I am trying to replace the thermostat on one of my RCBS pots with a voltagel controller. At one time there was a web page about doing this using something from Home Depot or Lowes. Well I had this on my favorites but the last time my hard drive crashed I lost it. Does anyone know about this?????
Any help with this would be of a great help....Thanks Wes
A thermostat works with a temperature sensative resistor to keep the temp constant. A given resistance = a given temperature.
A voltage regulator does just that. So yes you can sort-of control temp by varing your voltage but it wont be as accurate. Its more of an on or off switch.
so what is the point of going to a less accurate system? Is your going bad and want a cheap alternative.
That being said any voltage regulator that can handle 120VAC @ 15AH will work. They are very simple to wire up either inline with the power cord w/ the thermostat shorted, or in place of the thermostat.
P.S. its better to limit your amps VS the voltage.
NVScouter yes the thermostat has gone south. I do have several replacements available. I just remembered looking at this persons pictures and reading his comments about how much better it controlled the temp. and thought I might try it No special reason just something to tinker with....Wes
Will this help?
Voltage Controller for Electric Lead Pot
I've been experimenting recently with a method to regulate the temperature in an electric lead pot with more precision than the factory thermostat. The heating element in the pot, an old Saeco from which I removed the bottom pour valve so that I might use it as a dipper pot, is rated (I believe) at 1000 watts. I went to Home Depot and purchased a Luton Electronics commercial 1000 watt dimmer ($29.97)and mounted it in a 4" wall box along with a standard receptacle. A heavy duty plug and four feet of 12/3 wire completed the major parts.
The heat sink on the dimmer has a score mark on either side of it so that it may be broken for an install where it will be close on the side of another dimmer or in the case of this install against the receptacle. I cut with a nibbling tool and then drilled the metal switch/receptacle cover so that the dimmer could could be mounted. I reduced the size of the plastic cover so that the greatest area of the heat sink would be exposed as the device does get warm during operation. Enough of the cover should be left that index marks can be made so that the knob positions can be noted.
The dimmer was turned up to it's maximum position for initial warm up of the lead pot and was monitored until it reached approximately 800 degrees. The controller was turned down by increments until the pot stabilized at 810 degrees. The pot was then left alone for about an hour and stayed exactly at 810 degrees, which is my nominal casting temperature for large BPCR bullets. Instead of the On-off-on-off of the thermostat the controller keeps the heating element at a constant temperature similar to the constant but adjustable heat of a propane burner type pot. Normally the thermostat would have caused fluctuations of up to 75 degrees (at least in my lead pot). The thermostat was set at approximately 850 degrees so that the pot would heat quickly, but have a safety cut off so that the pot would not get too hot if ignored.(The thermostat had been damaged previously by being dropped on the knob while unused in the box, was to an extent repaired, but has never been particularly accurate. The pot set in unused rusty condition in a garage for at least 20 years before I got it.)
A digital voltmeter was used for repeatability of settings. The pot was plugged in one of the receptacles and the leads of the voltmeter were plugged in to the other. Under load the voltage reading was 103.5 at the controller's highest setting, which was used for initial warm-up. The pot was allowed to heat to 800 degrees at which time the controller was turned down to 83.3 volts and the pot was allowed to stabilize for 10 minutes. The temp at this time was 808 degrees. 14 bullets were cast during which time the temperature began to drop to 790 degrees. The controller was turned up to 88.4 volts and by the 21st bullet the temp had stabilized at 800 degrees. If casting is stopped for a few minutes the temperature will creep up. It took about 10 minutes sitting undisturbed for the temp to increase to 820 degrees with the controller at 88.4 volts. 30 bullets were cast before the pot was topped off. The next 30 were cast with similar results. The initial temperature drop was caused by cooled lead dropping from the sprue plate into the pot and from the dipper cooling during pouring. Bumping the voltage up about five volts from 83.3 to 88.4 took care of the cooling problem. Once a cadence is established it's very easy to keep the temperature of the pot within a few degrees.
Of the thirty bullets cast in the second session the first two cast light at 415.1 grains. The remaining 28 weights were as follows 4-415.9, 10-416.0, 5-416.1, 1-416.2, 2-416.3, 4-416.4, and 2-416.5. The bullets were cast with a Saeco 740 mould of 20-1 alloy.
The cost to assemble the controller with all new parts was about $45.00.
One point, once you put the controller together, if you try to use a 100 watt lamp or something small to test it it will not work correctly. It requires a pretty good load, so plug your lead pot in one outlet and the lamp in another. With a low wattage load the controller causes the lamp to flicker when rotating the potentiometer and not be linear in output. I took one dimmer back because I thought it was malfunctioning. It wasn't, I was.
Below are some comments and observations by a gentleman ("44man" of Shooters.com) who fabricated a controller.
Trapdoor84, I check Low's and some electical shops around here and they wanted $40 to $44 for the dimmer. I finally got to Home Depot and found a 1000 watt slide type dimmer for $29. The first thing I found out, after I broke the 3 tabs off one side to fit in my box, is that reducing the heat sink also reduces the wattage to 800. I made a large soft aluminum heat sink to bend over the side of the box and screwed it to the top of the existing heat sink. I used heat sink silicon grease between the metal. I set the box on a stool with a fan blowing on it and the thing just barely gets warm. This should extend the life of the dimmer. I cast a bunch of real nice bullets today and the temperature of my lead only varied about 4 degrees. I set mine for 80 volts and it held my pot at 820 degrees. I don't drop my sprues back in the pot but into a coffee can to put back when the pot gets low. I need the lead a little hotter because I use a Hoch nose pour and it has so much metal on it that I will not fill the bases unless I can keep it hot. I'm using a Lee 20# pot. Thing works like a charm. Thanks for the info. Jim
P.S. The original article had pics, but thye've somehow disappeared from this file.
Maven that is what I was refering to. Now if I can just follow along. I generally use an ingot feeder or a premelt pot to keep the lead level about the same. I would like to try this however eletricity scares the hell out of me, so any help would be very much appreciated.
Anyway I will have to sit and think about this for a while. I looked at the Luton dimmer and thought the price was about 79.00. But let's get over that what I may have missed is did you get rid of the thermostat or keep it? I am using an RCBS pot for this and so may have many
questions.....Wes
hammerhead357, I just cut & pasted the earlier info. from a folder on my hard drive, so I can't take any credit for it. However, I believe the intent was to bypass the thermostat completely and rely on the heavy duty dimmer + heat sink to control the wattage and hence, the temperature. If you go this route, ask the electrical supply house that you'll buy it from to show you how to wire it.
Hammerhead357,
Are you talking about a PID controller? It's not really a voltage controller as much as an accurate thermo-controller. That's what I use on one of my lead pots and it works great. You can buy the controller fairly cheap on Ebay and just use a simple relay circuit for the higher AMPs that the pot will draw. Do a search here for PID and you will find more info. If you are interested in seeing my schematic I can scan it and send it to you. I probably have under $50 tied up in the entire setup (although I work for a large electronic manufacturing company, so I got the relay and socket free)
I only hope that someday I can be half the Man that my Dogs already think I am!
I wouldnt trust that write up one bit.
Thats some home cooked stuff. The writer never states how he read the temp. Uses load drop to calc something..maybe P but come on ExI=P, so if its a 1000W unit at 115 VAC its pulling 8.6 amps. Measuring like that is only good for calculating total load on a circuit. Since he has no clue what the load of the entire curcuit is and nice "lamp test"he is risking an electrical fire at one point in the circuit.
I like the 12/3 wire he uses, I'm sure its home stype solid core instead of braided soft and insulated application wire. Solid core has bad habbits of breaking after being moved 30-40 times.
The load is your big resistor in the circuit, to vary temp vary the load by adding variable resistance to the circuit. Many electronics places sell these and the cord to wire it with. Buy a good box, wall mount it if you can, and use strain reliefs. Look for a reg that lets you vary in the ranges I stated above.
Watts are ExI=P or voltage times current = Watts
divide W with I or E to get the other one to figure amps or volts.
Last edited by NVScouter; 12-06-2007 at 12:32 AM. Reason: privacy
Sundogg, I was refering to the voltage regulatror, however I think I will pass on this for now. I would like to try a PID controller at some point, especially if it will hold a more even temp.
Yes I am interested in schematics for this if you wouldn't mind. Any other information that you could provide would be very nice also.
I went ahead and replaced the thermostat on the pot that had gone belly up. But now the highest temp. that I can get in a full pot is 750 deg. I don't know maybe my thermometer is giving up the ghost on me. I have had it for 23 years so it may be time to replace it and no it wasn't one of the cheap ones. I is an industrial thermometer with a top reading of 1000 deg. I think it was made by Weksler but not sure right now....Wes
I've been using a cheap dimmer switch from Home Deopt for about a year now with good results. I think it was about $6. I probably spent another $4-5 on an electrical box to put it in, a duplex outlet & a plug. If I watch the pot thermometer, I can find a sweet spot to set the dimmer at to keep the pot temperature pretty constant. The setting is usually around 85% clockwise. I've been using this rig on a Lyman 10 lb pot.
There are other dimmers that are much more expensive. The little ones are cheap. When I checked the wattage requirements for the little 10 lb Lyman pot, they were small enough to let me use the cheap dimmer.
If you want to go haywire spending money, you can get a temperature controller from somebody like Wattlow or Omega & hook it to a thermocouple that you sink into the lead. Then the controller can fire a SSR that will control power to the heating element. That's probably about $300 worth of hardware, but it will allow you to digitally set the temperature that you want the pot to reach. My little $10 box is good enough for what I’m doing.
JIMinPHX, no I don't want to spend 300 or more dinero on this. I have 5 RCBS pots. I just was wanting to find a cheap alernative to the thermostats if it was available and if I could do the pid controller for 40 or 50 dollors per pot I would probably go this route.
I had at one time 5 extra thermostats for the pots and have used 3 of them so am left with 2 spares, and hope I don't have to replace anymore soon.....Wes
There is probably a cheap source of bi-metal thermostats someplace that have a metal coil attached to a mercury switch, but I don’t happen to know what it is. The OEM buys those things somewhere. If it has any markings on it, you might want to feed them into Google & see what pops up.
Another possibility might be to take a standard wall thermostat & gut it. If you can rig the coil & mercury switch to an area of the pot that has a proportional temperature to the pot temp, but isn’t out of the temperature range of the coil, then that might be a quick & dirty way out. I don’t know the configuration of the particular pot that you have so I can only give you a general idea about that.
PID for $50 is probably a pipe dream, at least as far as new equipment is concerned. Used…may be another story. PID started being standard on controllers that were $150 & up when I used to sell that kind of stuff. But PID is probably not really needed here since the heat capacity of the material that the element is made out of is much smaller than the heat capacity of the lead in the pot.
PID is short for proportional integral derivative. It’s a fancy buzzword that means the controller has an algorithm inside that monitors how fast the temperature set point is being approached & then makes allowances in the power provided to the heating circuit to prevent the system from overshooting the target temperature. In thermal systems where the heating element has a high heat capacity or where the temperature sensor is far away from the heating element, this can be a problem. In other systems, a dumb controller that just shuts off when it sees the set point is reached will do fine.
A wall thermostat is a good example of a dumb system. The $300 system that I spoke of is a good example of a PID system.
You can get a Chinese made PID on Ebay for about $35. ( http://cgi.ebay.com/Dual-Digital-F-C...QQcmdZViewItem )add a relay and socket (mine was free from work probably about $15) It is very accurate. I'm sure it's not top of the line, but it make a Lee 20 pounder very very even from full to empty. I think it was a great investment. I bought a second thermocouple to use on my Star Sizer's heater as well. (I haven't done it yet though)
I only hope that someday I can be half the Man that my Dogs already think I am!
Wow, Sundog,
That’s a pretty good looking deal. That looks very much like the units that I was selling for $150 10-years ago. Mine either came from the US, Japan or Europe. I guess that the Chinese have finally gotten into that market too. $45 with a K thermocouple is a bargain indeed.
A K-thermocouple is good for over 1000 degrees, even with crummy wire on it. One thing about thermocouples, you need to use thermocouple wire on them & not just regular garden variety stuff. The other thing to consider is that you need to get the thermocouple to the material that is being measured. That thermocouple looks to be threaded, so you might need to weld a nut or thermowell onto your pot.
Like Sundog said, you will also need a relay with that controller. There are two basic types, mechanical & Solid State Relays (SSR). Most of the controllers out there don’t have proportional voltage outputs. Most of them have what’s known as pulse width modulated outputs. That’s a fancy word for an output that just turns on & off real fast & varies the power delivered to the heating element by varying the amount of on time vs. the amount of off time. If it is on 90% of the time & off 10% of the time, then you get a lot of heat. If it is on 20% & off 80%, then you don’t get so much. A mechanical relay will work fine if the switching rate isn’t too fast. If the relay sounds like a buzzing bee when the thing is running, then the relay will not last long & a more expensive SSR would be a better choice. Since the specs for this thing say that it has a 3-amp dry contact & also a SSR output, it can probably be used with either a mechanical relay or an SSR.
Heating elements are considered an incandescent load. They draw 10 times their rated current when starting up cold. Even compared to a motor load that draws a locked rotor current of 6 times the nameplate current at start up, this is a heavy starting load & should be considered when selecting a relay. If you use a relay that is rated as a lighting contractor, then the current rating can be used as is. If the relay that you use has a motor current rating, or an AC3 current rating, then you should select one that is rated a little higher than your expected steady state current. If you use a DP, AC1, AC2 or general purpose rated relay, then you should use one that is rated for at least twice the steady state current of your heater. Any relay that you find at Radio Shack is going to be general purpose type. automationdirect.com has motor rated contactors at fairly reasonable prices. As was said earlier, P/E=I or watts divided by volts = amps. So if you have an 800 watt heater that runs off 110v, you would need 800/110=7.27 amps steady state & a 15 amp general purpose relay would probably work well.
Then again, the cold start current isn’t put to that thing very often, so you might get away with a little less robust relay rating with intermittent use.
Sundog,
What kind of relay did you use?
Wow, that same guy on e-bay has a 40A SSR for less than $20. Incredible
http://cgi.ebay.com/New-40A-SSR-Sold...QQcmdZViewItem
Nice post Sundog, I take it your using this set up w/the Lee 20" furnace now and it helps maintain a more constant temp. Was it very complicated to wire in or not and have you posted or can you post a picture of the set up please? I believe I'd like to try this one myself too.
Creekwalker
IM with creekwalker, I am very interested in trying this out any pics or more info you can give on this set up Sundog
why not just sent the pot to rcbs. they will fix it for free.
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