I have a Back-UPS XS 900 on a standalone Debian server that seems to randomly start sounding a constant overload alarm, even with nothing plugged in. The alarm continues to sound until I manually turn the unit off. Additionally, nothing seems to be logged when the alarm starts to sound.

Here is the output from apcaccess while alarm is sounding an nothing is plugged in. The BATTDATE should actually be 2007-07-05, but apcaccess is reporting it incorrectly (the correct value is returned if I query it in apctest). The only difference appears to be that STATUS changes from ONLINE to a blank value.

APC      : 001,038,0925
DATE     : Sat Dec 05 16:37:38 MST 2009
HOSTNAME : kamui
RELEASE  : 3.14.4
VERSION  : 3.14.4 (18 May 2008) debian
UPSNAME  : kamui
CABLE    : USB Cable
MODEL    : Back-UPS XS  900 
UPSMODE  : Stand Alone
STARTTIME: Sat Dec 05 16:22:24 MST 2009
LINEV    : 117.0 Volts
LOADPCT  :   0.0 Percent Load Capacity
BCHARGE  : 094.0 Percent
TIMELEFT : 557.7 Minutes
MBATTCHG : 5 Percent
MINTIMEL : 3 Minutes
MAXTIME  : 0 Seconds
SENSE    : Medium
LOTRANS  : 088.0 Volts
HITRANS  : 139.0 Volts
BATTV    : 25.4 Volts
LASTXFER : No transfers since turnon
TONBATT  : 0 seconds
CUMONBATT: 0 seconds
STATFLAG : 0x07000000 Status Flag
MANDATE  : 2007-07-05
SERIALNO : [removed]
BATTDATE : 2145-00-36
NOMINV   : 120 Volts
NOMBATTV :  24.0 Volts
NOMPOWER : 540 Watts
APCMODEL : Back-UPS XS  900 
END APC  : Sat Dec 05 16:37:48 MST 2009

I have already tried it without anything plugged into it and with the server alone. I have also used a Kill A Watt to measure the outlet voltage and it measured 117.4 V when I tested it and the alarm began to sound.

Is there anything else I can check?

EDIT: The lights that show up when this happens is the blinking red overload light and nothing else.


I had a MOSFET failure on my APC RS-1000 with the same observations as yours:
Overload light and constant alarm even when nothing was wired on the outputs.

They changed the board (rather the entire unit) and retained the batteries which were still functional.
Uh, I had some hard time working this out with the APC Service though. That was not exactly stellar.

  • Yes, it does indeed need to be repaired/replaced. I didn't seem to have a problem getting a return set up. – Lara Dougan Dec 7 '09 at 16:17

On this UPS, the 24v 40mmx40mmx10mm DC cooling fans were defective after a few months use, if you listen you can hear a grinding, screaching sound emmiting from the fan, the fan drag sends a error code to the CPU warning that the unit is under overload.

This fan cools the regulators just behind the fan. Replace the 24V cooling fan, and your problem is solved.

You can try a shot of Radio Shack tuner cleaner in the space between the fan boday and the fan blade, (don't get carried away, just a squirt or two) to maybe get a few more days, weeks from it, while you wait for the new fan to come in the mail from China.

eBay sellers from China stock this part and it costs only $3.50 shipped to the USA.
Search for "DC Cooling Fan 9 Blade 5V 12V 24V 40mm x40mmx10mm NEW", at check out specify 24v fan, as they sell 5v, 12v, and 24v units in the same auction.

It kills me that APC will not tell you this, only to go do a trade up, which when you go to do the trade up, they give you maybe $5.00 for your unit, RIPOFF! I would never give them the satisfaction of getting there defective product back, so they can factory refurbish, and re-sell it in there satellite store for full price.

Also Mouser and DigiKey sell a fan to replace it, but the shipping will kill you.


According to the manual if it happens every 5 hours, then the battery need change.

You don't describe what indicators light up though.

  • The battery chirp every 5 hours is different from this tone. The alarm tone stays on until I manually turn the unit off and the only light that is on is the blinking overload light. – Lara Dougan Dec 6 '09 at 1:57

Replace the 40mm 24v fan and your problems will be over. Snip the wires, twist, solder, shrink tubing. It works like magic. I would never have believed that the fan could cause the overload problems. But... it does. I bought mine in a local electronics shop, but they are also available on ebay. Remember, that fan is 10mm thick, not 20mm thick. The 20mm thick fan will fit if you buy longer metric screws. That's how I put mine in about a week ago. It has been working very nicely, and the fan is much quieter.


I was able to get my APC xs 900 fixed by removing the fan and cutting away the decal to expose the bearing and giving it a shot of WD-40 while it was running. I actually felt the fan RPM double with the oil. I reinstalled the fan and my unit was back in operation!


It sounds to me like it is either dead / old battery or a general malfunction.

One thing about APC UPSs... Their price, you generally pay more, but they are generally brilliant quality and come with good support. You may want to email them and see what they say.

protected by Community Jan 19 '14 at 6:25

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