I want to be able to plug my APC Smart-UPS RT 8000VA 208V into a diesel generator when our power will be down for an extended period of time. The max OUTPUT of the APC unit is 6400w. Does that mean I need at least a 6400w Generator?
If the unit is rated 8000 VA, and the output is 6400 W. that hints that the through-put efficiency is about 80%. You need a generator that will supply at least 125% of the load you apply to the UPS.
Your problem is not that simple. Average generator is either 220 or 110 volts or three phase. If three phase, you have to know weather delta or wye connection. You are talking about a leg of a 440 volt 3 phase. Not totally familiar with voltages between phases or one phase to neutral. Cheapest is to get a 220 volt generator and a buck/ boost transformer to convert the 220 to 208. Since your ups output is 6400 watts, power your application directly with a generator that will power your buck/boost transformer with at least 6000 watts. 7-8000 watts is a better guess. Or I assume that you want to use the UPS to give perfect waveform to whatever you are powering. In that case --- you will need to use the buck boost transformer after a generator that gives 220 volts at least 9000 watts.
yes, plus extra for loses and to charge the battery. I'd get a 10kW unit, at least. But that is a lot of power, do you actually use all of that, or is the UPS oversized? In that case you can reduce the size of the generator. .
