Kiln Failing to Reach Cone 6, New Controller

[OVMI_Designs]

Hello all,

I am trying to work out an issue with my kiln. It will take some explaining so bare with me. 

I have an older Evenheat 1820. It's rated at 240v 24 Amps. I replaced the elements a year or so ago, and haven't had but maybe 30 firings on the new ones. It has been reaching cone 6 with no issues.

Recently, I decided I wanted more control over the kiln so I set out to build a controller. Pre-made ones cost around $1000, out of my price range, so I did some research and built my own for around $450. I have attached a wiring schematic I drew up for it. It is a Bartlett Genesis Mini controller. I confirmed the wiring diagram with a Bartlett tech. 

Also, during this process I decided to move the kiln location. I extended the circuit about 30 feet using a junction box. It is a 50 amp circuit with 6 gauge copper wiring, which I assumed would be plenty enough big for a 24amp kiln. The total distance from the outlet to the breaker box is about 85'.

The first firing I did was an 04 bisque. It fired fine, actually going over a cone. I adjusted the Thermocouple Offset to account for the over-fire. Today I attempted a cone 6 glaze firing. When it got to around 1965 F it threw an error code saying it failed to ramp quick enough. I adjusted the program to a full ramp 9999 to attempt to see if I could get it up to temp, but couldn't manage to get past 2020F. I am wondering what went wrong. The power cord plugged into the the outlet was a little warm, as was the control box. The controller said the board was about 120F. What should I check / test to solve this issue?

I measured the voltage at the outlet when I rewired it and got 240v. I haven't tested the voltage level under a load yet though. Is there anything else I can check or should know?

More Info: The original power cord from the kiln is 6 gauge copper. The new power cord going from the outlet to the new control box is 10 gauge copper. The wire connecting the relays to the control box outlet (which the kiln now plugs into) is 10 gauge tinned copper wire.

 

I appreciate all the help in advance!

 

Kiln_Controller_Wiring_Diagram v3.pdf

[neilestrick]

So you unhooked the Automate controller?

Why do you have a contactor after the relay?

There's no ground going to the transformer or controller.

If the whole thing is going back to a 50 amp relay, then your power cords must be 6ga wire. Otherwise you could end up pulling 50 amps through your 10 gauge wire, which is not safe. However that doesn't really matter becase you can't just say '50 amps should be plenty big enough'. Code says that kilns must be on a breaker that is 25% greater than the draw of the kiln, but no more than 50% greater. That means either a 30 amp breaker (ideal) or a 40 amp breaker for your 24 amp kiln. You should put a subpanel with a 30 amp breaker between the 50 amp breaker and the controller, so you can use the existing 10ga power cords. The wire from the 50 to the 30 must be 6ga. From the 30 to the outlet can be 10ga.

I'm surprised the controller is hitting 120 degrees in an external box. Either something is running hot, or there's just too much heat building up in there since there are so many relays in there.

[Bill Kielb]

Neil is right, change your breaker to 30 amps then everything can stay over rated. I am assuming your relays are drawn a little different from convention and the double pole contacts connect correctly. If I have this right you have a safety relay in series with the output relay that drives a 30 amp contactor which powers a plug To your sitter which keeps your sitter timer in circuit to run your kiln as before with the timer wound up and sitter armed with a cone When you are firing.

So many contacts and things to do for each firing.

• Wind the timer
• arm your sitter with a cone
• program your control

anyone of these can shut it off plus any bad connections will sap some power from this 7200 W kiln. So I would start with measurements, ohms, Amps and voltage drops across all contacts and connections. It appears this is a cone 8 kiln so  not much wiggle room as far as power to spare. if the elements have risen in resistance by 10% you probably don’t have enough power to get to cone six. That may also be the result of element wear and or some drop across all these contacts and connections. Measuring things under load is the only way to determine voltage drop. If the connection is warm, there is voltage drop. Safety first, live wires and live diagnosis demands lots of care and safe practice.
 

All elements in parallel should be 8 ohms for 7200 watts. If your drawing is correct they are 32 ohms each. If you measure everything, the problem should become apparent.

Its interesting that your bisque over-fired.  One sign of not enough power, is your firings Begin to take longer which increases the heatwork and your kiln begins to over fire. An offset will not fix this condition for long. How long did your bisque firing take?

[Mark C.]

With so many connections -you should make sure they are all are tight and clean-I would check all these connections again-hopefully you have the controller vented as well?

The two above posts tell explain the 30 amp breaker well as its not safe with #10 involved as the fire hazard is real.

[OVMI_Designs]

Thanks for the replies.  I want to make sure I do this right. 

I forgot to update the drawing, there is no contactor between the output outlet and the relays. Also I unwired the timer on the kiln sitter. And yes the fire right is disconnected. There is a ground going to the box I installed the equipment in. The way it is wired with the relays in series is based on the bartlett manual. You are correct in saying the drawing of the relays is not to convention, I suppose I should change it make more sense. 

So as you all suggest I need to change to a 30amp breaker. Is it ok to do this in my main panel or should I put in a sub panel?  If I changed the breaker in the main panel, can I wire the controller straight to the circuit, removing the plug? That way I dont have a 50amp outlet on a 30 amp circuit.

I will also check connections with a multimeter today. 

[Sorcery]

The distance seems quite far.

I had to use 6ga. (I believe) for just over 40ft for the next larger kiln.

I bet there is a jump to 4ga for yours after 80, or it might not even be recommended. 

I had the manual with the info but I believe I lost it, I'll check.

I don't know if I believe this is your problem. But it's worth checking.

Sorce

 

[ronfire]

Found this calculator.

 

[Bill Kielb]

19 minutes ago, ronfire said:

Found this calculator.

 

Yeah, sort of. Change your breaker to 30 amps was the point because your kiln requires it and your #10 wire requires it.
With The current 50 amp breaker your #10 wire becomes a potential fuse. BTW this may be good but picking from a table based on whether it’s in conduit and the temperature rating of the insulation of the wire is a bit more specific. This is handy, but we don’t know the conditions it addresses.

[neilestrick]

If you change the breaker to 30 amps, then your 6ga wire is oversized by 2 sizes, which will counteract any issues with the run being too long. If you don't need the oversized wire, then you could put in a subpanel  at the end of the run with a 50 amp main, and a 30 and 20 coming off it. That would allow for hooking up a little test kiln in the future. 

A 50 amp outlet on a 30 amp circuit is not a problem because you'll never get more than 30 amps through the outlet. The other way around would be a problem.

[OVMI_Designs]

So I just tested the outlet by itself and then the outlet under load. I looks like it is around 241 volts without a load. With the kiln running it is dropping down to 236.5 volts. Neil do you think if I changed it to a 30 amp breaker, it would solve the voltage drop?

Thanks again for all the help!

 

-Matt

[neilestrick]

I'd add a ground wire to the transformer, and also run one from the center tap on the controller to ground (you'll need a double connector there) to rule out any electrical interference.

The size of the breaker isn't causing the voltage drop, and the size of the wire isn't a problem since it's oversized for 30 amps. I don't think the drop you're experiencing is enough to cause the problem. It's only about 2%. Usually we don't see problems until closer to 5%.

Double check all connections in the entire system, from the breaker all the way to the elements. There could be something loose that's causing heat in the system. Also check your thermocouple connections, including all the wire connections. Could be a loose connection that's causing a bad read at higher temps.

Have you verified that all the elements are still working? Put a meter on them and check them for continuity and measure their resistance. 

[OVMI_Designs]

I measured voltage at each element. 238.5v for each, that shouldn't be an issue. The resistance to each element was 42 ohms (the kiln was at 250degrees when checked, I will recheck when they are at room temp.), all together they were 11 ohms. The kiln shows wattage on the side at 5760. According to Evenheat they should be 38.3 ohms.

 

At this point I have checked the connections, check voltage at each stage, and checked the resistance of the elements. I wonder if I just got a little paranoid and should give it a longer time to fire. In the past it took 9.5 hours to reach cone 6. Dividing that out its around 245 degrees an hour. I loaded a program on from digitalfire for a drop and soak schedule that had the ramp rate at 350 d/hr, perhaps to fast for this kiln. I will reprogram and try to refire.

The last thing is, I tried to swap out the 50amp breaker for a 30amp, but the 6 gauge wire would not fit in the terminals. Maybe I can find a different brand with larger terminals, or maybe I will just have to install a sub-panel at the kiln. Thanks for the help all, I will keep you updated. 

 

-Matt

[Bill Kielb]

1 hour ago, OVMI_Designs said:

I measured voltage at each element. 238.5v for each, that shouldn't be an issue. The resistance to each element was 42 ohms (the kiln was at 250degrees when checked, I will recheck when they are at room temp.), all together they were 11 ohms. The kiln shows wattage on the side at 5760. According to Evenheat they should be 38.3 ohms.

 

At this point I have checked the connections, check voltage at each stage, and checked the resistance of the elements. I wonder if I just got a little paranoid and should give it a longer time to fire. In the past it took 9.5 hours to reach cone 6. Dividing that out its around 245 degrees an hour. I loaded a program on from digitalfire for a drop and soak schedule that had the ramp rate at 350 d/hr, perhaps to fast for this kiln. I will reprogram and try to refire.

The last thing is, I tried to swap out the 50amp breaker for a 30amp, but the 6 gauge wire would not fit in the terminals. Maybe I can find a different brand with larger terminals, or maybe I will just have to install a sub-panel at the kiln. Thanks for the help all, I will keep you updated. 

 

-Matt

To me at 5760  watts (even smaller than I thought)  that is too much voltage drop. Check all connections are clean and tight. Any connection that is heating has voltage drop. Your elements  are 10% worn, this is an underpowered kiln to start. It’s time to replace them.  If your voltage drop becomes 5%, that’s Half your element life  so 5% would be too high as an allowable. On such a short run with oversized wire I expect virtually no drop. Your measurements say you need elements and you have some marginal connections. Fix that and you are in business.

[neilestrick]

238.5 volts vs 240 volts shouldn't be an issue. That sort of variation is normal.

Try a firing with the final 200F degrees at a rate of 100F/hr and see if it can keep up.

Read THIS. It may have something we haven't covered.

If you're only getting 30 firings from a set of elements, I'd start looking for another kiln.

[Bill Kielb]

22 minutes ago, neilestrick said:

238.5 volts vs 240 volts shouldn't be an issue. That sort of variation is normal.

Try a firing with the final 200F degrees at a rate of 100F/hr and see if it can keep up.

Read THIS. It may have something we haven't covered.

If you're only getting 30 firings from a set of elements, I'd start looking for another kiln.

He has no power to spare so every percent is significant. I highly advise finding any bad connections .... they will heat up and become worse. A 5% drop literally would take a brand new set of elements and cut their firing numbers in half. If you get 100 firings from a new set,  starting with a 5% voltage drop is like starting with elements you will only get 50 firings out of.

We did an analysis awhile back for marginally powered  kilns and suggested that the ordinary 3% electricians rule of thumb was probably too much for most kiln owners. Everything still works but less firings available for their elements. I really like 1% or less and often the utility likes to supply just over 240v, it reduces their transmission wire loading. (Amperage)

[neilestrick]

24 minutes ago, Bill Kielb said:

He has no power to spare so every percent is significant. I highly advise finding any bad connections .... they will heat up and become worse. A 5% drop literally would take a brand new set of elements and cut their firing numbers in half. If you get 100 firings from a new set,  starting with a 5% voltage drop is like starting with elements you will only get 50 firings out of.

We did an analysis awhile back for marginally powered  kilns and suggested that the ordinary 3% electricians rule of thumb was probably too much for most kiln owners. Everything still works but less firings available for their elements. I really like 1% or less and often the utility likes to supply just over 240v, it reduces their transmission wire loading. (Amperage)

He's not at 5%, or even 3%. At 238.5 he's at less than 1%, which is why I said it's not a problem. I also never said that 5% is allowable, it's just when problems often start showing up. But of course that depends entirely on the kiln and how you're firing. If you're only firing to cone 05, a 5% drop might not even be noticed. I think we're on agreement here that he's within a normal range, and connections should be checked.

[OVMI_Designs]

I order some new elements. I checked the last time I bought some was Nov. 2018. I am not sure how many firings I have done, I don't think its 100 though. I will try and keep better track this time. I am also adding a kiln vent which may help element longevity. We shall see.

I also tightened the female disconnects connecting to the relays, tightened any wire nuts, and added vent holes to the panel. I will measure the voltage at load when I get the new elements in. I also have ordered new wiring for the elements themselves. I'm sure it still has the original wiring, so putting new stuff in may help. 

Thanks again for the help. Feeling better about it. I'll let ya know how the next firing goes. Wish me luck.

-Matt

[neilestrick]

100 firings would definitely be the end of the elements for a cone 8 kiln trying to get to cone 6. I often see as low as 75 firings in that situation.

[Mark C.]

(With so many connections -you should make sure they are all are tight and clean-I would check all these connections again)

I still would not rule out bad connections

also 

The #6 wire should go to a subpanel not a 30 amp breaker-then in that subpanel (which can be a small one( with 4-6 slots) thats where the 30 amp breaker goes with the #10 wire feeding into that breaker.

30 apm breakers are not made to accept #6 wire so do not do that.