Building a PID melting furnace for under $40

[Big brass ones]

This is my first official thread!

Why so long?

Because I was too busy reading other threads and acquiring knowledge. the more I read here the less I feel I know about casting and guns in general. Thanks guys for keeping me humble.

I had to share my PID experience with others so that they might learn from my mistakes.

I choose to work on my Lee 4-20, because I have seen other peoples work and saw it was nothing new.

My goal was a cheap casting pot with temperature control and little modification to the existing pot should I desire to change is back. This was a bare bones setup and something anybody could do.

I choose a rex-c100 series pid because they are cheap on ebay <$20
A good k theromcouple < $5
A 12a SSR because it was also cheap < $6
A used cpu heatsink (free)
home depot parts 15a outlet, handy box, and a few odds and ends.

Here are the results!



I used PVC as the building material for the box so that I could glue the whole think together. the backside has the 15a outlet and box as well as the power cord.





I mounted the thermocouple inside the pot by drilling a hole next to the pour rod. I can't take credit for this as another fellow caster did this first and it works great! Any other method I tried had poor results compared to this one. I removed the pour rod so that the thermocouple could been seen (notice that it is at an angle). the probe does not touch the rod, but comes close. I used the home depot silver solder and it didn't work too well. I ended up using a low temp brazing rod for aluminum, but brass might work too.


Lessons learned:

Cost was under $40 but you get what you pay for.

The PID was suppose to be either C/F but is only Celsius (I even tried to change the program to accept F data).

I originally ordered thermocouples from china and it took over a month! thank God I bought extras!

The cpu heat sink is a great idea (drilled the heat sink and mounted the ssr)

Update: I forgot I opted for the larger heat sink (unnecessary), but the cpu heat sink works too!

the 12a SSR on ebay was the best deal of all $6 bucks and plenty of power.

In closing:

try the 12a SSR and cpu heatsink.

Don't buy A PID from China unless you like the metric system or know it is a C/F model!

thermocouples should be bought close to home.

[40Super]

Would you be able to post some pics of the thermocouple location and some other angles of the install. I am setting up my system and would prefer to go this route so I can figure what temps work best for me quicker and keep closer records on my alloy melt temp.

[Big brass ones]

new pictures added.

[snuffy]

OMG, get that PID out from under that pot! The base of a lee gets quite warm, but that's not the major concern. Lead dropping/drIpping on that PID controller could short out the electronics if the front is not sealed very well. Heat build up will kill that SSR, you're already drawing around 5.8 amps, you don't need heat to possibly overload that SSR.

[Mal Paso]

A SSR running a 120 Volt Lee 4-20 only generates about 8 watts of heat. Not a lot to worry about. Looks like air will vent past the j-box fine. The base overhangs the PID. You get extra points for stealing the thermocouple idea. I Like It!

[Big brass ones]

yes the shadow is from the base hanging over the pid so no lead can splash onto it. I thought about the problem of the heat dissipation and have yet to have any problems.

8watts!!! I didn't even know it was that much

I also used ceramic insulation around the heating element in the bottom of the pot to help with hold the heat in. This might also explain why it hasn't been a problem yet.

They say imitation is the most sincere form of flattery!

[Mal Paso]

That's 8 watts only when the element is heating. Once the pot reaches temperature the SSR takes a break every time the heater does.

I bought the big aluminum Auber box and just bolted the SSR to the inside back between the air vents. Works fine, doesn't even get warm.

I love turning my pot on, seeing 68 degrees and watch it climb. No more cranking it up to melt, watching like a hawk, then finding out where the Knob needs to be today, for whatever level the pot is full.

[Big brass ones]

I think my next project will be A ultra compact Pid controller with a single plug, switch, and thermocouple socket. Also considering a computer power supply as the box, and adding on to it. I'll also use a larger ssr and heatsink maybe even a fan so that I can use it for heat treating and warming up molds.

[40Super]

Does anybody know of a way to hook up to a laptop, like have the laptop as the control? I'd still need a relay so the power is taken from a seperate power source ,but rather than the PID,the laptop could control the temp(and hopefully not get molten lead on it).

[Big brass ones]

Yes I do know of a way to do that, but a software engineer would need to write the program. you could use the USB drive to power the SSR, but a more effective way would be to use a pic micro-controller to drive SSR as well manage the thermocouple. Being a flash based microprocessor they are cheap, and do a great job for applications like this.


The Program on the other hand would be rather complex being all three part equation



you can see by the diagram that one would require an extensive knowledge of calculus, more specifically differential equations, and maybe even thermodynamics and that's not even the programming

I'd go into more depth but at the risk of sounding like Scotty on Startrek i'll take a pass.

save yourself the and buy a PID.

[Big brass ones]

I'm sorry if my last post was a little know it all sounding. Please excuse the enthusiasm in this topic as I gave many good years in college to this very subject.

[nanuk]

and I can't even spell PID!!!!!

[hunter64]

I think my next project will be A ultra compact Pid controller with a single plug, switch, and thermocouple socket. Also considering a computer power supply as the box, and adding on to it. I'll also use a larger ssr and heatsink maybe even a fan so that I can use it for heat treating and warming up molds.

Did that.

Here is the Power Supply with the lid off.


With the guts out.


My Old Cell Phone Charger.


Cell Phone Charger with top off. Two wires on right were 110v and left 5v DC.


Side view. You can see the power supply on/off switch and plug in for the computer power cord.


Top View. On the left you can see the fuse holder and in the middle is the connection block.


Right side view. On the left is the PID controller, below it is the tie wrapped in power supply and on the right is the SSR.


Front view. Top left is where you plug in the Lead pot/Lube sizer etc. Below it is the thermocouple connection box and to the right is the PID.


Since this picture I have changed the cell phone charger to a 12v version and changed the small SSR to a big 25A version but it still fits in the box and works like a charm.

[40Super]

I actually do have the "means" to get the program written, I was looking to see if anyone did do it to save myself a lot of time and searching for the parts.

Hunter: I am looking to not even use a PID. I am more interested in making it way too complicated so later I can say,"Why the H**L did I do that."

[felix]

For those seriously interested, this is a good description of the PID functionality and mapping a design to the application. ... felix

http://ece.ut.ac.ir/classpages/S84/M...roller/pid.pdf

[Big brass ones]

Nice work Hunter!

Felix that is perfect! you must be a ham radio guy! I owe you a slide-rule!

[popper]

40Super - Lots of code written and available for the PID - but then you get to get the code for the LED and buttons and thermocouple. If you use a laptop, you get to write code for the USB , printer port or serial port and build an interface.

[40Super]

I'm thinking a hvac control program can be used ,just would have to get it to go through the usb or ethernet port.It wouldn't be a given though, just doing the thinking part right now and picking some brains.

[Frozone]

The easiest control port I can think of on a lap top is the USB.
Check out the USB to RS232 converter chips that provide a virtual RS232 port. They run ~ $10 complete.

They will provide 4 lines you can control from the windows op system Outputs are DTR (you can use this to steal power too.) and RTS. You can Poll DSR and CTS states as inputs.
This leaves Sin and Sout as null modem.
The biggest problem with using a PC is how to read the thermocouple. I don't think there is an ADC available.
You would still have to use a PIC to read the TC and convert it to a number then transfer that number back to the PC. But that is not hard and the code is simple. The ~$1 8 pin PIC would do the job nicely.
I'm sure you could steal enough power from the USB to run everything fine.

So for hardware you're looking at a USB/RS232 chip, a PIC, and a SSR. pretty cheap, < $25 I'd guess. Of course you still need to program/burn the PIC, Pic burners are in the $200 range

USB/RS232
PIC

[nanuk]

The easiest control port I can think of on a lap top is the USB.
Check out the USB to RS232 converter chips that provide a virtual RS232 port. They run ~ $10 complete.

They will provide 4 lines you can control from the windows op system Outputs are DTR (you can use this to steal power too.) and RTS. You can Poll DSR and CTS states as inputs.
This leaves Sin and Sout as null modem.
The biggest problem with using a PC is how to read the thermocouple. I don't think there is an ADC available.
You would still have to use a PIC to read the TC and convert it to a number then transfer that number back to the PC. But that is not hard and the code is simple. The ~$1 8 pin PIC would do the job nicely.
I'm sure you could steal enough power from the USB to run everything fine.

So for hardware you're looking at a USB/RS232 chip, a PIC, and a SSR. pretty cheap, < $25 I'd guess. Of course you still need to program/burn the PIC, Pic burners are in the $200 range

USB/RS232
PIC

How do you spell PID again???

thanks...

Wow... I have absolutely no idea what you just said!

I think I need to buy a book!