# Using UPS with generator?



## 211-Bob (Mar 3, 2014)

Generator Experts,

We're a small non-profit, we plan to buy a generator.
I'm trying to do a sizing calculation, to figure out the right size of generator we need.

We have about 20 staff members in our building, half of them have UPS battery backup systems.

I've been told by one company that UPS battery backups put a heavy load on the generator. More than the rating of the UPS.

Question: Is this correct? Has anyone else heard this?
For example: an 800 watt UPS battery backup would put a load equivalent to 2,500 watts, for purposes of calculating load. 
Is that correct?


Our non-profit provides 211 service for our area. 
This is a number people can call to help figure out what services might be available. 
2-1-1 is also the number to call after a disaster, for disaster-related information, like: Where is emergency shelter, or food/water and other needs?
www.211.org

Thanks for any help you can give,
Bob


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## sysrq (Feb 23, 2014)

Whoever told you that is highly inaccurate. Unless these are hardwired UPS in a server room on a dedicated 30A circuit, they pull nowhere close to that kind of power. If they are the typical under the desk UPS for phone/computer workstation, then they can never pull more than 1500 watts form a typical wall outlet, that being a UL standard. I would first calculate load based on what is plugged into each UPS, maybe invest in a kill-o-watt meter, and plug it into each UPS, see how much draw there is. Most of the time, I see a 800VA rated UPS with a computer load of maybe 200-300 watts. To further answer your question, when the generator kicks on, and the UPS transfers back to the generator, and starts recharging its internal battery, they are but a trickle charger, taking hours to recover a depleted battery, I have yet to see a UPS that isnt dedicated pull more than 200 watts on recharge, not including computer load, which then was about 600 watts total load in that one instance. Your situation will obviously vary.


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