SSR and contactor confusion

[schwartzr33]

I am starting to think about an eBiab build, based on a drawing by P-J (man, that guy is amazing). The drawing is https://www.homebrewtalk.com/f170/240v-5500w-ebiab-planning-please-help-401409/index2.html.
I plan to make a couple of changes, I will have a dedicated 240v GFI circuit, instead of a spa panel, and I plan to use the Auber SWA-24X1 pid, for the timer feature.

A couple of questions:
1) I assume I should go with the 2451, to control an SSR?

2) I would like to understand how the contactor and SSR work together. I've done a fair amount of reading on HBT and I understand that SSRs can fail "on" and you also want piece of mind that your element is truly turned off--both good reasons to use the contactor and a switch. However, what I don't understand is how the contactor interacts with the SSR. As I understand it, contactors cannot switch on an off as quickly as an SSR. In the drawing, it looks like Line 2 goes from the SSR to the contactor. Won't that make the contactor switch on and off as fast as the SSR switches on and off? Again, I've tried reading up on this and a couple of posts came close to answering my question, but I still don't get it. Perhaps it goes without saying, but I have pretty much zero electrical experience and I really want to understand what and why I'm doing something.

Thank you for your help!

 

[jeffmeh]

The mechanical contactor is not switched by the SSR, the contactor opens and closes the circuit that runs between the SSR and the element.

You run the load wire out of the SSR to the line side into the contactor, then run from the load side out of the contactor to the element. You control the contactor coil with a switch. When the switch is off, the contactor is open, so regardless of what the PID tells the SSR to do there is no power to the element.

Alternatively, you could put the contactor before the line side into the SSR. Same result.

 

[tyzippers]

Well, to answer your questions, as best I can:

1. Yes, you should use the SWA-2451 to control the SSR.

2. Sounds like you're on the right track to understanding how the contactor "interacts" with the SSR. in reality, the SSr and contactor do not directly interact. If you follow the individual circuits, you'll find that you have two "control circuits" and the power circuit for the element. The power circuit is responding to the two "control circuits" The first control circuit consists of Switch 1 and its associated LED and the contactor COIL. When the switch is closed, it provides current to the contactor coil thereby mechanically closing the two contacts in the contactor. All this does is provide a physical disconnect of the power to the heating element. So, in review, the contactors are open when Switch 1 is open and closed when Switch 1 is closed. So, in order to isolate power completely from your element, regardless of the state of the SSR, you can open Switch 1.

Now, when Switch 1 is closed, the power circuit (which consists of the Contactor CONTACTS and LINE 1 and LINE 2) is being controlled ONLY by the SSR which is being controlled by the PID output. So, when the PID output goes hot, it will allow the SSR to conduct electricity in LINE 2 which powers your Element. So, the SSR does not directly interact with the contactor in terms of opening or closing the contacts. Only Switch 1 does that.

I hope that answers your question in a bit more detail than you've found before.

 

[tyzippers]

The mechanical contactor is not switched by the SSR, the contactor opens and closes the circuit that runs between the SSR and the element.

You run the load wire out of the SSR to the line side into the contactor, then run from the load side out of the contactor to the element. You control the contactor coil with a switch. When the switch is off, the contactor is open, so regardless of what the PID tells the SSR to do there is no power to the element.

Alternatively, you could put the contactor before the line side into the SSR. Same result.

You beat me to it, but essentially said the same thing!

 

[schwartzr33]

Thank you both very much, I get it now!!

 

[SilverZero]

Is there any danger in using a DPST toggle instead of a mechanical relay? Seems like the most inexpensive option compared to high-amperage switches or relays.

http://www.grainger.com/Grainger/NK...PF6&seoUrl=NKK-Toggle-Switch-2TPF6&Pid=search

 

[tyzippers]

Is there any danger in using a DPST toggle instead of a mechanical relay? Seems like the most inexpensive option compared to high-amperage switches or relays.

http://www.grainger.com/Grainger/NKK-Toggle-Switch-2TPF6?BV_UseBVCookie=No&ItemKey=2TPF6&seoUrl=NKK-Toggle-Switch-2TPF6&Pid=search

Not any immediate danger. And yes, that switch would work. Most use a contractor to isolate themselves from the high voltage. So unless you don't mind mixing high voltage and low voltage on your control panel, you could use that switch. It's not considered to be best practice though.

 

[SilverZero]

Not any immediate danger. And yes, that switch would work. Most use a contractor to isolate themselves from the high voltage. So unless you don't mind mixing high voltage and low voltage on your control panel, you could use that switch. It's not considered to be best practice though.

I'm not worried about mixing voltages, I'm using a lab power supply for this and other components so I could add a contactor, but I haven't seen any that aren't prohibitively expensive, unless this one would work. Seems like it would if I'm reading the specs right, but I'm learning.

 

[tyzippers]

Yes that would work, but the coil voltage is 240V. Kind of defeats the purpose. So instead, you could use this. This one has a 120V coil. Both contacts are rated at 30A.

 

[SilverZero]

Yes that would work, but the coil voltage is 240V. Kind of defeats the purpose. So instead, you could use this. This one has a 120V coil. Both contacts are rated at 30A.

Ah, I failed to mention I'm planning to put the switch on both legs of the 220v line so it's a full kill-switch application. I'm going for this sort of setup.

So I guess I could just replace your suggestion with the 240v version if I wanted to use a contactor, right?

 

[jeffmeh]

Ah, I failed to mention I'm planning to put the switch on both legs of the 220v line so it's a full kill-switch application. I'm going for this sort of setup.

So I guess I could just replace your suggestion with the 240v version if I wanted to use a contactor, right?

No. What you linked to will work, but will require you to activate the contactor with 240v. Tyzippers linked to a two pole contactor (both hot lines run through the contactor) that is activated by 120v (the coil voltage). Coil voltage is different than the rating and number of poles.

 

[SilverZero]

No. What you linked to will work, but will require you to activate the contactor with 240v. Tyzippers linked to a two pole contactor (both hot lines run through the contactor) that is activated by 120v (the coil voltage). Coil voltage is different than the rating and number of poles.

Oh, so I would not need to activate it off of a DC power supply, correct? I would just run a 120v AC line to it.

 

[jeffmeh]

Correct. Run one hot leg and neutral to the coil contacts, run both hots into the two line contacts and out the two load contacts.

 

[SilverZero]

I assume I can just tie the coil into one of the hot legs of the main 240v line instead of running a separate hot to the coil all the way from the breaker or service panel, correct?

 

[BadNewsBrewery]

Correct - jumper one hot leg from the load side of your 240v supply to half of the coil. Run a dedicate switched neutral to the other half of the coil. When you close the switch, the coil sees 120v, the contactor closes and allows 240v to the load side.

 

[jeffmeh]

Also, I would recommend against the Auber PID 2451 with the included timer. https://www.homebrewtalk.com/f170/auber-pid-swa-2451-experience-301167/

You can go with a 2352 and a separate timer in the panel, or skip the timer and use a portable one so you can take it with you and still be alerted.

 

[SilverZero]

Very cool. Thanks for letting me hijack, guys!

I guess at this point I'm starting to re-think whether I'd still rather just put a high-amp DPST switch on the 240v lines to kill both legs when not in operation. I guess I'll have to weigh the pros and cons.

Also, I would recommend against the Auber PID 2451 with the included timer. https://www.homebrewtalk.com/f170/auber-pid-swa-2451-experience-301167/

You can go with a 2352 and a separate timer in the panel, or skip the timer and use a portable one so you can take it with you and still be alerted.

If this was aimed at me, I'm going to use a PWM. It's just for my boil kettle.

 

[lukez]

The mechanical contactor is not switched by the SSR, the contactor opens and closes the circuit that runs between the SSR and the element.

You run the load wire out of the SSR to the line side into the contactor, then run from the load side out of the contactor to the element. You control the contactor coil with a switch. When the switch is off, the contactor is open, so regardless of what the PID tells the SSR to do there is no power to the element.

Alternatively, you could put the contactor before the line side into the SSR. Same result.

Just want to make sure I understand that last statement. Does it mean that you can have both hot legs come into the input of the contactor, and on the output 1 goes to heat element and the other goes to the SSR and then to the heat element?
So regardless if the PID is telling the ssr to be on or off, there is no hot wire going to the ssr unless the push button activates the contactor?

 

[LandoLincoln]

Just want to make sure I understand that last statement. Does it mean that you can have both hot legs come into the input of the contactor, and on the output 1 goes to heat element and the other goes to the SSR and then to the heat element?
So regardless if the PID is telling the ssr to be on or off, there is no hot wire going to the ssr unless the push button activates the contactor?

Yep. That's how it works.