AC outlet tester

Why buy a $20 AC outlet tester, when you can build one for free?


The parts necessary are:

  • 1 – old AC plug. I got mine from an old power cord.
  • 3 – 100K Ohm resistors in parallel. This keeps the power dissipation down so they don’t get hot.
  • 1 – LED. I chose red, size T-1 3/4
  • some heat shrink tubing for electrical insulation between the leads

NOTE: this circuit will not detect reverse polarity of the AC lines, or missing earth ground, etc.

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11 Replies to “AC outlet tester”

  1. man, you are smart! I don’t even know what you need an outlet tester for!

    hmm…after some analysis–is it for testing outlets?

    Couldn’t you just take a lamp or an alarm clock around to each outlet and plug it in to see if it works?

  2. Lol! The female mind constantly… surprises me. Just when I think something is self-evident… very good question. Yes, it’s to test outlets. Especially when you just move into a new place and there’s like 3 switches that don’t seem to turn anything on.

    The alarm clock/lamp approach would work, true, but they are unwieldy. ๐Ÿ™‚

  3. So…what do the resistors and LED cost if you don’t have them? I’m guessing it’s a “free” $10 outlet tester…or something like that.

    Hope you’re doing well up there my friend!

    1. Ahh, very good point, Jesse. ๐Ÿ˜€ Same could go for the soldering iron, solder, shrink tube, and solder sucker (when you mess up!). That brings the price up to, oh… about $150?

      In that case, Evie’s, Melissa’s, and Ciera’s methods are much cheaper. ๐Ÿ˜‰

  4. :roll:What a great idea. I guess I would have to go with the other females in the room, I would have just carried around something and plugged it in. Wish I knew how to do stuff like that.

    Miss you and hope all is going great!

  5. Very sweet.

    As I already bought a circuit alert pen & receptacle analyzer (open & reversed wiring & what not) and have some lamps ๐Ÿ˜› I’ll stick to those ๐Ÿ˜‰

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