BATTERY CHARGERS AND BATTERIES
UNINTERRUPTED POWER SUPPLY
Introduction to Uninterrupted power supply.
AC to DC conversion (Rectification)
Battery charger system
Batteries
UNINTERRUPTED POWER SUPPLY
Uninterrupted power supply as the name suggest is power supply available without any interruption.
This is required for maintaining power supply to critical system/equipment, failure of which may result in process disturbance, equipment damage or safety hazards.
Generally provided to DCS system, SDV supply, emergency pumps, and control supply to PLC and electrical switchboards.
UNINTERRUPTED POWER SUPPLY
TYPES
1. DC SUPPLY :SOURCE : Battery chargers located at substations.USED FOR : Electrical panels control supply, Fire alarm system, Telecommunication, Solenoid valves (SDV), Switches at field (e.g. flow, pressure), & Emergency lighting supply.
2. AC SUPPLY : SOURCE : Provided by UPS system located at Control room buildings.USED FOR : DCS, Analysers, and Instrumention field control panels, ECS stystem, PLC, VFD etc
BLOCK DIAGRAM OF CHARGER AND UPS
LOAD
LOAD
3 phase AC supply
3 phase AC supply
Rectifier
Battery
Battery
Rectifier InverterUPS SYSTEM
BATTERY CHARGER
RECTIFIER
RECTIFIER
Rectification is the conversion of Alternating current (AC) to Direct current (DC).
This involves the use of a device called Rectifier that only allows one-way flow of electrons.
Rectifiers can be classified as uncontrolled and controlled rectifiers.
Uncontrolled rectifier circuits are built with diodes.
Controlled rectifier circuits are built with SCRs.
RECTIFIER
A Diode is an electrical device allowing current to move through it in one direction.
1 2
3 4
+ve cycle Diode 2&3
- ve cycle Diode 1&4
THREE PHASE UNCONTROLLED RECTIFICATION WAVEFORM
SILICON CONTROLLED RECTIFIERS (SCR)
The SCR is a semi-conductor device with 3 terminals i.e. Anode, Cathode and Gate.
The main load current is carried by Anode and Cathode while the control current flows through Gate and Cathode.
The characteristic of SCR is such that it blocks the forward voltage until the Gate current reaches the specified level.
Therefore the instant at which the SCR goes into conduction can be controlled by changing the instant at which the gate current or pulse is applied.
Once the SCR is triggered it remains in conduction till Anode current is reduced to Zero or reverse voltage is applied to anode
SILICON CONTROLLED RECTIFIERS (SCR)
Uncontrolled rectifier
Controlled rectifier
Period, range of q SCR Pair in conduction
30o to 90o S1 and S6
90o to 150o S1 and S2
150o to 210o S2 and S3
210o to 270o S3 and S4
270o to 330o S4 and S5
330o to 360o and 0o to 30o S5 and S6
R
Y
B
R
Y
B
Fully
Controlled
Bridge
Half
Controlled
Bridge
SCR1 SCR2 SCR3
SCR4 SCR5 SCR6
SCR1 SCR2 SCR3
D1 D2 D3
Load
Load
BRIDGE RECTIFIER DIAGRAM
SCR1 SCR2 SCR3 CHOKE CAPACITOR
SCR4 SCR5 SCR6 F/W DIODE LOAD
3 PHASE AC INPUT
Us RMS AC
U o DC
EQUATION FOR O/P VOLTAGE U o = 0.675*Us( 1+ CosA)
A= FIRING ANGLE OF SCR , Us= RMS AC VOTAGE INPUT
R
Y
B
THREE PHASE CONTROLLED RECTIFICATION WAVEFORM
DCFILTER
Ripple is the small AC voltage or current occurring in a DC component as an unavoidable byproduct of rectification. Ripple filter is a combination of inductance and capacitance used to reduce the level of ripple.
BATTERY CHARGER SYSTEM
Input Transformer
RectifierBridge
FilterCircuit
Control And alarm
section
Load
Battery
Block Diagram of Battery Charger
BATTERY CHARGER
BATTERY CHARGER is a Controlled Rectifier which converts AC power to DC power.
It uses a Three phase Controlled SCR bridge Rectifier.
The output voltage of a rectifier is controlled by changing the firing angle of the SCR.
Output of Rectifier is smoothened by Filter comprising of Capacitor and Inductors (Choke).
The output of the rectifier supplies the DC supply to load and at the same time charges the battery.
Basic components required for Charger
System. Termination terminals, Switches/Fuses/MCB’S/MCCB’S; Contactors and relays. Meters Voltage and current both at Input and output. Transformers Mains and control. Semiconductor devices ie THYRISTORS & DIODES. Choke and Capacitors. Shunts. Printed circuit boards (PCB’S).
FEATURES OF BATTERY CHARGERS
Soft start (gradual build up of DC at start). Output DC voltage maintained constant for +/-
10% AC voltage variation and 0-100% load variation .
Operation in float and boost charging modes
possible. Load current limit feature. Output voltage droops
in event of load current exceeding rated current. Battery current limit. DC earth fault detection.
FEATURES OF BATTERY CHARGERS
Constant current charging in boost mode.
Auto changeover to boost mode if desired.
Ripple content of max 2% with battery. Operation in Auto and manual mode (during
control card failure only in Chabbi Chargers).
Input Switchgear (Switch + fuse + contactor +
Thermal overload relay or MCCB) for isolation &
protection
Indications and measuring instruments
Transformer for stepping down the voltage suitable
for the thyristor bridge.
Input Section
Rectifier Bridge Section
•Single Phase, Full Wave, Half Controlled Bridge consisting of thyristor & diodes.
•Three Phase, Full Wave, Half Controlled Bridge with thyristors & diodes.
•Three Phase, Full Wave, Full Controlled Bridge consisting of thyristors.
•Rectifier protection fuses.
Time (s)
Time (s)
Vmax
Vrms
Volts (V)
Volts (V)
Vripple
Filter combination of choke and capacitor
Designed to reduce output ripple.
Filter Section
Voltage wave form after filter
Maintains voltage regulation of ±1% and current regulation of ±2% for load variation of 5-100% and input variation of ±10%
Independent current limit protection for battery and charger.
Protection for DC over-voltage, AC under-voltage, AC over-voltage and phase fail and phase sequence fail.
Adjustable time settings for boost charging and reverting back to float mode after boost charging.
Audio Visual alarms and indication with common fault contact for remote indication.
Control & Alarm Section
Controls Alarms & Protections
1. Regulation of +/- 1% for load and line variations.
2. Short circuit/Overload protection.
3. Reverse polarity protection.
4. Soft start5. Battery current limit6. Total current limit.
1. Input supply fail2. DC under-voltage3. DC over-voltage (T)4. Charger fail (T)5. Input under-voltage(T)6. Input over-voltage (T)7. Earth fault8. Rectifier fuse fail9. Output fuse fail10. Current limit operated.
CHARGER CONTROLS AND ALARMS
MODES OF CHARGER OPERATION
Float mode : Normally the charger is in float mode and supplies the load and charges the battery. This is constant voltage mode.
Boost mode : During power failure the load is supplied by battery. On resumption the battery needs to be boosted to a higher voltage under current limit. This is done after isolation of the charger from load. This is current limit/Constant current mode.
TYPE OF SYSTEM CONFIGURATION
Float Cum Boost Charger. Float and Float cum Boost Charger. Dual FCBC with Common Battery. Dual FCBC with Two Batteries. Dual Float and Boost Charger with Auto
change over.
FRONT PANEL OF HBL BATTERY CHARGER
FRONT PANEL OF HBL BATTERY CHARGER
Faults Probable CausesBattery are discharged and need boost chargingShort-circuit in filter capacitorsOutput wiring short
Control card faulty.
Feedback section faulty or open
SCR of bridge faulty
Float Volatage audjusment Potentiometer faultyPower devices or their fuses defective/blownControl card defective
Charger Output drops when loaded
Battery is taking high current after power failure.
Charger is tripping on Overvoltage
GUIDELINES FOR TROUBLESHOOTING
Dual FCBC with Common Battery.
CHARGER CONFIGURATION
Dual FCBC with Common Battery. In each system there are two battery chargers
for redundancy operating in parallel. One charger is rated to supply the connected
load in case of failure of one charger. Each charger can operate in floot mode and
boost mode. During an emergency, when AC power fails,
the battery supplies the load & it discharges to certain extent depending on the load and duration of emergency.
CHARGER CONFIGURATION
Dual FCBC with Common Battery. Upon resumption of Mains power the Charger
automatically restarts and develop Float Voltage. At the time of restoration of input power supply
battery needs to be boost charged. Under such condition one charger will supply the load and other charger will be in boost mode charging the battery.
In case of Auto boost facility the charger goes to boost mode if the battery takes current more than a set value.
Once the charger goes to boost mode it comes back to Float mode after a set time.
110V DC CHHABI BATTERY CHARGER BLOCK DIAGRAM
Charger A
SW5 A
BATTERY BANK
DC
DB
MCCB 1A
SW 7
C3Tap cell diode
MCCB 1B
MCCB 1B
SW5 B
MCCB 1A
Fuse
SW1A
C1A O/L1A Tr. Fuse
Charger B
B Diode
C1B O/L1B Tr.
Fuse
SW1B
B Diode
Fuse
80%
HBL CHARGERS IN PREP & PXPTA
Charger A
SW 2
BATTERY BANK
K3
SW 5
Tap cell diode
K4
K4A
SW 4
K3A
Fuse
SW1
K1 OLR Tr. Fuse
Charger B
B Diode
K2 OLR Tr.
Fuse
SW2
B Diode
Fuse
80%
Only in MCCB model
HBL CHARGERS IN PREP & PXPTA
There are two Nos. of float cum Boost chargers(Charger-1 and 2) with common battery bank.
The chargers operate in parallel to float charge the battery and feed the load.
The output of the chargers is fed to a common DCDB. Each charger can be put in boost mode to boost charge
the battery . The charger has a facility of Auto as well as Manual mode boost
charging. In Auto Boost mode the if the battery current is more than 10%
of Battery current (AH/5) one of the charger will go in to boost charging.
The load output contactor/MCCB of charger which goes into boost charging will trip and the other charger (float mode) Battery Contactor/MCCB will trip.
When the time set for boost charging is complete the Charger which was in boost mode returns to Float mode.
HBL CHARGERS IN PREP & PXPTA
In Contactor model charger the output and battery contactor of respective chargers will get ON after the battery voltage comes to the float charging voltage.
In MCCB model the MCCB are required to be switched ON manually.
In case of mains failure of both the charger during boost charging, all the four contactors will get ON as soon as the battery voltage comes down to Float voltage.
In case of mains failure of both the charger during boost in MCCB model charger Battery to load contactor will get ON and load will be supplied by the battery bank.
Till the contactor get ON in both the schemes the load is fed by battery through Tap Cell.
HBL 24 V DC CHARGERS AT CPP (STG)
BLOCK DIAGRAM
3 PHASE AC INPUT
CHGR - 1
CHGR-2
BB-1
BB2
DROPPER DIODE BYPASS CONTACTOR K1
DROPPER DIODE
O/P SWITCH S1
O/P SWITCH S1
DCDB1
DCDB2
HBL 24 V DC CHARGERS AT CPP (STG)
There are two Nos. of float cum Boost chargers (Charger-1 and 2) with separate battery banks.
The chargers operate in parallel to float charge the battery and feed the load.
The output of the chargers is fed to two Nos of DC distribution boards .
Each charger can be put in boost mode to boost charge its battery .
The charger that is put in boost mode has to be disconnected from the DCDB by switching OFF the Output Switch S1 prior to putting it in boost mode.
The load is fed via dropper diodes under normal condition so that reduced voltage is available at the load.
In case of mains failure the load is fed by the battery. The DVR contactor gets energized the moment the voltage falls below load requirement. The dropper diodes are shunted once the contactor energizes.
Ch
arge
r-1
Ch
arge
r-2
Blocking Diodes
DCDB -1 DCDB-2
Tie Bkr
Bat
tery
Ban
k-1
Bat
tery
Ban
k-2
220V DC Charger System at CPP/ MSQ
I/C Bkr-1 I/C Bkr-2
3Ph.415V 3Ph.415V
SW Fuse TH relay SW Fuse TH relay
Tr. Tr.
220 V DC CHARGER AT CPP/ MSQ WITH INDEPENDENT BATTERY BANK
There are two float cum Boost chargers viz Charger-1 and Charger-2.
The output of each charger is connected to a DCDB through a incomer breaker/ Switch.
There is a tie breaker/Swtich used to connect the two sections of DCDB,s whenever required.
Each charger has its own battery bank which is connected to the respective DCDB
Normally each charger feeds loads connected to its DCDB and float charge its battery bank. The tie breaker is normally open.
Load of both the DCDBs can be fed from one charger by closing the tie breaker .
In Case of boost Charging the Tie breaker is closed and the Incomer from Charger of the battery bank to be boost charged is switched OFF.
Boost charging is switched ON and the battery is boost charged for the set time.
The Charger comes back to Float mode after the set time. Incomer and Tie Breakers/Switches are normalised thereafter.
OPERATING PROCEDURE (Float mode)
SWITCHING ON BATTERY CHARGER IN FLOAT MODE
Ensure that the Auto/Manual switch is in Auto position Check the DC output switches of both chargers are ON. Ensure that Main AC input switches for both the chargers in
ON. Check that all the MCCB’s of both the chargers are ON. Put the chargers On/Off switch to ON position for charger
A/B. Observe that the DC output voltage gradually rises to the set value.
Switch ON charger B/A and observe that the output voltage gradually rises to the set value.
Switch ON the battery switch. Check the load current is within the charger limits. The chargers will share the load approximately equally .
OPERATING PROCEDURE (Boost mode)
Normally both charger A and B will be operating in float mode in parallel sharing the load and trickle charging the battery.
Ensure that the DC output switch of both chargers are ON. Decide upon the charger to be used as the boost charger
(Charger A/B). Ensure that the battery current limit pot is in minimum
position. Switch the selected charger to Boost mode by pressing the
Boost PB. The MCCB connected to the load will trip for the charger put
on boost. Adjust the battery current to the desired value using the
battery current limit pot. Continue boost charging for the set time after which the
charger comes back to the Float mode. It can also be put back to float mode by pressing the float PB.
Ensure that the load MCCB is switched on again after the charger is put back on float.
GUIDELINES FOR TROUBLESHOOTING
Faults Probable CausesIncorrect Battery Polarity
Short-circuit in filter capacitorsOutput wiring short
Input transformer faulty
Control transformer, contactor, relays defective
SCR/Diodes of bridge faulty
Varistors/ SCR snubber circuits faulty
AC/DC fuses blownNo /unbalance input voltageDefective control cardsDefective power devices
Overloading
Defective cells in battery bank
Control card faulty
Feedback circuit faulty
Incorrect(High) setting of float or boost voltage
Input Voltage Low
Faulty control card
Float Voltage adujstment Potentiometer faulty
Charger Output Low
DC Fuse blows /Breaker trips
AC input Fuse blows/breaker trips
No output voltage developed
Charger continuously operates at Current limit
BATTERIES
What is a Battery /Cell ?
Cell: A storage device which stores the electrical energy in the form of chemical energy allows to recover back in the form of electrical energy.
Battery: Combination/group of cells
Battery / Cell
Components of a Battery / Cell
BATTERY
A battery is a electrochemical device that stores energy and makes it available in an electrical form.
The basic principle of rechargeable cell is the conversion of electrical energy into chemical energy and vice versa.
It a important part of Battery charger & UPS system and supplies the energy during power failure.
TYPES OF BATTERIES
ZIN C C A R B O N A LK A LIN E
D ISPO SA B LE
PO C K ET PLA TE FIB R E PLA TE SIN TER ED PLA TE
N IC K EL C A D M IU M
VEN TED SEA LED M A IN T FR EE
LEA D A C ID LITH IU M IO N N IC K EL M ETA L H YD R O XID E
R EC H A R G A B LE
B A TTER Y
LEAD ACID BATTERY
The oldest form of rechargeable battery still in modern usage.
Generally there are two types of lead-acid storage batteries, based on their method of construction
Flooded or Vented type Sealed Maintenance
free During charging, a lead-acid
battery generates oxygen gas at the positive electrode.
Lead Acid Battery
Electrolyte in a lead-acid battery is a dilute solution of Sulphuric acid (H2SO4 ).
Negative electrode of a fully charged battery sponge lead (Pb)
Positive electrode is composed of lead dioxide (PbO2 )
Flooded/Vented Lead acid battery
The electrodes/plates are immersed in electrolyte.
Gases (oxygen) created during charging are vented to the atmosphere.
Distilled water must be added occasionally to bring the electrolyte back to its required level.
Regular checking of specific gravity is required for checking charging status.
Sealed Maintenance Free Lead Acid Battery
Electrolyte is confined in the battery in absorbed condition, held within the pores of the glass mat separator.
Oxygen generated during charging is captured and recombined in the battery.
This is called an oxygen recombination cycle and works well as long as the charge rate is not too high.
If oxygen generation exceeds the rate of recombination due high charging rate the excess pressure is released through specially designed self resealing relief valve, hence the name Valve Regulated Lead Acid Battery (VRLA)
Electrolyte levels are preserved by trapping and recombining of gasses, and there no need to add distilled water over the life of the battery.
Sealed Maintenance Free Lead Acid Battery
Constant voltage charging is the most preferred charging method for Lead-Acid batteries.
When charging the battery with a constant voltage charger in float applications, the charger must be set at the following voltages. Boost: 2.35V per cell, Float: 2.25V per cell.
Lead Acid batteries are rated at the 10hr rate of discharge to end 1.75 V per cell at 20ºC.
ADVANTAGES: Low cost, Low Self discharge Mature, reliable and well-understood technology .
DISADVANTAGES : Cannot be stored in Discharged condition Limited no. of full discharge. Thermal runaway with improper charging Chances of open circuit faults in VRLA batteries Flooded battery needs more maintenance. High Sulphation
Lead Acid Battery
CHEMICAL REACTION OF LEAD ACID BATTERY
NICKEL CADMIUM BATTERIES
NICKEL CADMIUM BATTERIES
Most popular type of rechargeable batteries. Used where reliability is key factor. Provide long service life. Require minor maintenance. Rugged with outstanding resistance to electrical
(overcharging, deep discharging etc) and mechanical abuse.
Long shelf life (1-2 yrs in filled & Charged condition and 10 yrs in dry and discharged condition)
Operation over a wide temperature (-20oC to +50oC) No open circuit failure Nearly constant discharge voltage
NI-CD BATTERY PARTS
+ve Electrode: Nickel Hydroxide Ni(OH)2
-ve Electrode : Cadmium Hydroxide Cd(OH)2
Electrolyte : Potassium Hydroxide (KOH)
Container : Polypropylene Separator : Micro porous PVC
NICKEL CADMIUM BATTERIES
ELECTROLYTE Aqueous solution of Potassium hydroxide
(KOH) containing small quantity of lithium hydroxide to improve cycle life.
The electrolyte is only used for ion transfer and is not chemically changed or degraded during charge/discharge cycle
ELECTRODES Consists of active material enclosed in pocket of
double perforated nickel plated steel strips.POSITIVE PLATE ACTIVE MATERIAL- Nickel
hydroxide NEGATIVE ACTIVE MATERIAL - Cadmium
hydroxide
2 Ni (OH)2 + 2 OH- 2 NiOOH + 2 H2O + 2 e- V+= 0.49V
Cd (OH)2 + 2 e- Cd + 2 OH- V- = 0.809V
Over all reaction of a Nickel Cadmium Battery is as follows
2 Ni (OH)2 + Cd (OH)2 2 NiOOH + Cd + 2 H2O
Potential difference of Ni-Cd cell shall be Vo = 0.490 – (-0.809)
= 1.299
* Electrolyte does not take part in reaction; it is only a carrier of ions
Charge
Discharge
Electrochemistry
Charge
Discharg
e
Charge
Discharge
NICKEL CADMIUM BATTERIES
ELECTROCHEMISTRY Discharge
2Ni(OH)2+Cd(OH)2 2NiOOH + Cd + 2H20 Charge
During charging the active materials initially present as hydroxides are changed. Cadmium hydroxide is reduced to cadmium and nickel hydroxide attains a higher degree of oxidation.
On Discharge the process is reversed and active materials revert to their original state.
The Potassium hydroxide electrolyte takes no part in these reactions and acts only as carrier of ions.
Nickel Cadmium Battery Designation as per IS 10918:1984& IEC 60623:2001
291 K P/B H 290 P
No of cells in a BatteryThis varies
System Voltages
Type of Plate P – Pocket Plate
S – Sintered PlateF- Fibre Plate
B - Block
Alkaline Vented Rechargeable cells in prismatic containers
Type of Cell L-Low
M-MediumH-High
X- Ultra HighVaries with Application
Ampere Hour Capacity
of cells in the batteryThis varies with back up
Duration for same Number of cells
Type of Container
P- Polypropylene
BATTERY CAPACITY
The battery capacity is rated in Ampere-hour (AH) and is the quantity of electricity(AH) at +20 oC, which it can supply for a 5 hour discharge to end voltage of 1.0V, after being fully charged for 8.0 hours at 0.2xC5 Amps.
C5 = AH of battery for 5 hrs discharge time
Nominal Voltage of Ni-Cd battery is 1.2 Volts
Nominal voltage of Lead acid cell is 2.0 Volts
Three type series -KPH, KPM and KPL with different performance characteristics for selection of an optimum battery for a given application.
TYPES OF NI-CD CELLS
Typical applications for NCPP L - type
• Emergency Lighting
• Fire Alarm Systems
• Photovoltaics
• Cathodic Protection
• Railway Signalling
• Telecommunication• Switchgear Protection
Typical applications for NCPP M - type
• Instrumentation & Process Control
• Switchgear Protection
• Emergency Lighting
• Train Lighting
• Air-conditioned Coaches
• UPS
• Motive Power
Typical applications for NCPP H - type
• Diesel Locomotive Cranking
• Generator Starting
• Electro Magnets
• Helicopter Ground Starting
• UPS
• Aircraft Ground Starting
0
20
40
60
80
100
30 Mts 1 Hr 5 Hr 0
20
40
60
80
100
30 Mts 1 Hr 5 Hr
1.14 1.1 1.05 1ECV :
Useful Capacity – H type Useful Capacity – L type
Discharge graph for KPL type cells
Discharge graph for KPL type cells
Discharge graph for KPM type cells
Discharge graph for KPH type cells
POCKET PLATE NI-CAD BATTERIES
The active material in each electrode is enclosed in metal pockets of finely perforated steel strips. Several pockets are laced together and cut in suitable lengths to form blanks. Both cut edges of the blanks are sealed in frames made of mild steel and nickel plated. The frame is the current collector of the plate. Plates of the same polarity are bolted or welded together along with terminal posts. Each plate is insulated from the next by a grid separator. The stacks are placed in plastic or stainless steel containers and top lid is sealed or welded. Negative and positive plate groups are interleaved so that plates of opposite polarities are alternated. The plate groups are insulated from one another by using micro porous PVC separator.
POCKET PLATE BATTERY
SINTERED PLATE NICAD BATTERIES
Nickel powder is sintered onto a metallic sheet, resulting in matrix with porosity greater than 80%, into which active materials are chemically or electrochemically impregnated.
Pore size of sintered mat is extremely small.Finely divided particles of active mass makes good contact with conductive substrate.
Active mass is present in its purest form.
Very thin electrodes (0.5mm to 0.8mm) can be produced for ultra high rate discharge performance.
Electrodes are flexible & strong, can be wound to producesealed cylindrical cells.
FIBRE PLATE NI-CAD BATTERIES
The active material in each electrode is impregnated in the pores of the Nickel coated polypropylene fibre current collector. The Nickel-plated tabs are welded on the extra nickel portion of the plate. Several plates of same polarity are welded to the terminal post and strap arrangement with projection welding technique.Negative and positive plate groups are interleaved so that plates of opposite polarities are alternated. The plate groups are insulated from one another by using
micro porous PVC separator.
Ni-Cd BATTERY CHARGING
Generally battery are in parallel operation with the two rate charger (Boost & Float) and load.
FLOAT CHARGING : is done during continuous parallel operation at float voltage in the range of 1.40 - 1.42 volts per cell.
BOOST CHARGING : or high rate charging are required after a discharge with a charging voltage of 1.53 - 1.67 Volts/cells
Charging current limit should be within 0.1 to 0.2 C5
Ni-Cd BATTERY CHARGING
High rate charging or overcharging within reasonable limits will not damage the battery but increase water consumption.
Battery can be left standing for short periods at any state of charge without damage.
Continuous undercharging combined with deep discharging will affect the battery life.
When the battery is charged separate from its load recommended charging is for 8 hours with a current of 0.2C5 amps to recharge a fully discharged battery to full state of charge.
CHARGING CHARACTERISTICS AT 0.2C5 RATE
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
CHARGED CAPACITY (%C5)
CEL
L VO
LTA
GE
(V)
KL
KM
KH
KX
0
10
20
30
40
50
60
70
80
90
100
110
0 20 40 60 80 100 120 140 160
CHARGED CAPACITY (%)
%
Available Capacity
Charge Efficiency
AH efficiency is good at early state of charge (85% on 100% AH input)
Efficiency falls at higher SOC, as more charge is used in gas formation.
Charging Efficiency
Ni-Cd BATTERY MAINTENANCE
CLEANLINESS Keep the battery dry and clean. This will
contribute to maximum service life and non-contamination of cells during topping up.
In case of deposition of potassium carbonate crystals(grey white deposits) on the top of battery, rub with soft brush and wipe with clean damp cloth followed by a clean dry cloth
Vent plugs should be kept clean to avoid blocking of holes. These can be rinsed in clean water if required.
Do not use wire brush or solvent of any kind, such as naptha, thinner for cleaning the battery.
Ni-Cd BATTERY MAINTENANCE
TOPPING UP The electrolyte level should always be kept
between maximum and minimum level marks by replenishing the water.
Use only DM water for topping up Never let the level fall below the top of the
plates. Avoid splashing water while topping up as
wet battery can result in earth faults. Always keep the Vents caps closed except
for the moment of topping up.
Ni-Cd BATTERY MAINTENANCE
CONNECTORS Check at least once a year or during
shutdowns that all the connectors are tight.
The connectors and terminals screw should be corrosion protected by coating with a thin layer of neutral grease or anti corrosion oil.
Ni-Cd BATTERY MAINTENANCE
SPECIFIC GRAVITY The electrolyte specific gravity shold be
1.18-1.20 at the maximum level. The specific gravity is not influenced by
the state of charge but increases slightly with the electrolyte level is lowered due to water loss.
Electrolyte specific gravity should not be measured immediately after water has been added.
Ni-Cd BATTERY MAINTENANCE
Battery Bank discharging The battery bank shall be discharged through at least once in
two years to ascertain the back up capacity. This can be done during shutdown of the respective unit. Battery load discharge unit or Water load can be used for
discharging the battery bank at around .2C5 rate i.e. 20% of the AH rating.
The voltage readings of the battery bank and all the individual cells are to be taken at regular interval to monitor the health of the bank/cells.
If a cell voltage comes below 1.0 Volts it should be bypassed and the test shall be continued.
All the cells which are weak should be removed from the bank and charged seperately by Cell boosters.
The battery bank should be boost charged at 0.2C5 rate for atleast 7-8 hours for full charging after every load test.
Ni Cad Batteries - DO’s
Use tools with insulated handles to prevent accidental short circuits.
Wear protective clothing when handling electrolyte. Check Inter-cell connectors for proper tightness. Keep the electrolyte at the proper level. It should not fall
below minimum level. (Mentioned on the cell marking label)
Use only demineralised water for topping up. Batteries should be clean and free from dust. Water wash facility should be ready in the battery room. Keep vent caps always closed during charging and
discharging. Ensure proper functioning of charger and proper
connection to the battery. Use alkaline electrolyte only.
Ni Cad Batteries - DON’T
Do not smoke or permit naked flames near the battery. Do not use apparatus like hydrometers, thermometers, etc.,
used in lead acid batteries. Do not Allow metal objects to rest on battery or fall across
terminals. Do not use petrol, kerosene or any strong chemicals for
cleaning batteries. Do not use wire or any hard brush to clean sulphation on the
inter-cell connectors, terminals. Do not keep vent cap open. Do not measure specific gravity immediately after adding de
minerilised water. Do not adjust terminal connections during charging to avoid
fire hazards. Do not remove vent caps for topping up. Gently press the
catch to open the spring-loaded vent lid. Do not use acid.
Gloves
Glasses
Eye wash
Apron
Safety shoes
SAFETY PRECAUTIONS & PROTECTIVE EQUIPMENT BATTERY MAINTENANCE
Insulated tools
Adequate ventilation
Reference and soft start
Trigger pulse generating unit
Bridge rectifier
Thr
ee p
hase
inpu
t
Amplifier forCurrent signal
Shunt Filter block
HV card with PST
Phase seq Phase fail circuit
+12 v
-12v
Power supply
Voltage regulatingamplifier
Current regulating amplifier
Current limit adjustmentpotentiometer
Manual voltageAdjustment potentiometer
Block diagram of three phase SCR controller of CHHABI Make Charger
A/M S/W
Auto Voltage adjustment potentiometer
3 Ph. 415V from mains