Give an old broken Lyman Mag20 a PID transplant?

[Ziptar]

Could use some advice from those more PID savvy than I.

A few months ago I was given an old Lyman Mag20 furnace. The only thing the person that gave it to me knew about it was that it belonged to a relative that had passed and that it didn't work.

Finally got around to messing with it this week. Thermostat was the problem, multimeter read an open loop when turned on. Cheapest replacement I found is $70. I took thermostat apart to find that one of the tabs the contact arm had come loose from the notch it was supposed to pivot in. After reassembling the thermostat now when I turn it on I get a definitive and satisfying click of contacts well uh... contacting and and my meter confirms the circuit is closed. I still need to do a little temp testing to make sure its working as expected but before I bother...

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I'd been planning to build a PID this winter anyway for my other pot so as I was looking at this Mag20's innards strewn about my workbench I thought to myself... Why bother with the thermostat at all and just install a PID in place of the thermostat like a Mag25. The Mag25 looks like a sideways Mag20 even, at least to me. I Google Image searched for a bit but couldn't find any pictures of a disassembled Mag25 but I did find one of the back of one (which would be the side of a Mag20).

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Noticeable differences:

The mag25 has louvers and a fan added for ventilation which I assume is to keep the PID from overheating / melting.
Noticeably absent behind the Mag25 louvers are the gobs of ceramic fiber insulation that the MAG20 was stuffed full of.


Internally there is more than enough room for the pid, ssr, and an 80mm or 92mm cooling fan and adding additional vents to the back and sides is easy enough.

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Not being fully familiar with PIDs just yet. Would it cause the PID to be less accurate? I could reuse some of the ceramic fiber insulation to "wall off" the PIDs ventilated compartment from the heating element and pot. What concerns or precautions are there with installing it into the furnace itself? In other words, why wouldn't someone want a PID installed into the furnace itself?

Thanks

[HATCH]

One word. Heat
I wouldn’t install one inside the mag20 case. There isn’t enough space to provide enough cooling.

[Ziptar]

Thanks Hatch, that was fast. When I saw the picture of the back of the Mag25 with its vents and fan it was clear heat is a concern. The Mag25 must really circulate some air. If you're saying don't do it that's good enough for me.

I'll reinstall the thermostat but won't bother temp testing it. It'll just be an on / off switch and I'll run the pot off a external PID.

[Valley-Shooter]

I wouldn't put a PID that close to a lead melting pot. To much heat. Also you have to run the cooling fan forever after shutting down the pot.

A PID is better as a stand alone unit. I use mine with 2 different lead pots and my toaster oven.

Sent from my Pixel 4 XL using Tapatalk

[HATCH]

I'll reinstall the thermostat but won't bother temp testing it. It'll just be an on / off switch and I'll run the pot off a external PID.

You could temp test it once you have your PID hooked up.
Crank the factory thermostat up to 800 and use it for a backup to the PID. Sort of a max limit

[georgerkahn]

You could temp test it once you have your PID hooked up.
Crank the factory thermostat up to 800 and use it for a backup to the PID. Sort of a max limit

One of my Lyman Mould Master furnace's thermostat failed -- their wire came off and I could not manage to solder it back on (?) -- so I simply eliminated their thermostat from the circuit. A fellow who used to be on this forum used Auber components to purvey PIDs and I bought one from him which has worked famously since. I like Hatch's suggestion re using the thermostat as a failsafe :) -- but, imho, this is/was the weakest link in their design, and prone to failure again. For one of my lub-sizer's heat control, I simply have it plugged into a 0-110VAC Variac, and this works quite nicely. I do have a couple humongous 20A rated auto-transformers and my initial thought was to do similar with the Mould Master. However -- I bought and have been using the PID and -- as oft' is voiced -- "haven't looked back".
geo

[wv109323]

My Lyman was an older model than yours. The thermostat ,wire terminals and plug in connection were a constant problem. There was always loose connections that lead to burnt wires and the bi- strip rusted away. My thermostat was mounted in the housing and relied on the air temperature to switch the bi- metal strip on and off. Yours looks to be an upgrade to the one I had. I done away with the thermostat and all connections I did not have a fan.. My heating element used the 1/4" slip terminals. I simply ran wires from the heating element to a male 120V plug. Plus a ground.
I built a separate box that contained the PID and solid state relay and all the other necessities. From the SSR I ran a female 120V female plug with about 6 ft. of length That way the PID does not take up bench space near the pot. For the probe I used a piece of flat stock and used one of the holes in the top if the pot to extend the flat stock into the center of the melt. I just drilled a small hole where the probe extends down into the melt. I removed the probe when I am through casting.
Adding the PID was a major improvement in my casting. My cost several years back was $80.

[jsizemore]

One word. Heat
I wouldn’t install one inside the mag20 case. There isn’t enough space to provide enough cooling.

Amen to that. Your looking at reduced PID life and accuracy. If you make a separate, well ventilated stand alone control, you can move it to any pot, oven or lube heater you own. Also buy good components form a good vendor that backs what they sell. I swap my pot PID amongst 5 pots and it's been going for 8 years without issue.

[jsizemore]

Thanks Hatch, that was fast. When I saw the picture of the back of the Mag25 with its vents and fan it was clear heat is a concern. The Mag25 must really circulate some air. If you're saying don't do it that's good enough for me.

I'll reinstall the thermostat but won't bother temp testing it. It'll just be an on / off switch and I'll run the pot off a external PID.

It's smart to keep the original thermostat in the circuit so you have a backup in case the SSR fails in the on position.

[jsizemore]

Yesterday I cast Accurate 35-115Y and ended up with 814 bullets. After my pot was up to temp, the PID kept the alloy temp at 700degF with a +/- of 5degF for the next hour + while on auto tune. I did the powder coat thing afterward and while on bake in the large Oster convection oven PID set at 400degF, I started the timer for 30 minutes when the temp hit 375degF and the temp peaked at 411degF and took 5 minutes to settle at 399degF for the next 25 minutes with a +/- of 1degF variation. The convection oven PID was on auto tune too. Both units are in a separate well ventilated reclaimed box from the scrapyard or electronics recycling outfit. Sized after the PC. One repurposed mayo jar full of bullets waiting to come to hardness over the next 2 weeks. Good stuff.