Let me start off by saying that I'm fairly new to casting. When I decided to get into it, I bought the Lee Pro 4 20 Lb Furnace because it was inexpensive and had good reviews in the user community. The only downside to using this furnace was temperature control. It has a rheostat with numbers from 1 - 10 for controlling the amount of current going to the coils to heat up the lead.
This created an issue for me. In order to tell what temperature I was at, I bought a VWR Traceable Workhorse Thermometer 4425. I would constantly have to check the temperature and could only maintain it within 20°F - 30°F of my desired 700°F. It was a pain to do and time consuming. Occasionally, I would find myself way above the desired temperature resulting in burning off my tin and causing some nice colors to form on top or I'd find myself way too low and my pours would slow down to a trickle. There had to be a better way other than buying another pot that had temperature control.
The solution is to install a proportional–integral–derivative (PID) controller to the pot and let it maintain the temperature for me. As a coffee geek, I had heard of people using these to control the brew temperatures of the espresso pours to within 1°F accuracy. I almost bought this for my Isomac Millenium espresso machine but then learned it isn't very effective on heat exchanger type machines such as mine. I had also heard of people using these for Sous Vide Cooking and almost bought one for this, but didn't. So now I thought this is the perfect opportunity to finally get to use a PID controller to solve an issue that I was having.
As I researched this, and not to my surprise, I found others had already done it. Through postings of others, I was turned on to a website auberins.com, Temperature control solutions for home and industry. It had all the equipment I needed at and at reasonable prices to achieve my goal. I placed my order for my parts and got them in yesterday. Now the project begins...
The goal is to have a furnace that I can set the desired temperature and this temperature will be maintained with no interaction by me to within 10°F. The PID controller should maintain it within 1°F so my goal should be easily met. My other goal was to install this as part of the furnace rather than as an external box that the furnace plugs into. The external box is simple and can be easily used for another purpose so there are benefits to it but I want a clean single unit to plug in, melt lead, and store.
Here is my somewhat dirty Lee Pro 4 20 Furnace that I am starting with.
Here is the equipment that I bought from auberins.com, Temperature control solutions for home and industry.
- 1/16 Din PID Temperature Controller (SSR control output)
- 25A SSR (Solid State Relay)
- Heat Sink for SSR
- K type high temperature thermocouple
- Compact extruded aluminum box for 1/16 Din controller
- Panel mount for K thermocouple
- Flashing Buzzer
First step is to disassemble the Lee Pot controller housing. This consists of removing just a few screw on top and the bottom. As you can see, there isn't much to them inside. It is mostly just empty space. A rheostat and wires to the heating coil. I was glad to see this because it meant I had room to work with on my project!
I had been wondering where I was going to mount the relay and heat sink and after I had the Lee housing apart, I found that the relay barely fits within it; but not the heat sink. So I decided to mount the relay to the base of the Lee Pot and allow the base to act as a heat sink. The heat sink I bought came with some thermal coupling grease so I lightly coated the bottom of the SSR, drilled a couple of holes and screwed the SSR to the Lee.