H/T oven control issues w/ PID

dbalfa

dbalfa

Joined
Jun 23, 2008
Messages
67
I have just completed my build of an electric H/T oven and am having control issues. I am using a Auber PID with SSR capabilities. I have dual SSR's controlling a single 3000 watt, 240v coil. My oven gets hot plenty, but overshoots- sometimes a lot! At high temps, it may overshoot 500 degs. The coils seem to remain hot and the temp continues to creep up even if the PID has turned the control off.

The PID is also "pulsing" the controll on/off/. Is that normal?

Any suggestion on control parameters would be greatly appreciated.

Thanks
 
Some overshoot is normal, and usually the PID's have a fuzzy logic feature that allows them to learn over time and reduce the overshoot. But 500 is a good bit of overshoot. My oven overshoots by about 25 degrees or so when it's one a steady climb and reaches temperature. The SSR just switches the coil on/off, with longer off times to hold temps. This, I think is the pulsing you're referring to. If so, that is normal. Like TJ below, I'm not sure about the two relay setup?

edited to admit I am apparently mostly blind and just now saw your full setup in your original post.

--nathan
 
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I built the oven by Andy Gascoigne in British blades. I have an Auber control that was originaly set up for a relay. I converted it to ssr with a lot of forum help. I don't see any reason for 2 ssr?? Mine just turns power on or off. It does pulse on & off to regulate heat.
The overshoot you have is to much check out the 2 relay system I'm using 220 volts with about the same coils.
Tj
 
I may have found the problem - I talked to Auber and he told me to do an Aotutune sequence at desired temp which I did. I set it at 1480 and at 1900 I decided something was amiss. So I took the panel off and put a tester to the PID. The output had no voltage but the coil side of the relays still had 250v. I then turned my safety switch off to confirm, and the coils went off. I turned the PID off, opened the door. Turned the PID back on, the temp had dropped to 1400. The output indicator light was on so I tested the SSR lugs and got 12 volts.

So I'm thinking it may be a wiring problem or I've got two faulty SSR's.
Any suggestions? I wired the SSRs both to the SSR lugs on the PID +/+ , -/- (double checked that) I wired them in series. This should not matter should it? as opposed to having two sets of wires all the way back to the PID?

I feel like I'm almost there....
 
I wired my ssr to turn on the oven coil.My coil is connected in series. I wired 1 hot side to the ssr and continued the same wire; or side;from the other sideof the ssr to the coil.
The other end of the coil is wired to the other hot side.
I still don't see any reason for 2 ssr relays.
TJ
 
I'm thinking he has 120V SSRs and is using one for each leg. It would be simpler to use a 220V SSR.

If I am getting your problem right, it may be that you have something wired wrong, and one (or both) of the coils is energized all the time. It could be that or one of the hot leads is switched with the common lead and the coils runs on 120V when the SSR is off and 240V when the SSR is on, or some similar mis-wired circuit.

Whatever the case is check the wiring well. Draw it out on paper, and see if it looks right. Draw an "ON" diagram, and an "OFF" diagram. That may show you where the problem is.
Check the output of the controller. The SSR may be hooked to the wrong terminal. Check the program to make sure it does not have something like a 500 degree hysteresis accidentally programed.

Stacy
 
Thanks gentlemen.

I found the issue last night. I had a blown up SSR on one side. This allowed current to flow non-stop. Turns out, as some have said, two SSR's can work but is overly-redundant. I checked them both and still had one operational and am using it. Now it keeps temps to within 5deg or less. I had installed a kill switch to the coils for safety and that works well.

I consulted with the dude at Auber Instruments. SUPER GUY!! I can't say enough about his service and willingness to help. That is to say nothing about his expertise and understanding of what was going on. He told me one SSR is more than sufficient. The biggest issue was I did not install a heat sink. YOU MUST INSTALL A HEAT SINK ON ANYTHING PUSHING MORE THAN 15 AMPS! Yeah, I learned that he hard way. Good thing I started with two, now I have one that works. I installed a heat sink of his recommendation. It is a 2" piece of 1/8" square steel tubing. Works great. Mr. Auber gave me several recommendations to use for heat sink without pushing me to buy one of his. He even offered to sale me replacement SSR at cost if I needed one. Once again - SUPER COMPANY. They have a customer for life in me. I encourage everyone to buy their controller needs, thermos, etc. from AUBER INDUSTRIES>
 
Glad you got it figured out. I had a hard time figuring out the program instructions. Had to develop a whole new sense of understanding. When testing my oven out it wouldn't go over 1350. My Home Depot furnace cement was bubbling and melting. I was into celcius. 2300 degree test was a little to much but it survived.
Good luck with yours.
TJ
 
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