An intermittent fault ( ie internal short) in the load.

That induction heating coil is a non- trivial device running at high voltage
& frequency.

The briefest short or arc between adjacent turns would take out one or both
IGBTs instantly.

I've got a look at the coils, seem OK, not a trace of burn, and the
turns are isolated by section to distribute the voltage equally.


On 29/11/2012 07:45, wrote:
I want to know if both devices were replaced. Don't you ? Before you
battle with me that is. I would hate to find out later I was right.
It's not all that fair because it has happened so much on my life.

On my first and only test, I've changed only the shorted IGBT, ie. the
bottom's one. Worked, but the top got tripping two or three times and
failed again. Now I've removed the both IGBT, the 3 polypropylenes caps,
and the both MKT snubbers for replacement. I've also inspected the
kapton isolation behind the IGBT, saw no damage here.

Now i'm stuck at finding the polypropylene caps. They are expensives,
and what i found can handle only 17 amps. Seem a bit underrated for such
that case.

Doing measurements is not easy as, without load or transistors, the
drive shuts itselfs (not detecting anything), just trying shorts pulses,
and i would not wasting my replacements parts.