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Oldbatt    0

Hi all, I'm hoping someone can give some technical tips on repairing my Cromartie Hobbycraft kiln with controller and which is not hard wired but runs off a 13 amp plug. It is a top loader.

Bought as a used kiln, I have been using this quite happily for a number of years until recently where it has stopped reaching a stoneware glaze firing of 1240C.

I have replaced the elements and ceramic insulators, checked and cleaned up all the connections and tightened the belts around the body and lid. I have also changed the electrical lead from a short one which fitted into a socket not on the main circuit to a longer lead, about 5-6 meters, to reach a socket on the main circuit as I understand it can cope better with the energy required. I wondered if it makes a difference that the lead is much longer than the original which was no more than 2 meters.

Any advice or tips will be very gratefully received.

Thanks

Kathy

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neilestrick    1,378

By 'lead' I assume you mean the power cord? 5-6 meters is really long for a power cord and may no be up to code, but it won't affect the firing.

 

Is this a digital or manual kiln? How hot is it getting? Have you confirmed that all the elements are heating up by turning it on high and seeing if they glow after a few minutes? What voltage does it run on?

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Bob Coyle    113

A six meter cord, if it is not the correct wire diameter,  May give you a voltage drop that will cause the kiln to not get as much current to drive the elements.

 

If the cord gets hot to the touch when you are firing, then it may be a problem.

 

If you are running 15 amp wire for a 13 amp kiln, then  6 meters is pushing it.

 

 Ohms law       i= e/r 

 

amps = line voltage/ element resistance.

 

measure the total resistance of the kiln by unplugging it and turning on all elements to high. measure directly across the plug at the kiln 

 

if the line voltage divided by the measured resistance doesn't give you pretty close to 13 amps then you have a problem.

 

Try the same same thing with it plugged into the long line. Measure at the end of the line and see if you get a difference.

 

If you don't know what I am talking about...don't even try it.

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Oldbatt    0

Thank you for your replies.

 

Firstly I should state I am in the UK. 

 

Neilestrick, yes I do mean power cord and the same type of cord has been used as the original. Kiln is the model HT45 with a rating of 3-3.5kw, 230v, 13 amp.  I use a H3i controller with 9 programmes. 

 

The problem seems to be with the bottom element.  I have bought 2 full sets in less than a year and used the kiln on average 2 or 3 times a month.  Glaze firings have reached around 1220, then 1200, 1160 etc with F1 fault, so the kiln stops when it has been firing on full whack for more than 20 minutes without gaining 1 degree.  When I have tested the elements by putting them on full heat, I can see there are cold areas on the lower element but no obvious reason for cause (I regularly gently hoover).  I originally used the kiln for about 2 years without any of these problems.  I have changed the elements more often than I should be.  The last time I changed the bottom element and it is still not reaching 1240 so I'm trying to work out if there is another problem.

 

Bob, the cord is 1.25mm2 .  I could drastically shorten the cable but I would be plugging it into a regular socket in our brick shed that runs from the house electrics and not directly on the main circuit so I was concerned this might be like running it off an extension lead (but perhaps not?).

 

 

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neilestrick    1,378

Check your voltage at the elements and make sure your getting full power. Also check the amperage.

 

Are you getting the elements from the manufacturer? Have you verified that they are the correct resistance?

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Bob Coyle    113

Sounds pretty strange that an element would have cold areas.  The same current will be flowing through the entire element.  I have had places where the element was thin, and glowed hotter than the rest of the coil, Maybe that is what you are seeing. It is usually isolated to a small section.

 

The only way you can know if the element is not pulling enough current is measuring resistance of both elements. If one is way high, then there is a problem.

 

Another place to look is the relay in the controller. If it is getting overly hot during the run, the amount of current it can pass goes down. This happened to me once in a setup I did where the fan cooling  the relay was not strong enough. If it is a solid state relay,and getting up to temperatures greater than about 170F then you may see a drop off as the kiln heats up.

 

Can't think of anything else... measure the resistance, otherwise we all are just guessing.

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