SSRs on 240V

Thread Starter

Thenextman

Joined Feb 3, 2017
49
I want to upgrade my kiln to digital control.

Looking at using a PID to control relay to cycle kiln on/off based on temperatures in the kiln.

Would I interrupt both hots, each with its own SSR? Inputs to the SSR wired parallel from the PID?

Please see attached, each hot goes to its own element / pair of elements it seems.
 

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Thread Starter

Thenextman

Joined Feb 3, 2017
49
If supply is L & N then you do not need to switch the N.
There are two line voltage leads and a neutral. Each 120V hot powers it’s own set of elements and the

I need both sets of elements to respond to PID.

Can I power The PID with one of the hots + neutral, and interrupt both hots with their own SSR? SSR inputs wired in parallel to PID output?

Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
Are you just needing ON/OFF control with the SSR's?
Where does PID come in, you would need phase angle control for SSR/Triacs etc.
Always fuse a mains powered unit like this.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
49
I am looking at using this: https://www.amazon.com/CGELE-Temperature-Controller-180-240V-Thermocouple/dp/B08ZYHFBYW/

With an additional SSR

I am not familiar with how this type of equipment works. All I NEED is on/off / to keep the temperature within a +/- 5 F range.

Do PIDs actually modulate the current to the coils? Is the 100-240V input directly to the PID just to power it up, or is it actually doing something to the current on that line?
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
OK I think it is clearer now what you are intending, the PID controller will regulate the temperature by switching the SSR, as required.
Either on of via PID control.
I am not sure however if the controller can control both SSR's with no problem, this remains to be seen.
Depends on what the controlling device is.?
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
What you could look at is turn one on via the unit and turn the other on at the same time from a different source, permanently on when heating is called for.
 

MisterBill2

Joined Jan 23, 2018
17,814
If the kiln already has an ON/OFF switch that breaks both of the line leads, then the SSR will not be serving as the on/off control but only cycling heater power. So only one side would be opened for temperature control, while the power on/off is controlled by the kiln power switch. Of course, the power switch will still be what de-activates all the power within the kiln.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
49
That is what I was saying. so only one SSR is required.
If you look at the wiring of the kiln (all the old school drawing in my schematic) you’ll notice each hot is split off to it’s own set of elements. I believe only interrupting one hot with an SSR would result in one set of elements being on all the time. But I could be wrong?
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
I believe only interrupting one hot with an SSR would result in one set of elements being on all the time. But I could be wrong?
Yes, they are (3) 120v elements split between L1 L2 to N, i.e. two elements on L1, one on L2.
But even if they were 240v type, they should still be switched with two SSR's.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
49
Yes, they are (3) 120v elements split between L1 L2 to N, i.e. two elements on L1, one on L2.
But even if they were 240v type, they should still be switched with two SSR's.
Any thoughts on grounding? Would I wire the ground from the outlet to the control box case (which houses the PID and relays), and then continue it and ground to the existing grounding point in the kiln?
 

MisterBill2

Joined Jan 23, 2018
17,814
The "green wire safety ground connection" is not part of this discussion. I had not noticed that the elements had independent control switches. One SSR per hearer will be adequate.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
49
In case someone is looking at installing a similar controller, the wiring described in my post did work. The SSRs really do get stinking hot, so keep that in mind!
 
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