12v fan not starting up

Troubleshooting
1

I found an old 12v PC kicking about so I hooked it up to the 12v DC power supply and it all worked fine.
I butchered one of the lines in the power supply to add in an SSR and have configured my brewpi to use it, however…
The SSR turns on when heating/cooling as expected (the LED comes on), but the fan does not start up.
If I disconnect the fan while the SSR is on, swap over the positive/negative inputs, then it starts and continues running until the end of that heating/cooling period. It then stops working until I do the same thing at the next cycle.

Has anyone seen this before? Would a new fan fix it or do I need to do something else? Given the SSR can output 10A, I can’t see current being an issue?

Any help would be much appreciated!

2

SSRs are not suitable for DC current. They switch on a zero crossing, which will never happen with DC current.

There are special DC SSRs, but you are probably better off just using a transistor.

3

Oh, that would explain it!

BrewPi is pretty much my first foray into knocking electronics together in 15 years, are you able to elaborate a bit on the transistor approach?

Alternatively, I suppose I could just get something like this -http://uk.rs-online.com/web/p/axial-fans/5440302/ ?

What sort of device is the brewpi expecting for the fan type, am I barking up the wrong tree with my axial/pc fans?

4

Yep, that one would work with the SSRs.

For a DC fan, you would need a circuit like this: