Another forum member, hobbles, asked for more information about the PID Temperature Controller I built to control the temperature of my Lee Pro 4-20 lead casting pot. In case anyone else is interested, I decided to post the information here for all to see. Please understand, this is not an original idea I had. I used information obtained from another forum to build this controller.
PID stands for Proportional-Integral-Derivative. A fancy way of saying "high-tech" thermometer. In a nutshell, the PID controls the heating element of the lead pot using a Solid-State Relay (SSR) to control when the heat is on or off. It monitors the temp of the lead via a high-temp Thermocouple and is "smart" in that it can and will "learn" how the heating element and lead react (how long it takes to heat up, how quickly it cools down, how much thermal carry-over takes place, etc.). Building it was pretty easy with basic, and I do mean BASIC, electronics knowledge and parts from Radio Shack and Auberins.com.
The PID will maintain the temp of my lead at 670 degress +/- about 2 degrees. It effectively eliminates one variable of the casting process by allowing me to concentrate on casting without constantly checking the temp and messing with the heating control of my Lee melter.
Here is the parts list I used and a schematic…
Solid-State Relay: http://www.auberins.com/index.php?ma...&products_id=9
Radio Shack Project Box (I used the large one, but medium would probably work): http://www.radioshack.com/product/in...ductId=2062284
Terminal Block: http://www.radioshack.com/product/in...ductId=2103983
The rest of the parts are common and can be picked up at any Radio Shack.
Wire for internal connections
Extension Cord – I cut it and wired it in so that I could plug the Lee pot into the PID controller, then plug the controller into the wall and not have to wire the Lee pot directly into the PID.
I also used some Aluminum from Lowe’s to build a simple bracket for holding the Thermocouple in place in the pot, with the tip of the thermocouple about ½” from the bottom of the pot.
PID.jpgPOt and PID.JPGschematic.jpg