Re: What happens when you over current an inductor?

John_H wrote:
Rene Tschaggelar wrote:

First at reaching the current specification its
inductivity decreases as it becomes saturated.
At further increase of the current over the
specification, it becomes warm, then hot until
a solder joint melts. The inductivity is lower
than expected at overcurrent.
You cannot permanently damage an inductor,
except by damaging the insulation and the solder
joints. Meaning the media, usually ferrite doesn't
care.

Rene


But won't there be troubles when the temperature exceeds the curie temp? I may be getting my cores mixed up with the rare earth magnets I work with.

all materials that exhibit ferromagnetism become paramagnetic when heated above the Curie temperature - IOW the (relative) permeability drops to ~ 1, so the core "disappears". Cool it down, and it comes back.

note:
- if you melt or vaporise the core, it wont come back.
- iron powder can (and probably will) degrade if you do this, as the insulating material degrades with temperature (micrometals go into this in some detail)


I once had to fix a problem with a 1500W dc-dc converter that exploded at low battery. I traced it to the 40mm long 8-AWG wire going thru a 400T CT - the wire got so hot that the high-perm (IIRC J material) ferrite in the CT saturated (140C). This caused the CT secondary inductance to plummet, so nothing came out the end of the CT. The current controller saw this, and immediately cranked the duty cycle up to max.

at higher battery voltages/lower loads, the ferrite cooled down and it all started working again.

Initially I tried to hand-make some litz using 9 strands of magnet wire, but it was solder strippable wire, and because it was so short the insulation came off when soldered. So I got a new CT made using 3C85 (I forget the mag inc name) which has a Tc of about 230C. end of problem.


The permeability will still be there because of the raw material; what happens to the properties of the core if it becomes magnetized?

Cheers
Terry
.

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