Correct SSR for my setup?

So I'm muddling my way through my first RIMs build (I'm just using a closed RIM's circuit on my mash tun, the rest of the process will be using conventional propane burners) and I'm trying to find the right SSR and heatsink. My element is a camco 4500W 240V and my temp control is a MYPIN TA4. The SSR's Im looking at sometimes dont go as high as 240V (an issue?) And why would the SSR convert the AC signal to DC? Is that necessary for the element? If someone could just tell me what to get I'd be very appreciative.

Cheers,

Biermann

The SSR will control one leg of your 240 line, so it will only see 120 going through it. It does not convert ac to dc power. Your controller sends a dc signal to the ssr. Think of the ssr as a very high speed relay.

Alright, so let me try and trace this as simply as possible. Household current -> temp controller -> SSR -> heating element. Am I missing a step here? Should there be "contactors" in the loop somewhere and what do they do? I feel like the concept is so simple but since starting this project im regretting that I didnt major in electrical engineering. And any SSR and heatsink in ebay or the equivilant will suffice?

Main power in, that supplies power for your temp controller(pid). The controller sends a signal to the ssr ( two wires from controller to ssr). Then one leg of your 240 in goes to the ssr in, ssr out will go to element power out. You can put a contacter between the ssr and element power out and have it on a switch. Look at some of PJ's wiring diagrams. That should help explain.

cheers

nitrousjunkie said:

The SSR will control one leg of your 240 line, so it will only see 120 going through it. It does not convert ac to dc power. Your controller sends a dc signal to the ssr. Think of the ssr as a very high speed relay.

Click to expand...

Not true - the SSR needs to be rated for at least 240 VAC. This is because even if you use two, one to control each leg, slight timing differences could cause one to "see" 240 VAC. And 240 VAC for even a very short time will blow out a 120 VAC rated SSR.

Also, for 4500 Watts @ 240 VAC you need a SSR rated for at least 20 Amps (4500 / 240 = 18.75). A 40 Amp SSR is over kill. a 25 or 30 Amp gives you some safety margin.

I concur, in a 240 volt circuit both wires are hot and carry the full voltage. You need a 240 v ssr.

Also, I see some designs with 2 SSRs, one for each leg. I don't understand why since you are switching current & not voltage and you only need one.

I'm sure someone will chime in with "I use two SSRs to switch off both legs for safety". I suggest you measure the voltage across both sides with the SSRs off & the element disconnected - you will measure 240 VAC!

Using two ssrs would be safer, without switching off both lines there is still hit voltage at the wire. You can accomplish this with a switch rated for 240 on the second leg. I think you measure voktage at ssrs when they are off because of leakage. I'm not sure but i think you can measure voltage but no appreciabke current will flow.

Relying on the SSRs for safety is dangerous. Using a disconnect or some type of switch ahead of the SSRs is the only way to guarantee safety.

This is why folks put in definite purpose contactors.

Household current -> temp controller -> SSR -> Definite Purpose Contactor -> heating element

Whats a definite purpose contractor? And what are my risks? I currently have it wired as simply (and i guess as dangerously) as I can have it, wall power to PID and SSR and SSR to outlet (gfci) that controls element. What should I add/change?

An SSR is a solid state component, i.e. no moving parts. As such are are subject to failure. When they fail, it's usually in the closed position. The kicker here is that the control circuit for the SSR does not indicate if the SSR has failed or not. This could put you in the situation where the SSR is constantly sending current to the element when you may not want it to. Your only recourse is to unplug the element, if possible, or to unplug or power off your control panel.

A definite purpose contactor is a type of relay. It isn't meant to switch as quickly or frequently as an SSR. But it can very easily switch both legs of a power circuit. This gives you a definite switching of the power that an SSR can't do (which is usually only the hot leg of a 120v circuit or just one leg of a 240v circuit).

In a way you can think of it as another failsafe in your control panel to control the electricity.