Any problems with Skutt APM elements purchased after July 2022?

[PeterH]

Help, I'm having trouble understanding these figures.

8 hours ago, Lilith Rockett said:

The amps are 28-23-28.

Problem 1.
28+23+28=79Aamps, but the 240V kiln seems to be rated at 60amps.
https://www.sheffield-pottery.com/SKUTT-KM1231-3PK-240V-1PH-p/skkm12313pk.htm

... note that 79/sqrt(2)=55.9, so it might be interesting to know if the current sensor is reading RMS or not.

Problem 2
Currents of 28+23+28 indicate that the centre section has a higher resistance than the end sections.

But the ends seem to have 2x 8.9ohm elements in parallel, and the centre 3x 11.3 ohm elements in parallel.
https://skutt.com/images/KM1231PK-1PH-and-3PH.pdf
https://www.armadilloclay.com/uploads/5/1/2/8/51288343/element_resistence.pdf

So, ends should be 8.9/2=4.45ohms & the centre=11.3/3=3.76...ohms.
... where the  centre has a lower resistance than the ends
... and the currents are very high at 240*2/8.9=53.9amps, 240*3/11.3=63.7amps and 240*2/8.9=53.9amps compared to 28-23-28.

[neilestrick]

36 minutes ago, PeterH said:

Problem 1.
28+23+28=79Aamps, but the 240V kiln seems to be rated at 60amps.

It's a 1231PK 240V1P, so 72 amps.  @Lilith Rockett Is your voltage right at 240 or is it running high? What size breaker is it on?

[neilestrick]

@Lilith Rockett I would still like you to check the temperature of the power wires when the kiln is reaching its peak temp. I assume you have a disconnect box by the kiln? Open that up and see if the wires are hot in there. Also feel the whip everywhere from the kiln to the disconnect and see if it's getting hot. Also check your breaker and see if it's running hot.

[neilestrick]

38 minutes ago, PeterH said:

But the ends seem to have 2x 8.9ohm elements in parallel, and the centre 3x 11.3 ohm elements in parallel.

The top and bottom sections do not have the same 2 elements in them. The 1231PK has 2 top/bottom elements, 2 intermediate elements, and 3 center elements. So top and bottom sections each have 2 different element in them- T/B and intermediate. They're wired with crimp connectors, so you can't unhook them, which is why Skutt only publishes the resistance of each section, not of each element.

[Lilith Rockett]

22 hours ago, Bill Kielb said:

For me I would initially be interested in the following:

• a context picture of your control board showing the connections to it , maybe from about two to three feet away so we can see the connections and the wires leading away
• a context picture of the element connections showing them and the wire that leads to the relays
• post the element resistance if you can measure them, if not can someone measure them for you so you can post here? So top elements measured resistance =______ ohms, middle section measured resistance = ____ ohms, bottom section measured resistance = ______ ohms.
• post a picture of the thermocouple itself and the wires leading to where it connects and tell us why you believe it is a type S

If you hit the little  + quote  below this message and post the items named above it will be a  direct response to this message

I know they are type S, and I know the difference between type K and type S.  I replaced t2 and t3 last night with brand new (type s) thermocouples and wires even though t2 had already been replaced a few months ago. Now everything is new. The test I did last night looked perfectly normal, cones dead on. I am repeating the test because the problem has been intermittent, making things more confusing.  So far the temperatures are reading within a few degrees, so completely normal again. I'll check the logs tomorrow and if good likely start a third test, but I can test the resistance before starting the next test, just to know. There is another identical kiln right next to this one that has had none of these problems, although less identical now that the problem kiln has all new parts. 

[Lilith Rockett]

16 hours ago, neilestrick said:

It's a 1231PK 240V1P, so 72 amps.  @Lilith Rockett Is your voltage right at 240 or is it running high? What size breaker is it on?

It is on a 100 amp circuit. Voltage is 240, not running high. I tested it throughout a firing once in each section.  There is another KM1231PK right next to it firing perfectly with none of these problems (on it's own circuit, obviously).  

[Lilith Rockett]

16 hours ago, neilestrick said:

@Lilith Rockett I would still like you to check the temperature of the power wires when the kiln is reaching its peak temp. I assume you have a disconnect box by the kiln? Open that up and see if the wires are hot in there. Also feel the whip everywhere from the kiln to the disconnect and see if it's getting hot. Also check your breaker and see if it's running hot.

I checked all of that and nothing is hot. Phew!

[Lilith Rockett]

17 hours ago, PeterH said:

Help, I'm having trouble understanding these figures.

Problem 1.
28+23+28=79Aamps, but the 240V kiln seems to be rated at 60amps.
https://www.sheffield-pottery.com/SKUTT-KM1231-3PK-240V-1PH-p/skkm12313pk.htm

... note that 79/sqrt(2)=55.9, so it might be interesting to know if the current sensor is reading RMS or not.

Problem 2
Currents of 28+23+28 indicate that the centre section has a higher resistance than the end sections.

But the ends seem to have 2x 8.9ohm elements in parallel, and the centre 3x 11.3 ohm elements in parallel.
https://skutt.com/images/KM1231PK-1PH-and-3PH.pdf
https://www.armadilloclay.com/uploads/5/1/2/8/51288343/element_resistence.pdf

So, ends should be 8.9/2=4.45ohms & the centre=11.3/3=3.76...ohms.
... where the  centre has a lower resistance than the ends
... and the currents are very high at 240*2/8.9=53.9amps, 240*3/11.3=63.7amps and 240*2/8.9=53.9amps compared to 28-23-28.

Perry has confirmed that the amps are as they should be. I have not tested the resistance yet. I know that the elements are in the proper places as they were installed by a tech and looked over by 2 more. I have been wondering if there was some sort of contamination in the center elements that is causing this problem, which has been somewhat intermittent while also being consistent as it is the same intermittent problem for 18 months. Often I will make an adjustment (replace a part, like the relays, or thermocouples) and the first test will be normal, then the second firing will finish but have an anomaly that is easy to miss, then the third firing stalls. Sounds cursed, I know, but there must be a reason we just haven't been able to nail down. 

But, as I mentioned in a prior response, after changing t2 and t3 and their wires last night, the kiln fired perfectly.  And now a second test is in progress and looks normal too, so far. T2 was a new thermocouple that was replaced with a different new one. T3 was not new but had functioned in each section with the same problem in the middle section. So it had been determined that it wasn't a problem. But now absolutely everything has been replaced at least once, so if it doesn't work it should be related to the elements and/or some sort of interference there, right?

[Bill Kielb]

9 hours ago, Lilith Rockett said:

But, as I mentioned in a prior response, after changing t2 and t3 and their wires last night, the kiln fired perfectly

Thanks for the pictures, will just scan and see if I notice something, but they look pretty good. The sequence single zone anomaly and kiln stall could be tc related so that would be great if it works fine now. One thing I may have noticed in the picture goes to the wires that feed the kiln. I would expect this kiln to be on a 90 amp breaker and likely #3 wire run to it. It’s really hard to tell from the picture but the liquidtight flexible conduit appears to be 3/4” to which only one #3 wire would fit by code. I think it’s worth checking what size are these wires (are they under sized) , if undersized they could heat up significantly while running and potentially cause mysterious operation.  I think it’s worth checking the main feeds are #3 or greater, and the flexible conduit is at least one inch (needed to cool them) and any temperature measurement that can be made from the kiln to the breaker, including the breaker with a non contact thermometer while this kiln is in operation could reveal these are at issue. Hard to Judge from a picture though, but worth double checking I think.

Since this is a production kiln (pk), Skutt has designed this for 75c wire, so while a very obscure thing, it also has bearing on the rating of the wire and breaker terminals. If you can read the wiring labeling somewhere along the way it would be good to know it’s temperature rating as well a wire guage. 

[neilestrick]

@Lilith Rockett did you check for the grounding wire? It should go from the Center Tap terminal on the circuit board to a grounding stud in the control box.

[Lilith Rockett]

8 hours ago, neilestrick said:

@Lilith Rockett did you check for the grounding wire? It should go from the Center Tap terminal on the circuit board to a grounding stud in the control box.

Yes, grounded.

[Lilith Rockett]

9 hours ago, Bill Kielb said:

Thanks for the pictures, will just scan and see if I notice something, but they look pretty good. The sequence single zone anomaly and kiln stall could be tc related so that would be great if it works fine now. One thing I may have noticed in the picture goes to the wires that feed the kiln. I would expect this kiln to be on a 90 amp breaker and likely #3 wire run to it. It’s really hard to tell from the picture but the liquidtight flexible conduit appears to be 3/4” to which only one #3 wire would fit by code. I think it’s worth checking what size are these wires (are they under sized) , if undersized they could heat up significantly while running and potentially cause mysterious operation.  I think it’s worth checking the main feeds are #3 or greater, and the flexible conduit is at least one inch (needed to cool them) and any temperature measurement that can be made from the kiln to the breaker, including the breaker with a non contact thermometer while this kiln is in operation could reveal these are at issue. Hard to Judge from a picture though, but worth double checking I think.

Since this is a production kiln (pk), Skutt has designed this for 75c wire, so while a very obscure thing, it also has bearing on the rating of the wire and breaker terminals. If you can read the wiring labeling somewhere along the way it would be good to know it’s temperature rating as well a wire guage. 

I think the wiring is correct, correct gauge, also conduit and 100 amp circuit, all of it has been checked by Skutt techs, and the wiring from the box is how it comes from Skutt.  It has worked fine for a decade like this as well and there is another 1231 next to it with no problems. Also, no heat on the wire or circuit during firing.

The 3rd test is firing right now and is on target. The second test came out perfect like the first. It seems like it may be fixed, but still pretty mysterious as the thermocouples had already been changed and checked several times. But the goal is a functioning kiln, so I'll be happy with that. I'm bringing the replaced thermocouples and wires to Perry to have checked at Skutt. It will truly be baffling if they find nothing wrong with them. I'll just be happy to be able to fire work in the kiln rather than simulated loads and tests.  It's been an expensive and time consuming 18 months for both me and Skutt. Thanks for thinking through this with me.

[Bill Kielb]

3 hours ago, Lilith Rockett said:

I'm bringing the replaced thermocouples and wires to Perry to have checked at Skutt. It will truly be baffling if they find nothing wrong with them

Thermo couples are literally like a battery, they generate very precise voltage for a given temperature. Lots of folks try to measure their resistance but this is not really a meaningful way to check them.  One of many temperature and output charts online here: https://www.thermometricscorp.com/PDFs/type_s_tc_in_F.PDF  This output voltage is very precise and defined so all thermocouples should track reasonably and precisely with their chart values.

One easy characteristic folks take advantage of is their output at 32f (0C) and 212 f. So home testers will often check the output in an ice water bath and boiling water. For upper range general tests I have seen two clamped next to each other and torched to highest torch temp (probably 1200f - 1500f and compared against each other  (two meters required ) Anyway, a way to do some  meaningful testing. K type have a similar chart, just different voltage output at various temperatures. So easy to get some simple,tests done on these in a pinch.