RE: Charging inductors for resonant charging

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

 >You sure? I still think it should work.

In theory, it probably would, as long as the charging inductor is small
enough to make the charge current discontinuous. The flux should collapse to
zero when the current stops.

In practice I'm not so sure. The core flux is proportional to the integral
of the voltage, and as you know, when you integrate, you add a constant. In
an ungapped high permeability core, this "constant" is poorly defined and
tends to gradually wander into saturation, unless the driving circuit forces
equal currents through the windings in both directions. A DC resonant
charging choke only passes current in one direction because of the de-Qing
diode, so there is nothing to enforce the volt-second balance and the airgap
is compulsory.

For my DC coil I used an "MML", a series string of four off-the-shelf chokes
designed for power supply filtering in vacuum tube gear. They were about $10
each.

In the OLTC II I used an MOT core shimmed with a piece of acrylic. I got rid
of the secondary and used the primary as my winding, giving about 10mH of
inductance. If I had used the secondary instead, I would have got about 1H.

Steve C.