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Errors from a Miswired Digital Kiln Transformer

A miswired transformer can cause the keypad to “freeze” or the relay to fire intermittently.


Errors from a Miswired Digital Kiln Transformer

Reader Response: How often should you check your kiln?

Recent Q&As: Firing a freshly kiln washed shelf; repairing a gouge in a shelf

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News: The New Paragon Glass Kiln Instruction Manual



Recently I heard of an interesting kiln problem that was caused by a miswired transformer. A small, 120 volt kiln fired correctly almost every time. But for no apparent reason, occasionally the kiln underfired. The problem turned out to be a transformer wired for 240 volts in the 120 volt kiln.

The transformer, which is inside the switch box of a digital kiln, converts the electric power to 24 volts AC. The transformer is easy to recognize. It is a square electrical part that is wired between the power cord and the controller. (See accompanying picture.)

The temperature controller turns on the elements through an electromagnet called a relay. When the controller needs to raise the heat, it sends a 12 volt signal to the relay. That energizes an electromagnet inside the relay, which pulls electrical contacts together and sends power to the heating elements.

The relay in question operates on 12 volts. But because the transformer in this case was wired for 240 volts, the relay received only 6 volts. This was barely enough voltage to operate the relay. So occasionally the relay failed to turn on when it should have, which caused the kiln to underfire.

When dealing with an intermittent relay problem, check the jumper wires on the transformer. Make sure they are wired for the correct voltage. (Please see the accompanying photo.) Also check the voltage from the controller to the relays. A transformer wired for 240 volts barely produces enough voltage for a single relay in a 120 volt kiln. On the other hand, a transformer wired for 120 volts that is mounted in a 240 volt kiln will give a very bright controller display.

Low voltage from a miswired transformer can also make the controller lock at a particular temperature; the keypad will not respond to key presses.



The last Kiln Pointer was entitled “How Often Should You Monitor a Kiln?” Lyna Taber wrote, “I set my timer on my kitchen stove and monitor my kiln every two hours. I have had 100% success with all my firings including cone 9. Yes, a few things have blown up, but that was because I let my niece and nephew make what they wanted the way they wanted, and I think their clay had moisture or air bubbles.

“The results have been amazing as I am finally doing what I want as an artist. AND I LOVE IT! Check kiln every two hours to be safe!”



Q. Should I fire the kiln shelves by themselves after cleaning them and re-applying kiln wash, or is it okay to fire freshly coated shelves with a glaze or bisque load?

A. It is okay to fire bisque or glazed ware on the freshly kiln-washed shelves. Allow the shelves to dry before firing them.

Q. Glaze has eaten into a shelf. Scraping the glaze off the shelf has left a low spot. Can the shelf be repaired?

A. Yes, in some cases. Coat the shelf with kiln wash. Apply several coats to the low area where you removed the melted glaze. The kiln wash will fill in the depression. This is only a temporary repair.



"In the long run, men hit only what they aim at. Therefore, they had better aim at something high." —Henry David Thoreau



Paragon has just published the new 48-page “Paragon Glass Kiln Instruction & Service Manual.” Thank you to those who offered suggestions for the manual. You can download it from our website:


"Foyle's War" has become my favorite TV show. It is set in the 1940s and takes one to a place in time that feels so very real. The main character, Detective Chief Superintendent Foyle, is a quiet, unassuming Sherlock Holmes type.

I hope you had an enjoyable Memorial Day weekend.

Thank you,

With best wishes,

Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd., Mesquite, Texas 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 / / /

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Copyright 2013, by Paragon Industries, L.P.

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