I was given a Ceramics Kiln that is designed for 208V and I am trying to see if there is a way I can run it at 240V. It has 6 elements made of 16AWG Kanthal APM resistance heating wire. Each element having a resistance of 26 ohms. Elements are wired in parallel pairs.
I tried changing the element pairs to run in series to reduce the voltage across each element to 120V. This worked; but, the power reduction was too much and the kiln only got to 1100F. Goal is at last Cone O4 (1945F) with stretch goal to Cone 6 (2232F).
My next thought is to try running the some of the elements at 240V. This would be 9.2A compared to the 8A at 208V; but, I would really like to know if the wire can safely handle the 9.2A before I risk damaging the element wires.
How to figure the max current capacity for different gauges of Kanthal wire.
I have been looking for a while and I can't find anything.
Update: I ran a test with some of the elements at 240V and they did not fail; but, presently I am testing using a 30A circuit so I can't run more than 3 elements. I have to move the kiln to a different location to test with 50A (which would allow me to run up to 5 elements. This empirical test is nice; but, I would like to have some analysis to know how much margin I have.
Best Answer
well, at 240V not that extra 15% voltage (over 208V) makes 33% extra heat. That could well be too much heat.
If you can get two microwave oven transformers and replace the secondary windings with 16V windings (about 16 turns of wire) you can build a step-down autotransformer,
simulate this circuit – Schematic created using CircuitLab
such a setup should be good for 60A output with no problems.
Running the primariries at 104 instead of 120 will significantly reduce heating of the transformer as they are normally run fairly close ot saturation.