Caution - InterAv "Spike Guard" Capacitor

On Saturday, June 28, 2003 11:52:13 PM UTC-5, MikeremlaP wrote:
If you have a "Spike Guard" filter capacitor on your alternator output, you may
wish to inspect it immediately and perhaps remove it.

I was noodling around the engine the other day, shaking baffles, when I heard a
"rattle." Investigating further, I discovered the noise was coming from our
"Big Fat Capacitor" (a Mallory brand 6000 mFd Electrolytic), mounted on the
front baffle next to the alternator. (Lyc O-320.) Ours was offered by InterAv
(Alternator conversion kit maker) and purchased through Chief. It's basically
a big filter capacitor that hangs on the output of the alternator to catch
noise and voltage transients.

My guess is the electrolyte has dried up, leaving the guts of the capacitor to
rattle inside the can. It measures zero capacitance. Fortunately, it failed
in an open, but could have just as easily failed in a short - and a short
directly across the alternator output could be catastrophic, especially while
flying. (Hopefully a diode would open in the alternator, but who knows?)

I've yet to pull the logs, but I think this has been in service for about 5
years now (roughly 1000 hours). The capacitor was mounted vertically, with the
lugs down. It was mounted on the "cool" side of the front baffle, but gets
baked during shutdown by cylinder #1.

I suspect an electrolytic capacitor is not a good choice for hot engine
compartments, but it's hard to get 6000 mFd any other way. If they continue to
be sold, perhaps there should be a life limit (time-wise) on them? As a
minimum, an in-line fuse should be added to the circuit, so that the fuse will
blow if the capacitor shorts.

In any event, the potential for disaster seems high if you have one of these,
since most people don't mount fuses in line with filter caps, and as most
people don't shake capacitors as part of a routine inspection, I thought I'd
better alert you all.

Hope this helps,

Mike Palmer
Excellence in Ergonomics

Maybe, just maybe it was stupid to assume how the part was utilized on an STC'd system. The wiring schematic is online. The part is sold by Inter Av to be utilized on their system. It has been utilized since about 1965 on literally thousands of installs, with many application working trouble free for 40+ years. Yet here we have an " expert" blaming Inter Av for using the part for an application it was never designed for, on a system it was never designed for, without any documentation or wiring schematics. Only a vivid imagination. Go ahead blame Inter Av for your bogus engineering claims. I have the system on 3 planes and it works well for me.