New use of UPS' as charge controller

[Sunking]

Vince what size UPS systems are you talking about?

What I am driving at is size matters. Smaller KVA UPS can and do operate at lower battery voltages. For example let's say a rather small 5 KVA UPS operating on 48 volt batteries will draw up to 120 Amps from the batteries. For a 15 minute reserve capacity you can use small 50 AH AGM batteries. 120 amps is not a lot of current.

But now turn the table for something like a 1 or 2 MVA UPS. If you tried that at 48 volts we would be dealing with 21,000 amps. There is no conductor or battery that could handle that much current. So for those systems you have to use much higher voltages to get the current down to something manageable.

[SunEagle]

Vince what size UPS systems are you talking about?

What I am driving at is size matters. Smaller KVA UPS can and do operate at lower battery voltages. For example let's say a rather small 5 KVA UPS operating on 48 volt batteries will draw up to 120 Amps from the batteries. For a 15 minute reserve capacity you can use small 50 AH AGM batteries. 120 amps is not a lot of current.

But now turn the table for something like a 1 or 2 MVA UPS. If you tried that at 48 volts we would be dealing with 21,000 amps. There is no conductor or battery that could handle that much current. So for those systems you have to use much higher voltages to get the current down to something manageable.

The UPS I was talking about was only about 12 kva which would keep the amps to about 300 with 48 volt batteries.

I understand now. It is similar to a large power distribution system. To keep the amps down and wire size within reason you need to go with a higher voltage. It keeps the overall costs down and helps with minimizing any voltage drops.

I don't think I need to worry about that since the portable system I am looking to build will only use about 700 watts max.

Again. Thanks for your input and perspective.

Vince