Maximum distance between control board and relay modul


I've a very simple question : I use a ESP32 adafruit feather board 3.3V and I want to tun on /tun off a relay module.

The problem/question is : distance between my board and the relay modul il about 70meters.

Will it work? Any voltage loss? Is there a best practice to follow?

Thanks a lot for you answer


Maybe you could try my non technical approach. If you have 50m or 100m drum of cable, connect the relay and board to either end of the cable, and see what happens. You can do this on the test bench.


Almost certainly no problem, but it depends on your overall electrical environment. Using optoisolated relays becomes interesting to protect the relays from voltage spikes on the long wires (they double as antenna, can give interesting results in case of nearby thunderstorms)

I'd be looking into wireless solutions at those distances.

I want to tun on /tun off a relay module.

WHICH relay module? What size wire? And with only 3V outputs?

there is a formula to calculate the wire resistance look it up, you can then get an accurate voltage drop calculation, EMI might get in your way so you might have to use some small capacitors, coax cables and such, for that distance it would be nice to amplify the signal, and have a trigger circuit at the other end, but it might work as is depending on the conditions…

Until it is explained which relay module we are talking about, the discussion gets nowhere. :astonished:

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