[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: THOR: SMPS warmup behaviour followup



Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jwagner-at-cc.hut.fi>


> I have now identified what I believe is the actual cause: there is some
corona
> between the SMPS transformer secondaries and the ferrite cores. As the corona
> grows together with charging voltage it is a good explanation for the
charging
> profile bending. I can also "ear" the corona. A week ago I had also a
discharge
> through the secondary (SMPS, not TC) coil former and the core, resulting
in one
> of the driver getting damaged.

Grounding the core is definitely good. That is done in most SMPS
supplies, AFAIK.

Just a hint, have you already tried using some epoxy / pour on resin
insulation on the secondary windings? Yes it probably will add some
capacitance which might not be desirable, but at least it should kill
corona effectively. On my small scale ~10kV ferrite transformer I
tried out crafts shop polyester resin ("Giessharz") some weeks ago,
and it sure was very effective (although not very cheap either) - no
corona, not even when testing transformer voltage strenght with a car
ignition coil. Your power levels are of course "slightly" larger :o),
but maybe it would work...

> 2. as the core is double-U shaped, smooth the ferrite sharp corners below the
> secondary coil former. This should lower the electric field density in that
> area.

Or just install copper/metal corner bars or thick copper strip that
can be clamped along the ferrite core edges and then weld these bars
to the rack ground? If you take the bars along the whole length of the
edges, this would ground the whole transformer very effectively
(better than relying on ferrite core to conduct, after all it has
large resistance).

 - Jan