Digital furnace controllers - a warning!

Robber58

Robber58

Joined
Oct 9, 2008
Messages
478
A couple of days ago I was tempering some blades in my Evenheat furnace. I had set the controller for 400 degrees and 2 hours. I verified it settled at 400 before moving on to other things. While I was elsewhere, my wife decided to fire up the mitre saw to cut some trim. It was plugged in to a 110 outlet close to the 220 I use for the furnace. I happened to look over at the furnace after about an hour and saw it was at 460 degrees, well above my setting, and slowly cooling. Since it had never done this before in hundreds of sessions I was concerned something had failed in the controller.

After thinking awhile, I decided to try a test. In another life, I was a mechanical engineer designing equipment for satellites, rockets, space shuttle, etc. One thing that we had to deal with was electrical interference from other equipment, particularly high power stuff. The electrical noise could be conducted down power lines or radiated from the other equipment and cause all sorts of strange problems. Since my wife had been running the saw, I turned the furnace on, set it for 400 and let it settle. Then I started the saw a few times and sure enough, after 5 or 6 trys, the furnace started heating beyond the set point. I have since run it several times with no problems at all so I an convinced the electrical noise generated by the saw caused a problem in the controller. Whether conducted or radiated, I don't know, but it definitely caused it to behave badly. So, if you have an Evenheat, I recommend being cautious when you are running something else at the same time. Fortunately, my blades tested fine but it could have been ugly.
Randy
 
Robber58 said:
... Fortunately, my blades tested fine but it could have been ugly.
Click to expand...

The fact that your blades tested fine leads me to believe the interference problem affected your readout and that the temperatures were fine... 460F would have a done a number on your blades.


Rick
 
Rick,
That is definitely possible. I did not put my themocouple readout in to check when it happened.
Randy
 
Sounds like you might benefit from some filter capacitors in the power to the controller. Give Evenheat a call and see what they say. I wouldn't be surprised if they said to send back the controller for testing, and sent you a new one.
 
Hmmm........sure sounds like noise. I have forwarded this thread on to our controls manufacturer for their opinion.

Noise has never been a problem. Until we do get the situation figured out I would suggest looking at the placement of the wires within the ovens panel. The goal would be to keep the colored control wires away from the black and white power input wires (and even the black wires leading the the heating elements). If noise shows up on the power input, which it sounds like it is, it's possible that this noise is being induced into the colored control wires.

Separation is best. If they do need to be near each other cross them at 90 degrees to defeat noise. Wires in parallel to each other like to talk and the big, dirty ones tell lies. They always win too! In the words of the band The Offspring......"Gotta keep 'em separated".

This goes for the thermocouple wires as well.

Hope this helps. I'll find out more from our controls guys and we'll go from there. I will be out of the office for a week starting the 9th. Separate and hang tight.

Thanks,

Mike at Evenheat
 
Hey, there seems to be a collection of some pretty electrically talented brains here, perhaps somebody could help me out with a problem I have had for a very long time but have been unable to solve to date.

I run two PID controllers side by side, on on my high temp salt bath, the other on my low temp salt bath. Both run mercury displacement relays to regulate the equipment, 220v 2 pole on the low and 110v single pole on the high temp. Quite often when the 110v single pole relay cycles to shut the juice off to the unit, it will dump and restart the opposite controller, the one not connected in any way to that circuit. I even wired a separate circuit from the breaker box to the single pole relay to try to stop this but to no avail.

I realize why it is happening from what I have been told by techs, the controllers are VERY sensitive to surges and will shut down to protect themselves, what I desperately need is a way to stop it. Can anybody think of a way to stop the surge from the 110V relay from knocking out my other PID?
 
Randy,

Our controls manufacturer is interested in speaking with you regarding the suspected noise problem with the oven. I did post some wire separation info. That may help but let's get the controls people in the loop. It's no fun having trouble and the more help the better.

The company is Bartlett Instrumentation, located in Iowa. His name is Dave Bartlett and he can be contacted at (319) 372-8366. e-mail at dave@bartinst.com.

He's pretty sharp and I think he'll nail it.

Best regards,

Mike at Evenheat
 
Kevin... you have probably thought of this but it doesn't hurt to ask... When you say two salt pots side by side... what are they separated by? Do the have to be CLOSE together? I know, humour me. Stacy has a smart idea with his filter capacitor fix. This may not even be in the same ballpark, but a former nieghbor turned his basement into an arcade... old machines and modern electronics. He had to use filter capacitors because of surges and electrical noise.

I also commend Mike at Evenheat for chimming in........ 3rd post in 6yrs!! Slow down bud! When you reach 5 are you going to celebrate with a giveaway?:p



Rick
 
Hi Kevin :) Have you tried a "line conditioner" ? They can be had for ~ $100 and might fix your problem.


:thumbup:
 
Rick Marchand said:
I also commend Mike at Evenheat for chimming in........ 3rd post in 6yrs!! Slow down bud! When you reach 5 are you going to celebrate with a giveaway?:p



Rick
Click to expand...

LOL. Maybe!! We'll find out in a few years. Off to a place where snow doesn't fall. Noise problem seems to be moving in the proper direction, see ya' in week or so.
 
Check the grounding system of your electrical system, including the receptical for both the furnace and the one for the saw. In addition check all the connections from the grounding rod to your electrical pannel to make sure they are tight.
 
Mike,
I sincerely appreciate your interest in the problem. I will check the wire routing to see if there are any obvious problems and then give Dave a call.

Gorunding was something I thought about. When we moved into this place a few years ago, I put ground fault outlets in the bathrooms. In the process, I discovered that ground wires were in the box but none were connected to the outlets. It seems that when this place was built 30 years ago, code did not require them to be connected to the outlets. I spent a lot of hours going through the shop and house cutting the tough metal crimp splices and connecting all the grounds to outlets and each other. I also checked the grounds in and to the main. It should all be good now.

Filter capacitors of the right size in the right location would probably help if the problem is conducted rather than radiated noise. I suspect that is the case since the controls are in a grounded metal box, much like a faraday cage. That should help to reduce succeptability to radiated noise.

I really appreciate all the inputs and suggestions.
Thanks,
Randy
 
Kevin Have you tried an uninterruptible power supply? They generally guard against those kinds of momentary power fluctuations and could IMHO fix your salt pot issue.

Jason S. Carter
 
A quick update. It is a bit awkward to get at the wires but by pulling the controller out carefully from the kiln I was able to see well enough. There are areas where the colored control wires do appear to touch the power leads. However, in all cases they are running at close to 90 degress across them. I was a bit worried about going in and moving things around since I had to hold the box and keep from straining any connections at the same time.

Mike, I did call Dave and leave a message.
Randy
 
Kevin and Rob,
When I did electronics, we had this type of problem from time to time. The solution was normally to install large line filter caps in the power supply. A second solution is to power one or both PIDs from regulated power supplies ( which have large filter capacitors in them). In some severe RFI cases you may even need RF chokes. A commercial line filter ( noise filter) is just a device with all the math figured out for you. They run from $5 to $50, depending on the current and voltage.
 
Please make sure you post whatever solution that worked for you. I have a friend with an Evenheat oven who complained because he thought he had messed up a batch of blades but could not figure out why. I asked him to look at this thread and he said he was working on his air power hammer next to the oven when the problem occurred. He is testing now to see if the oven might have done the same thing and overheated the blades without him noticing.
 
I have yet to hear from the controls guy but I will let you all know what I learn.
Randy
 
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