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MMC cap power dissipation
Hi All,
Tonight I finally got the great MMC power tester going. I had to "tune"
out the inductance of my four big power resistors (50 ohms + 68.3uH) and
get a "real" thermal couple to measure the cap temperature but it finally
all works.
These are 0.056uF 1600 volt Panasonic ECW-H 16563-JV.
With 3.0 A RMS of 373kHz current going through them, they heated 3.41
degrees C above ambient (still air). All the equations said they would go
to 9.9C. So it appears the manufacture padded their current numbers which
is what I expected. It appears they can safely take 3.5 amps RMS for a 5C
temp rise. Maybe 6 amps max.
I only put about 23 volts across them in this test so there may be some
differences when they get pulsed with 100 amps at 2k volts to get 3 amps
RMS. ;-))
One thing I did notice that may be of great importance, is that they took
30 minutes to reach temperature! Thus the inside is probably not that much
hotter than the outside. If there were a fan on them they would stay far
far cooler. If the outside were kept cold, the small heating on the inside
would be very small compared to the high cooling capacity of a fan blowing
on the outside. This may be very important if one runs the caps under very
high current such as a big coil might. Instead of having a very large
number of strings, one may be able to use far fewer stings and cool them
with fans.
This also shows that if the caps get hot (~20C) fast (~1 minute), they are
probably in big trouble, but we knew that already...
The science goes on...
Cheers,
Terry