Skutt km-1018 low voltage problem

[Marita]

Hi! I run a skutt km-1018 208v single phase kiln. I’ve had it for ten years but I bought it used (circa 2004). At my old studio the kiln had no issues. When I brought it to my new space I started getting error-1 messages, so I replaced the elements, problem solved. Now the elements have aged a bit but are still only about 1/3 of the way through their life (checked resistance) and I am again getting error-1 on every cone 6 fire- it’s close but can’t exceed 2100 f . Voltage at the element pigtails is low- 198v on each leg under load and 204v in the outlet, but skutt says it should be in operational range. I have replaced all the interior parts, and am constantly checking for carbon buildup (there is more than I’ve had before, I think due to the higher amperage I must be getting). Everything looks good currently. 
 

Wondering- if this is a low voltage issue what are my possibilities for solving? Considering buying some top and bottom elements and replacing the two interior high resistance ones with them, but would this be problematic in any way (I have a vent)? Other ideas? Any help would be appreciated. 

[Bill Kielb]

198 v is approximately a 5% reduction, when elements wear by about 10% (Resistance goes up 10%) many kilns fail to fire fast enough and elements need to be changed.  The formula for the power (watts) used to heat the kiln  is V^2/R. So power to heat the kiln is more sensitive to voltage than resistance.  In effect a 5% voltage drop equates to about 9% drop in available power. In theory brand new elements might struggle with this reduction.

Voltage is super Important so I would determine why the excessive voltage drop first. Carbon buildup should not occur if you are making it to 2100 degrees so I am not sure what that is all about. Something else you mentioned could be interesting - vent fan. This kiln could very well have power issues so if the vent fan over draws it will add a bunch of thermal load to the kiln. The vent fan should be adjusted to withdraw a very very small portion of kiln air and mostly room air by proper adjustment at the mixing manifold.

Usually so much room air is mixed with a tiny amount of kiln air that the vent pipe doesn’t exceed let’s say 110 - 120 degrees even when the kiln is firing at its peak temperature.

so my list would be

• Voltage drop first — appears undersized wire, bad connections, worn relays, bad main breaker ……
• How worn are the elements 5%, 6%, 7% ?
• Kiln vent is not over drawing and creating excess load

Edited October 1, 2023 by Bill Kielb

[Marita]

Thanks Bill, I appreciate your thoughts.  Here's where I'm at with these so far.

- Voltage drop- I have been trying to solve this, replacing all contacts, replacing and upping the gauge of the harness wires, replacing relays, transfer strip on the baffle board. The only thing I haven't done is replace the power cord, although I did hard wire it in a year ago.  My studio is in an industrial space and our neighbours run an electric car delivery service. I have been wondering if our building is overdrawing power and this is the reason for the voltage drop- not sure what to do about this if it is the case. It could still be a bad connection I suppose, but lord have I gone crazy trying to eliminate this as a cause. 

- Elements are 10 and 10.1 ohms- factory is 9.7.  so 4% . I called skutt and they said they should be good until 11+ 

- I have also suspected the vent overdrawing as an issue, and so tried to stop using it, but it still gives error-1 around 2100f (it struggles for so long that this is a nice hot cone 5, but i expect it will only get worse)

I have noticed that the skutt resistance chart seems to recommend using all the same resistance elements (chart attached) for this kiln only- possibly because of it's low wide build. But when you go to purchase elements they have two options for this kiln, top/bottom and middle. Certainly my middle elements glow much less than the top/bottom ones, so this is why I'm considering just installing all top/bottom to see if this will help.  I must admit I am confused as to why they have different listings for top/bottom and middle elements when it appears they shouldn't be different. Also- its possible if the middle ones were a lower number than 9.7 from the factory (totally forget what they were separate when I installed them) then they are actually more than 4% worn. 

 

resistance.pdf

[neilestrick]

The resistance chart is not showing the resistance of each elements. It is showing the resistance you will get when you use your meter on each element while everything is hooked up. Because the elements are wired in parallel, you're actually measuring both elements in that section, so both sections will have the same reading even though the top/bottom and middle elements are different. If the elements were actually 9. ohms, the kiln would pull 85 amps.

How many firings have you done on the current set of elements?

If the elements are 4% off and the voltage is low by 10 volts, that's the problem. If the voltage was a full 208 then the elements would still be functional. With the low voltage they cannot wear as much before they can't do the work. You'll have to replace them or figure out why you're getting a voltage drop. 

What size breaker are you using, and what size wire was used between the breaker and the kiln? It should be on a 50 amp breaker with 6 gauge wire.

[Bill Kielb]

I understand your frustration. The low voltage needs to be solved, remember you suffer from an 9% reduction in wattage with that low of voltage already.Electrical safety reminder - use appropriate safe practices when measuring energized circuits.

1) measure the voltage at the breaker

• Kiln turned off =
• Kiln operating = 

2) measure the voltage at the kiln plug

• Kiln turned off =
• Kiln turned on =

3) measure the voltage at the elements in the kiln during operation (see drawing)

Measure the voltage drop across each relay while the kiln is on (see drawing - all 4 contacts) when a relay is connected it should be just like a solid piece of wire and virtually no voltage will be read across the contacts. As relays wear, this measurement will rise by tenths of volts or more as more voltage is dropped across these contacts.

Elements may be series parallel according to the drawing so the only way for any to be brighter is to be a different value (currently you measured all as 10 ohms though) which could point to a poor connection between the series wired sets. Post good pictures of these if you can, else you can measure the voltage drop across the wire jumper, it ought to be zero or very very near zero.

Your kiln requires a 50 amp breaker and #6 wire. If the wire run is quite some distance, then heavier wire may be required. If you measure the above stuff, it will likely tell us the where part.

Edited October 2, 2023 by Bill Kielb

[Marita]

Thank you both for your help- replying to everything below. Ah that makes sense about the resistance charts, thanks Neil. I just assumed since the other small kilns had different readings for different elements that they were the individual resistance, but I see some are wired in series. 
 

50 amp breaker for sure, not sure of the gauge of the wire running from the panel but I have a good electrician I think! The main panel for this building is located in a different suite that I must request access to. I have a shut off in my unit that my lil is hard wired to. 

When under load I get 204v in the shut off outlet, 198v at each of the element sets.

when kiln off I get 207v in the outlet.

I’ve never measured at the relays, but I will the next time I’m at the studio. 
 

I have about 37 cone 6 firings on these elements and maybe 30 cone06 ones. I can definitely replace them just curious about other solutions as it seems so soon compared to other kilns I’ve serviced. 

Edited October 2, 2023 by Marita

[Bill Kielb]

16 minutes ago, Marita said:

When under load I get 204v in the shut off outlet, 198v at each of the element sets.

when kiln off I get 208v in the outlet.

 

Knowing that, that 4 volts at the breaker and wire to your kiln  so 4-1/2% between your kiln and the breaker. For kilns, this is excessive. Could be wire size, could be connections / splices, could be breaker or lugs ….Marginal connection. Easy to figure out for an electrician. Work backwards while loaded ti find it.

now the other 4-1/2% is from the outlet ( receptacle) to the kiln. Again easy for an electrician to find loaded. Power cord, connections …..

Really good practice for kilns is to limit voltage drop to nothing if possible. Electricians often have a 3% rule of thumb, this is too much for kilns, they are not designed with excess power to spare. 

At the very end, if voltage just cannot be provided, and you are certain all connections are good there still is one last technique you can use to bring this kiln back to its rated power.

Edited October 2, 2023 by Bill Kielb

[Marita]

Thanks Bill- I will call my electrician and hopefully he can track down at least part of the voltage drop. Skutt said this was within an acceptable range so I had assumed it was somewhat normal. Knowing that no voltage drop is possible gives me some hope! 
 

I’m curious what the other idea you have to to fix the issue is? Do you think it would be ill advised to switch the middle elements out for top/bottom ones? Ha, grasping at anything. 
 

thanks again 

[Bill Kielb]

6 hours ago, Marita said:

I’m curious what the other idea you have to to fix the issue is? Do you think it would be ill advised to switch the middle elements out for top/bottom ones? Ha, grasping at anything. 

Switching elements is a thing, but this kiln already was designed and calculated using uniform graded elements. Besides, the voltage drop produces unwanted heating wherever it is occurring (wire, connections, sub panel, breaker ….) which then becomes a fire hazard. Find and fix the issue first and foremost. Applying load changing techniques will actually increase the heating in the defective areas (wire, breaker, sub panel …) for which they are likely not designed or rated. So really a last resort that requires verification for entire system safety appropriately and then this kiln cannot suddenly be used at its standard rated voltage so marking appropriately. I would suggest It’s really something that can only be done by those appropriately skilled in doing so as it can increase the risk of fire in the whole system without appropriate precaution and verification.

[Marita]

Understood- Thank again for your advice. 

[neilestrick]

Like Bill said, you can't just put the T/B elements in the centers. Yes, it would give more power, but it wouldn't be balanced anymore, and the middle would run too hot. You could, in theory, replace all the elements to compensate for the low voltage, but they would all have to be increased appropriately to maintain that balance, and the whole system may have to be modified to deal with the increased amperage draw. Fix the voltage issue and everything else will work as it should.