SSR code for DC to DC PWM fan control

1st post ever -forgive me if I come off like a jackass. I have searched everywhere I can think but can’t find a simple instruction for setting up a DC SSR to control a DC fan. I have everything wired up to my particle (direct wire without any resistors) but just comes on and stays on when powered up. There is an audible change in speed using tinker and setting the digital output to high/low. However, again the fan doesnt fully stop. Can anyone point me in the right direction? I ultimately want to use PWM to make the fan pump continuous bursts for approx 10 min then completely stop for 5 min and start again.

I think we need to see how you have it wired up.

Adding to @Ric his response, are you sure you have a DC SSR? Sounds like you accidentally got an AC one. You can’t use an AC SSR for DC loads, it will turn on but wont turn off. (normally, AC SSRs switch off on the zero crossing of the AC)


Its definitely DC to DC. Pic attached.

The picture really doesn’t give enough information to know how you have things wired. You should post a wiring diagram to show how things are connected. It’s not at all clear what that silver box at the top center of your picture is, or where the thick black cables coming out of it are going.

thanks for your help

I don’t see anything in that setup that would cause the effect that you’re reporting. You should probably test your relay to make sure it is operating correctly. Disconnect the wires from the load side and measure the resistance between pins 1 & 2 with the input being either high or low. It should be near infinite with a LOW input, and quite a low value (tens of ohms) when the input is HIGH.

:unamused: i guess i cant put off buying measurment equipment any longer …womp womp. Ill give it a try thanks for the suggestion.

A simple DMM is all you need and they are quite cheap :smile:

A few things to try (without a meter). Disconnect the control side of the relay when it is running (simulating an off command to the relay). If it stays on, then you know the relay is clamping on regardless of the input signal. Next if you command the relay off, then while the fan is running, disconnect the fan load to the relay. It will definitely turn off… but then hook it back up. Does it turn on then? Just throwing out some ideas to try until you get a meter. Also, check out the datasheet for the relay, check out maximum switching frequency , etc. Might be a bum relay, but on the other hand, you might be operating it out of its specification.

Turns out this particular SSR has an atypical load terminal arrangement. Once I reversed the wiring it worked as expected.

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Glad you got it!

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