PID question

[Chris C]

How close is a PID supposed to keep the temperature on a lead pot?

[Beagle333]

If you aren't using it and it's just sitting idle at temp.... around 2 degrees of set temp. If you are using it, it depends on how fast you are using it and if you are putting sprues/cull back in the pot.

[AbitNutz]

It keeps it close...the only issue is and it may not be an issue, is that it keeps turning the pot on and off about every couple of seconds to keep it within 2 degrees or so. I always suspect that it's not good for anything to be cycled on and off that much and that quickly. So far so good though, and no one else seems to complains, so it may not be an issue...but it still bugs me.

[Chris C]

As Beagle333 says, mine will hold within + or - 2 degrees if not being used. Of course it turns off and on frequently to keep the temp steady. However, when I'm using it, it will climb as high as 7 degrees above my calibrated temperature and as low a 9 degrees below..............at least that was during today's casting session. I don't add anything to the pot as I run. How can I cast consistently with the temp varying that much?

[Mike W1]

It keeps it close...the only issue is and it may not be an issue, is that it keeps turning the pot on and off about every couple of seconds to keep it within 2 degrees or so. I always suspect that it's not good for anything to be cycled on and off that much and that quickly. So far so good though, and no one else seems to complains, so it may not be an issue...but it still bugs me.

My 2¢ on the cycling is my opinion but when I built a 2nd unit and then a 3rd I definitely noticed that the Mypin unit cycled a LOT oftener than my Auber or my Rex did. And it didn't maintain a steady temperature nearly as well as the other 2 did and do. Gave up trying to use it to control my hotplate as that was not happening. The Auber generally keeps it within a degree of set temperature so it's on there unless I use it to regulate my lube heater. Sent the Mypin back and both pots are now regulated with Rex units and they keep it within ± 2° C so my might say ± 3.6° F. I haven't found the Celsuis only feature of the Rex to be any big problem and they're considerably less expensive.

[Chris C]

Is it normal for the PID to have a 16 degree temp swing during casting?

[Beagle333]

I don't think "varying that much" is having as much effect as you might think. Also, as the pot level drops, the amount of "power-on time" the PID sends has to constantly be adjusted, since it doesn't take as much power to keep half a pot at temp as it did when the pot was full. The PID learns how much power to add to get something to a certain temperature and keep it there, and by lowering the amount of lead that needs to be heated, we're messing with the learning it just did and there's really no way (known to me) that the PID can know how fast you are going to drain that pot. But I really doubt that will mess up your batch of boolits.

[Chris C]

I re-calibrate the PID as the level goes down in the pot for that very reason. Shouldn't it then "re-learn" how to hold the temp at that lower level?

[Mike W1]

I re-calibrate the PID as the level goes down in the pot for that very reason. Shouldn't it then "re-learn" how to hold the temp at that lower level?

I don't how rapidly you empty your pot but if memory serves it takes about 3 cycles of highs and lows before autotune shuts off automatically. In that amount of time you'd likely be pouring a lot of lead and seems like you'd be defeating the process. From what I've noticed when I've AT'd the unit to a pot it doesn't even seem to be necessary to run AT again even when I change the set temperature. You'll notice even when you leave things basically the same and run AT it'll come up with a different set of figures than the previous ones. I find I'll get the same amount of control with either set of them long as it's regulating the same equipment. Switching to the hot plate or the lube heater would of course generate an entirely different set of figures and trying to use those on the pot won't do much of a job of regulating things.

[William Yanda]

Anybody know offhand the swing of a stock non-PID temperature controller?

[dragon813gt]

I re-calibrate the PID as the level goes down in the pot for that very reason. Shouldn't it then "re-learn" how to hold the temp at that lower level?

You need to pick a level and tune it there. Because of the load on the pot it's not going to be able to maintain the temp from top to bottom. I tuned mine when full. When it gets below a quarter full the temp will start to gradually rise above set point. But this makes sense because it's trying to maintain temp based on a full load. When the load is cut by 3/4 the pot heats up a lot quicker so it overshoots.

Anybody know offhand the swing of a stock non-PID temperature controller?

It's going to depend on the controller. Each one is going to have a different spec. Some may be +-5 while another may be +-10.

[edctexas]

The regulation is a complex process. The size of the heating element (watts max), the mass of alloy, and the rate of alloy leaving the pot are the major variables. The PID tries to compensate for that. Some PIDs are really thermostats with an advanced algorithmn. The "real" PID can apply any amount of heat from maximum that the pot allows to 1/120 of a second of energy. A good consumer unit should hold +/- 2 degrees with no added alloy or no output alloy. As alloy is removed from the pot, the heat stored in the alloy and pot is removed. A single 200gr boolit removes 0.001 percent of the heat stored. So a short burst of power applied can make up for the lost heat and keep the alloy near the set temp. Adding alloy is more difficult to keep the temperature constant. The PID models the heat loss and gain with an algorithmn which doesn't exactly match the pot and heater characteristics. The "tuning" tries to make the "I", "D", and time factors get closer to matching the pot. I write down settings stored in the PID for different casting scenarios. The "tuning" will give you different numbers for each set of runs. Look at them and you can see a pattern. I like the REX and AUBERINS units better than the MYPIN units.

Ed C

[AbitNutz]

If you happen to have a wired up functioning temp controller that has a MYPIN or AUBERINS PID in it...how difficult is it to swap in a REX PID to replace them? Is it a straight one for one wiring deal?

[Mike W1]

It's not a big deal to do so, you just have to know what goes where obviously. All you're really doing is basically changing 6 wires. The TC leads, the power leads and the signal leads. Both the TC and the signal leads are polarity sensitive so you have to know which side is which on them. The diagrams on all units show which is which but naturally which particular terminals are not going to necessarily be the same number on different units. Not difficult just tag the wires first.

I am happy with my Rex's but I wouldn't swap my Auber for them. But the Rex can be had for about 1/4 the price of it too. If you buy a Rex make SURE it has a SSR output!!!!

If you have alarm leads those also would have to be changed over. Didn't even wire em' on my Rex's and don't bother to set them on the Auber. They're basically useless overkill as the temperature values are right there anyhow.

[Walter Laich]

Mine hangs in there at ± 3º pretty much though entire pot. I don't add while casting cause it throws my rhythm off.

It's an Auberins with a wonky one's display--one of the 'bars' that makes up the numbers has burned out or whatever those kind of lights do.

I would think the head pressure between full and almost empty pots would also affect the casting of the bullets.

for me: neither is a big deal

[Chris C]

Don't know what caused the situation that prompted my original post, but yesterday and today I cast 200 bullets each day and the PID held the temp to + or - about 2 degrees the whole time. Go figure!