Build or Buy 2nd PID? For Stacked Lee 4-20s

[psychbiker]

I’m diving into a stacked lee 4-20 setup so I can cast about 35-40lbs per session before having to add more lead.

I’ve got a pid I built and use for my current lee 4-20 for molds.

Debating building another or buying a completed one for the upper lee 4-20 that will be used just to refill my bottom pot.

I priced out building a PID and it’s about $60 I think.

Pid, ssr and heat sink, and thermocouple - $35-$45
14awg extension cord - $10
Plug for k thermocouple into box - $8
Female socket plug for pot to plug into - $8
Spade connectors - $10
Box - free. Making out of wood.

More like $70-$80.

When not using for lead I can use this for a powder coat toaster oven I think too. It is fun to build but kind of has me wondering if for $40-$50 more I can have it done on my door in a few days.

Thoughts?

[RedlegEd]

Hi psychbiker. I think you kind of answered your question in the last sentence, "When not using for lead I can use this for a powder coat toaster oven I think too." You said it's fun to build and you'll get double duty from it (maybe even more,) so I see it as a win-win. I think some of your guestimate pricing is kinda high, so I see you in for about $60 vs buying one plug and play for a good bit more. If you're stuck at home like many of us, what else are you going to be doing? My thought....make your own and enjoy yourself.
Ed

[Rizzo]

Having two PIDs is a good idea.

You built one already, so I recommend building another one.
There's that satisfaction of firing up your own built unit and seeing it working.
It puts a smile on your face.

Hmmm,.....maybe you need a third one for controlling a hotplate temp for your mold?
<grin>

[Valley-Shooter]

I really don't see any benifit to add a PID to the top pot. The top pot is just melting the lead and maintaining the temperature higher than the bottem pot. When the lead is poured into the second pot, that stream of molten lead is losing a ton of heat. The final temperature in the second pot will depend how much lead that is currently down there. The PID in the lower pot will react and change to the final temperature.
It also depends on when the bottem pot is being filled. Are you filling the pot when it is half empty or are they linked together and it is always being topped off.

[psychbiker]

^^^ Oooohh linked together, damn, that's an idea.

Just to fill was my thought. Once lower pot gets half full I'd pour from upper to lower, then add a few lbs back into upper.

[Petrol & Powder]

I agree with Valley-Shooter, there isn't much to be gained be adding a PID to the top (feed) pot. That one simply feeds the bottom pot. I wouldn't run the top pot any hotter than needed and I would let the PID do its job on the bottom pot.
If you keep a fair amount of mass in the lower pot, the input of molten lead to the bottom pot will not greatly affect the temperature. The PID on the lower pot can then address the minor variations.

[HATCH]

You always get what you pay for.

To be totally honest with you, a Lee 4-20 pot only pulls around 6 amps
You won't need a heatsink if you use a 25 amp SSR.
You will need one if you use a 10 amp SSR as you are pushing the device to its limit.

Its gonna cost you slightly more then your initial estimate.
The PID kits that are sold on Ebay and Amazon normally don't have the correct Thermocouple. The design is a screw in and you need a probe. The other thing is that you need to double check the temp range of the TC. Most are only rated to 400C which is 750 F. I personally cast at 750 F so I would be at the top limit of the TC range. You may not have a issue if the TC is of high quality as those most of the time will operate 10% higher then rated so they are good for at least 800F. But you might have issues with the cheaper units.

May I suggest that you purchase higher quality connectors as those are your failing points for sure.

I do offer a PID with a inline connector and extra TC. Its $25 more just because the cost of the connectors. Keep that in mind when you pricing it out.

My secret in keeping cost low is buying everything in bulk. The main cost on a project (besides the initial parts cost) is shipping cost.
If you have to purchase from three or four different sources then you have to add in the additional cost at $5 or $10 per unless you order them from china on a slow boat.
Just things to keep in mind.

With all that being said, if you have any build questions then shoot me a PM and I am more then willing to help you figure it out.

[dragon813gt]

I’d want to control the upper pot. The temp of it will rise quite a bit as it empties. The stock “temperature control dial” does nothing to maintain a steady temp.

Build one of you have the time and like the build process. Buy one if your time is more valuable than anything else or you want one that’s plug and play.

[Petrol & Powder]

Maybe I'm missing something here but I don't see much benefit from placing the upper pot under the control of a PID.

Having better control, maybe even some self regulating intelligent control; over the temperature of the lower pot that you are casting from - makes sense. The temperature of the upper pot isn't that critical. The job of the upper pot is to just allow us to feed the lower pot with already molten lead so that we don't get those huge temperature variations from introducing room temp lead into the pot.
The upper pot handles the huge temperature swings from taking room temp solid lead and heating it up to the melting point. The finesse is all in the lower pot.

A PID on the upper pot seem superfluous to me.

[psychbiker]

^^ That’s what I thought but then if I dump half a pot in the temps are off a lot, that could change things in my casting. Nothing like having to stop and wait for 10lbs to melt again.

I decided to build another one. Went with a 40a ssr for safety reasons as I can use this new one for my powered coat toaster oven.

I did get pretty pissed trying to order from amazon. Everything I wanted got pushed to April 30th delivery. No way I’m waiting that long. I went with three vendors, eBay, Amazon, and Auberins for parts and schools get them mid next week.

I work In special education so I still ha e weekly tele chats with staff and half a dozen students. Just got word school is done for the year. I’ll have time until baby #1 comes early July. I want to cast as much as I can until then...as well as build wife a rocking chair, move a couple walls in the house, and other crap. Maybe I should have gone the pre built route hahaha!

[Petrol & Powder]

Mass is Mass. Dumping a 1/2 pot (10#)into that lower pot is going to have an effect on the overall temp of that lower pot if that incoming mass is a drastically different temperature than what is already in that pot. Having a PID controller on the upper (feed) pot may help if you're dealing with drastically different temps but I doubt that's the case.
The upper pot just needs molten lead in it and I would want it to be just hot enough to be molten. The real control is in the lower pot. You'll have a lot more control if you limit the amount of mass you introduce to the lower pot at a time rather than worrying about maintaining a narrow window of temps in that feed pot. Adding 1 pound of molten lead at a time as opposed to adding 10 pounds at a shot will let the PID on the lower pot achieve the control you desire.

[HATCH]

Unless both pots have the same temp lead in them your going to have the same fluctuations just not as far of a swing.

Example , lower pot is 750
Upper pot is just above your alloy melt so let’s say 700 (even though you ain’t gotta clue as your just melting it with no temp reading)

You dump 1/2 a pot of lead from the top to the bottom it’s gonna drop the temp at least to 725 as it averages out the new lead temp with the temp in the pot. The. Your gonna have to wait a couple mins for the temp to get back up to 750 again.
That’s just a example.


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[RedlegEd]

I’ll have time until baby #1 comes early July. I want to cast as much as I can until then...as well as build wife a rocking chair, move a couple walls in the house, and other crap. Maybe I should have gone the pre built route hahaha!

psychbiker,
Congratulations on the upcoming arrival! That little one will rock your world, so getting as much casting done as you can now is a good idea. Very best wishes to your family and hopes that all turns out well.
Ed

[Mike W1]

I have stacked #10ers with both on PIDs. Dumping 6-8 pounds doesn't drop the bottom one more than 2°. FWIW

[Petrol & Powder]

Unless both pots have the same temp lead in them your going to have the same fluctuations just not as far of a swing.

Example , lower pot is 750
Upper pot is just above your alloy melt so let’s say 700 (even though you ain’t gotta clue as your just melting it with no temp reading)

You dump 1/2 a pot of lead from the top to the bottom it’s gonna drop the temp at least to 725 as it averages out the new lead temp with the temp in the pot. The. Your gonna have to wait a couple mins for the temp to get back up to 750 again.
That’s just a example.


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RIGHT, SO DO NOT dump 1/2 of a pot [10 pounds !] in ! Maybe add 1 pound or a 1/2 pound to the lower pot at a time instead of 10 pounds.

You could string 6 pots together and put PID controllers on ALL of them but at some point you're just chasing your tail.

Let's say you want to run the lower pot at 725 and you dump in 10 pounds at 700. It will take a few minutes to get the lower pot back up to 725.
So in that situation you have a couple of options:
A. Put in 10 pounds at 700 degrees and wait several minutes for the lower pot to equalize at 725.
OR
B. PUT IN LESS and wait a smaller amount of time for the lower pot to catch up.

Putting a PID controller on the upper (feed) pot is an eloquent solution but is it really necessary to achieve what we are after?

If our goal is to achieve a fairly constant temperature in the lower pot do we really need to hold the upper pot to a very narrow temperature range or do we just need use the upper pot to feed 650-750 degree lead into the lower pot instead of putting 70 degree lead directly into the one pot?
HOW MUCH CONTROL DO WE REALLY NEED IN THAT FEED POT ?

[fralic76]

Dual PID controller, box built out of wood. 1 side controls my melting pot the other co controls my hot plate that is use to pre warm molds.

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[dragon813gt]

It’s not all about control. Well it sort of is indirectly. It’s about time, which some may consider wasted. And this depends on the setup. If the pots are linked and you’re dropping lead from the top pot every time you fill a mold you’re effectively doubling your capacity. So to keep moving along w/ no stoppage you’d want no variation in lower pot temp at any point.

Now if you’re dumping the top every couple pounds and there’s no control in the top you will have to wait for the lower to come up to temp. This is the potential “wasted time”. For some people, like myself, time is more valuable than anything else. And I’m willing to spend more money to speed up processes. But I understand that it’s not this way for everyone. Remember that everyone has different needs.

[Petrol & Powder]

You have ask the question, "What am I attempting to accomplish"?

A PID controller on the feed pot is an eloquent solution and I have no doubt that it would result in smaller temperature variations when lead is fed into the lower pot. However, that fine control over the temperature of the upper pot will not make that pot melt lead any faster. It will not hurt but it will not help much either. The upper pot is already doing the bulk of the work by taking solid lead at say 70 degrees and bringing it up to say 650-725 degrees. You don't really need the finesse of a PID controller to do that. A simple thermostat that turns on that 700 watt element (if you're using a Lee 4-20) will accomplish that task.

Where the PID controller shines is on that lower pot where we are attempting to hold a tighter temperature range.

The PID controller doesn't make that 700 watt element melt lead any faster in that upper pot.

I agree that a PID controller on the upper pot would help hold a tighter temperature range on that upper pot but I doubt that the additional expense and complexity is necessary. I think once the lead in the upper pot melted, the simple thermostat control (which is admittedly crude) is more than sufficient to control that feed pot. The real work of temperature control is occurring in the lower pot.