PID control question

[Mike Romo]

Hello all. Long time lurker.

Here goes.

I picked up an older Cress kiln. Specs are: model C-200-E. 230 vac. 8.5 amps. Manual control knob from Lo to Hi with graduations 0-100. Old school pyrometers. Warning in front states do not exceed 1700F.

I want to use it now as my heat treat oven for simple carbon steel, 1084 mostly and perhaps some 5160. It will eventually become a tempering oven to keep me out of her kitchen. Yes, I said her kitchen. She owns it.

I want to build a PID controller that I can simply plug the kiln into and then plug it into the outlet in my garage. 240vac, 50, new construction so no worries about capacity.

My question is would someone post a schematic showing the wiring for such a project. My concerns are as follows:

1. How do I deal with the incoming 240 and allow it to power the PID controller and then have a switch on the output side for a receptacle?

This is really to keep from rewriting the kiln and simply using it as it is with a new thermocouple.

Does this make sense?

I know nothing about this save for watching many YouTube videos and not seeing anything that explains using 240 vac.

Thanks in advance.


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[EdCaffreyMS]

I want to build a PID controller that I can simply plug the kiln into and then plug it into the outlet in my garage. 240vac, 50, new construction so no worries about capacity.

That simply will not work. The PID will have to be wired into the oven itself and the thermcouple in order to be used in the manner you want. Chances are good that you would also have to wire in a SSR (solid state relay) for the voltage/amps the oven requires. Basically in this situation, the PID will have to replace the "control knob". That DOES NOT mean it can be a direct replacement! Likely the addition of the SSR will be required.

I suspect that the current control knob is setup to work like a variac does in a DC current application. That being said, there are a number of different way these types of kilns were/are wired, so unless someone has specific knowledge/experience with the wiring of the specific type kiln you have, to give any type of wiring diagram would only be guessing, and could very well be dangerous. If you don't feel capable, or comfortable doing a job such as rewiring this kiln, either find somebody that does, or seek the assistance of an electrician. In many cases such as this, in terms of time, money, and end usability/accuracy, a person is often money ahead to just purchase a commercially available heat treat oven. The reason I say that is because I have wired PIDs into a number of devices from Salt Pots to heat treat ovens, and each one has required different wiring, and different additional parts. Although you can sometimes economically convert a device to PID controlled, more often then not its much more complicated and expensive then you first think.

 

[Mike Romo]

Thanks for the reply Ed.

Let me explain a bit more about my idea. I planned to turn the control knob up to near the high level (if it were plugged in as built, it would be near the high setting) so that the plug in PID controller package would turn on and off power to the kiln based on temp input from the thermocouple. In essence, the power would be metered before it energizes the kiln. The addition of an SSR along with the PID was a given based on designs I've seen. (Pardon me not mentioning that). Basically it would be a switched power input based on thermocouple temp input.

Most designs I've seen include a PID controller wired with a SSR and heatsink to control power.

Does that make sense?


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[EdCaffreyMS]

Yes, I understand what you're wanting to do, but it won't work out the way you're hoping (at least it didn't for me).

I tried the same thing, and ran into all kinds of problems. On a 220V circuit, 12 gauge wiring won't handle the amount of cycling without overheating, the breaker that the circuit is attached to will trip after about 3-4 cycles once the circuit "heats up", unless it's 10 amps larger then what the circuit should use, and the thing that made me end the endeavor.... while the kiln would hold 30-50F of the setpoint with its built-in analog controller, when I added the setup you're looking at doing, the kiln temps would swing 100-125F from the setpoint.

After a couple months of trying to get it to work, I'd wasted enough time and money....and chalked it up to a learning experience. Hopefully if you decide to go forward with the idea, it will work for you, but coming at it from the lens of my own experiences, I think it will end up frustrating you, and if you're not careful, create a dangerous fire hazard for your shop/property.

 

[Mike Romo]

Ed, thanks again. Your lessons learned are valuable. Your explanation of the heating circuit tripping is enough to make me discard this idea. The kiln works as it is, so I will use the pyrometer and verify its accuracy with another thermocouple and just keep an eye on things. I am much appreciative of the time you took to answer my questions and concerns. Thank you again.

I will be sure to post here once I get things running with my new tools. It appears an evenheat or similar is on the horizon sooner than later.

As a topic change, I am going to move forward with your forge pyrometer from your tutorials page. I really like the idea of a readily available temp measurement in my forge.


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[scott.livesey]

Hello all. Long time lurker.

Here goes.

I picked up an older Cress kiln. Specs are: model C-200-E. 230 vac. 8.5 amps. Manual control knob from Lo to Hi with graduations 0-100. Old school pyrometers. Warning in front states do not exceed 1700F.

I want to use it now as my heat treat oven for simple carbon steel, 1084 mostly and perhaps some 5160. It will eventually become a tempering oven to keep me out of her kitchen. Yes, I said her kitchen. She owns it.

I want to build a PID controller that I can simply plug the kiln into and then plug it into the outlet in my garage. 240vac, 50, new construction so no worries about capacity.

My question is would someone post a schematic showing the wiring for such a project. My concerns are as follows:

1. How do I deal with the incoming 240 and allow it to power the PID controller and then have a switch on the output side for a receptacle?

This is really to keep from rewriting the kiln and simply using it as it is with a new thermocouple.

Does this make sense?

I know nothing about this save for watching many YouTube videos and not seeing anything that explains using 240 vac.

Thanks in advance.


Sent from my iPad using Tapatalk

really no big deal. you need a controller, a two or three pole SSR, an on/off switch, a 240 disconnect switch, and a fuse/circuit breaker or two. you power the controller with 120vac, regular house outlet. the 240 you route thru a switch, then a 2 pole breaker or two fuses, then to the input side of the SSR. the controller will turn the SSR on and off depending on the tempature inside the kiln and how you program it. the output of the SSR goes to your kiln. your thermocouple will be connected to the controller. with a manual kiln like you have, when ready to heat treat, turn the kiln switch on, set the dial to 10 and off you go. you will need to play with the controller settings, like cycle time and such. the "How To" that comes with the controller will walk you thru the process. if you have more questions, send me a PM.

PS: after re-reading this and sleeping on it, i think this is no big deal because it is the sort of thing i did at work for the last 15 years. if you are not familiar with industrial electrics/electronics, it may all sound like greek. for now, wire the kiln so you can plug it into your 240 recepticle and use it as built. keep pencil and paper handy and record how long your kiln takes to heat and cool. for Aldo's 1084, i have found it best to heat your kiln to 1475F and adjust the manual knob so the temperature is steady(write down that number). turn the kiln off if it does not have a door switch, put your blade in, kiln on with knob at 100, when temperature reaches 1450F or so, turn knob to the number you recorded. temperature should stay around 1475F. once at 1475F, let the blade soak for about 5 minutes, remove blade and quench. if the kiln does not have a door switch that automatically kills power, always turn the kiln off before opening the door. again, if you more questions, please ask.