Emergency help...Just discovered mid firing @ 543 C that 1 to 2 elements are dead! Student work inside

[neilestrick]

29 minutes ago, feistyfieryceramics said:

How did you find the 29 ohms number? What does it mean if the resistance is lower than it is supposed to be? I thought that the resistance becomes higher in older elements and I thought that was one way you know you need to replace them?

Ohm's Law:

Watts = Volts x Amps
Amps = Volts / Ohms
Ohms = Volts / Amps

So if you take the resistance measurements you got-  26.2, 27.5, and 27.8 Ohms and do the math:

220/26.2 = 8.4 amps, 220/27.5= 8 amps, 220/27.8= 7.9 amps for a total of 24.3 amps x 220=5346 watts. If you do the same math, to be exactly at 5kW you'd need the resistance to be 29 ohms for each element. And yes, you're correct that as elements age the resistance increases. But who knows what the deal is with these elements? Used kilns are always a bit of a mystery, especially when there's no documentation available. And if you were taking the measurements while the elements are still connected, the hardware could be affecting the measurements.

These numbers are all consistent with 75 liter kilns (18x18 inches). They're all in the 22-25 amp/5-5.5kW range.

I missed the 3 phase situation in my previous comment, so the 24.3 amps on 3 phase (24.3 divided by the square root of 3) is 14 amps, so it should be on a 20 amp breaker if I did all that right.

[Bill Kielb]

1 hour ago, feistyfieryceramics said:

How did you find the 29 ohms number? What does it mean if the resistance is lower than it is supposed to be? I thought that the resistance becomes higher in older elements and I thought that was one way you know you need to replace them?

 

Just a note, I would not spend much time speculating on element resistance. The original design may have been at 210 v so the resistance of the elements would have been designed originally for that scenario and to provide 5000w. (In the US we have gone from 110v to 115, and now 120v in forty years) The important point is the design and sale of 5000 watts, kind of like selling a car with 100 horsepower. It better be 100, that’s what you paid for.

Worldwide grid or mains voltages have increased over the years to reduce transmission losses. This may mean  your next set of elements will come  designed to provide 5000 watts at the new voltage which means they will likely be higher in resistance.

At an old voltage if originally 210v your element resistance would be expected to be (210vx210v)/5000w or 8.82ohms for three sets in parallel which means 3x8.82=  Prox. 26.46 ohms each (funny that it matches your elements right now)

It’s really hard to know all that history or speculate what it was. Your next elements should come from someone familiar with this kiln. For now, at 220v and about 9 ohms (3 sets in parallel) you have  (220x220/9) = prox. 5377 watts. If your grid voltage has gone up to 240v, this is a 6400 watt kiln.

All fine as long as your electrician has checked thoroughly after installation. Most folks have the opposite problem actually with wattage decreasing as the elements wear. Your next NEW set of elements might be a step back to design wattage actually.

I am curious what your mains voltage is today, if you can measure. (Leg to neutral)

[Bill Kielb]

26 minutes ago, neilestrick said:

I missed the 3 phase situation in my previous comment, so the 24.3 amps on 3 phase (24.3 divided by the square root of 3) is 14 amps, so it should be on a 20 amp breaker if I did all that right.

I think you are fine, they tend to run a neutral plus earth ground and run these in wye so just as likely it is running on three 220v to neutral per element set. Kind of all speculation at this point but if  leg to leg at 380 v + the elements likely would be toast and would require a set of (3) 87 ohm elements to get to 5000 watts.

[Bill Kielb]

31 minutes ago, neilestrick said:

1 hour ago, feistyfieryceramics said:

How did you find the 29 ohms number? What does it mean if the resistance is lower than it is supposed to be? I thought that the resistance becomes higher in older elements and I thought that was one way you know you need to replace them?

Ohm's Law:

Watts = Volts x Amps
Amps = Volts / Ohms
Ohms = Volts / Amps

@feistyfieryceramics
Neil is pretty much spot on, here is an aid you might find useful. Always work from the design wattage at the original design voltage if known else you have too many unknowns. I left out any reference to three phase here as it’s a bit more complicated. But if it was operating that way we would use the 380 volt number as the voltage. Very unlikely, almost impossible  actually yours is operating this way. 
 

[feistyfieryceramics]

43 minutes ago, neilestrick said:

Ohm's Law:

Watts = Volts x Amps
Amps = Volts / Ohms
Ohms = Volts / Amps

So if you take the resistance measurements you got-  26.2, 27.5, and 27.8 Ohms and do the math:

220/26.2 = 8.4 amps, 220/27.5= 8 amps, 220/27.8= 7.9 amps for a total of 24.3 amps x 220=5346 watts. If you do the same math, to be exactly at 5kW you'd need the resistance to be 29 ohms for each element. And yes, you're correct that as elements age the resistance increases. But who knows what the deal is with these elements? Used kilns are always a bit of a mystery, especially when there's no documentation available. And if you were taking the measurements while the elements are still connected, the hardware could be affecting the measurements.

These numbers are all consistent with 75 liter kilns (18x18 inches). They're all in the 22-25 amp/5-5.5kW range.

I missed the 3 phase situation in my previous comment, so the 24.3 amps on 3 phase (24.3 divided by the square root of 3) is 14 amps, so it should be on a 20 amp breaker if I did all that right.

Thanks! This is really interesting. Good point about the elements. The people I bought it from said it was a floor model and only fired a couple times before they got it (Why would a floor model be fired?) and that their mom only fired it a couple times after buying it. But she has A LOT of clay and glazes like 20 different glazes so that seemed a bit suspect. And there is clearly damage around the vents (from sulfuric acid?).

The kiln was unplugged when we took the measurements. But I forgot to mention that thermocouple was reading 65 C at the time, I think, while we were checked the resistance. I think that is relevant because when we were looking at buying Kanthal to coil ourselves to create elements, I think there was a table that listed "resistance at room temperature" or something like that.

This is all really great info. I am going to feel so much more informed and less nervous moving forward!

 

[feistyfieryceramics]

18 minutes ago, Bill Kielb said:

@feistyfieryceramics
Neil is pretty much spot on, here is an aid you might find useful. Always work from the design wattage at the original design voltage if known else you have too many unknowns. I left out any reference to three phase here as it’s a bit more complicated. But if it was operating that way we would use the 380 volt number as the voltage. Very unlikely, almost impossible  actually yours is operating this way. 
 

I'm definitely a visual person so I think this will be helpful...eventually  right now it is still overwhelming to look at. But I'll try to look over everything carefully tomorrow or next weekend.

 

[feistyfieryceramics]

52 minutes ago, Bill Kielb said:

Just a note, I would not spend much time speculating on element resistance. The original design may have been at 210 v so the resistance of the elements would have been designed originally for that scenario and to provide 5000w. (In the US we have gone from 110v to 115, and now 120v in forty years) The important point is the design and sale of 5000 watts, kind of like selling a car with 100 horsepower. It better be 100, that’s what you paid for.

Worldwide grid or mains voltages have increased over the years to reduce transmission losses. This may mean  your next set of elements will come  designed to provide 5000 watts at the new voltage which means they will likely be higher in resistance.

At an old voltage if originally 210v your element resistance would be expected to be (210vx210v)/5000w or 8.82ohms for three sets in parallel which means 3x8.82=  Prox. 26.46 ohms each (funny that it matches your elements right now)

It’s really hard to know all that history or speculate what it was. Your next elements should come from someone familiar with this kiln. For now, at 220v and about 9 ohms (3 sets in parallel) you have  (220x220/9) = prox. 5377 watts. If your grid voltage has gone up to 240v, this is a 6400 watt kiln.

All fine as long as your electrician has checked thoroughly after installation. Most folks have the opposite problem actually with wattage decreasing as the elements wear. Your next NEW set of elements might be a step back to design wattage actually.

I am curious what your mains voltage is today, if you can measure. (Leg to neutral)

"I am curious what your mains voltage is today, if you can measure. (Leg to neutral)" how would I measure? Here are some photos of the electrical "stuff" in the studio. Some of it old and out of use, but I thought you might find it interesting

[Bill Kielb]

44 minutes ago, feistyfieryceramics said:

I thought you might find it interesting

Very! Looks like your grid or mains voltage these days is 230v ! So in actuality you probably have a prox. 6000 w kiln! Interesting but similar throughout the world actually. No worries about measuring actually.

Thanks!

let us know if your firing goes well.

[feistyfieryceramics]

@Bill Kielb @neilestrick The kiln was able to keep the ramp rate and achieve the desired temperature! I unloaded it this afternoon and everything is intact! So I am VERY relieved. Thank you! Thank you! Now we are wondering if it is a good idea to have an extra relay and elements on hand so that when something breaks down in the future, we won't be out of commission for weeks waiting on parts. Is that a good idea?

[neilestrick]

1 hour ago, feistyfieryceramics said:

@Bill Kielb @neilestrick The kiln was able to keep the ramp rate and achieve the desired temperature! I unloaded it this afternoon and everything is intact! So I am VERY relieved. Thank you! Thank you! Now we are wondering if it is a good idea to have an extra relay and elements on hand so that when something breaks down in the future, we won't be out of commission for weeks waiting on parts. Is that a good idea?

Definitely a good idea to have spare parts on hand. Does Cromartie still supply elements for your kiln? If not, is there a place you know of in your part of the world that can make elements for you? In the US we use Euclids.com (in Canada) for elements that are no longer made by the original manufacturer. I'm sure they could help you out but I don't know if the shipping costs would be worth it.

[Bill Kielb]

3 hours ago, feistyfieryceramics said:

weeks waiting on parts. Is that a good idea?

I don’t think you have relays. I think Looking at your picture you have a group of switches which you likely leave on high and the safe fire seems to  have  one giant contactor in the bottom left that should last forever but likely can be rebuilt with contacts or even disassembled and burnished in a pinch, if ever needed......... best I can tell. Cromartie has 5kw elements listed on their site........ I believe.  A clearer picture of the backs of the switches and one of the contactor in the lower left  would help confirm this.

As far as your elements, unless these burn open you have a long way to go before they won’t perform, just because of the change in design voltage or however they ended up to be 26 ohms. They will get thinner and eventually fail though so a spare set that fits is a great idea.

[feistyfieryceramics]

On 1/1/2021 at 9:48 PM, Mark C. said:

Your kiln looks to be three phase

goggle (3 phase explained)

Its used world wide

your elements are 220 on the plate I think

Thanks @Mark C.! I'll do that!

[feistyfieryceramics]

On 1/3/2021 at 12:59 AM, Bill Kielb said:

I don’t think you have relays. I think Looking at your picture you have a group of switches which you likely leave on high and the safe fire seems to  have  one giant contactor in the bottom left that should last forever but likely can be rebuilt with contacts or even disassembled and burnished in a pinch, if ever needed......... best I can tell. Cromartie has 5kw elements listed on their site........ I believe.  A clearer picture of the backs of the switches and one of the contactor in the lower left  would help confirm this.

As far as your elements, unless these burn open you have a long way to go before they won’t perform, just because of the change in design voltage or however they ended up to be 26 ohms. They will get thinner and eventually fail though so a spare set that fits is a great idea.

@Bill KielbHa! Yes! We were looking online before I read your post and in our ignorance we were like, "I guess they call relays "contactors" in Englad!" Hahahaha.

Oh! I love that it can be rebuilt or altered to work again. That's amazing! My husband would love to try something like that. I have the kiln running again right now, but I'll try to remember to take photos of those things and get back to you. Even if we never end up needing a spare set! I think it would feel like a relief to have it here! 

[feistyfieryceramics]

On 1/2/2021 at 11:47 PM, neilestrick said:

Definitely a good idea to have spare parts on hand. Does Cromartie still supply elements for your kiln? If not, is there a place you know of in your part of the world that can make elements for you? In the US we use Euclids.com (in Canada) for elements that are no longer made by the original manufacturer. I'm sure they could help you out but I don't know if the shipping costs would be worth it.

@neilestrickYes. Cromartie sells the elements! They are wound when you order them. We should check with our local pottery place does the same!

[feistyfieryceramics]

@Bill Kielb @neilestrick I completed the bisque firing and a glaze firing with no problems! Before the glaze firing I put extra space between the "pac man" and the switch arms! I noticed that the kiln REALLY does warp when it gets hot! When it's cool the latch for the lid sits quite crooked! When it's hot, it aligns perfectly! Again I really appreciate your help. I have so much more confidence now that we were able to figure out and fix the situation!

[oldlady]

glad it all worked out for you.   just one question, is that kiln sitting on a stand above the floor or is it resting directly on the tile floor? 

[feistyfieryceramics]

2 minutes ago, oldlady said:

glad it all worked out for you.   just one question, is that kiln sitting on a stand above the floor or is it resting directly on the tile floor? 

@oldladyIt has built in wheels that keep it 7.5 cm off the floor. It also has a metal bottom. I asked someone at some point if I needed an additional stand... but I can't remember who I asked. Do you you think this is sufficient? It is on a tile floor with concrete underneath that. Thanks!

[Bill Kielb]

42 minutes ago, feistyfieryceramics said:

but I can't remember who I asked. Do you you think this is sufficient? It is on a tile floor with concrete underneath that. Thanks!

I did notice that when I originally looked at your picture. Ceramic tile floor,  ( actual ceramic base ) over concrete should be fine. If my reading is correct of the correct literature for that kiln it was designed with those wheels it’s a fiber insulated kiln.............. On top of ceramic tile over concrete, should be just fine IMO.