Jump to content

help troubleshooting SSR/PID kiln control...


Recommended Posts

Any electrical folks who can help me troubleshoot my SSR/PID control on my kiln? It's 220 volt and I have a main switch that turns on the PID and fan and a toggle switch that activates the SSRs to turn on the elements. All of a sudden the elements fire as soon as I turn on the main switch and the SSRs don't control the heat. I've checked all the contacts and fuses and everything seems fine. I'm wondering if the toggle switch is bad? I've included the diagram that I used to design the system...

 

264580_530077177033708_1323453126_n.jpg

Link to comment
Share on other sites

If you are getting power to your coils as soon as you power up then you've got a bad SSR. Probably number 1. Your SSR's are pretty much a change at PM part and they fail on. I run into this problem every now and then on the environmental test chambers I work with. Even changing them once a year as part of our PM.

Link to comment
Share on other sites

Thanks Bret....

 

Well... there was a bad SSR. It melted due to the fact that it had come loose from the heat sink. But I replaced it with another and it's still doing the same thing. But.. I got this batch of SSRs from ebay... and they all seem used. I have one more from that batch.. will check it out.


I have an electrician friend coming out today...

Link to comment
Share on other sites

well we are at a road block. I switched out the bad SSR and everything tests out as working. The PID tells the SSRs to go on or off at the target temps.. but the elements run regardless. They fire up as soon as the unit is powered on. And they continue to run after reaching the target temp.. even though the SSR lights go out. Any ideas?

Link to comment
Share on other sites

Try disconnecting the DC input to the SSRs and switching on. If the elements still power up, you definitely have bad SSRs.

Link to comment
Share on other sites

Yeah we've confirmed that its the SSRs. I've been running this with one 40 amp and two 25 amps... And that arrangement is not working. So I'm going to just order two 40 amp relays and that should solve it...

Link to comment
Share on other sites

Relays or new SSRs?

 

I've tried both SSRs and contactors for the output stage and find SSRs preferable for the speed of operation; I find that a 2-second cycle time is definitely better than 4 seconds.

 

I can't see any improvement going to 1 second, but I'm not sure whether that's because there's no improvement or because my testing setup is not good enough to detect any improvement there might be.

 

I've found Fotek branded SSRs, bought from the far East via ebay, to be pretty good.

 

All of the five HT ovens I've built so far have gone to people I like.

 

I fit RCDs (GFCIs?) and use an "extra" electromechanical contactor in the mains supply to the SSR, simply because I'm not happy with the idea of an SSR as the only thing between a friend and electrocution.

Link to comment
Share on other sites

No.. I meant SSRs.

 

Your comments on the extra stuff and electrocution are a bit over my head and nothing I've seen in any other plans. Ughhh.. I'm done building tools.

Link to comment
Share on other sites


Scott,

 

There's some risk attached to everything we do and common sense goes a long way towards keeping us safe.

 

My day job involves designing, modifying and maintaining machinery. I have no control over the end users of the machines, so I tend to assume they will find some new and interesting way of killing or maiming themselves if given the chance. Common sense doesn't enter into it. That thought process tends to get ingrained.

 

When I've built ovens for other people, it's seemed pretty safe to assume they have no real interest in the technical details of how the oven works (if they did, they'd have built their own), so I try to build something that is as close to foolproof as I can make it. Also, once it has left my hands, I have no control at all over who gets to use it.

 

The first HT oven I built was for an electrician. I could reasonably assume he'd understand the risks, so the control circuitry was broadly similar to the majority of the wiring diagrams on the web. The second was for a young knifemaker who was still at school, so I added a couple of extra safety features to bring it up to a standard I'd be happy to let my own kids loose on. The extras only added about $15 to the cost and perhaps 15 minutes to the build time, so I've stuck with that design on the others.

 

In the wiring diagram in your original post, there is mains power to the SSRs at all times, unless the main power is switched off by the operator. The toggle and door switches only interrupt the switching signal to the SSRs, so if one of the SSRs fails in the way that yours seems to have failed ("closed" in relay terms), the elements will be live. I add an electromechanical contactor (basically a big relay) in the AC feed to the SSRs and pull in the contactor with the door and toggle switches.

 

I gather there are some significant differences between Europe and North America in the way mains power is distributed and these may affect the danger posed by contact with conductors; here in Europe, our domestic supply is 230V on the hot leg and the Neutral is at Ground potential. Touch live and you get the full 230V to ground. It's not nice.

 

I'm not entirely sure what you'll get if you do the same on a 220V circuit in the USA. I hava the impression you usually have a centre-tap to ground on the transformer, so would only effectively see half the voltage to ground if you touch live.

 

Things are also different when building for ones own use; the user will have had the technical knowledge to build the oven, so will be able to make informed choices about its use based on that knowledge. The combination of the control circuit and competent operator normally provides adequate safety for most real-world situations.

 

Apologies if my earlier post came across as doom-mongering. It wasn't my intention.

 

Regards

 

Tim

 

 

 

Link to comment
Share on other sites

Thanks Tim.... And you don't need to apologize at all. I was just voicing my frustration at this entire kiln build. It was been very difficult with lots of issues. Now that I've had an SSR fail I understand that you would need an additional means for cutting power. But.. like you say.. it was built for me and I know to turn the main switch off every time. Although... the thing I don't understand is why anybody in the world would reach in and pull a blade out when the elements are glowing???

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...