Max inverter power questions

Q&A and troubleshooting
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1

I am looking for some clarification on maximum inverter power. The 10 KVA model is the largest available for US power and I want to make sure that two of them in split phase are adequate. I have tabulated most loads and come up with around 8,500 to 9,000 watts on each leg but these numbers include loads which typically run for a few minutes at a time and typically not all at once. I am in the process of logging actual consumption but need to know better how to capture consumption averaged over various time periods.

I have read the post from the old forum:

and also watched Johannes Boonstra’s webinar:

I am confused about the difference between the VA rating for an inverter and the maximum POWER rating and how the 130% applies.

The calculations seem to use the VA rating as the 130% power value but this value from the spec sheets is slightly less than 130% of max continuous power at 25 C:

For a 10KVA Quattro, VA max is 10,000, Power max is 8000 W and 130% of that is 10,400 W, so the 10 KVA number is close.

So am I able to consume 10,000 WATTS for 30 minutes or less assuming the unit starts at idle and ambient temp remains at 25C?

What happens for shorter duration power peaks? Is there any way to predict this? From the Q&A post referenced above, I see a number of 150% for 5 seconds. However, this is not mentioned in the webinar. Is this a figure I can rely on?

Any help would be very much appreciated. Thanks.

2

The peak power rating is typically for indicating motor starting capability, this gives a sharp peak - typically 6-7 times the motor’s power rating, but for only 1 second or so, with an exponential decay. this rating is 2x the inverter’s nominal VA rating. At maximum power, the power factor rating of the inverter is 0.8, this gives the ratio between the VA rating and the active power rating.

So the inverter power rating depends on what your average power needs are, and the ‘crest factor’ of your load. So you need to look at what motors you have as load, typically fridge and A/C compressor motors. swapping ‘old’ models of these for inverter driven compressor designs is also a great help - this eliminates the motor starting surge, that inverters typically find difficult to deal with. They also tend to operate more efficiently than the older designs.

I have used EKM meters (from California) previously for doing load assessments, these smart meters are very good and quite inexpensive for their function. This can give you a very good idea of your load and crest factor with on line logging.