
Figure 13.3.2. A comparison of IEC discharge voltage is shown for all 5 modules (S1 through S5). No significant change was noticed after the deep discharge.
Telecom Capacity Before:
IEC Capacity Before:
Telecom Capacity After:
IEC Capacity After:
24
Increasereaction
rate
Exothermicreaction
Heatgenerated
Increasetemperature
Heat escapeslows reaction
Abusive operation
14 Abusive operation
Tel.X batteries are able to sustain electrical abuse. Occasional complete discharges, charging in reverse, overcharging, short circuits, lack of charging, etc., have little effect. However, continuous and excessive abuse may cause some maintenance problems and should be avoided.
14.1 Short circuit
The short circuit current depends on several factors such as battery capacity, state of charge and temperature. A fully charged Tel.X battery string can deliver a short circuit current of about 10 C8A. This means that a 100 Ah Tel.X battery string can deliver up to 1000 A in a short circuit situation. This is more than enough to melt any metallic watchstraps or jewelry, and such objects must therefore be removed before handling batteries to avoid serious burns. All charged batteries must be handled with respect and care.
The Tel.X was tested in accordance with GR-3020 and the results meet the minimum safety requirements.
14.2 Thermal runaway
The Tel.X has demonstrated compliance to the thermal runaway requirements of GR-3020. It was also confirmed that while under abusive operating conditions like electrolyte dry-out on top of the GR-3020 requirements, the Tel.X was fail safe.
Thermal runaway is a process by which an exothermic (heat generating) chemical reaction goes out of control and often ends with a meltdown, fire or even an explosion. Figure 14.2.1 shows how a thermal runaway process can feed itself to its detrimental end. In aqueous batteries used in telecom applications, the exothermic reaction is oxygen recombination. During normal float operation, oxygen recombination is a large percentage of the float current. In the Tel.X, it is greater than 95%. Even so, with a normally low float current (0.16 to 0.34 mA/Ah), the amount of heat generated is insignificant. An equilibrium of safe operation exists while the battery maintains its high state of charge. On the other hand, abnormal or abusive operating conditions like higher than
Figure 14.2.1. Schematic view of the thermal runaway process is shown and how it can feed itself to a destructive end.
recommended voltage or dry out of the electrolyte can cause the normal float current to increase significantly. When this occurs, the oxygen generated on float charge also increases. In turn, if the oxygen recombination is allowed to increase and the heat escape is too low, thermal runaway can be set in motion.
The Tel.X limits the oxygen recombination reaction with its separator system. This concept inhibits the amount of oxygen which is transported between the electrodes. Further, even with a low pressure valve in the cell cap raising the oxygen partial pressure inside the cell, the transport of oxygen is adequately hindered in all normal and abusive conditions of operation. As a consequence, the oxygen recombination reaction is limited and the thermal runaway process is maintained at a safe level.
As another artifact, temperature compensated voltage (TCV) control is not required with Tel.X operation. A constant level of voltage allows the float current to increase with temperature which benefits the ability to maintain a high state of charge.
One of the stringent requirements of GR-3020 states that if 13% of the cells (5 cells out of 38 cells for a 48 V nominal string) are shorted to 0 V, the string continues floating operation for 8 hours. The ambient was controlled to begin the test with the string temperature at 40°C (104°F). For the Tel.X, that means operating at
1.67 V per cell (rather than the normal 1.43 V per cell). The results of the 8 hour test are shown in Figure 14.2.2. The float current initially increased and eventually stabilized to less than Cn/65, approximately 40 times higher than with normal operation at the same ambient. The string temperature stabilized at 45°C (113°F) which demonstrates compliance with GR-3020. It also verifies that the built in design features of the Tel.X govern safe operation in the most abnormal operating conditions.
Further, in order to demonstrate the fail-safe nature of the Tel.X, the test was taken one step further. Electrolyte was removed to represent a level where the reserve was consumed. This simulates a condition where a dryout may be eminent. In particular, it would be a likely condition towards the end of the Tel.X’s useful life. The string then continued operation at 1.67 V per cell. After about approximately 480 hours of continuous float charging at 1.67 V per cell the current and in turn the temperature began increasing. Figure 14.2.3 shows the string temperature, current and voltage in this time frame. After a total of about 550 hours, the string temperature reached a peak of 63°C (145°F) and the float current peaked at Cn/6. After, the current and temperature both decreased back to normal as the cells continued to dryout over a 700 hour period. The internal resistance increased enough to eventually create an open circuit in the string. In summary, under abnormal
25
20
25
30
35
40
45
50
55
60
65
70
0 1 2 3 4 5 6 7 8High Voltage Float Charge Time (hours)
Tem
pera
ture
(°C
)
1.60
1.61
1.62
1.63
1.64
1.65
1.66
1.67
1.68
1.69
1.70
Ave
rage
Cel
l Flo
at (V)
C-Rate (1/h)
Average Cell Voltage
Ambient Temp.
String Temp.
0
10
20
30
40
50
60
70
80
470 480 490 500 510 520 530 540 550 560
Continued High Voltage Float Charge Time (hours)
Tem
pera
ture
(°C
)
1.60
1.61
1.62
1.63
1.64
1.65
1.66
1.67
1.68Ave
rage
Cel
l Flo
at (V)
C-rate Amps (1/h)
String Temperature
Average Cell Voltage
Figure 14.2.2. The measured parameters in this 8-hour period of high voltage float charge demonstrate compliance with GR-3020.
Figure 14.2.3. The fail safe nature, without catastrophic incident, is evident as shown with the measured current and temperature of the Tel.X. While transitioning to dry out, the high voltage float operation eventually returns to normal levels of current and temperature.
operating conditions and even when given the best opportunity for oxygen recombination and promoting the onset of thermal runaway, the Tel.X design demonstrated safe operation.
14.3 Mechanical abuse
With their solidly welded internal metal (steel and nickel) structure, Tel.X batteries can handle continuous abuse from shock and vibrations. This is one of the reasons why they are the batteries of choice onboard passenger rail cars all over the world.
Tel.X battery strings were shock and vibration tested and certified by an independent laboratory. Tel.X meets and exceeds the functional and safety requirements of GR-63 in accordance with NEBS Level 3. That includes the worst case scenarios of shock, transport vibration, office vibration and earthquake (Zone 4).
As the steel structure is virtually immune from destructive corrosion during the life of the battery, the mechanical integrity will not deteriorate as the batteries age.
14.4 Corrosion and carbonates
The electrolyte protects the internal structural steel from destructive corrosion. Tel.X batteries are, therefore, completely free from a common ailment of lead acid batteries: grid corrosion which is associated to subsequent grid growth and weakening of the plate structure.
All external metal parts are nickel-plated steel. In addition, a protective coating of NoOx is applied to all exposed metal surfaces. The top of the battery module is further protected from electrical and mechanical damage by the use of the dead top cover.
Once the right torque has been applied to the terminal bolts and with a thin coating of NoOx after, there is no need to reapply torque on a regular basis. Experience has shown that repeated use of a wrench may do more harm than good as it may disturb the protective coating and ruin the nickel plating. A properly installed Tel.X battery should not suffer from external corrosion during its lifetime even when operated in relatively high humidity.
Carbonate crystals or carbonates are white salts and can be mistaken for corrosion. The crystal is formed when the potassium hydroxide reacts with the carbon dioxide in air. Under normal operation and handling, the Tel.X is contained and sealed so carbonates should not become evident. The carbonate crystals are salts and not a result of corrosion. Carbonates do not affect the performance of the Tel.X battery string.
If carbonates are noticed on a terminal connected to a DC bus power wire, it is recommended to brush it away with a soft bristle brush or dry cloth. This will prevent the possibility of dissolved carbonate crystal migration in the power cable. Dissolved carbonates can affect the integrity of the power cable and breaker if left un-brushed.
26
Paralleling with other battery string technologies
15 Paralleling with other battery string technologies
As a basis for the following discussion, consider the baseline mode of operation where a Tel.X is paralleled together with other Tel.X strings of the same size capacity. In this case all is normal. There are no increased risks or no degraded performances. They operate as expected and this baseline mode of operation is stable and the delivered power is well balanced.
Nevertheless, operating different battery technologies on the same DC bus can be considered as long as their operating modes are identical. For example, for two different Ni-Cd
technologies like the Tel.X and the NCX (S/PBE technology produced between years 2000 and 2010), parallel operation can be done since both need 54.4 V set point and both don’t use temperature compensated voltage (TCV). In contrast, if operating modes are not identical, then it’s not advisable to parallel connect since fixing one operation mode or mixing operation modes may be unsafe, detrimental or performance degrading to one technology or the other.
For another example, for VRLA, it’s normal to operate using TCV control in order to prevent thermal runaway. For Tel.X, it’s not recommended but if active it may be performance degrading. On the other hand, if TCV is not active, it may be detrimental or unsafe to the VRLA. Not using TCV
may significantly reduce the VRLA’s life and expose it to a higher risk of thermal runaway.
Another consideration when paralleling different technologies is the amount of current imbalance that may be encountered. With parallel connected strings, the string voltage remains the same and it remains the same in all modes of operation including charge, float charge and discharge. Depending on the internal resistance difference, it’s likely that the current divided on the power bus will be shared unequally. With internal resistance variations, current imbalance will be encountered in all modes of operation. This consideration helps to confirm whether the power system components are adequately designed to handle the highest level of current imbalance.
27
Battery sizing
16 Battery sizing
For new installations, past experience and recommendations from the equipment manufacturer usually dictate the battery capacity. If calculations have to be made, the load current is estimated or obtained from the electronic equipment manufacturers. Most manufacturers will give conservative load estimates, corresponding to high traffic conditions. Allowances may be made for near future expansions.
The load current is multiplied by the required standby time, normally 8 hours. A 25% aging factor is often added and the required capacity can be determined. Most installations utilize parallel strings of standard battery sizes. A sufficient number of strings must be installed to cover the calculated battery capacity.
See Figure 16.1 for an example of sizing calculation. The calculated number is always rounded up to the next integer. We encourage the practice of adding 25% as an aging factor or margin factor since Tel.X will lose some performance with time and may not always be able to provide 100% capacity in some severe telecom environments. We do not encourage that a redundant string is installed, as Tel.X batteries are highly reliable.
Figure 16.1. Example sizing calculation. CS = C8
N = 1.25 x I x T/CS
N = Number of strings required
1.25 = Aging factor or margin factor
I = Average load current in amperes
T = Standby time in hours
CS = Ah capacity per string
28
RectifiersRectifiers
Telecom loadTelecom load
InstalledInstalledbattery stringsbattery strings
BreakersBreakers(45 A rated)(45 A rated)
++
Pow
er b
usP
ower
bus
AvailableAvailablecharge currentcharge currentto share withto share withall installedall installed
battery stringsbattery strings
Total rectifierTotal rectifierAmpsAmps
Telecom loadTelecom loadAmpsAmps
minusminus
equalsequals
100 Amps100 Amps
minusminus
equalsequals
20 Amps20 Amps
80 Amps80 Amps
((40 Amps40 Amps each eachwhen sharedwhen sharedbetween twobetween two
installed strings)installed strings)
20 A20 A
40 A40 A
40 A40 A
100 A100 A
RectifiersRectifiers
Telecom loadTelecom load
InstalledInstalledbattery stringsbattery strings
BreakersBreakers(45 A rated)(45 A rated)
++
Pow
er b
usP
ower
bus
AvailableAvailablecharge currentcharge currentto share withto share withall installedall installed
battery stringsbattery strings
Total rectifierTotal rectifierAmpsAmps
Telecom loadTelecom loadAmpsAmps
minusminus
equalsequals
100 Amps100 Amps
minusminus
equalsequals
20 Amps20 Amps
80 Amps80 Amps
((40 Amps40 Amps each eachwhen sharedwhen sharedbetween twobetween two
installed strings)installed strings)
20 A20 A
40 A40 A
40 A40 A
100 A100 A
RectifiersRectifiers
Telecom loadTelecom load
InstalledInstalledbattery stringsbattery strings
BreakersBreakers(45 A rated)(45 A rated)
++
Pow
er b
usP
ower
bus
AvailableAvailablecharge currentcharge currentto share withto share withall installedall installed
battery stringsbattery strings
Total rectifierTotal rectifierAmpsAmps
Telecom loadTelecom loadAmpsAmps
minusminus
equalsequals
100 Amps100 Amps
minusminus
equalsequals
20 Amps20 Amps
80 Amps80 Amps
((40 Amps40 Amps each eachwhen sharedwhen sharedbetween twobetween two
installed strings)installed strings)
20 A20 A
40 A40 A
40 A40 A
100 A100 A
Appendix A – Parallel currents
Available charge current is distributed among parallel connected battery strings. The available charge current is equal to the rectifier amperage capacity minus the telecom load. If the battery strings are starting from the same state of charge, this available current distributes evenly among the parallel connected battery strings. Figure A.1 shows a schematic view of a typical telecom power system with two parallel connected battery strings. In this example, the total rectifier capacity is 100 A, with a telecom load current of 20 A leaves 80 A available for battery string charging. Each string receives 40 A of initial re-charge current.
The highest level of charge current can be anticipated when the string is fully discharged and re-charge starts. See section 7.2. Depending on the available current from the power system, the Tel.X battery string may receive this maximum level of current when initially charged.
Figure A.1. Schematic view of a telecom power system showing the distribution of parallel currents.
The Tel.X will tolerate available current from the rectifier shelf exceeding 0.7 C8A per battery string.
It should be noted that the Tel.X battery strings are shipped from the factory at a 10% state of charge. This level of charge makes the Tel.X behave as if it is completely discharged. This is most important when installing Tel.X battery strings.
When connecting and operating battery strings to a DC bus, care must be taken in order to prevent excessive and imbalanced current. There are three cases that are common.
Case 1: If the site is receiving its first installation of one or more Tel.X battery strings, make sure to assemble and connect all battery strings prior to applying charge power. This will prevent one battery string from charging and becoming at
+
a different state of charge from the others. If a state of charge difference occurs, the higher state of charge battery will discharge into the lower state of charge battery when they are connected. In most cases, this parasitic inrush current will exceed the breaker value battery string circuit.
Case 2: If the site is receiving an add-on Tel.X battery string to an existing installation, make sure to charge the Tel.X battery string at the garage or depot prior to installing it at the site. This brings the state of charge of the new Tel.X battery string to the same level of the already installed strings.
Case 3: If a site has a power outage and the AC power is restored the installed battery strings should begin normal re-charge. There should be no interruption since the breakers in each battery string circuit and rectifier capacity is size matched.
29
Glossary
Capacity A coulombic quantity that is the result of the integration current over time. With the special case of constant current, it is equal to the ampere hours with units of Amp-hrs or Ah.
EODV End of Discharge Voltage
Gas evolution Hydrogen and oxygen gas that evolves from the positive and negative electrodes during overcharging.
IEC Capacity See Rated Capacity.
Nominal Capacity This is the telecom capacity of the battery and is sometimes referred as the 8-hour capacity using the symbol C8. It is measured at an ambient temperature of 25°C (77°F) and is the delivered capacity at 8 times the current that can be sustained for 8 hours to an end voltage of 1.10 V per cell. This follows a prolonged charge period with a constant voltage set point of 1.45 V.
Overcharging Continuous charging after the battery has accepted a maximum amount re-charge capacity. In the Tel.X, the result is gas evolution.
Rated Capacity This is the IEC capacity or the 5-hour capacity using the symbol C5. It is measured at an ambient temperature of 25°C (77°F) and is the delivered capacity 5 times the current that can be sustained for 5 hours to an end voltage of 1.00 V per cell. This follows a constant current charge at the C5/5 charge current for a period of 7 hours.
SOC State of Charge or the level of charge normally referred to as a level of capacity where a percent of 100% = C8 Amp-hrs
Doc N° 21788-2-0313 Edition: March 2013Data in this document is subject to change without notice and becomes contractual only after written confirmation.Photo credits: Bruce Burr, PhotoDisc, SaftSociété par Actions Simplifiée au capital de 31 944 000 € RCS Bobigny B 383 703 873Produced in the UK by Arthur Associates Limited.
Saft is committed to the highest standards of environmental stewardship.
As part of its environmental commitment, Saft gives priority to recycled raw materials over virgin raw materials, reduces its plants’ releases to air and water year after year, minimizes water usage, reduces fossil energy consumption and associated CO2 emissions, and ensures that its customers have recycling solutions available for their spent batteries.
Regarding industrial Ni-Cd batteries, Saft has had partnerships for many years with collection companies in most EU countries, in North America and in other countries. This collection network receives and dispatches our customers’ batteries at the end of their lives to fully approved recycling facilities, in compliance with the laws governing trans-boundary waste shipments. This collection network is undergoing minor adaptations to meet the requirements of the EU batteries directive. A list of our collection points is available on our web site.In other countries, Saft assists users of its batteries in finding environmentally sound recycling solutions. Please contact your sales representative for further information.
Saft Industrial Battery Group 12, rue Sadi Carnot 93170 Bagnolet – France Tel. : +33 1 49 93 19 18 Fax : +33 1 49 93 19 64
www.saftbatteries.com
