homemade electric casting pot

[killbox]

I pour weights for decoys as well as book its and need a high volume high flow rate casting pot. Has anyone made a pot with an electric oven element? I have also considered using this plan

http://firstpatriotpress.blogspot.com/2012/08/i-want-magma-type-melting-pot-1-of.html

I have no idea how to control temperature though. Any suggestions would be appreciated.

[Russel Nash]

look for a thread by forum member "jmorris" . he made his own electric and automated casting pot. I am not all hip on all the Radio Shack type electronics.

I will be back in a second.

[Russel Nash]

It's on another forum, but still look for the posts by jmorris, the ones with the little pics:

http://www.brianenos.com/forums/index.php?showtopic=70411&hl=%2Belement#entry817131

you can click on the pics and I think they will expand into their own window and be bigger/easier to see.

[Russel Nash]

Maybe my old thread will help here, it is on the innards of an RCBS Pro Melt furnace:

http://castboolits.gunloads.com/showthread.php?41055-Here-are-some-PICS-of-the-inside-of-an-RCBS-Pro-Melt&highlight=rcbs

it has lots of pics.

The last time I called RCBS to ask about their thermostat, IIRC, for all the parts it was going to be like $40.

[killbox]

I think I am going to go pretty much with the design above using the oven heater but I think I want to use a bulb and capillary style thermostat. Does anyone know where I can get a high temp one? Most of the ones I have seen go up to about 550 degrees.

[dikman]

Thanks for that, Russel Nash (one of my all-time favourite films, btw). I didn't think there would be too much inside the RCBS, and at least now I know how the thermocouple is connected. One thing I might mention is those wire connector covers. My wall oven has the same type (had is probably a better word!). I've had to do a few repairs on it over the years, and the heat from the oven slowly cooks the plastic covers, they get brittle and fall apart! And the oven doesn't get as hot as the melting pot!

At some point I'll probably drill out the rivets and replace them with screws so that I can keep an eye on the insides. I'm amazed at how hot the whole thing gets (burned myself a couple of times on the case until I learned my lesson).

[bangerjim]

At Pb melt temps, you best bet is a K thermocouple ( it is designed for hi-temp measurements) feeding a on-off/proportional controller. Some controllers have a 1A relay some have a 10A. You will probably need an interposing relay (contactor) in there to control higher currents you may see with scrap oven stuff.

banger

[kayak1]

Looks like a great pot. Adding a PID will take care of the temp.

[killbox]

So I have all my parts ordered and have some questions on the pid. Here is the one I ordered.

http://www.ebay.com/itm/AC-110-240V-Digital-PID-Temperature-controller-25A-SSR-K-thermocouple-Sensor-/141021325676?pt=LH_DefaultDomain_0&hash=item20d586a96c#ht_936wt_1120

It states in the listing it controls 0 to 400 deg C but in the manual it looks like for the type K thermocouple it will go to 1372 C so I think I am good.

My main question is on the wiring. I will pulling my power from a 50 amp plug with three wires in it. Two hot and one ground. In the wiring diagram for the pid which is here:
https://app.box.com/s/5uson7bv0nvjzygjefwy
It only shows two wires coming into the pid so I am not sure what two wires that would be. I assume to get 240 it would have to be the two hot wires but I don't want to fry this thing. Any help is appreciated.

[el34]

Does the heating element need the neutral wire, as if it was actually a pair of 110V elements?

If it's a heater with just 2 connections and you know it works at 220, then one hot AC leg goes to one heater end, the other heater end goes to either of the SSR output terminals, and the other SSR output terminal goes to the other hot leg.

The SSR is good for 380VAC so you're ok with 220. It would be useful to know how many amps your heating element will need (or how many watts it will produce) to be sure the 25amp SSR is good but it probably is. 2200 watts would take 10 amps at 220V.

I'd hook up the PID controller power input to just one AC leg and the neutral, just 'cause 220 is scary.

And that's a pretty short thermocouple, that ok?

[CGT80]

240 volt single phase service is not any more scary than 120 volt. It is actually two 120 volt legs that are out of phase from each other. While one leg is positive, the other will be negative. The difference between 120 positive and 120 negative is actually 240 volts. If you read the voltage from two different 120 volt breakers that are on the same leg of the panel, you will get 0 volts. They are both either 120 *** or 120 neg at the same time. They both have power to them, but you will not have a voltage difference. The neutral is equal to 0 volts and so is the ground. You will get 120v when you read voltage from either of them to a hot. A 3 phase panel gets more complicated.

The PID should be fine with either 120v or 240v. I would just use the two hot legs. Some panels have the neutral and ground tied together and it is possible to use the ground as a neutral on your 3 pin 250v plug. It isn't right and new codes, in some cities, require the ground and neutral buses to be split. My house has the two bonded together and I use only 3 wire 250 v receptacles. If you are running a plug to supply devices that are 125 v and 250v, then it should be 4 wire. If your heating element is actually 240v, then the 3 prong receptacle would be proper.

Having and knowing how to use a volt meter for basic electrical work is a great thing. Without it, you may be in the dark as to what you are really working with. I do agree with how el34 said to hook up the heating element.

The SSR will get hot as well. I enclosed mine in an aluminum box with the PID, to run my lee 20 pound pot. I used the box as a heat sink, and it does get warm. Your heater may end up being quite a bit bigger than mine and may create more heat in the SSR. I have read that heat build up around the PID will cause it to not be accurate.

[killbox]

Sorry I haven't got back on this in a few days guys. Thanks for all the great advice. I purchased a box to store my pid and my relay in and I purchased a heat sink to mount the ssr to. The heaters I am using are 1150 Watts/240 volts and i am using three of them. I had a friend of mine who works with some great electricians to ask them and here is how they said to wire it. It looks like exactly what el34 was saying. The length of the thermocouple won't be a problem as I will mount the box to the side of the pot with some air space inbetween so when not in use I can get it all off my bench easily.

94098

[el34]

Each heater will have about 5A through it, the 3 in parallel means 15A through the SSR. The specs on my Crydom D2425 SSR shows it'll dissipate about 15 watts at that current. No doubt you'll need decent heatsinking but you'll probably be ok. If it gets almost too hot to comfortably touch you're getting close to too hot.

Something to note- the SSR is only continuously on when initially melting the pot. After it's up to temp the SSR is mostly off so it's not generating heat. Hard to take that to the bank, just worth noting.

[killbox]

Well I finished my pot.....almost. A few things I did different from the plan link I posted. I used a 10inch pot instead of a 8 inch pot. I had a machine shop bore my three holes for the cartridge heaters. I also had them drill the pour hole and machine the end of the stopper to a point. I had them thread the bottom half of the hole in the one inch plate to 1/4 inch npt which allows me to drill holes in 1/4 inch plugs to control my flow rate.

The reason I say it is almost done is because got my contacts backwards on my pid and think I fried it. It reads the temp from the thermocouple and says it has output when needed but it never powers my ssr. When I test the positive and negative leads to the ssr I only get a small amount of miliamps and it jumps all over the place. I ordered another one and it should be in tomorrow. I am hoping for better results after learning my lesson the hard way. I did test the pot by powering the relay with a 12 volt battery and it melts lead and it pours great.

Can anyone tell me if testing the leads to the ssr for dc volts should work?

Thanks for all the help!

Mike

[killbox]

95607

[killbox]

Okay so I got my new pid and wired it up and still nothing. I switched the hot and ground on the signal wires going to the relay and it worked......for a while. I am wondering if my ssr is getting too because it has to run for quite a while before it cycles off. I am running three cartridges heaters that are 1150 watts each and using a 25 amp ssr. Is it possible this is overheating?

[VHoward]

Yes, it probably is over heating. http://www.auberins.com/index.php?main_page=product_info&cPath=2_30&products_id=45 You might want to get a heat sink to mount your ssr on then have a fan blowing across that.

[killbox]

So I went back out tried it again but this time I blew air across the heat sink to keep the ssr cool. The pot heated up to my set value and overshot a few degrees then once it came back to one degree below the light on the ssr came back on but my heat never returned. When it did that I tested the positive and negative from the ssr and had 20 volts but no heat. The ssr never got hot at all. I am wondering if the ssr is faulty. I have no idea how to set up the pid so I left it on factory settings.

[Tech2]

Sounds like you cooked the SSR. If it came on and was working for a while it is probably wired right. You just need to keep the SSR cooler

[killbox]

Well like you said I think I cooked the ssr. I built a test light using a porcelain light base and tested first with the signal coming from the pid. No light so ran a 12 volt battery to the ssr and still no light. I will get a new ssr ordered and use thermal grease this time. I think I will go with a 45 amp ssr too.

[VHoward]

If you go with the bigger ssr, then you will need the bigger heatsink as the bigger ssr won't fit on the heatsink for the 25 amp ssr.

[killbox]

I got my new 40 amp ssr in and everything works great
. This thing is a beast. Thanks for all the help!