Devices runs longer on UPS with meter attached (very odd) - AVS Forum
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post #1 of 5 Old 01-18-2013, 06:18 PM - Thread Starter
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I’m hoping someone can help me.

I have several UPSs. Amongthem is a cheap Newpoint UPS. It’s something like 275W/550VA. I was recently experimenting with it, and found some very interesting behavior.

I have a 120V lamp with a LED bulb in it. It takes about 8W, 15VA.

if I fully charge this UPS, hook the lamp up, turn it on, and yank the plug, the light remains on for about 3 minutes.

here’s the kicker – if I fully charge the UPS, hook the lamp up with a “Kill-A-Watt” power meter between lamp and UPS, then pull the plug, it runs for 24 minutes.

the meter itself is simply measuring usage, yes? surely it doesn’t increase runtime 7x.

yet, this behavior is reproducible – at least with this lamp and UPS.

can anyone explain why?
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post #2 of 5 Old 01-18-2013, 07:18 PM
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Some UPSs require a minimum load and will shut down if it isn't there. The LED lamp is not much of a load. Adding the Kill-a-Watt was apparently enough to push you over the threshold.
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post #3 of 5 Old 01-19-2013, 06:37 AM
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Quote:
Originally Posted by Colm View Post

Some UPSs require a minimum load and will shut down if it isn't there. The LED lamp is not much of a load. Adding the Kill-a-Watt was apparently enough to push you over the threshold.

The meter is in series with the load, decreasing the load presented to the UPS...still doesn't make sense.
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post #4 of 5 Old 01-19-2013, 07:22 PM - Thread Starter
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well, what started all of this was my suspicion that the battery had gone bad.

with a 60W incandescent, it goes out immediately in both configurations. this confirms my suspicion of a bad battery, and explains why it quits in under a minute on my Verizon FiOS ONT, but doesn't add any data to the runtime conundrum.

interestingly enough, after it fails with 60W, I can turn it back on and run the LED without plugging it back into the wall. That 60W load is too much.

other fun fact: when the UPS is plugged IN, the meter (between UPS and lamp) shows 8W, 14-16VA usage. when the UPS is unplugged, it shows 0W, 0 VA, yet the light is on.
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post #5 of 5 Old 01-21-2013, 07:53 AM
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It doesn't take much current to light an LED.
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