PID electronic pot controller

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Built a controller using a REX C100 PID for my electric lead pot.

This PID has an internal relay that is not heavy enough so I removed the internal relay and put two jumpers to #4 and #5 terminals to get voltage to those terminals - This voltage is enough to run a 25 amp SSR.
This runs my lee pot at 350C (the REC PID is supposed to be switchable to F but it stays in C no mater which value I set the internal switch)

The advantage of this is that the K thermocouple and PID give an accurate temperature reading of the alloy in the lead pot.
You can watch the pot temp drop and recover when you add the sprues back into the pot.

The REX PID was $12.00, the SSR was $2.50, the K thermo couple was $2.50, the high amp connectors (80 were $4.00) The wall cord was salvage off of a deep fryer, the outlet was 70 cents. This PID will keep a clean pot at 350C (348C to 360C) and gives excellent heat control. Total cost about $21.00.

My next project is to salvage a PID and SSR out of discarded electric stove and see if I can make it work as a temperature controller. The Rex C-100 came with a preset max at 400C, that was easily changed to 600C - way higher than the controller will ever have to work.

Just a note, the REX C-100 come in two styles - one is an internal 3 amp (Relay will be on the outer label of the unit) the other comes as SSR out put (SSR on the output type)
If you get a REX C-100 with the internal rely it is probably best to take the relay apart, remove the internal relay and solder in jumpers to control an external SSR (CRoss out relay on the label, write SSR so you know you have done it .

This is a video on making the change.

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Ever since I built a pid for my pot it's been so much nicer casting. I've yet to see a frosted bullet.

I got my kit from eBay for $50 and an longer probe that sits in the lead by the spout.

I installed it into an old power supply.

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The ssr is installed on the heatsink which you can see through the fan opening.
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on my 10lb pot i screwed the sensor so it was touching the bottom of the pot, i believe it worked alright but i didn't measure it.

on my 20lb pot it's 6" probe that is mounted on the side of the pot with the sensor in the lead.
 
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For the first while when testing the thing I just had the probe sitting in the pot.
I have Lee bottom pour production pot so it was a simple matter to remove one of the screws from the top of the pot and use a couple of strips of flat stock metal ( strips cut from a tin can would work) with 3/16" holes on each end.
The screw goes through one hole and holds them - the strips then get bent so the probe can go through the other holes and hang into the alloy.

And I just finished casting ten pounds of wheel weight with 5% tin added. Casting temp for the lee post was 325 C. Mold was a 6 cavity 452-200 grain.
The PID could detect the temperature drop from adding a 6 sprue strip to the pot ~ 3 degrees C to 322C, After the PID settled down it would bottom at 325C and creep up to 330 (max) that is 18F varioation.

With this mold ( it was a used mold and it took several hours of undoing the smoking, getting the wax and oil off, cleaning the vents, and breaking the edges of each cavity with 400 grit emery cloth) I started to get good bullets on the second cycle of casting.
No wrinkles, no voids. The mold was preheated on a hotplate ( I had cooled the sprue plate before casting).
It was 12 to 17 seconds between pours into the mold. The mold has one sticky cavity, another light touch on the edge with 400 grit should fix that.

BTW, when you smoke an aluminium mold, start with a clean cold mold, use a wood splinter, not a candle - the smoke will stick to the cold metal and it will look just a little hazy if you can see it at all. If you smoke it until you see soot you may or may not get good bullets,
 
On the first SOHMCO newsletter I will see if anyone is interested in a group buy. I am more than capable of cobbling them together for those that can't. Just have to find a decent box to put all the stuff in that is not too expensive.
 
zuke said:
What size box and made of what? Plastic or metal?
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The box is from a gutted power supply box for a computer. The box is grounded.
It is important that you get crimp connectors that are rated for at least 3 amps 120 volt.

Any box will do so long as there is room for the PID, SSR, and wiring.

Right now mine is a work in progress, I will be cutting a hole in the back of the box for the household outlet.

Oh, in looking at how the alarm for the high and low limits relay is wired, that relay could very easily be removed and the direct current can be used to power 12 volt LEDs for the high low alarms that can be programed into the REX C-100 unit.
You really don't need these alarms and the translated instructions to set them are a loose guideline rather than a detailed account.

You can get a PID that does not have an internal relay and you don't need to do this.

This is the youtube you need to follow to adapt the REX C-100 to switch a SSR - not rocket science.
The guy used leads from a resister for the jumpers, I used the copper core from coaxial cable as soldered jumpers.
 
Spawn-Inc said:
If you want pre-made, auberins sells pre-made, they also sell everything to make your own. They just cost more then the eBay stuff.

https://www.auberins.com
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It was much more fun and satisfying to build this - there are guys putting these together and selling them for the same price as a lead pot.

This would be a better PID for the project. The short K thermocouple is not ideal for immersion - you should use 4" K type thermocouple (~ $3.00 on Ebay, shipping included)

Just an update on this PID - it would not keep constant and would over heat on startup. The REX C-100 has it beat

Another note - the N2006P PID failed after about 4 hours - I had changed the duty cycle so that it was at 50 (1/2 second) rather than zero. This PID also ran the SSR (Solid state relay) much warmer than the REX C-100

 
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