Current sensing overview

I am trying to use a Spare Core to detect when a pump receives power from an outlet. The pump draws about 6A. I do not need to measure the amount of current, just know when it’s switched on or off. The outlet is controlled by another controller that I do not want to disable or disturb in any way. I also do not want to disturb or directly connect to the circuit being monitored.

So I’ve been reading threads about clamp-on current sensors like the CR2550 or the SCT-013-005.

Do I just need one of these to clamp on the AC power cord, connect it to pins on the Spark, and that’s it for hardware? Seems deceptively simple… I want to be sure this route is 100% isolated from the circuit and the mains.

Hi @ssstraub

You should run only the “hot” side of the AC through the current transformer. It will be very highly isolated (up to millions of volts) if you keep things physically separate. I usually replace the LED on the CR2550 with a optoisolator just to avoid any transient problems but you already have one level of isolation, so back-to-back zener diodes would work fine too.

Just be careful!

Ok, so it’s not as easy as simply clamping over a stock AC cord… I would have to first separate out the hot wire. Do I understand that correctly? If so, that’s probably not going to work in this application as I do not want to modify the existing setup, just add to it in a completely and easily reversible way.

Thanks for the help.

Hi @ssstraub

You can use this kind of device

with a clip on current probe.


Wow, i have so much to learn. :smile: Of course there is exactly a device that solves that problem too.

Thank you sir!

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