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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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Why DC and not AC Power Supply ?
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 ?
Why DC and not AC Power Supply ?
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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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Overview/Components in a Power System
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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Overview/Components in a Power System
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
Current Flow in a System
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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 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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