Hey guys, I just bought a 20KW inverter system from a Cellular company. I also got the associated battery system. It puts out 208VAC in 3 phase. What will it take to make it's output into single phase? Or is that possible?
It already is three phase 120V. A 20 KW 208V three-phase inverter is actually three 6 2/3 KW 120V inverters, constrained to operate at 120 degrees from each other and connected in a wye with neutral in the middle. Instead of two hot wires (black and red) "208Y/120" has three hot wires (typically coded black, red, and blue, though the NEC doesn't actually require that).
Obviously this inverter is intended to power racks of 120V single-phase equipment without further conversion, as well as three-phase devices.
You should be able to get a three-phase distribution panel from your local hardware store. It's like a two-phase except it has three hot wires.
In runs to individual circuits you make the hot black regardless of the phase feeding it, just as you lose the black/red distinction in a single-phase 220V distribution panel.
208 is close enough to 220 that typical "220V" appliances can use either. So you can pick any two phases to feed your 220 appliances. (Again make it red & black hot to the appliance run, like a single-phase 220 circuit.)
Could I run a 3 phase motor and turn a single phase generator?
Actually you could use just a motor, spinning away in a corner. Motors, when running and excited, ARE generators. This is a standard hack to transfer power from one phase to another (or to generate three-phase from a single-phase feed, using a starting capacitor to get the motor running in the right direction.)
You'd need a BIG motor. If it's wye connected internally it would have to be wired for 2/3 of 20 KW on each phase to avoid overheating when pulling the other two phases worth of input into the output phase. That corresponds to a 30 KW motor, about 40 HP. Maybe waist high, and a full load for a half-ton truck. And it would burn maybe a KW into heat as it spins. Like having a space heater turned on in your equipment room 24/7.
But why bother? You've got THREE 55A 120V feeds coming out of this inverter and can use them as is with no further conversion. That's as much power as an 85A 220V utility feed (if there were such an animal), just arranged a little differently - but no less conveniently.
