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Uninterruptible power supply crackles, causes light flickering

Uninterruptible power supply crackles, causes light flickering

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  #1  
Old 08-17-19, 05:37 PM
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Uninterruptible power supply crackles, causes light flickering

My home office has a 15 amp circuit (14 ga wire) with a PC, UPS, and a few small loads like a clock, router, and ceiling light. I added a second PC and UPS, and occasionally the second UPS will crackle, which I assume is it switching from line voltage to battery and back again quickly. The ceiling light also flickers when this happens. I checked the fixture and changed the bulbs, but it keeps happening. I also tried using the new UPS with the old PC and leaving the second one off, and the problem doesn't occur, so apparently the problem is not a defective UPS.

The UPSs have 1000W capacity each, but they don't draw anywhere near that with just a PC, clock and router attached. I don't know what the residual draw of the UPS is, but I can't imagine that even with both UPSs and PCs connnected, I'm pulling more than 10-12 amps. If I turn on a printer, the ceiling light definitely dims--the printer pulls 400W when printing--but the breaker has never tripped.

Looking online, I found that the UPSs have a sensitivity setting that controls when they kick in. They came set at high, and I changed them to medium, which didn't help. There's a low setting, but the mfr. doesn't recommend it.

Will putting in a 20 amp breaker and rewiring with 12 ga solve this problem? Or is it something else?
 
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Old 08-17-19, 06:26 PM
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The flickering lights is a power fluctuation. That is why the UPS is switching. It is doing its job.
If only the lights in this room are flickering then it could be a loose connection somewhere on the circuit.
 
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Old 08-17-19, 07:11 PM
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But the light doesn't flicker except when the second UPS and PC are connected. And it's not the UPS, because I swapped the new one with the one on my main PC. One PC and UPS doesn't cause a problem. Add a second one and I get flicker and crackling, which is why I'm wondering if uprating the breaker and wiring to 20A will solve it.
 
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Old 08-17-19, 08:37 PM
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The extra load from the second UPS and PC could be causing a poor connection to act up.
 
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Old 08-18-19, 05:13 AM
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Hi, check the connections on the receptacles where the UPS’s are plugged in, also check other receptacles on that circuit, make sure the conductors are wrapped around the screws and now back stabbed into the receptacles.
Geo
 

Last edited by Geochurchi; 08-18-19 at 06:02 AM.
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Old 08-18-19, 11:18 AM
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joed and Geochurchi, thanks for the suggestions. I'll check them out. Am I correct that a properly wired 15 amp circuit should be able to handle 2 PCs, 2 UPSs, a light, a clock, and a router without flickering?
 
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Old 08-18-19, 11:42 AM
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It should be no issue for a normal home PC. If the PC loads were the problem the breaker would be tripping not power flickering.
 
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Old 08-18-19, 12:26 PM
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Hi, to much load would either trip a breaker for the circuit or the one on the UPS.
Is there any indicator LED on the UPS to show if it is switching to battery?
Geo
 
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Old 08-18-19, 12:33 PM
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Geochurchi, probably. I'll have to take a look if it happens again.
 
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