Woodtroll
04-02-2007, 11:21 PM
I worked out an electronic pot control based on some ideas I'd seen here on the board, and with lots of help from Lurch (many thanks again, sir!). I thought I'd pass on the parts list and how I made it work, and what didn't work, in case someone else was pondering the idea.
I used these components from Auber Instruments:
PID Controller: http://auberins.com/index.php?main_page=product_info&cPath=1&products_id=14
Solid state relay: http://auberins.com/index.php?main_page=product_info&cPath=2&products_id=9&zenid=ea21c5203a9365113a4863b949226ba0
K-type thermocouple: http://auberins.com/index.php?main_page=product_info&cPath=3&products_id=2
The gentleman running this outfit ships fast, is courteous, and promptly answers questions about his products. These three pieces with shipping cost me about $66.
I put these together in a wooden box, using a piece of scrap aluminum about 6"x7" I had on hand to make a face plate to mount the components on/ in. I used a 2-amp glass fuse in the power source for the controller, although it could probably use an even smaller fuse. I hooked the relay to the PID, and the relay in turn is hooked to a receptacle so that I can plug in different pots if I wish. One thing that is important, is to mount the relay to a large piece of metal to act as a heat sink, so that the relay itself does not overheat. I also left the top and bottom of the box open, and covered them with some hardware cloth, so that the electronics could get plenty of air. I hung this assembly on the wall out from under my vent hood, hopefully far enough away from the heat of the pot.
The pot I set up to be controlled is the Lee 20-lb. Pro 4-20, but it should work as well with about any other pot. Anxious to get the thing working, and trying to shortcut any welding to mount the sensor, I got the bright idea that I could drill a small hole in the aluminum bottom pot cover, swage the metal down enough to form a sleeve to accept threads to hold the thermocouple, and screw the thermocouple in through the cover, using the tension provided by the cover to hold the thermocouple up against the pot bottom. I placed this hole directly behind the pour spout, near the rear edge of the pot, to make sure that I had it out of the way of my moulds, but you want it in away from the very edge, I think, for a more accurate reading. Mechanically, this worked fine, and I thought I had shortcut a lot of work. I found, though, that the thermocouple reading and my immersion thermometer (maybe not the right word- my regular analog casting thermometer that I stick in the pot) were off by a full 200 degrees F! Lurch pointed out that the cover was acting as a heat sink, and maybe the thermocouple wasn't tight enough against the pot bottom, so I resorted to welding.
Ideally you would use a MIG or other wire-fed welder for this, as the pot liner is very thin. I didn't have one at my immediate disposal, so I left the pot half-full of frozen lead, turned it upside down, took enough parts off to take the bottom cover off, and very carefully welded a 1/4x20 nut on the bottom of the pot liner in the spot that I had originally drilled through the cover for the thermocouple. All I have is a stick welder, so using my smallest 6013 rod I welded the nut down, and built up a big puddle of weld all around the nut so that there would be lots of conduction from the pot bottom to the thermocouple and its retaining threads. I cut the hole in the bottom cover out to about 3/4" diameter, so that it would not contact any part of the thermocouple or the welded nut "boss", and carefully placed a little fiberglass insulation around the nut, and between the pot bottom and cover, leaving a little sticking out of the hole. I screwed the thermocouple in snug, arranged the insulation around the thermocouple connection, and held it in place with a small piece of tin foil. I used this "rigged-up" method of insulating to make it easier to switch out the thermocouple if I wanted to use the controller on a different pot. I'm not sure how far down the cable the wires themselves can tolerate heat, so I used care not to insulate any of the wiring, just the metal connections on the end of the cable.
This time the thermocouple reading and the casting thermometer agreed to a very minor difference of only 3-5 degrees once the lead melted!
Initially, this seems like a very worthwhile setup. I cast lots of big bullets for my BPCR guns, and some of these I use to shoot in matches on the very odd day that I have time. Consistent temperature, of course, makes it a lot easier to keep weights and sizes uniform. In the past, I had dumped a sprue or stray bullet into the pot at appropriate times to fine-tune the temperature of the melt. If this electronic setup works as well as my limited experience so far leads me to believe, it will be money well spent. The only flaw so far is that the controller overruns the temperature by 20-30 degrees initially, but then it settles down and smooths right out. Lurch told me the term for this, but I can't recall it right off hand. By the time the mould reaches the right casting temperature, the pot seems pretty well stabilized.
Again, none of this is my original thinking- I'm a mechanical person, but not a computer or electronics whiz! All the ideas are ones I read here already, plus a lot of input and help from other folks made this a success. I just thought that I'd post it here all in one place, start to finish and with a parts list, so that it may be easier for someone else to follow through.
Good luck, guys, and thanks for all I learn here on the board! Take care, Regan
I used these components from Auber Instruments:
PID Controller: http://auberins.com/index.php?main_page=product_info&cPath=1&products_id=14
Solid state relay: http://auberins.com/index.php?main_page=product_info&cPath=2&products_id=9&zenid=ea21c5203a9365113a4863b949226ba0
K-type thermocouple: http://auberins.com/index.php?main_page=product_info&cPath=3&products_id=2
The gentleman running this outfit ships fast, is courteous, and promptly answers questions about his products. These three pieces with shipping cost me about $66.
I put these together in a wooden box, using a piece of scrap aluminum about 6"x7" I had on hand to make a face plate to mount the components on/ in. I used a 2-amp glass fuse in the power source for the controller, although it could probably use an even smaller fuse. I hooked the relay to the PID, and the relay in turn is hooked to a receptacle so that I can plug in different pots if I wish. One thing that is important, is to mount the relay to a large piece of metal to act as a heat sink, so that the relay itself does not overheat. I also left the top and bottom of the box open, and covered them with some hardware cloth, so that the electronics could get plenty of air. I hung this assembly on the wall out from under my vent hood, hopefully far enough away from the heat of the pot.
The pot I set up to be controlled is the Lee 20-lb. Pro 4-20, but it should work as well with about any other pot. Anxious to get the thing working, and trying to shortcut any welding to mount the sensor, I got the bright idea that I could drill a small hole in the aluminum bottom pot cover, swage the metal down enough to form a sleeve to accept threads to hold the thermocouple, and screw the thermocouple in through the cover, using the tension provided by the cover to hold the thermocouple up against the pot bottom. I placed this hole directly behind the pour spout, near the rear edge of the pot, to make sure that I had it out of the way of my moulds, but you want it in away from the very edge, I think, for a more accurate reading. Mechanically, this worked fine, and I thought I had shortcut a lot of work. I found, though, that the thermocouple reading and my immersion thermometer (maybe not the right word- my regular analog casting thermometer that I stick in the pot) were off by a full 200 degrees F! Lurch pointed out that the cover was acting as a heat sink, and maybe the thermocouple wasn't tight enough against the pot bottom, so I resorted to welding.
Ideally you would use a MIG or other wire-fed welder for this, as the pot liner is very thin. I didn't have one at my immediate disposal, so I left the pot half-full of frozen lead, turned it upside down, took enough parts off to take the bottom cover off, and very carefully welded a 1/4x20 nut on the bottom of the pot liner in the spot that I had originally drilled through the cover for the thermocouple. All I have is a stick welder, so using my smallest 6013 rod I welded the nut down, and built up a big puddle of weld all around the nut so that there would be lots of conduction from the pot bottom to the thermocouple and its retaining threads. I cut the hole in the bottom cover out to about 3/4" diameter, so that it would not contact any part of the thermocouple or the welded nut "boss", and carefully placed a little fiberglass insulation around the nut, and between the pot bottom and cover, leaving a little sticking out of the hole. I screwed the thermocouple in snug, arranged the insulation around the thermocouple connection, and held it in place with a small piece of tin foil. I used this "rigged-up" method of insulating to make it easier to switch out the thermocouple if I wanted to use the controller on a different pot. I'm not sure how far down the cable the wires themselves can tolerate heat, so I used care not to insulate any of the wiring, just the metal connections on the end of the cable.
This time the thermocouple reading and the casting thermometer agreed to a very minor difference of only 3-5 degrees once the lead melted!
Initially, this seems like a very worthwhile setup. I cast lots of big bullets for my BPCR guns, and some of these I use to shoot in matches on the very odd day that I have time. Consistent temperature, of course, makes it a lot easier to keep weights and sizes uniform. In the past, I had dumped a sprue or stray bullet into the pot at appropriate times to fine-tune the temperature of the melt. If this electronic setup works as well as my limited experience so far leads me to believe, it will be money well spent. The only flaw so far is that the controller overruns the temperature by 20-30 degrees initially, but then it settles down and smooths right out. Lurch told me the term for this, but I can't recall it right off hand. By the time the mould reaches the right casting temperature, the pot seems pretty well stabilized.
Again, none of this is my original thinking- I'm a mechanical person, but not a computer or electronics whiz! All the ideas are ones I read here already, plus a lot of input and help from other folks made this a success. I just thought that I'd post it here all in one place, start to finish and with a parts list, so that it may be easier for someone else to follow through.
Good luck, guys, and thanks for all I learn here on the board! Take care, Regan