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When my window AC kicks on, one of my two monitors kicks off for a couple seconds. It's never the same monitor when it happens. I installed a very large UPS thinking it was power drops, but it doesn't help at all. Any other suggestions?

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    When my window AC kicks on, ... What does this mean to you? To me, it says you are starting the computer and the monitors reset.
    – John
    Sep 15 at 14:32
  • The opposite monitor would still be on and fully functional when this happens, mouse and everything.
    – Steve
    Sep 15 at 14:35
  • Is the UPS a "continuous conversion" or a normal pass-trough?
    – DDS
    Sep 15 at 14:42
  • Dont know. How do I find that out? Its a Cyberpower 1500 AVR with voltage regulation. I have the monitors and tower on the battery backup.
    – Steve
    Sep 15 at 15:00
  • Please answer the first comment.
    – harrymc
    Sep 15 at 15:16
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The voltage is dipping when your air conditioner kicks in. This will happen if your PC and/or AC is a long distance from your breaker panel AND they are on the same circuit. On start up, the AC is drawing more current which means the voltage drop to the wire or I2R losses goes up decreasing voltage at load and hence the monitor shuts down.

From Fundamentals of Electricity - Voltage Drop - Definition

enter image description here

Without knowing the info on your UPS, but I'd guess the voltage never goes away so your UPS does not kick in.

The true solution is thicker wires and/or separate wires to the air conditioner and the computer. That is not realistic for most users.

Alternatively, the air conditioner and the computer must be on different circuits. Move your computer to different outlets in your home and see if this impacts the problem. All outlets in the same room are typically on the same circuit. But if another outlet is closer to the breaker box, the impact of AC starting will be less. Extension cords will make the problem worse.

You do need to investigate the problem a bit more. This info should help.

If moving the computer has an impact on the problem, then the problem is voltage dip and you can select a solution to fix the problem. Options for solutions are outlined in: Case Study: Choosing among Voltage-dip-compensation Devices on the Market.

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  • OMG! Nice answer to balance my comment :) !!! +1 Such a detailed explanation. Also.. (for the OP).. like the answer says.. try to understand what outlets are connected to what line to the breaker. Just moving the cord will likely put you on the same circuit breaker so you need to figure out what outlets are on a different breaker switch. Sep 15 at 15:25
  • @SeñorCMasMas I couldn't fit it in a comment! Sep 15 at 15:28
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    Oh.. one trick I use it to use a high wattage (incandescent) light bulb plugged in to the system when it kicks on. You will see it dim. You could also use a multi-meter if you have one and know how to use it. Sep 15 at 15:32
  • I appreciate the help, but why would one monitor do that and not the other one? They are both plugged into the UPS. Ive had the power stop in an outage and the whole computer kept going as it should. So is it the voltage regulation part that isn't working correctly?
    – Steve
    Sep 15 at 22:06
  • No idea. I have a test setup with dual monitors and both go out when a small fridge on same circuit kicks in. I live with it and I know how to fix it without a UPS. I don't know your setup, so any other info is pure guesswork. Sep 16 at 3:01

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