Power usage by UPS

[BillP]

Looking to purchase an SMC1000 to run a tankless water heater, which uses very minimal amps only a few times a day, never for more than a few minutes.  What is the power usage of this unit when it is sitting charged, with no load?  And what is the additional power used by the unit when there is load?  Please say more than just "minimum."  I would like to know if anyone has numbers.  Thanks.

[voidstar_apc · Accepted solution]

You can derive it from the technical specs on this page:

http://www.apc.com/shop/us/en/products/APC-Smart-UPS-C-1000VA-LCD-120V/P-SMC1000

UPS power usage = P_out * (1/efficiency - 1)

The efficiency graph says its 94.6% efficient at 25% load and this is a 600W unit, so:

UPS power usage at 25% = 600W * 0.25 * (1/0.946 - 1) = 8.6 W

UPS power usage at 100% = 600W * (1/0.981 - 1) = 11.6W

So, around 8W at no load seems like the right ballpark. That's 0.07A. And when fully loaded, 11.6W is 0.1A. Power draw while charging will be greater.