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I've got a home-built watercooler that I've been using for more than a decade on my personal PC. The unit has a single switch for the AC mains (120V 60hz) that splits to power both the AC waterpump, and the computer's ATX Power Supply. Over the years, I has worked well, but I have seen a large amount of power supplies die while attached to this computer. Average PSU lifespan connected to that system has been 1-2 years. For a while I just thought I was unlucky, but it finally occurred to me that this setup might actually be causing the PSU failures by sending the AC transients caused by the AC motor start-up straight to these PSUs.

I realize that due to the sporadic nature of the problem, I can't prove that is the problem, but I thought it might be worth looking into a surge suppression circuit to shield transients from the pump from hitting the PSU. (They need to stay on the same switch to be a failsafe from the computer running without the pump turned on.) I figured it'd be more fun to build a circuit than to buy something off-the-shelf.

I'm seeing three types of surge suppression circuits:

  1. An inline NTC resistor with a MOV between line and neutral. (The NTC prevents inrush current until is warms up enough to pass full current through)
  2. Inline inductors on line and neutral with MOVs between line and neutral on both sides of the inductors. (Example)
  3. Similar to #3 but with inline resistors instead of inline inductors. (Example of both this and #1)

What pros/cons do each of the circuits have with regards to motor transients and ATX PSUs? Also, I'm not finding component values for these circuits. What are reasonable component values (the MOVs, the NTC, the inductors) for them to work?

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  • \$\begingroup\$ That is a suspiciously woeful lifetime for the power supplies and should definitely be investigated further. Have you eliminated other causes like dirty environment, too much load, bad brand? Protection circuits of the kind you are describing should be present already in any halfway decent power supply. \$\endgroup\$ – replete Dec 17 '17 at 1:09
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    \$\begingroup\$ a small water pump like for a tabletop fountain or PC cooler is likely a shaded pole induction motor (same type as used in desktop fans etc) these don't have large startup surges, the PC powersupply's input capacitors should eat up any surge the motor produces. \$\endgroup\$ – Jasen Dec 17 '17 at 1:27

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