Blew Up My PID tonight

[rbertalotto]

Well...That was fun!

I went out into the garage to cast some bullets. Hooked up my LEE 20 pot to the PID and when I went to move the probe, the sheath on the probe wire touched the hot lead on the relay on the back of the PID and sparked. The leads on the back of the homebuilt PID are simply covered with a plastic cover. There was just enough room on the side for the probe wire to barely touch the hot lead.....Damn!

The PID still turns on and it is reading temperature, but it wont shut off the AC power going to the furnace. I thought maybe the relay was stuck.

But I checked to see if there was 32V DC going to the control side of the relay.......nothing. So I just ordered up a new PID controller and relay from Auber.

BTW, interesting to note. The Lee Precision Pro4-20 pot really maintained temperature. Once I set the rheostat to 680 degrees, it held within 10 degrees for an entire pot of lead. I thought the knob on the back was simply a rheostat but I could hear the pot cycling on and off...........??????

[Frozone]

I'm sorry to hear of your trouble.
But I won't lie to you: I'm also sitting here with a smug look on my face.


Oh, and the contol on the LEE pot is an "Infinite" control. It reads the current passing through it and opens after a given number of watts have passed.

A Bimetal switch and a known resistance in the main conductor is what it has. The current through it causes the conductor to heat up, once the control itself is at a certain temp the Bimetal trips off and stays off until it cools down. It does not sense the pot temp at all but if the pot is hot and heats up the case in back it efffects the control, also ambient temp can effect its cycle time.

[rbertalotto]

So I ordered a new PID controller and a new SSR Relay. Took my damaged PID apart and replaced just the relay and PID. Works great now.

Then I tested the old relay and it was toast. I applied 12V to the control terminals and nothing happened. I then turned on the old PID controller and it was outputting 10 volts and turning on and off as the temperature was reached. (I set it at 60 degress so simply holding the probe in my hand would cause the temperature to raise over the 50 degrees ambient shop temperature. So I'm confident the PID is fine. I originally thought the PID needed to output 32V. But the relay will operate from 3V to 32V DC input voltage.

So when you do something stupid and short out your home made PID, just the relay will be damaged.

I ordered up another aluminum box, relay and probe. I'm going to make a second PID............Heck, ya can't have enough PIDs around the house , now can ya!

[Springfield]

My relay burned out 2 weeks ago also. I bought a 40 amp one this time, guess 25 wasn't enough for my 1500 watt Magna pot. I am also building a spare. I could have used the pot as it was originally designed but I sure got spoiled with the PID control.

[cbrick]

I could have used the pot as it was originally designed but I sure got spoiled with the PID control.

No kidding! Sure ya can cast perfectly good buulets without a PID, I did for many years. Once I got the PID every time I turn the pot on all I can think is . . . What did I ever do without this?

Rick

[HATCH]

My relay burned out 2 weeks ago also. I bought a 40 amp one this time, guess 25 wasn't enough for my 1500 watt Magna pot. I am also building a spare. I could have used the pot as it was originally designed but I sure got spoiled with the PID control.

You running your pot at 120vac?
I am controlling the pot on my master caster with a 10 amp SSR but its running 220v. It pulls less then 6 amps total and that includes the PID and the PLC controller too.

[Doc Highwall]

Kind of like less art and more science. Back to the lab Egor.

[Gliden07]

My relay burned out 2 weeks ago also. I bought a 40 amp one this time, guess 25 wasn't enough for my 1500 watt Magna pot. I am also building a spare. I could have used the pot as it was originally designed but I sure got spoiled with the PID control.

How long did you have relay hooked up?? 1500w at 120V is only around 13 amps?? Are all the connections tight?? Obviously the 40A relay won't hurt but, SS Relays have a really high on off count before there suppose to burn out thats why I ask?? Also I'm building one with a 25A SS relay and am looking to avoid problems.

[MtGun44]

Yes, the Lee is a thermostat. Sets temp, not power level.

Bill