• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

POT trade for??

I had considered an enclosure and it has a good heat sink but I may not have been clear about the IR radiation. Even a shield would help little. The chip and passives can hold their own but the weak link will always be the POT. Soot, ash, heat, fumes, ect.
Why would you put the speed control so close to the forge itself? That's why they make wire.
Yes true but the greater the distance from the forge is the greater distance between me and the switch responsible for stopping a potential hazard and it's very handy to have it close to the fan unit without extra wires tangling up or getting burned....also increasing the volume that a longer pipe creates will lower the pressure. Even still it's over 3ft away. Did I mention IR? It all boils down to a somewhat small POT that can take a little heat.


Well-Known Member
Most Helpful Member
Having worked in earlier years with both a forge and a foundry, plus heat treat ovens most of my working life. I never saw any controls that close, close enough that IR would be a problem. And as far as safety, if things are able to get out of control so fast that you can't turn to shut things down, you have bigger problems with your setup than this.
The hazard isn't about my or others safety, it's the fans ass I'm worried about. Should mention this is an oil fired forge, if it wasnt I could put the controls on the roof and the fan in a tree :p. Though the pot is still likely to be the only victim.


Well-Known Member
Most Helpful Member
Would putting that PCB in a small enclosure and adding a fan help?


Well-Known Member
Most Helpful Member
If a human can handle the heat then a pot should too. Can you post a schematic as it may be electrically stressed.

Mickster I was going to drill a hole in the fan housing to back flow some to the heatsink so it will completely eliminate any IC heat issues but im still stuck on the POT. I can make them interchangeable as needed but i need a bit of a bulk for cheap cheap. any using a carbon film track or even wire will be subject to carbon deposits. I dont think itll be easy to just enclose the pot. Also this is a very harsh environment so any amount of "permanentcy" will just delay the inevitable and make it that much harder to fix. Pommie its a standard LM317 circuit. however im using a 500ohm pot instead of the suggested 5k and a 15ohm bias instead of the 280? suggested. Its all i had on hand. I have tested it and it works fine so long as i keep it away from heat. Forge use......so no. it runs at 5sec intervals and say 1/4sec shutdown. its fine but it wont allow full temp and the sound is annoying hahaha. zzzzzzzzahhzzzzzzzzahh. BTW the heatsink shown is way overkill for this IC since its input is only 19v of 37v, so im giving it the best possible heatsink aside from liquid. Its my pots that are the issue. I sadly and stupidly ruined my only 2 10k pots via inattention and maybe booze.

Beau Schwabe

Active Member
"...These control a LM317 voltage controller for a fan used to provide air to my forge. SO HOT. The real issue is the low OHMs im using and it gets hot, the IC gets hot, the fan occasionally slows down. " ... Seems like replacing the burned POT is a bandaid solution when a switch mode regulator would be more efficient. What is your input voltage to the LM317 and waht voltage range are you trying to regulate?
Beau the AC adapter is rated at 19v but the current swing is 1.25-15.25 right now. Which is enough really. The full swing or close would be nice but not totally important. shortbus= this is for a forge. Not a smelter. I require that soot and carbon buildup. It's actually kinda difficult to keep it from burning clean at usable temperatures.


Well-Known Member
Most Helpful Member
500ohm pot instead of the suggested 5k and a 15ohm bias
That's putting 83mA through the pot!
That is probably why they do not last - they are only rated for low current / low power dissipation...

With the proper components on the 317, a 240 (or 220) ohm bias resistor, the pot current is well under 10mA.

Edit - or if you really want to stick with the low values, I do have an appropriate pot - a 40 Watt one.
It's only rated at about three times the current you are running through the tiny one you are using.

Last edited:
Wow that looks big. Well no the small value pot was all i have left. I dont like using them but im behind on a couple knives and needed my fan operational as quickly as possible so i used the 500s i had and i had to lower the bias resistor to compensate, else it was barely adjustable. Also its likely the cause of the over heating IC and the onoffonoffonoff. rjenkinsgb Id trade just to have the little beast. Im sure i can find some good use for it.
Last edited:


Well-Known Member
Most Helpful Member
this is for a forge. Not a smelter. I require that soot and carbon buildup. It's actually kinda difficult to keep it from burning clean at usable temperatures.
Can you explain the reason for that? Never heard of anyone wanting soot and carbon in forge work. Soot and carbon are usually part of a low temp air starved fire. I've used a natural gas, propane and coal forge, and never once had anyone tell me to get soot and carbon into the fire.

Even the US Navy back in the day, who did use fuel oil forges didn't want to have a smoking fire. https://books.google.com/books?id=6QbcySmHfesC&pg=PA210&lpg=PA210&dq=smoke+and+carbon+in+forging+oil+forge&source=bl&ots=OpyW2GWgDd&sig=ACfU3U35MaWauDNKQSid57p2aULdxgCQbQ&hl=en&sa=X&ved=2ahUKEwiuz7CsxPLmAhWCAZ0JHftgAtIQ6AEwCnoECAcQAQ#v=onepage&q=smoke and carbon in forging oil forge&f=false

And the guys using waste oil forges don't want to have it either. https://www.bladesmithsforum.com/index.php?/topic/21694-oil-burner-forge/

And as a sometime knife maker I had to look to see if I was missing something, but seems I'm not. So could you explain why you think soot and carbon is a good thing? Please?

If doing it to carborize your blades there are better ways of doing it.
shortbus= yes it's to provide a slight carborizing atmosphere. And yes I wasn't being very specific with the amounts of said soot and carbon. It's only during start up there is a bit much of it. During run there is virtually none. I mean just barely carborizing or neutral. However I don't risk a decarb so I'll let just a bit to much fuel in to be sure. The little wisps of white smoke. So far it doesn't smell, even on engine oil, and it's open outdoors. So I mean it's the first 5 minutes or so there is a bit much of carbon and soot. I'd think most oil forges aren't intended for blades either? So carbon loss doesn't matter that much.
Yes I've read that and I'm a member. I build them as a hobby. That style is for heating a vented chamber, not so great for forging steel. If I so chose I can use mine indoors so long as I use alcohol or kerosene. Even old engine oil burns with a near yellowwhite flame. And no the large amount of carbon and soot isn't good but it's not readily bad either. It burns off. Also that's a very interesting design.
Last edited:

Latest threads

EE World Online Articles