BR900GI (900VA) possible with 850Watt PSU on low load?

[eazrael_apc]

This was originally posted on APC forums on 1/26/2013

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Hi,

i am the proud owner of a Back UPS PRO USV 900 VA (BR900GI). It's really a superb device, I wish I had bought one earlier.

Now i want to replace the server protected by the UPS. I got a 850Watt PSU (Corsair Professional Series HX850) very cheap and would like to use it with the UPS. The measured average load of the system is 100Watt and does not exceed 250Watt under stress. Can i use the PSU with the UPS or should I buy a weaker PSU with a lower max load?
I am not sure about the inrush current of the PSU during power on or during the switch from mains to battery. Can the UPS cope with that? Or is that not a problem at all?

Thanks in advance for any answer 🙂

[BillP · Accepted solution]

This reply was originally posted by Bernard on APC forums on 1/28/2013

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The total output power capacity of the BR900GI is 540 Watts/ 900 VA, the PSU you're thinking about using is 850 watts. There is a good chance that using so will overload the UPS because of the inrush current. Find out as well if the PSU is PFC, because if it is then its input power can be as high as 1063 watts when the it senses that the UPS has changed state (On utility to On battery operation.