darryl

01-17-2016, 05:17 PM

Have gotten to the point where today I want to fit the heating elements into my heat treat oven. It turns out that the original elements were exactly twice as long as these now need to be. I can cut them in half and unwind a bit of each coiled end to use for the connection, and they will fit.

I'm used to dealing with nichrome, but this wire is quite brittle and has an oxide film on it. Everything points towards this being kanthal wire, which doesn't increase in resistance much as it's heated- less than 5% depending on the exact composition from what I've been able to find. My half pieces measure 8.2 ohms, which translates to drawing about 15 amps from 120 vac, or say 14 amps once the wire is hot. That in turn represents about 1600 watts or so per section.

What's interesting is that the original kiln was rated at 6000 watts and 240 vac. It had 8 elements in it, all wired in parallel, so each would have been rated for 750 watts. A half section of each element would then be rated for 375 watts at 120vac- quite a difference from 1600 watts.

I guess my next test would be to apply 120 to this half section and see whether the current drops to the point where the draw would be more according to the calculations. Perhaps I'll also apply 120 to a full length section and see what happens there. Maybe I got fooled by thinking that all the elements were in parallel where they might in fact have been in series/parallel- I don't think I made that mistake but it's possible.

At any rate, I have 5 grooves in which to install element coils- not a good number for a wiring combination. I'll have to see what I can do about that.

I'm used to dealing with nichrome, but this wire is quite brittle and has an oxide film on it. Everything points towards this being kanthal wire, which doesn't increase in resistance much as it's heated- less than 5% depending on the exact composition from what I've been able to find. My half pieces measure 8.2 ohms, which translates to drawing about 15 amps from 120 vac, or say 14 amps once the wire is hot. That in turn represents about 1600 watts or so per section.

What's interesting is that the original kiln was rated at 6000 watts and 240 vac. It had 8 elements in it, all wired in parallel, so each would have been rated for 750 watts. A half section of each element would then be rated for 375 watts at 120vac- quite a difference from 1600 watts.

I guess my next test would be to apply 120 to this half section and see whether the current drops to the point where the draw would be more according to the calculations. Perhaps I'll also apply 120 to a full length section and see what happens there. Maybe I got fooled by thinking that all the elements were in parallel where they might in fact have been in series/parallel- I don't think I made that mistake but it's possible.

At any rate, I have 5 grooves in which to install element coils- not a good number for a wiring combination. I'll have to see what I can do about that.