SSRs and/or Contactors?

Im planning an electric build with PID switching between two 240v 5500 watt elements but in the near future incorporating my Raspberry Pi to make it more automated.

I have looked at many wiring diagrams, mostly from the great PJ, and I have seen some with only SSRs and some with SSRs and Contactors.

How is one to decide which option is best? Is it based on application, types of equipment used, or just better use of equipment? Are there requirements to using one or the other?

If you have any other helpful advise, please share.

Many folks use both. Plenty of discussion in Electric Brewing sub-forum.

cank said:

Im planning an electric build with PID switching between two 240v 5500 watt elements but in the near future incorporating my Raspberry Pi to make it more automated.

I have looked at many wiring diagrams, mostly from the great PJ, and I have seen some with only SSRs and some with SSRs and Contactors.

How is one to decide which option is best? Is it based on application, types of equipment used, or just better use of equipment? Are there requirements to using one or the other?

If you have any other helpful advise, please share.

Click to expand...

Contactors are a great cheap solution for something that's going to be on a while once it's on, like the heat to your brew kettle.

SSRs are great for something that cycles on & off like the heat for your mash tun or RIMS tube. The downside to SSRs is they dissipate about 1 watt of energy for every amp pushed through them. While that's not much compared to a 5500 watt heating element it's still heat you have to dissipate. In other words, you need to mount your SSRs to heat sinks or to the outside shell of your brew panel to dissipate the heat.

But SSRs are cheap enough that most users on this site use SSRs for everything and they use a contactor as a main disconnect.

SSRs are needed for things that need to be switched on and off very frequently, like heating elements. Those things can be switched on and off multiple times every second.

Contactors are needed for things that need to be switched on and off, but not nearly as frequently, like power to the entire control panel. You turn a key switch, and that sends power to the contactor coil, and then the contactor coil allows electricity to flow to the rest of the panel.

cank said:

Im planning an electric build with PID switching between two 240v 5500 watt elements but in the near future incorporating my Raspberry Pi to make it more automated.

I have looked at many wiring diagrams, mostly from the great PJ, and I have seen some with only SSRs and some with SSRs and Contactors.

How is one to decide which option is best? Is it based on application, types of equipment used, or just better use of equipment? Are there requirements to using one or the other?

If you have any other helpful advise, please share.

Click to expand...

There are many reasons for the choices I make when drawing diagrams. The first is to provide the plan for someone with a specific want list.

Keep in mind that most E-Brew builds are for 240V systems using either 30A or 50A power feeds. When the request is for specific switches (mostly illuminated low power units), contactors are required to switch the amps required to power the elements. Also - depending on the power feed (30A or 50A) circuit breakers might be incorporated within the wiring plan.

It is also critical that on 240V circuits both legs of the 240V power be switched together.

If the choice can be made for the use of mechanical switched (bat handle units) then they can be found and placed to switch the high power required.

Bottom line? It all depends on the wants and implementation of the members request. I try my best to accomodate.

Hope this makes sense & helps for an explanation.

P-J

P-J said:

It is also critical that on 240V circuits both legs of the 240V power be switched together.

Click to expand...

If that's true, then why are all of the SSRs I've seen on here only single-pole? Is there a reason why people don't use 2-pole SSRs for heating elements?

LandoLincoln said:

If that's true, then why are all of the SSRs I've seen on here only single-pole? Is there a reason why people don't use 2-pole SSRs for heating elements?

Click to expand...

That's the purpose of the contactors.

Great, thanks for the replies. I haven't had time to search the threads, so this helped. Now I need to look at some more diagrams and apply my new knowledge!

P-J said:

Keep in mind that most E-Brew builds are for 240V systems using either 30A or 50A power feeds. When the request is for specific switches (mostly illuminated low power units), contactors are required to switch the amps required to power the elements. Also - depending on the power feed (30A or 50A) circuit breakers might be incorporated within the wiring plan.

P-J

Click to expand...

Low power, as in 120v or Low power like in 3v LED's?
I have several 120v lights that I planned on using if I could use one leg of the 240v lines after the switch.

P-J said:

It is also critical that on 240V circuits both legs of the 240V power be switched together.

If the choice can be made for the use of mechanical switched (bat handle units) then they can be found and placed to switch the high power required.

P-J

Click to expand...

I do have a bat handle 3 position switch that I wanted to use to switch between the Brew Kettle Element and the Hot Liquor Tank Element.


Thanks again everybody. Now back to work...

LandoLincoln said:

If that's true, then why are all of the SSRs I've seen on here only single-pole? Is there a reason why people don't use 2-pole SSRs for heating elements?

Click to expand...

SSRs control current and you only need to open one side of the circuit to turn off current. But because SSRs control current, you can still have voltage present with no load (like a open element or no element plugged in). And there is no value to adding a second SSR because the fastest one of the two will interrupt the current first. When switching on & off often, like cycling power to your element, you need a SSR because it has no contacts to burn or wear out.

Contactors disconnect voltage, which also stops current, and a single pole contactor can be used like a SSR. A contactor used in place of a SSR won't last long because the contacts will burn out. When safety is an issue, like disconnecting the main power, you need a contactor with a pole for each feed to disconnect all voltages from the element.

LandoLincoln said:

If that's true, then why are all of the SSRs I've seen on here only single-pole? Is there a reason why people don't use 2-pole SSRs for heating elements?

Click to expand...

I used dual SSRs in my build. 2 of them. I guess you haven't seen all the designs posted on this site

To be fair, SSRs are usually SPST. Electromechanical relays do lend themselves better to multipole switching.

For the power shut off, another reason to prefer a contactor is that you can set it up so that it latches with a momentary contact.