Abstract on DC Power Supply and Batteries

7/27/2019 Abstract on DC Power Supply and Batteries

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Why do we need ELTEK Power Supply?

- And why do we need Batteries?

Why Power & Batteries


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1. PROVIDE A RELIABLE DC-POWER SUPPLY TOTHE TELECOM EQUIPMENT.

2. CHARGE THE BATTERIES

3. MONITOR AND CONTROL THE SYSTEM

TO ACHIEVE A LONG LIFETIME AND A HIGH MTBF(MEANTIME BEFORE F AILURE)OF THE COMPLETE SUPPLY- ANDBACK-UP SYSTEM.

Our main tasks !


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A filter for all the noise (EMC, surges etc) present on theAC power lines.

All telecom equipment (PABX, Base Stations, MainSwitches) have to operate when the AC supply (mains)is absent.

The telecom equipment have to be supplied by storedenergy while the AC supply (mains) is absent.

Batteries are today the cheapest and most efficient way tostore electrical energy, and can only be charged by DC.

Why DC and not AC Power Supply ?


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A DC Power Supply System converts the AC power to DCVoltage, to charge the batteries and to supply the Telecomequipment (load) when mains is present.

When the AC supply (mains) fails, the batteries will supplythe Telecom equipment (load) until the mains supplyreturns. The rectifier system will then recharge the

batteries.

The DC power supply will monitor and control the systemand provide alarms in case of failure.


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What is the key questions to be asked ? (minimum)

1. What is the desired system voltage ?

2. What is the maximum current or power needed ?

3. How many load outputs are needed ?

4. What is the redundant requirements ?

5. What is the desired back-up time ?6. What is the desired re-charge time ?

7. What end-voltage can be used ?



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TYPICAL POWER PLANT

Overview / Components

Current flow

Voltage sequenceDischarge - Recharge


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Overview/Components in a Power System

NONE

PRIORITY

LOAD

LOAD(pcs or different voltage)

UPS

AC/DC - DC/AC

ALARM

MODULE

Rectifier

#1

Rectifier

#2

Rectifier

#n

G

OVP

MAINS

FUSES

LVBD

BATTERY

DISTRIBUTION

BATTERY

BANK

DC-DC or

DC/AC

REDUNDANT

RECTIFIER

SYSTEM

AC/DC

DIESEL

GENERATOR

Rectifier#n

LVLD

Battery &

LoadDistribution

PRIORITY

LOAD

BATTERY

BANK


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Ic x tc = Id x td x 1,2 x 0,9

Id x td x 1,2 x 0,9Ic =tc

Ic = re-charge current

tc = re-charge timeId = discharge current

td = discharge time1,2 = is the 20% efficiency loss

0,9 = is the 90% re-charged level

i.e:

100A x 10t x 1,2 x 0,9 (= 1080Ah)

10t

= 108A, in 10hrs up to 90%


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All Eltek rectifiers (some exceptions):

Is designed for Single-phase 220Vac !

Have active power factor correction (cos.)

Active current sharing between modules in a system

Fused input

Constant Power (48-56Vdc)

Short circuit protected DC output

Blocking diode on the DC output

OverVoltage protected DC output


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Current Flow in a System

RECTIFIER

SYSTEM

TELECOM

EQUIPMENT

BATTERY

BANK

AC

INPUT

MAINS INPUT OK

LOAD SUPPLIED BY THE RECTIFIER SYSTEM

BATTERIES ON FLOAT CHARGE.


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RECTIFIER

SYSTEM

TELECOM

EQUIPMENT

BATTERY

BANK

AC

INPUT

MAINS INPUT FAILED (ABSENT)

LOAD SUPPLIED BY THE BATTERIES

BATTERIES ARE DISCHARGING



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RECTIFIER

SYSTEM

TELECOM

EQUIPMENT

BATTERY

BANK

AC

INPUT

MAINS INPUT OK

LOAD SUPPLIED BY THE RECTIFIER SYSTEM

BATTERIES ARE RECHARGING


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Voltage Sequence in a DC Power System

Normal

operation.

Battery Discharge Battery Re-Charge

Mains failure

t

U

53.5

43.2

- w/Charge Current Limitation

LVBD level

(43,2 / 24 = 1,8v)

Mains OK w/Charge Current Limitation

Normal Charge current

Battry collapse


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BATTERIES

1. Operating principle of the Recombination

Technology

2. Open Circuit Voltage in relation to the state

of charge of the cell

3. Float Voltage versus temperature


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Operating principle of the Recombination

Technology For conventional lead acid cells water is lost during cycling, due to electrolysis.

The result of this is regular battery checks and periodic topping-up operations.

Sealed, valve regulated lead acid battery design eliminates/reduce these problems

through continuous recombination of the oxygen during overcharge.

During overcharge the following reactions occur:

1. Oxygen is evolved at the positive plate by the reaction; H2O -> 1/2 O2 + 2H

++ 2e

-

and diffuses through the unfilled pores of the seperator to the surface of the negative plate

2. At the negative plate oxigen combines with Pb and sulphuric acid;

Pb + H2SO4 + 1/2 O2 -> Pb SO4 + H

2O

3. The charging process electrochemically regenerates the lead in the negative plate, compl. the cycle;

Pb SO4 + 2H+

+ 2e-

-> Pb + H2

SO4

As a result, the recombination process with an efficiency higher than 98% completes and

reverses the water oxidation. At the end of the process, teh recombination has replaced

the water, the electrolyte and the lead in the negative plates without having modified the

state of charge of the plates.


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Open Circuit Voltage in relation to state of

charge of the cell.

State of charge (%)

VDC

1.90

Open

CircuitVoltage(perc

ell)l

1.95

2.00

2.05

2.10

2.15

25 50 75 1000

Charge Voltage


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Float Voltage versus temperature(Example from Exide)

2

2,05

2,12,15

2,2

2,25

2,3

2,35

2,4

2,45

2,5

2,55

-50 -40 -30 -20 -10 0 10 20 30 40 50

Degrees Celsius

Volt/Cell(eks:3mV/C*)

AD-590 sensor

AD-592 sensor

Test of AD-592: 273uA is 0 grad.C and 293uA is 20 grad.C (i.e.1uA per deg.C)


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To be continued..

END OF SESSION....

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Abstract on DC Power Supply and Batteries