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Uninterruptible Power Supply

  1. Sep 27, 2014 #1
    I have a small refrigerator in my projector room. Many times when the compressor in the refrigerator turns off it sends a voltage spike through my home circuitry and distorts the projection image.

    Example: When I'm watching a movie on the projector everything is working correctly. Then the refrigerator compressor turns off and the movie screen goes out and I can only see white noise on the projection screen.

    I would like to know if an uninterruptible power supply would correct this issue. I know they work for power outages, however I'm not sure if they will protect over voltages with a reaction time fast enough to correct this problem. I currently have the projector plugged into a simple surge protector and this obviously does not help. Thank You for taking the time to read this and any help is appreciated.
  2. jcsd
  3. Sep 27, 2014 #2
    Have you tried using a surge protector for the refrigerator also? That should limit the amount of spike energy going into your house wiring. If you're in the US then it might help if you put your projector and refrigeration on opposite legs of your house wiring (if possible).

    I don't know about the UPS. I don't think it would give you any more protection than a surge protector when on AC power.
  4. Sep 28, 2014 #3
    Yes, I forgot to mention that I am in the U.S. and that it is not possible for me to put the refrigerator on a different breaker in the house without running an extension cord into another room. I was trying to avoid that by getting a UPS. The refrigerator is currently plugged into a surge protector however. Thanks for the reply.
  5. Sep 28, 2014 #4
    These problems can be difficult to remedy. It's normal for inductive loads to spike the power line when they switch off. I once had a programmable thermostat (which was connected to the ac mains for power) that would randomly lock up when the heatpump switched off. After being unsuccessful at fixing it myself I called the manufacturer and found out that it was a design oversight. They replaced my thermostat with a new redesigned unit at no cost to me.

    The only other thing I can think of that might help you is an isolation transformer. These are probably in the same price range as the UPS that you were considering. But of course there's no guarantee that it will work.
  6. Sep 28, 2014 #5


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    When I've worked on solving any kind of noise problem in the past; go to source of the noise. Just sayin'
  7. Sep 28, 2014 #6

    jim hardy

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    I'd start with real simple stuff first.
    This little $5 tester should be in every homeowner's tool drawer.
    First thing to check is - are the outlets wired right?
    I have an incandescent touch lamp that acted erratic. Turning on any CCF bulb on the same outlet turned the touch lamp off.
    Found the outlet wired wrong: hot & neutral swapped and earth ground not connected.

    Surprising it happens on the transition to OFF. That sounds more like arcing in the thermostat than an inductive voltage spike.
    Does it happen every time, or intermittently ?
    Does it happen when you simply unplug the fridge while running?

    Next - do the fridge and projector perhaps share an extension cord ? Separate them if you can.
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