30-40 Hz on battery?

[Anonymous user]

Hi, I am new and here is the first post.

I have kill-a-watt and I checked both APC UPSes I have

First, an APC Back-UPS ES 550

I plug the kill-a-watt into ES 550 and I plug a 40W incandescent lamp in it. the ES is plugged into a GFCI outlet. I push the TEST button on the GFCI, the power goes out and now I run on battery. I use my Mac laptop to monitor the charge left in the battery and when I get to 50% I stop and restore the power. All this time, the kill-a-watt showed 115V and 59.9 Hz.

I do the same thing with a APC Back-UPS XS 800. Before I cut the power off, the kill-a-watt shows 59.9 Hz and 125V. I trip the GFCI, the lamp is now running on battery, the kill-a-watt shows 115V but the frequency jumps anywhere between 30 and 40 Hz. Occasionally I see a 42Hz, a 28Hz, but most of the time it's 32-35-36 Hz in that range. I can actually see the lamp flickering. Of course, because this is a much higher capacity UPS, it takes forever to run down the battery to 50%, (50 minutes with the 40W lamp) and eventually I stop after about 30 minutes at 70% charge. I restore the power, and now the kill-a-watt goes back to 59.9 Hz.

So is the second unit functioning properly? can the 30-40 Hz power damage something? I was about to hook this up to my Plasma TV (average 200 W, max stated in the manual 540 W but I never saw this on the kill-a-watt).

thanks.

[Erasmus_apc · Accepted solution]

The output from that unit should definitely be 60hz, or within a range of roughly +/- 1hz when on battery. A frequency of 30-40hz is not normal and should not be used to power any attached load. I would call into tech. support @ 1-800-800-4272 and let them assist you with a few more troubleshooting tests, then investigate whether you are in warranty to provide an RMA.