SSR always on? Hardware / wiring advice

Hi all,
I’ve got my system setup and seems to be running/working just fine, however… I’m a little concerned about my wiring because the heater and cooling pump are running when the SSR’s are off, so i think there’s a problem with my wiring. :face_with_raised_eyebrow: :

I’ve had a good look through the forum to find some answers, but I’m not finding answers.

My setup is a FTSS type setup. Heating belt for warmth and a pump in an esky full of ice water to cool (circulated through a coil running through the fermenter) with DC SSR’s.

Here’s a basic wiring diagram:

Plus a couple of photo’s

So both the belt and the pump are on when I plug it all in, however the SSR’s aren’t switched.
Is this normal? Or rather have I been a bit of a twit with my wiring?
Hope I’ve given enough info, any advice would be great!


Just to be sure, you are running on 12V DC, right? You used a cable that’s for 230V AC (brown, blue, green/yellow).
Your choice of plugs suggests AC too.

Your wiring diagram doesn’t make sense.

To control a 12V heating pad:

12V+ --> heating pad --> SSR +     /     SSR- --> 0V/GND

If you want to switch AC, you have the wrong SSRs.

Thanks for the response.

Cool, I think you’re right about the SSR’s.
I’m just getting the hang of this, both the pump and my belt are both 240V AC. That was pretty silly.
Might be making another purchase through your store unless I can find it locally (any suggestions for Australia?

Also, how warm do the SSR’s get? Will I need a heat sink?
(Noting the pump is 7w and the heating belt is 30w)

Thanks again for your help.

With only that amount of power, they won’t get hot.

The brand I used to sell was PQLYT, you’ll be able to find those online but maybe not with quick shipping. They are good quality. I switched mainly because the new ones had all the certifications (CE/UL) and even better quality.
Most SSRs will work, especially with so little power. Fotek has a lot of bad quality/counterfeit. I’d avoid those.

I think you probably fried the DC SSRs.

A couple quick notes here. Elco stated the obvious issues. New SSDs required. Here are a few more notes that I learned the hard way. First DC switch current polarity matters, + to +, - to -. Second even though you won’t generate much heat with a 220v line. Understand that SSRs fail closed, not open like a normal magnetic relay. If you have any concern that they will get hot, put a heat sink on them and even install a smal fan on your box. Inkbird SSRs are cheap and seam to work well.