MOT's as inductors with DC bias updated info

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: tesla <tesla@xxxxxxxxxxxxxxx>

Team

Recently  (months ago) I posted some measurements about the drop off in L in
the secondary of a MOT as DC bias current is increased. This was to provide
information about their use in DC resonant charge systems.

I had great success using two MOT's in series ungapped as per the DC design
using a single MOT and shifters as illustrated by Steve Conner et al
(scopeboy)

The drop off in L as DC bias current figures I gave were in error because I
overlooked the significant AC current being diverted into the DC bias
injection system as the DC current was raised. The Z of the DC injector
varied a lot due to saturation in that system.

I have since made a few  better measurments and they showed the following
for a standard 900w MOT

Gap 0.3mm
L=22H at 0mA DC bias dropping to 18H at 300mA DC bias and 11H at 400mA DC
bias

No Gap
106H at 0mA DC bias dropping to 16H at 100mA DC bias and 3H at 300mA DC bias

IMHO measuring L in the presence of DC bias is the best method of looking at
a MOT for DC inductive charging use.

FWIW:
I have completed the Tesla using  up to 6 MOT's in AC mode (ref recent post
by ??)

Those who suggest using other cores and winding your own HV chokes should
reflect on the cost effectiveness of MOT's and their free availability. In
NZ the MOT is probably the only practical avaialble core. It actually
surprises me some of the anti MOT sentiment out there, properly used they
seem to me to be a great resource, they are not invulnerble in tesla service
and from what I can tell nothing actually is.

Many have referred to excellent results using MOT's as charging chokes
without flashovers and this has been the case for me in my first DC system
(as noted above)

Best
Ted L in NZ