Two basic electronics questions

Hi guys

I’m in the midst of installing my brewpi and had a couple electronics questions I was hoping you could help me with.

  1. does a 40 amp SSR used to control a small dorm style refrigerator require a heat sink?

  2. I want to put two SSRs in a project box, and then have them wired to an dual plug socket on the outside of the box. Why? Because I want to easily be able to plug / unplug my heater and remove it from the fridge (my fridge doubles as a kegerator)
    If I have one wire going into the project box, can I split the internal wiring - with one set going to one SSR / electrical outlet, and the other set to the other SSR / outlet - or do I need to run two dedicated wires for each SSR/ outlet?


I only use 15A SSRs for my refrigerator and they do not need a heat sink. They don’t run often enough to in my situation. I do have a case that they are in and I do have a few 40mm fans that cool the box but they rarely ever kick on. I doubt yours will get all that hot with just a fridge and heater (not sure what your heater pulls though).

The “one wire going into the project box, can I split the internal wiring” I’m not sure what you mean. Like one cable with 4 individually wrapped wires in it? Like a 22-4 wire? Then yes, you can use two of them for one SSR and the other 2 wires for the other SSR.

You will need 4 wires total going to the 2 SSRs. +&- 5v to each. You can use small 22g wire there. You will then have your larger current hot going into that box, through the SSRs and to the outlets.

I’ll try and clarify the wire thing.

I have some 3 core wire (live, neutral, Earth). I was wondering if I can use some connectors, and split the live into two wires, the neutral into two wires, and the ground into two wires.

One live would go into one SSR, and then from the SSR to the live on the plug outlet. One neutral would go straight to the plug, and one earth would go straight to the plug.

The same thing would be done for the other SSR.

This would eliminate the need for two x three core wires going into the box - one for each SSR.

Does that make a bit more sense?

Okay, so you’re talking about the A/C wires only then and not the SSR signaling wires. Got it.

Yes, you can just take into the box one cable with 3 wires (hot, neutral and ground).

Send neutral and ground to your plug and then you could send the hot wire to one terminal of SSR#1 input and then jump it to SSR#2 input. Then you would run just one small hot wire from SSR#1 output to outlet #1 and then another similar wire from SSR#2 output to outlet#2.

Thanks bryancm1

With the neutral and ground wires, can I simply jumper these between the two plug outlets? Both plug outlets require a dedicated hot, neutral and ground.

So, three core wire into the box, hot wire to SSR1 input, jumped to SSR2 input, one small wire from SSR1 output to live on plug outlet 1, and one small wire from SSR2 output to live on plug outlet 2. Then, the neutral and ground from the three core wire go to neutral and ground on plug outlet one, and jump these to neutral and ground on plug outlet 2.

Sound ok?

I might just use screw on connectors to split the neutral and ground wires so that I don’t need to ‘jumper’ as such…

That should work just fine.

In regards to my 15A SSRs not heating up, I am on 120V fwiw. I have a thermistor circuit that kicks on my fans if the box temp heats up to 90° and they haven’t kicked on once from what I just saw.

On my RIMS system, that is not the case. That 40A SSR does heat up even w the heat sink but it’s running a big element that runs pretty constant for a long time.