Question about APC Back-UPS® XS 900 (BX900R) UPS System

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Brand new apc 900 ups and when plugged in it after a while will beep loudly & overload button will flash..

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  • TdiPWR May 11, 2010

    Does overload come on while nothing is plugged into the UPS ??



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I bought an APC 900XS UPS for $10.00. at a garage sale. I know you’re going to tell me that you take a gamble at a garage sale whether it works or not.
Please do not try to fix the device unless you are qualified electronic technician. There is high voltage and high current that is very deadly.
Before plugging the UPS in I opened the battery compartment and found the positive lead off of the battery. Took the batteries out and measured the voltage on both batteries and I couldn’t believe it, they were both good. Well at least they measured the right voltage. There are two batteries, each one is 12vdc. The real test would be to put the batteries under a load.
I plugged it in and ran for about six hours than the "Overload" LED and alarm turned on. I didn't have anything plugged into it "AC". When I first plugged it in, in the beginning I noticed the fan was running by the sound of it. But later that evening about an hour after plugging it in the fan was off. Don’t know why unless there is a temperature monitoring circuit on that heat sink and the fan wasn’t needed? After opening the unit I found a component unsoldered at one end. It looks like a capacitor or a spark gap component across the AC line. I don’t think that’s original problem. Re-soldered the component back in place. Took the board completely out and unplugged all the connectors. Again, after talking the PCB out. I didn’t see anything damage / burned. Without a schematic diagram one really can’t troubleshoot. I did noticed that (small) fan was kind-a hard to move by hand. I applied an external 24 volts to the fan. It was almost drawing 0.120 amps. The fan is rated at 0.070 amps. Took the fan apart and applied Tri-Flow (oil) to both bearings. Now the current draw has lowered. I’m wondering if the PCB has a current monitor of the fan driver, if the fan is/or requiring too much current that the unit shuts down. That heat sink that the fan is on seems to not dissipate very much heat, if any. It seems the fan is an over kill. There is a temperatures sensor mounted to the heat sink, probably to monitor the temperature of the heat sink in case the fan stops. Temporally connected everything back together. Now it’s running fine, but time will tell whether it’s going to stay running. After running four hours without any alarms, I re-assembled the unit. It’s been two days and the fan is still running and without any alarms. I haven’t plugged the computer into it yet.

Posted on May 11, 2010

  • Billthetoolm Jan 30, 2015

    It's been working finr the last 5 years

  • Billthetoolm Jan 30, 2015

    working fine for the last 5 years


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Did you open up the battery compartment and connect the battery leads correctly? (At least once, I managed to get the lead that shipped in place to come loose as I put the battery back in to the compartment.) Then let the unit charge (while off for ~16 hours).Make sure you do not have equipment that takes more than 540 watts plugged in (many gaming systems have larger power supplies than this). That is the rated full load for this UPS..

If you have done all of the above, contact APC because you have a faulty unit.

I hope this helps.

Cindy Wells

Posted on Dec 09, 2009


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change the internal fan its a 18-24V type change it with a ball bearing type and yes a 12 volt will also work, with 120v input fine and under medium load the fan is only supplied with about 15 volts and only reaches 24 volts if the load shoots up or there is a power fail situation

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I have an APC XS 900 for about 1 1/2 now. I started getting a continuous beep with the overload light turning on. I could not get it to stop, even when the computer was disconnected. After reading the...

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.

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To confirm if your battery needs to be replaced or not, you can run a self test. Ensure that the battery has had time to fully charge (and that it is definitely correctly connected), and then turn off the UPS, and turn it back on. It will automatically run a self test.

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Ran for about 15 minutes. Hooked up to one

Ether the unit is overloaded or the internal battery is given out, or the overload circuit has failed there are only 3 problems that it could be. Not to go to much in depth on this unit APC does have a garentee and I trust you will call them and tell them this exact same issue if they find the unit is faulty they will replace it even though it may be out of warrenty if you get them on the phone and explain to them they will help I know a Greg over there.

Btw, I’m available to help over the phone in case u need at

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