Surface temperature sensor?

I’m using ESPHome to trigger two 40amp relays on a 240v circuit (controlling my air compressor). I want to measure the temperature of the relays and trigger a fan to turn on if the relays get to a specified temp. Does anyone know of a temp sensor that works with ESPHome that specifically measures the temperature of a surface? In this case, a relay heatsink?

I think I just took apart the dht11 and it worked as a surface temp?

The MLX9061 sensor measures an object’s temperature using infrared.

While there is no official support in ESPHome, you can find custom component code here:

You can thermal epoxy Dallas ds18b20 sensors to a surface. For a more easily replaceable sensor epoxy or friction fit it into an uninsulated ring lug (where the wire usually goes) and screw the lug to a surface. Another option (if you can find them) is a 2N3402 transistor TO-92 heatsink.


Thanks for the replies! I like Tom_I’s suggestion. In the end, I decided to go with a vibration sensor to see when the compressor is running then run the fans based on that. I figured a binary sensor that only updates when the compressor runs would be better than a temp sensor updating every x seconds when the compressor may only run once or twice per week.

Your relays should not be increasing in temperature, so there should be no need for fans. :slight_smile:

If you mean “relay” and not “contactor”, then it is the wrong device to control that load. For a big inductive load like a compressor pump motor you need a contactor. I use one to switch my air compressor (240V, 5HP, magnetic starter) and the contactor stays cool to touch.

I’m using these relays, and they get hot.

Should I be using something like this instead?

This is the air compressor, it’s a 5hp, 230v, 21.5 amps.

Ah yes, an SSR would definitely get hot because they are in fact a TRIAC which has, though very small, a resistance.

Yes, ideally you would use a set of physical contacts like the link you posted. It may be more convenient for you to get a contactor with a 240V coil and use a smaller relay to switch it rather than finding a source of 24V. That’s what I do.

The nice thing about a contactor vs. a SSR is that a contactor won’t fail closed, while the normal failure mode for an SSR is to fail closed. Plus you get a really satisfying “THUNK!” when it closes.