Skutt GlazeTech kiln issues. Relay still clicks but output voltage not as expected?

[cadenrank]

 

12 minutes ago, Bill Kielb said:

Good job on figuring out the mechanical relay part.

Thanks! 
 

12 minutes ago, Bill Kielb said:

Hmm, interesting. I wonder if that means being over voltage by 25% is ok? Just kidding, I am sure it’s not a deal breaker. Your continuity proved the mechanical relay was bad. His silence on the voltage reading while interesting, doesn’t answer much for me except he only wanted to know if the relay was being activated by the control.

I am not sure the real answer, but I do know if 16.5 Volts is accurate it will heat the relay a bit more ……. In fact, approximately 25% more heating so that may be just fine with some folks.

Not great with percentage math, but wouldn't it be more like 37% increase in voltage? If rated for 12, being 16.5? Either way.

That was also my reason of testing it, but it is something that I told her to keep in mind in case a similar situation happens prematurely either way. I can't attest to if the reading was accurate, there was nothing that I knew of around her that had a confirmed DC voltage to test affirmatively. But, did confirm with known AC voltage. And it was a brand new meter. (for what that information is worth) 

Just based on my knowledge of transformers, SSR's, and mechanical relays (grouping these three since they all share the same piece of metal that's acting as a heat sink in this kiln),  as well as being inside of a kiln control box, seems like heat would be in abundance in this control box. 

Edited August 9, 2022 by cadenrank

[Bill Kielb]

1 minute ago, cadenrank said:

isn't it more like 37% increase in voltage?

It might be, 37% would be worse for sure. Consider when a kiln drops by approximately 10% of its heating capacity suddenly there is not enough to finish top end firings.

 I don’t remember the acceptable high of the 78xx I think 1.2v above a max or 12.25 volts. Best case whatever that translates to or more strictly, 37% more than 12volts.

[neilestrick]

I have not seen any kilns with high output voltages have trouble with relays burning out prematurely. Any time I replace relays and then they burn out within 50 firings, a new wiring harness solves the problem.

[cadenrank]

1 minute ago, neilestrick said:

Any time I replace relays and then they burn out within 50 firings, a new wiring harness solves the problem.

Is this attributed to increase in resistance in the wires? Corrosion/oxidation? That eventually causes heat to build up in the relay? and is this the wiring that provides power from the terminal block for the relays to do the switching? Or the feeder wires to elements? Or are you referring to the low voltage control wires? 

[Bill Kielb]

1 hour ago, neilestrick said:

I have not seen any kilns with high output voltages have trouble with relays burning out prematurely.

Not sure either but not sure how common. Interestingly that relay is 14 ohms. At 12 volts it draws 0.86 amps, at 16.5 volts it draws 1.18 amps. The max continuous coil temp of the relay is 40c or prox. 129 degrees f. Basically hot water temp. One thing I know for sure, 16.5 volts will heat that coil  a bunch more than 12 v and the 40c temp limit by the manufacture isn’t a whole bunch. I would be really interested in how many kilns actually run at this control voltage level. Honestly Never really gave it much thought when measuring, I think it’s always been in the 12 v range for me else I would have stopped to understand.

Bad low voltage control wires ought to lower the voltage to the relay or simply be an open circuit. Bad high voltage control wires definitely can cause heat in the wire and heat at the connection which in turn heat the relay. A usual good way to spot is any infrared measuring device used to compare heating in like loads.

Top relay below has marginal connection causing 220 + degree local heating in the relay and wire end.

 

Edited August 9, 2022 by Bill Kielb

[neilestrick]

1 hour ago, cadenrank said:

Is this attributed to increase in resistance in the wires? Corrosion/oxidation? That eventually causes heat to build up in the relay? and is this the wiring that provides power from the terminal block for the relays to do the switching? Or the feeder wires to elements? Or are you referring to the low voltage control wires? 

The high voltage wires. I don't know if it's corrosion/oxidation or resistance (or both), but it's definitely a heat issue. I don't ever change out the low voltage control wires unless there is visible damage or they're really old and crispy, like when I rebuild an old control box. A Skutt wiring harness includes the wires going into and out of the relays, control wires, but not the element feeder wires. Feeder wires can't be changed easily since Skutt uses crimp connectors, and they don't seem to be the issue when it comes to relays burning out. Bad feeder wires can cause trouble at the element connection, though.

[PeterH]

Pedantically, as P=V^2/R  wouldn't a change from 12v to 16.5v to increase the power by a factor of (16.5/12)^2 = 1.89?

I've no idea how much this would change the operational life of the relay though.

[Bill Kielb]

5 hours ago, PeterH said:

Pedantically, as P=V^2/R  wouldn't a change from 12v to 16.5v to increase the power by a factor of (16.5/12)^2 = 1.89?

Yes, definitely more watts so strictly from a relay manufacture standpoint I guess worst case 89% (~9.17 w) more heating than the anticipated 12v relay nominal design voltage ………. or power increases by the square. Realistically the relay probably is designed to operate +/- 10% -15%. But more heating for sure. I just have no real sense of what these things are operating at though.

[cadenrank]

This kiln of a friends has still continued to have issues. A new relay was put in, and the kiln worked normally for three firings, before presenting with the same errors. Skutt had looked over connections, and recommended replaced all of the wires. That was done, and the relay was replaced again.  The result is now a kiln that when a program is running, fires max output and errors out with ERRD in a short span of time. Skutt said that it had to be the SSR (which is also new within the last month or two). 

I had some new measurements taken, and saw relatively similar results:

The transformer is outputting 30 volts AC. 15 from each leg to the center tap. (FD5-24) 
Still outputting 16.5 VDC from the controller to both relays switching appropriately when running and off. 
The SSR also still switches on and off appropriately on the output side to ground, still seeing 42 volts to ground on the output leg of the SSR when the relay is open. 120 when it's closed. 

And at the time that it was being tested with me, I could not find a source of constant output flow at all. Wiring is visibly correct from my knowledge and based on the diagram and Skutt's input too. 

I have some other things I want to test and look at, time was short when we did these tests.  But was interested to see the responses relative to the transformer output and the development of the situation. This friend already bought a new L&L kiln to replace this one, but wants to get it back working.

[neilestrick]

Error D is a difference between the thermocouples. This is a Glazetech kiln with only one thermocouple, correct? If that's the case, then the controller is probably set with the wrong number of thermocouples.

Still don't know why you're getting 42 volts out of the SSR when it's open. I just tested mine and they trickle 4 volts.

[cadenrank]

ErrD, at least in this kiln, is difference between thermocouple and target temp of +50 degrees for at least 18 seconds. And correct, only one tc. Temp when a program is started, just rises, but stops when the kiln stops. (presumably the idea of the safety relay)

 

[neilestrick]

41 minutes ago, cadenrank said:

ErrD, at least in this kiln, is difference between thermocouple and target temp of +50 degrees for at least 18 seconds. And correct, only one tc. Temp when a program is started, just rises, but stops when the kiln stops. (presumably the idea of the safety relay)

 

How hot is it getting before it errors? Also double check that the controller is set for one thermocouple. 

[cadenrank]

1 minute ago, neilestrick said:

How hot is it getting before it errors? Also double check that the controller is set for one thermocouple. 

From my understand, within a couple minutes of starting a program. 

This kiln uses Skutt's 3-Key controller, and I don't believe there's any user configurable options to change the number of thermocouples.

[neilestrick]

15 minutes ago, cadenrank said:

From my understand, within a couple minutes of starting a program. 

This kiln uses Skutt's 3-Key controller, and I don't believe there's any user configurable options to change the number of thermocouples.

You're correct, the little controller only has one TC input. Sorry for the dumb questions, I'm not familiar with the specifics of that model.

If it errors very quickly, it's usually because it's not getting any power at all, or something along the thermocouple system is installed backwards and as the temp in the kiln rises the controller reads it as going down and it reaches the 50 degrees difference very quickly.

[cadenrank]

3 minutes ago, neilestrick said:

If it errors very quickly, it's usually because it's not getting any power at all, or something along the thermocouple system is installed backwards and as the temp in the kiln rises the controller reads it as going down and it reaches the 50 degrees difference very quickly.

This would make more sense given my testing, however she said that the temp on the 7segment display is rising when this is happening. 

[neilestrick]

24 minutes ago, cadenrank said:

This would make more sense given my testing, however she said that the temp on the 7segment display is rising when this is happening. 

Interesting. We see quick error like that that on multi zone kilns if the relays and thermocouples aren't set together properly, like if the zone 1 TC is paired with the zone 2 relay. But on a single zone it would only happen if the TC system is backwards or it's not getting any power.

Just to rule out any programming issues, what firing program is she using when this happens? It could be that if she's putting in a rate of 500F/hr or something very fast like that, that the kiln simply can't keep up with the traveling set point at the start of the firing since it takes a little time for things to get hot. Does it happen with a rate of 9999? At 9999 the controller doesn't follow a traveling set point, it just goes as fast as it can and is happy with whatever speed that is.

[cadenrank]

19 minutes ago, neilestrick said:

Interesting. We see quick error like that that on multi zone kilns if the relays and thermocouples aren't set together properly, like if the zone 1 TC is paired with the zone 2 relay. But on a single zone it would only happen if the TC system is backwards or it's not getting any power.

The other option, would be a relay stuck closed, or a controller commanding power output improperly. This was Skutt's diagnosis. but both of those do not appear to be happening in this case from testing. I believe she said the error happens in less than 20 minutes. But possibly said it was happening even faster, and when the program stopped, temp does stop rising, and there's no output when the kiln is not in a program. 
 

19 minutes ago, neilestrick said:

Just to rule out any programming issues, what firing program is she using when this happens? It could be that if she's putting in a rate of 500F/hr or something very fast like that, that the kiln simply can't keep up with the traveling set point at the start of the firing since it takes a little time for things to get hot. Does it happen with a rate of 9999? At 9999 the controller doesn't follow a traveling set point, it just goes as fast as it can and is happy with whatever speed that is.

I will look further into the programming. I'm unsure of what she was using.

Edited August 27, 2022 by cadenrank

[Bill Kielb]

46 minutes ago, cadenrank said:

This would make more sense given my testing, however she said that the temp on the 7segment display is rising when this is happening. 

Since you tested the SSR and fixed the safety relay, I think the rate programming as @neilestrick mentioned is a great thing to check. This error seems to be one for overheating though so possible as the SSR operates and heats up, it gets stuck on. Which would be hard to diagnose unless you were there testing when it happened.

 

Edited August 27, 2022 by Bill Kielb

[cadenrank]

I will look further into the programming. 

What's everyone's thoughts on that transformer voltage? I know we discussed that 16.5 on the control side of the relays was technically high. But it seems excessive that it would be causing this many repeated relay deaths in this short of time. We don't know that the relay burn out issue is still an issue after wire replacements though. Just presuming it may still be present. 

[Bill Kielb]

14 minutes ago, cadenrank said:

ts on that transformer voltage? I know we discussed that 16.5 on the control side of the relays was technically high

Seems high to me especially if from a regulated circuit but your SSR functions 3-32 volts so not likely to make the SSR stick on.

Since the symptoms have varied since the start of this with lots of Odd measurements I would confirm exactly what it is doing first. Is it overheating beyond the traveling set point for sure? Then work from ther as to why.

Edited August 27, 2022 by Bill Kielb

[cadenrank]

In regards to testing the SSR while it's operating, that's not an impossible task with how quickly she says it happens, just would be difficult to be in there, and also have elements connected to produce the error and to have a load on it. But I'll start with A. verifying the issue still exists, because we didn't find any source of continued, or otherwise uncontrolled voltage. B. trying different programs. Then if all of that is normal findings, go with C. try to figure out how to test the SSR during the failure.

[cadenrank]

Just now, Bill Kielb said:

Seems high to me especially if from a regulated circuit but your SSR functions 3-32 volts so not likely to make the SSR stick on.

Yeah I don't think that voltage is the SSR's issue, but may be contributing towards the mechanical relay premature (3 firings) deaths. 

The transformer's data sheet said output should be 24 v, with 12 from center post to each outer post. Which isn't what it's producing. 

[Bill Kielb]

25 minutes ago, cadenrank said:

The transformer's data sheet said output should be 24 v, with 12 from center post to each outer post. Which isn't what it's producing. 

The transformer is a pretty passive device with a fixed ratio of windings. More likely the input voltage is high, so then why? That goes to does it measure the same as the mains voltage, does the home have an open neutral, etc….. from there if still really high a call to the utility company as you should be limited to 240 vac +/- 10% I believe.

Grounding is something I would confirm for sure as it will be used to mitigate any noise on the thermocouple input. Use of an unbonded  neutral for the ground can cause noise issues.  It needs to be a good earth ground.

Since this can still point to thermocouple input issues I would double check that the thermocouple does not contact the metal case. I have seen them inserted a bit off center and when the kiln heated the side of the thermocouple would just touch the metal of the kiln creating all sorts of random noise.

Edited August 27, 2022 by Bill Kielb

[cadenrank]

3 minutes ago, Bill Kielb said:

The transformer is a pretty passive device with a fixed ratio of windings. More likely the input voltage is high, so then why? That goes to does it measure the same as the mains voltage, does the home have an open neutral, etc….. from there if still really high a call to the utility company as you should be limited to 240 vac +/- 10% I believe.

Input voltage was 242v. 

I'll have her doublecheck all the thermocouple points as well. 

[PeterH]

33 minutes ago, cadenrank said:

The transformer's data sheet said output should be 24 v, with 12 from center post to each outer post. Which isn't what it's producing. 

That confuses me too. IIRC you measured 243V in and 16.5v from one arm of the output.

As the transformer is nominally 230v to (12+12)v surely you should have been reading (240/230)*12v= 12.5v. It's either a massive reading error, or the transformer isn't working as advertised. Barring shorts inside the transformer, or substantial "stray" currents through one of its coils this seems wierd.

If the joints are easily breakable/re-makable it would be interesting to measure the transformer outputs open-circuit (and recheck it's inputs).

... and confirm  the voltage across the relays input is now zero.

Edited August 27, 2022 by PeterH