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Power on switch?

I have a sump pump that I would like to be able to monitor. When it turns on it draws power from a plug box on the side of my house. Can anyone tell me if there is anyway to monitor the current flow in a circuit? If I had a way to tell me when the pump turns on and off it would be great.

Best Answer

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  • Depending on how your sump pump is plumbed and where the sump is, you might be able to use the moisture sensor to detect when the sump is full or empty. As I noted elsewhere, you can extend the sensor with wires to home-made water contacts that you would place in the sump, if that makes it easier.


  • Yes. You can use a CT (current transformer) with a NO or NC output and a settable trip point. I'm sure there are cheaper options, but here's something I use in commercial/industrial installs that's in the 'lower scale' of current settings. You'd tie the NO or NC portion of the CT into the breakout board and monitor the state for a change. You'd have to dial the trip point up or down as needed on the CT for your specific pump's draw. This will work for an oven, dryer, washer, fridge, air compressor, etc.

    It'll be overkill in your case, but it'll help you see what it is you're looking for and what options are out there (CTs w/ relays, adjustable trip points, etc). In commercial/industrial installs, I use these to know when water pumps, fans, and other motors are running as confirmation to some other 'smarter' signaling method.

    If you have trouble finding a smaller/cheaper option let me know; I just yanked this one out of memory, and I know it's bulletproof and covers a decent range of currents :)

  • As a 'related but not exactly what you asked' note, once the breakout board support is in place on the 0-3.3V signalling, I expect you'll be able to use items such as the current/voltage monitoring units such as this small 0-30A split core CT which'll output 0-.33V over the detected range; they're quite accurate as I sometime use CTs like this to do per-circuit monitoring and calculate total consumed power. They're best once you sustain >10% of the rated current, tho, so below 3A in this case it'd be flaky. They also have 10A units, but you might have to watch those on some household circuits as they're 16A on a 20A (at sustained 80% rating, etc)
  • Sean: Thanks. I looked on line and I will be able to get a number of different CTs that I should be able to use as soon as we can do analog inputs (as you pointed out). Some of them are really cheap so this should be a good approach. Thanks for the tip.
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