Sunday, November 13, 2011

Weird APC Back-UPS ES 650 BE650R-CN overvoltage behaviour

Today there is a sustained overvoltage at around 130V. I'm told they paralleled a bunch of feeder lines because of work being done today. I found out about this because an APC Back-UPS ES 650 (BE650R-CN) malfunctioned, and I noticed the "decreasing voltage" light on the line-interactive UPS which I used as the replacement.

I was told that the BE650R-CN was beeping a lot in the morning and that it stopped supplying power. When I plugged in and turned on the UPS without any load or computer connection, it initially seemed to start normally. However, when the power on self test was supposed to finish and the UPS was supposed to switch back to external power, it instead started repeatedly clicking as if it was switching back and forth between external and UPS power.

After seeing this, I took out the battery and tested it. The battery seemed charged, at over 13V, and it was capable of powering a car headlight. Later, when I put it back in the UPS, I could power a 100W incandescent lamp. The on/off button sometimes sticks and fails to pop up, but other than that, the UPS seems fine. It supplies external power, even though the external voltage is still 130V. The upper limit is set to 139V.

I'm left wondering what happened. Did I run into a firmware bug, which was fixed by removing the battery for a while? Could the sticking power switch cause this? Is the upper voltage limit stored in non-volatile memory, or was it possibly lower before and reset by removing the battery?

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