Dimensioning Of Dc Power Systems
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1 Dimensioning of DC Power Supply System The sizing of a DC Power Supply System is a complicated issue. The following information is required to secure that • The system can operate and provide the required back-up time • The input- and output circuit breakers and fuses are sized correctly • The rectifier unit can provide the required current output both for the load as well for the batteries. • The cables and bus-bars should not cause to high voltage drops and therefor make the load failing.
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Transcript of Dimensioning Of Dc Power Systems
1
Dimensioning of DC Power Supply System
The sizing of a DC Power Supply System is a complicated issue. The following information is required to secure that
• The system can operate and provide the required back-up time
• The input- and output circuit breakers and fuses are sized correctly
• The rectifier unit can provide the required current output both for the load as well for the batteries.
• The cables and bus-bars should not cause to high voltage drops and therefor make the load failing.
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Dimensioning of DC Power Systems
THE FOLLOWING INFORMATION NEED TO BE AVAILABLE:
• LOAD REQUIREMENT
• BACK-UP TIME / NO. OF BATTERY BANKS REQUIRED
• LOW VOLTAGE BATTERY DISCONNECT VOLTAGE?
• CONSTANT CURRENT OR CONSTANT POWER CALCULATION?
• REDUNDANCY OR NOT?
• % RECHARGE CURRENT (-OF BATTERY CAPACITY @ C10)
• MAXIMUM VOLTAGE DROP FROM SYSTEM TO LOAD
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Constant Current Discharge Calculation
• LOAD REQUIREMENT: 50 000W
• BACK-UP TIME: 1 HOUR MINIMUM 2 BATTERY BANKS
• LOW VOLTAGE BATTERY DISCONNECT AT 1.80 VPC (43.2Vdc)
• N+1 REDUNDANT RECTIFIER SYSTEM
• RECHARGE CURRENT LIMITED TO 10% OF BATTERY CAPACITY @ C10
FROM THIS WE CALCULATE:
CURRENT REQUIREMENT FROM BATTERY: 50000W/48V = 1042A FOR 1 HOUR
BATTERY SELECTED (EXAMPLE) : FIAMM 2SLA1000 x 2 BANKS (1208A)
TOTAL RECTIFIER CURRENT REQUIREMENT : 1042A (LOAD) + 2000A x 10% (BATT) = 1242A
BASED ON SMPS 5000/PRS 5000 (100A RECT) : 13+1 (REDUNDANT) MODULES REQUIRED
BASED ON SMPS 4000/AEON (85A RECT) : 15+1 (REDUNDANT) MODULES REQUIRED
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Constant Power Discharge Calculation
• LOAD REQUIREMENT: 50 000W
• BACK-UP TIME: 1 HOUR MINIMUM 2 BATTERY BANKS
• LOW VOLTAGE BATTERY DISCONNECT AT 1.80 VPC (43.2Vdc)
• N+1 REDUNDANT RECTIFIER SYSTEM
• RECHARGE CURRENT LIMITED TO 10% OF BATTERY CAPACITY @ C10
FROM THIS WE CALCULATE:
POWER REQUIREMENT FROM BATTERY: 50000W/48 CELLS = 1042W/CELL FOR 1 HOUR
BATTERY SELECTED (EXAMPLE) : FIAMM 2SLA1000 x 2 BANKS (54768W)
TOTAL RECTIFIER CURRENT REQUIREMENT : 50000W (LOAD) + 54768 x 10% (BATT) = 55476.8W
BASED ON SMPS 5000/PRS 5000 (4800W RECT) : 12+1 (REDUNDANT) MODULES REQUIRED
BASED ON SMPS 4000/AEON (4000W RECT) : 14+1 (REDUNDANT) MODULES REQUIRED
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Dimensioning of DC Power Systems
AC input requirements
Each Rectifier Module has an input current of:
Imax = (Pmax/Eff) / Vinput
where:
Imax : Maximum Input Current
Pmax : Maximum Output Power
Eff : Efficiency of the Rectifier Module
Vinput : Input Voltage of the Rectifier Module
NOTE! Max input current of Eltek’s SMPS 1000SI 48V is 5.5A/200Vac
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Heat dissipation
The heat dissipation of the module/system can be calculated as follows:
• Maximum output power of the module/system ; Pmax
• Efficiency of the rectifier module ; Eff
• Power loss ; Pheat
Pheat = Pmax/Eff - Pmax
NOTE! Normally we leave the heat dissipation from the batteries out of this calculation since it’s contribution is so low compared to the losses from the rectifier system. Be aware that during recharge there will be some heat dissipation from the batteries, but not enough to affect sizing of aircon etc.
