Question about APC Back-UPS XS900 (BX900) UPS System

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Apc xs900 will work off batteries not off ac

Unit has new batteries and new fan. When NOT plugged in to AC unit will come on and work as expected.( Delivering power to output ). Plug in AC cord, unit beeps and both online and on battery lights come on and blink. No power is being output. Also hear clicking sound that happens when both lights blink. Unplug AC cord, turn unit off then back on batteries will produce power to outlets. So then the unit works when not plugged into AC but works off batteries when unplugged.

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So something happened to this apc and the first thing is to replace batteries...
I'm going to guess major circuit board failure.
go to apc site, download Power Chute software and pray there are useful diagnostics.

Posted on Apr 01, 2014

  • Brown County
    Brown County Apr 02, 2014

    I will download software and try it but I am with you, I think AVR circuitry is bad. Wish I had figured it out before buying new batteries and fan.


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Check UPS relays one of the relay might be welded thats the reason why once you plug in on the Mains your UPS start blinking and shutdown the load. Hope this helps

Posted on Jul 09, 2014


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SOURCE: APC Back-UPS XS900 shut down

Replace the batteries. Your UPS needs a little battery power to start back up. once the batteries are replaced all should be well

Posted on Aug 29, 2011

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You need to reset the unit to recognize the new battery, I had same problem with one apc smart ups on the bench the other day.

On ours we had to turn off the unit unplug the battery wait 5mins

press the on key and hold for 20secs

reconnect battery

plug in to mains

and start as normal. We did this but still had very low battery time and the flashing lights, so we disconnected the comms interface, that sovled the problem.

It may work for your unit, suggest you check the manual before you try if you are unsure

Hope this helps
Thanks for using FixYa

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