I hope you've checked the voltage output of the alternator if you can
keep her working long enough to check, or disable the OV crowbar w/o
anything unnecessary ($$) switched on. A voltage "spike" won't trip a
fuse/breaker; sustained average current does. The difference in trip
behavior between a 5A P&B W-58 breaker and one type of 5A Littlefuse
Slo-Blo is: 25A for 1 second vs. 25A for .8 second. One difference in
the devices is that a single or few pulses of very high current and
much shorter duration favors the breaker, but doubt the Rotax PM
alternator if connected to a battery can do that much, nor should a
good regulator do it at all.
If one of the big semiconductors in the regulator has failed, it
should show up as higher DC voltage, not necessarily above the trip
voltage for the crowbar. It may even show a meaningful AC voltage,
like 1 or 2V RMS as a guess. The peak amplitude of resulting voltage
pulses at 50-100/second could be what initiated the failure sequence
on the electrolytic cap if rated only 25V or degraded to less, and
translated to "current squared over time" is popping the fuse.
If a breaker did fix the problem, I'd then want to know the voltage on
the bus and best yet, what it looked like on an oscilloscope B4
switching on my $2,800 GPS!
Good luck,
Fred F.
William Mills wrote:
>
> All,
>
> Thanks to Jerry and Fred for the comments. Just to up-date my last message,
I have discovered that even the slow blow fuse is too fast, as it blew yesterday
on start-up. Of course, it could have possibly blown on the previous engine
shut-down. I will now replace the fuse holder with a circuit breaker and see
if it pops and if so how often. It would be interesting to hear if anyone else
has had a problem with introducing the Crowbar mod, or if anyone else has
successfully used a fuse.
>
> Regards,
>
> William
|