Thermocoulple Temperature Contoller

[kinarfi]

Need to control the temperature of a solder / lead bath at 495 - 510 F or 257 - 266 C and plan on using a Type J Thermocouple, a 3-24 volt 120 VAC Solid State relay.
The expected output from the TC will be from 13.9 mvolts to 14.4 mvolts.
Thinking to use a 25 ohm pot and a comparator to control the SSR.
Any suggestions or already designed circuits?
Thanks,
Kinarfi

 

[ericgibbs]

Need to control the temperature of a solder / lead bath at 495 - 510 F or 257 - 266 C and plan on using a Type J Thermocouple, a 3-24 volt 120 VAC Solid State relay.
The expected output from the TC will be from 13.9 mvolts to 14.4 mvolts.
Thinking to use a 25 ohm pot and a comparator to control the SSR.
Any suggestions or already designed circuits?
Thanks,
Kinarfi

hi,
Are you going to use Cold Junction temperature compensation or Ambient.?
What amplified output level do you want.?

 

[kinarfi]

hi,
Are you going to use Cold Junction temperature compensation or Ambient.?
What amplified output level do you want.?

I would be using an ambient because it is simpler, and I admit to not completely knowing the proper way to use the TC, type J in this case. Do I need a 2nd TC or will one in the lead bath be enough?
Thanks,
Kinarfi

 

[Sceadwian]

This article may help, all the details you need.
**broken link removed**
It's done by Maxim so of course they have an example of one of their chips.

 

[ericgibbs]

I would be using an ambient because it is simpler, and I admit to not completely knowing the proper way to use the TC, type J in this case. Do I need a 2nd TC or will one in the lead bath be enough?
Thanks,
Kinarfi

hi,
As your pot temperature range is only 257 - 266 C , thats a 9Cdeg span, so if your ambient temperature changes by say 10C to 30C, it will affect the temperature reading, is that acceptable.?

 

[Sceadwian]

Cold junction compensation isn't difficult, all you need is standard resistive temperature sensor on the cold junction, that will generally give you a 1 to 2 degree accuracy.

 

[kinarfi]

hi,
As your pot temperature range is only 257 - 266 C , thats a 9Cdeg span, so if your ambient temperature changes by say 10C to 30C, it will affect the temperature reading, is that acceptable.?

Probably be OK, it's in the house in the reloading room, so ambient is fairly constant. A little story behind the reason for this project. My brother in law makes his own shot for shooting skeet, he was heating the lead, wheel weights, and the temp was basically good and if it got to hot, he added wheel weights to cool it and it stayed pretty stable just plugged into the wall using a #16 AWG cord, but it melted the cord, so he replaced it with a #12 AWG cord and now his lead gets too hot. He tells me that his best shot is made when the lead is between the stated temps, measured with an optical reader. The composition of modern wheel weights causes a lot of scum on top of the solution, any Idea what that might be? Any way, now I'm trying to build a controller to hold the lead at about the described temperatures and have all the heat in the lead instead of part of it in the cord.
Thanks,
Kinarfi

 

[Sceadwian]

The scum is slag, basically oxidized crap, any impurities that were in what you melted, lead being pretty heavy and liquid pretty much everything but lead will float to the top, it is extremely important for good castings (no matter what it is) to get rid of that stuff just before you pour, it's not usable. It should also NOT be thrown out as it still contains a decent amount of lead so should be disposed of at a recycling center. To avoid lead have you ever given thought to trying lead free solder compounds for shot? I'm all for target shooting but spraying that much lead into the environment is just not a good idea.

Considering the problems you're having with melting the chords and temperature I think it might be time to invest in a temperature controlled metling pot. A brand new controlled pot is only gonna set you back 100 dollars or so, depending on how big a pot you need. How big is the pot you're using?

 

[Reloadron]

Reloading room? Wow, you have a room just for me? Pay no attention to my screen name or avatar.

I have a perfect solution if you want it. Over the past year or two we have been converting everything from Type J to Type K. I have a small mountain of hockey pucks (OK, Temperature Transmitters) originally for Type J that are ranged for 35 to 700 Degrees F. (1.7 to 371.1 Deg. C.). They output 4 to 20 mA which when run through a resistor give you a nice 2 to 10 volts. Makes for easy and takes care of CJC for you. I may also have a Type J temperature indicator in the shed as I know I have some temperature displays out there. I may even have a nice dual type J TC you can have. Use 1/2 the TC for the indicator and 1/2 for the control. I also have a pile of type J TC wire and connectors.

If you scroll down this page you will see an example of the J hockey pucks.

So how much do I want for all this stuff? Yours if you want it including sending to Utah. I will never use all this in my lifetime and being an avid shooter it's the least I can do. Pretty good price huh?

Ron

 

[kinarfi]

The scum is slag, basically oxidized crap, any impurities that were in what you melted, lead being pretty heavy and liquid pretty much everything but lead will float to the top, it is extremely important for good castings (no matter what it is) to get rid of that stuff just before you pour, it's not usable. It should also NOT be thrown out as it still contains a decent amount of lead so should be disposed of at a recycling center. To avoid lead have you ever given thought to trying lead free solder compounds for shot? I'm all for target shooting but spraying that much lead into the environment is just not a good idea.

Considering the problems you're having with melting the chords and temperature I think it might be time to invest in a temperature controlled metling pot. A brand new controlled pot is only gonna set you back 100 dollars or so, depending on how big a pot you need. How big is the pot you're using?

I agree with all you said, but I'm doing this for my brother in law who makes his own shot, I think he said it give him better performance and is cheaper because the used wheel weights are cheap and I have no control over what he's upto and he definitely likes inexpensive , Fixed income and all and that what he has seems to be working for him, just getting to hot with the heavier cord. You gotta laugh at the fact that the heavier cord caused his problem.
Kinarfi

 

[Sceadwian]

Why converting to type K's reload? You don't need the extended range for most applications, and the J's produce a slightly larger output per degree C than type K's do. Type K seems to win defacto because of the wide range and it seems almost universally common among meters and many other thermocouple apps.

Kinarfi, actually the heavier chord changing the temperature makes perfect sense, the heating element you're using is obviously working right near the maximum temperature limits of the materials, and you increasing the wire gauge which decreases the voltage drop on the lead cable, this is good to keep the cable cool, bad if you didn't want to get extra power to the heating element, you probably added an extra dozen or so watts to the heat output. Have you thought of picking up an auto-transformer to vary the power to the pot? or is your main goal right now just to give him feedback on the temperature so he can flip the switch to control the temperature?

 

[Reloadron]

I agree with all you said, but I'm doing this for my brother in law who makes his own shot, I think he said it give him better performance and is cheaper because the used wheel weights are cheap and I have no control over what he's upto and he definitely likes inexpensive , Fixed income and all and that what he has seems to be working for him, just getting to hot with the heavier cord. You gotta laugh at the fact that the heavier cord caused his problem.
Kinarfi

Doesn't matter if it's your brother in law. It's like a code among shooters to always help each other out.

You are more than welcome to what I mentioned. I will have to check at the plant to see if I actually have an old type J controller that wasn't pitched out as we converted over. The nice thing is you get really good control over your lead bath temperature. Oh yeah, as to the scum on the top. Just skim it and use an old butter knife (or whatever).

Ron

 

[Reloadron]

Why converting to type K's reload? You don't need the extended range for most applications, and the J's produce a slightly larger output per degree C than type K's do. Type K seems to win defacto because of the wide range and it seems almost universally common among meters and many other thermocouple apps.

The environment. Most of the connectors are exposed to humidity and sometimes spills of water. Try as we will the damn Iron likes to corrode and rust in Type J. Figure a type K is alumel and chromel (trade names) it doesn't have a pin that will rust, unlike Iron and Constantan in a type J. Therefore the decision to move to Type K for most applications.

When most of this was done years ago everything was bought for type J. Today's newer temperature transmitters are sweet as they are fully programmable for range and type TC. Anyway, when I am around nothing goes in the dumpsters.

Ron

 

[kinarfi]

Reloadron, Thank you very much for you help, Looking forward to doing this project, I do have dual and quad comparators.
Kinarfi

 

[Reloadron]

Reloadron, Thank you very much for you help, Looking forward to doing this project, I do have dual and quad comparators.
Kinarfi

Great and since yesterday's PM I managed to find what looks to be a 15 year old type J indicator that is new in the box. Tomorrow morning I'll send everything as Kathy had a busy day and we have my mom (91 years old) up here visiting. I also found a 7815 which will fit into the scheme as well as I think I have a 24 VDC supply. Once I get home this evening I'll post more info and a drawing or two. This thing should work out real well and be pretty accurate. More later...

Ron

 

[Reloadron]

OK, a bag of goodies is on the way. I sent it all stuffed in a box via the post office. So figure Cleveland, Ohio to Utah maybe 5 to 7 days? Beats me.

When you get the box PM me and I'll cover what is in there including a board I partially built.

Enjoy
Ron

 

[kinarfi]

Here's what I have in mind for a temp controller, The 500 Ω pot on the LM334 will be a 25 turn trimmer pot. I figure the hysteresis of 20 pound pot of lead should be plenty so I won't too fast of an on-off switching action. Would be nice to figure in a PID loop but as it is, My brother in-law says he kind of controls the temp by adding cold lead as it makes shot.
Comparator is a LM393

 

[Reloadron]

That should get you going. Remember on the SSR to use a minimum of AWG 12 for your mains power. Also remember that you will have exosed mains power so be real careful as getting bitten by 120 VAC isn't much fun. See what you get and once you mess with it let me know if the old indicartor works out.

Ron