Re: [TCML] charging reactors

[bartb <bartb@xxxxxxxxxxxxxxxx>]

You certainly don't want to use THHN sized insulations and a single 
layer would not do. Magnet wire is the preferred choice here. The 
voltage is distributed through the winding and you want to attain the 
inductance in the least amount of "space" with the minimum voltage 
stress across the worst case opposing layers. A single layer is not 
possible without getting ridiculous with geometry.

Everyone seems to be thinking in terms of heavy gauge and heavy 
insulation wire. If I remember Jim's specs, it was 10kv to 20kv in the 
500mA to 1A range at about 5H. This really isn't that difficult to 
achieve. For example, consider a 1"D x 4.3"L core. Now imagine 100 
layers of 30Awg magnet wire. The result is a 5H inductor good for 1A and 
the worst case stress across the layers is 400V with 20kV applied. 
Obviously, this wire size is small, DCR is 166 ohms and net impedance is 
1.88k ohms. You could zap this wire size with too much current if no 
current margins were taken into consideration. So maybe head up to 2"D x 
4.75"L core and use 24 Awg (robust). This inductor ends up an outside of 
6.5"W x 4.75"L. Pretty hefty inductor, but it could be wound on a bobbin 
and would certainly do the job. Because the layers are still 100, the 
voltage stress is still near 400V worst case across joined windings.

Anyway, there are many layer/winding possibilities, but magnet wire is 
what you want here. Going with a thick insulation (if thinking about 
voltage standoff) is not practical nor is it needed in this case. I know 
Richie Burnett wound his large ballast with thick insulated wire, but 
the inductance was in the low mH range (it's a ballast application). 
Quite a different cookie than what would be needed for Jim's need.

Take care,
Bart

Ed Phillips wrote:
> What about a straight, stick-shaped core?  Think in terms of an 
> old-style induction coil, but with only one winding.  This would 
> greatly simplify homebrewing, as bundled iron or steel wire could be 
> used for the core, and the winding would be a simple solenoid.  Isn't 
> a straight core like this more resistant to saturation than a 
> shell-type core?
>
> Cheers,
>
> Greg"
>
>     Answer to last question is certainly.  Problem will be the size of 
> the thing to get the desired inductance when wound with wire that can 
> handle the current and insulated for the high voltage.  Almost 
> certainly impractical even with very modern core materials.  Iron or 
> steel wire wouldn't do - would need a large laminated stack.
>
> Ed
>
>
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