Lurked for long enough. couple of ?s on new build

[ed_denu]

I need yet another question for you guys. thermocouple that i have is about 2 foot too short. Can this be extended or will it interfere with the readings?

Generally it has always been stated that you cannot extend a TC. But recently a guy on another forum took 2 TCs, hooked them to a switch and got accurate temperature results back to the pid. I tried this by putting together a box with a digital readout, a 2 way switch and 2 TCs with alligator clips attached. From all the tests I've done the temperatures appear accurate.

The bottom line I believe is that you can extend a TC, but you need to use thermocoupler wire and keep the same wire orientation(red to red, black to black). It might be cheaper to just by a longer TC however.

[StlS_Ron]

[StlS_Ron]

[StlS_Ron]

Ok fired the oven up tonight. ran fine everything seemed ok. The SSR was sizzling as soon as i turned the oven on. Let the oven heat and was taking constant temp readings from the heatsink. it was running about 150 deg at the hottest point on the heat sink.

When I turned the power on to the oven it imediatly started heating. did not program or tune at all on the pid. as it was heating I reread the manual that was emailed to me from the guy on ebay that I bought it from. I noticed that factory setting on it was in Celsius. Soooo,,, long story short i open the oven and take a temp reading from a mid sized piece of scrap aluminum I had in there, it was 670 degrees F. A little too hot. Let the oven cool as i changed the default from Celsius to Fahrenheit. I sent power back to the oven and the sizzling stopped. A bunch of smoke started rolling off the SSR. It had separated from the base plate. The baseplate was still attached to the heatsink. Here is a pic.






Ok so obviously the ssr is trashed. I put a fan on it and sent power to the oven. It stayed cool enough and the oven heated up just fine.


My question. did I do something wrong here or was it a faulty SSR?

[mtg125]

Ron, nice looking build. I cant help you with the electronics though, I bought everything ready to hook up from Teds fabrication. Your the wheel guy right?

[ed_denu]

It looks like the elements you purchased would draw around 26 amps. What size ssr did you finally purchase? All your references were to a 25 amp ssr. You would have needed at minimum at 40 amp ssr and appropriate heatsink. Also for best results you should use a thermal paste between the ssr and heatsink to aid heat dispersion.

[StlS_Ron]

Ron, nice looking build. I cant help you with the electronics though, I bought everything ready to hook up from Teds fabrication. Your the wheel guy right?

Hey thanks. The wheel guy I am. I did track down another sand gun like mine if your still looking.

It looks like the elements you purchased would draw around 26 amps. What size ssr did you finally purchase? All your references were to a 25 amp ssr. You would have needed at minimum at 40 amp ssr and appropriate heatsink. Also for best results you should use a thermal paste between the ssr and heatsink to aid heat dispersion.

Yes ended up getting a 40a with heatsink. no thermal paste thou. Sounds like that would have been the problem.

[ed_denu]

Possibly that was the problem. I use a 40 amp ssr drawing around 23 amps and have been running this combo for a couple of years without a problem. Was your heatsink sized for the 40 amp ssr?

[StlS_Ron]

Possibly that was the problem. I use a 40 amp ssr drawing around 23 amps and have been running this combo for a couple of years without a problem. Was your heatsink sized for the 40 amp ssr?

Yes sir.

I think it may have just been a faulty glue job or poor assembly. I'll just order a new one and go from there.

The oven is wide open when you send power to it, I Think the ssr may have gotten stuck in to on position. I have the PID tuned I believe, but even if you drop the target temp to 0 it still has the elements burning wide open.

Need to fix the SSr to be able to nail the problem down.

The manual for the PID is obviously written by someone that english is not their primary language. very general. I'll keep playing with it

[ed_denu]

Yes sir.

I think it may have just been a faulty glue job or poor assembly. I'll just order a new one and go from there.

The oven is wide open when you send power to it, I Think the ssr may have gotten stuck in to on position. I have the PID tuned I believe, but even if you drop the target temp to 0 it still has the elements burning wide open. That's not right. If the SV is less than the PV then the ssr should not be energized. If it is, then something is incorrect, possibly the wiring.

Need to fix the SSr to be able to nail the problem down.

The manual for the PID is obviously written by someone that english is not their primary language. very general. I'll keep playing with it

See the above comment.

The pid controls the ssr on/off cycle. If you get another ssr and the same result occurs, shut it down immediately and trouble shoot the problem.

I would first test the pid without the ssr connected. Set the sv to be less than the pv and do a voltage check(DC) on the two pid output terminals that control the ssr. There shouldn't be any voltage on the mm. Then move the sv to be greater than the pv and check the voltage again. You should see a DC voltage of around 8 volts. If this is correct then the pid is working ok.