SMPS

Output/input = efficiency. I understand battery charging operations are about 60% efficient (battery technologists can refine this figure). 15 kw/input = 0.60. Therefore (damn, not in the symbols list) input = 15/0.60 = 25 kw (also = 33.5 hp). This is just ballpark.

At 48 volts, 15 kw = 312.5 amps. Thus the 300 AH battery will last a bit less than an hour, and the 600 AH battery a bit less than 2 hours (that is, if the batteries are 48 volts). Again rough numbers.

If Tornado is right (e.g. battery charging efficiency = 60%), then input current will be around 110 amps @ 230 volts (110A X 230V = 25300W; 25300W X 60%eff = 15180W).

DC output power: 15 kW

AC input : 15kW / (efficiency * power factor) = <example> 15kW / (0.92*0.99) = 16500 (VA)

Efficiency depends on Power supply manufacturer / converters / AC line voltage etc in use: up to 96% possible for 48Vdc telecom voltage

1 - phase system at rated 230Vrms: 16.5kVA/230V = 72A - check line voltage range e.g. 184Vrms -300Vrms. important: fuse discrimination and short circuit current capabilities when selecting breakers

3 - phase system at rated 230/400 Vrms: depending how the converters are spread over the phases, like 5x 3kW rectifier 2-2-1, or 10x 1.5kW rectifier 4-3-3:

case 2 rectifiers 3kW per phase: 0.4* 72A = 29A at rated voltage

case 4 rectifiers 1.5kW per phase: 0.4*72A = ca. 29A at rated voltage

Input power can be measured with a voltmeter across the input terminals and a current probe on the "high" wire. The product of these two is the power.

Output power is measured the same way.

Guest #3 is pretty much on the spot. He states UPTO 96% efficiency. That is attainable but exceptionally good. Low 90s might be a more realistic figure.

The efficiency of charging of the batteries doesn't come into the question. So you should be looking at about 16.5kW but you may be looking at considerably more kVA as these are notoriously low power factors, unless they have correction circuits. If it has a pf of 0.7 you will need about 100A to run it at full power.

Note however that you are looking at a standby charger whose normal duty will be considerably lower than the max since it must have enough power to run the PABX (or whatever) and recharge the batteries after a power-out.

Do You know the standing load on the system?

Chas