From: chance wolf (chance_wolf@shaw.ca)
Date: Sun Apr 03 2005 - 20:24:31 PDT
----- Original Message -----
From: "Mil-Veh Co." <milveh@sbcglobal.net>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Sunday, April 03, 2005 7:47 PM
Subject: Re: [MV] One more M151 Question
> What's the job of the capacitor in the M151, is that
> to filter A/C and only allow D/C current to flow?
>
> T-I-A
>
> Jack
It's part of the radio-filter system designed to keep "engine noise" to a
bare minimum when you're using radio equipment. If you've ever listened to
AM radio on an unshielded vehicle, you get all sorts of spark-plug pops and
alternator whine and a ton of other crap superimposed on the audio, so they
incorporated filters and grounding straps and shielded plug wires to help
reduce it all to a dull roar.
A capacitor passes alternating current but not direct current, and is rigged
in the 151 to pass that alternating current (all the line noise generated by
the points etc.) straight to ground, without interfering with the 24VDC
supply to your points and coil. When the capacitors dry out and go bad they
can sometimes act like big resistors and start shorting out a fair portion
of your 24VDC to ground right along with the AC component, effectively
delivering a substandard voltage to your points/coil (same with a
failing/failed condenser on the point-plate.)
What you can do is bypass the filter entirely and run a 24VDC wire straight
to your battery to the coil (i.e., remove the filter assy and run the wire
straight up through the resulting hole) and take it for a test-drive. If
your problems are solved - voila - you've nailed it. Most problems I've had
with the thing are right where the wire solders on to the far end of the
filter assy. I've had some which were poorly soldered or green'n'fuzzy with
corrosion or holding on by two strands of steel wire - all of which caused
major ignition problems.
Have fun.
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