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PID temperature controller for Lee 420 pot settings?

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Greg_E

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I'm going to build a PID controller for my Lee 420 pot, just received an Ink bird controller with 40 amp SSR kit and a few other parts. Getting it wired up is no problem once I figure out the size of the box I need. But the programming is a different story. Anyone have some rough settings for the controller they can share?

What size enclosure did you use? I plan on getting an aluminum box and using it for heatsink on the SSR. If needed I can still mount the bigger heatsink, but with a 40 amp rating, the 11 amps I'm using should barely get it warm.
 
Hi Greg,

I can probably help a little. Just commenting here so I remember to come back to it tonight.

The D setting, derivative, will be zero. So essentially you will have a PI controller.
 
ITC-106VH which can take 120 volts directly into the controller and output a level to trigger the SSR.

Still trying to figure out what size box I need, but now I have all the parts to layout.
 
Thanks. I was hoping it was the 106 model and not the 100.

I build a few cabinets for manufacturing equipment. I typically use the Hammond ENS4 series of enclosures. Automation Direct is a good source of enclosures. Enclosures that are too small get really annoying during a build. If I were putting an enclosure together, I would probably shoot for an enclosure that 10"x10"x8".

I'll look at the software settings for the 106 tonight.
 
Sticker shock at the price of enclosures! It's been a long time since I built anything that needed an enclosure. Looks like a Hammond 1550wf is probably going to be the choice. Yes a little tight, but should be plenty since the controller has a built in power supply.
 
Maybe I'm a Luddite, but a casting thermometer will cost a whole lot less than a PID device and won't degrade over time. I've used a "Tel Tru" branded one for my Lee furnaces for years and can highly recommend it. Btw, my furnaces don't vary much in temperature, and I remove the thermometer once the temperature of the melt has stabilized. And I forgot to add, the thermometer is much cheaper too. Just some food for thought....
 
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I have a thermometer, a Lyman digital. I can never get my pot to sit where I want, either runs too cold or too hot.
 
Greg, The thermometer I mentioned is analog, adjustable, and reliable. As for the thermostat on the Lee furnace, if you remove the top cover (with the adjustment knob), you can gently clean the thermostat's contacts, then gently bend the blade down to raise the furnace temperature. These adjustments have worked for me for +30 years.
 
Already bought everything, if I don't find it useful then I'll use it with my powder coat oven.
 
Sorry, things got busy this week. Sorry if this gets long, but to provide context for anyone in the future that looks back at this thread, I'll go into more detail than maybe is needed right now.

Yes, the enclosures get expensive. I think over the last 4 months I have spent $40k on enclosures for some of our production branches. I have had some luck using the plastic enclosures that you can get at Lowe's. I set up an Inkbird (different model) for a fermenting chamber and used a plastic enclosure.

PID (Proportional, Integral, Derivative) controllers work off the error of the control variable which in this case is temperature. To calculate error take the set point and subtract the actual read value. So T-error = T-setpoint - T-actual. Then Output = P*T-error +sum(I*T-error). Note that the integral output is the summation of error over time. The difficulty that we run into then is output due to the integral term spools up and causes overshoot until the error is negative for long enough that the integral error is reduced to zero.

Since we are melting lead, the system should have a long time constant, meaning that it does not quickly respond to changes in the input. This will result in a slow oscillation around the set value. Here is how I would set the system up if it were mine. Keep in mind that the documentation is pretty poor and I may be completely wrong in how I am interpreting the user manual.

I would be concerned about enabling the control as soon as the pot is started. This would give the integral term a huge amount of time to accumulate error and the temperature could way overshoot. But reading section6.24 of the user manual it says, "If the temperature control requirement is undemanding ..... low temperature point = SV setting value - dF and The high temperature point = SV setting value + dF." I think that this means that the controller is only active during the High and low temperature points. It appears that under screen ALP --> dF you can set the dF value. I would set Df to something around 10 degrees.

Then as far as the PID screens.

Control Period: 1 second: Since you have an SSR it can handle higher switching frequencies than a normal coil relay. Normal coil relays should not switch more than once in 20 seconds.

Proportional Band: 200: I would start at a low value and make sure that the I and D terms are set to 0. This should allow you see how the value of the P term effects the pot. Start with 200 and see how well the pot maintains close to the desired set point. If the temperature continues to fall over time, then increase the value in increments of 50. If the temperature starts to run away, then decrease the value.

Integral Time: It is unclear to me why the units on this are seconds. But anyway I would treat it just like we did with the P term. Once you have the P term set where the pot is maintaining temperature (we don't really care that the error is zero, but we do care that the temperature is stable), then increase the integral term to 100. This value should be low enough that the integral error will not cause huge overshoot. Once you have seen how this value performs, then turn the pot off and let it cool by 20 degrees. Once the pot has cooled, then turn it on and see how badly the temperature overshoots or how long it takes to achieve zero error. If the pot overshoots temperature by a lot, then turn the integral term down. If it takes FOREVER to achieve the set value, then increase the term.


There are more scientific ways to tune a PID controller, but I have found that they are often better suited to more complex problems where the risk is higher. For something simple like this, playing around with the values is typically the best approach. The only thing to really be aware of is don't change to many things at once. Change one variable at a time.


Hopefully that helps! Let us know how your progress is. You have me wanting to do this now too just for fun!
 
Thanks, that should definitely get me started. The box is due towards the end of this coming week, and I've taken time off the week following so likely to work on this a lot while I'm off. My latest rifle build is wrapping up, need to file a few screws and blue them, maybe more truoil on the stock. And now that it is back together I have a trigger issue with the set trigger I need to figure out.

I also need to program this for my powder coat oven, if I try to heat it fast after opening the door, it over shoots in a big way. This overshoot has melted bullets, especially high tin alloys.

I'm making this controller with a male and female AC connection, so I can plug anything that runs under 10 amps into it. I probably should have used the 20 amp SSR, but figured the lighter load would generate less heat in the SSR. Trying to avoid the massive heatsink and just use the aluminum case. But I can always bolt the sink to the outside of the case for extra cooling.
 
Time to get some programming done, need to get the instructions out so I can get everything set, currently it turns on when lower than set point. I did manage to push enough buttons to get in into degrees F so I could play with it a little. But so far, so good, it turns a light on and off (didn't want too big of a fire if I made a mistake with the wiring).

PSX_20221222_224532.jpgPSX_20221222_224609.jpg

Yes the thermocouple can be unplugged, I think I can also use the probe that came with my Lyman digital lead thermometer, it has the same plug and should be the same K type thermocouple. The reason for this is I have holes drilled through my powder coat oven that fit the smaller Lyman probe, so it could be an easy switch when powder coating, and I might see better use for the slow to react oven to get it back up to temp faster and not overshoot as much as the built in temperature control does. I hate watching an entire batch over shoot and start to slump, lots of work going straight back into the lead pot. That's why I went with dual plug design instead of wiring the lead pot directly into this controller, it can fill multiple roles with a little programming change. If people are interested, I can list all the parts I bought, everything but the handful of connectors and the box I bought from Amazon. The connectors I had. The box came from Mouser Electronics, it's slightly large but gave a lot of space to stuff the wires. A drill, hacksaw blade (no handle), and a couple of files made the holes. Yes you can still see some layout lines on the box, the SSR is screwed to the box on the inside and I can attach the heat sink to the outside if I start getting thermal problems with the SSR, just need longer screws and some nuts to attach it.
 
I know no one is really following this, but I think this controller may not be what I really need. I got my PC oven going and fooled around, get it to about 15 to 20 degree swing. Then I decided that some insulation in the oven might help and ordered the stuff. I also found out that my thermocouple was only rated to 750 F, so ordered something more appropriate. That stuff arrived, installed the insulation and calibrated the controller to the new probe. Then gave it a try.

Now getting more like a 30 to 40 degree swing, with most of that being on over temp. My oven uses quartz heaters. The controller does what it should, I can get it to start pulsing at +2 degrees, with full on at -2 degrees (from set point). But it continues to fall for another 6-8 degrees before it starts rising again. It then cuts off right at set point, but the quartz is hot and temp. keeps climbing to +20-30 degrees. The insulation seems to be working against me now.

It looks like what I need is something with a little more intelligence that can look at the speed that the temp rises, and predict where to shut off, and where the temp falls and needs to have the heaters on to keep from falling too low. A 10 degree spread would be more than tight enough. I'll have to risk a couple batches of ammo and see if it behaves better with more mass in the oven. Or maybe a controller that's 4x the money like an Auber with "fuzzy logic" and hope they are being truthful about adaptive logic.
 
After thinking about this for a little while, I went back up and reread the hints... Combined those with a change in the oven and I'm now within about an 8 degree spread. I turned off the bottom heater which cuts the power in half. It also prevents the 30 degree over run once the heaters are turned off. I can live with an 8-10 degree swing around my set point. Going to shake up a batch of ammo and see how well it handles things with more mass inside the oven.
 
Adding a tray of ammo, about 2 pounds worth, didn't really change the results. Now my oven is under better control so even if this doesn't work for my lead pot, it will be money well spent for powder coating. I'll have to get some casting done soon to try this out.

The odd thing is that the auto tune was WAY off, P was normally under 15 and I up around 25, with 2 or 3 for D. But that was with the massive over run from both quartz heaters running. I may need to try another auto just to see what happens.

Ultimately I'm hoping that the settings will be similar enough that I can just move the control from casting to coating with nothing more than changing the probe. I bought 2 of the higher temp probes and checked both in boiling water, within a couple of degrees of each other so close enough.

I appreciate the suggested settings above!!!
 
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