# Kiln Temperature control | Ongoing Project



## Jwest7788 (Feb 1, 2016)

Hey Everyone.

I've had this kiln project ongoing for awhile now, and thought for sure I had it complete.

The final step in the process, now that I have everything else complete, is learning about Solid State Relays (SSR), which are the stumbling block I am currently working with.

One died early on in the project, Stuck on (passing current through, closed circuit). @Johnwa kindly sold me two that he had on hand (After I fried one with 240V into the 12vDC input side, whoops.)

The new SSR I put in I carefully watched for two hours of testing, making sure it was switching off and on properly as the PID signaled it's commands. All was well. 

As such, I fired it up, set the temp, and put in some truck tie down anchors freshly covered in power coating powder.

Set a timer on my phone, and got back to work.

When I came to check on how things were going, the SSR had stuck on, heated to much higher then the set point, and melted the anchors (zinc?).


As such, It's something about my setup which is killing the Solid State Relays.

Due to the nature of a kiln being what it is, I'm working under the assumption that the SSR is overheating, as it's a known risk, and being so close to a kiln is not a "cool" place to be.


Questions:
Anyone have experience with cooling SSR relays? I'm trying to figure out a small fan or something to attach to the heatsink. Ideally it would run on 240v like the kiln?

Alternative cooling ideas?
Alternative relay ideas? (12Vdc input, 240Vac output)
Alternate temperature control methods?

Anyone have any other thoughts?


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## PeterT (Feb 1, 2016)

Electronics is not my forte. The closest thing I came to this is making a Lipo battery heater box for the race planes using a digi BBQ thermostat probe. Its what you call 'visual feedback human controller theory'. It worked awesome until I forgot about it & pack went poof. Lets just say I extended my welcome in a certain eastern block country 

Anyway my dumb suggestions:
-  how have you got the unit mounted? Is it possible its seeing conduction heat outside of its rated specs & failing in that mode? 
-  looks like you've matched the input voltage ok, but what kind of amps is supplying the SSR? Is it possible your source current is different than the specs?


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## Jwest7788 (Feb 1, 2016)

The SSR is mounted to the bottom of the inside of the normal control panel with heatsink of course. I'm thinking it's hot in that panel though, and there is limited airflow, so mounting outside seems better, but then I've got live leads outside the control panel.

40A SSR, should be enough for the kiln (30A breaker)


Good thoughts!


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