Military-Vehicles: Re: [MV] Batteries not charging right in M38A1

Re: [MV] Batteries not charging right in M38A1

Jim Davidson (datadoc@fia.net)
Wed, 27 Aug 1997 18:07:52 -0700

Stu:
Step one: Isolate the problem. Seems to me, one of three things:

- Bad battery
- Hidden discharge
- bad charging system

Don't know precisely what's wrong, but I can give you a partial
checklist of things to look for:

(These are not any any particular order...)

1. Get a hydrometer and check the specific gravity of the electrolyte in
each cell of the batteries. They should all be about the same, if there
is one cell way off, you have a bad battery. Even new diehards sometimes
fail. (Had it happen to me once, but only once! battery went from
seemingly fine to completely dead-flat in a 1 minute drive. damndest
thing!)

2. Check for a short. Is there any current drawn when the
engine/ignition is off? An easy test: Get a small 24v (even 12v'll work,
just not for long) lamp, and put it between the battery terminal and the
cable you just diconnected. If it lights up, you have a short. Voltmeter
will work too.

3. You didn't say how you checked the output of the generator. Was that
with the battery connected? Get a clamp-on ammeter and check the output
*current* of the generator. Better yet, check the current and the
voltage at the same time. What happens when the headlights are turned
on? The current should jump up, and the voltage should stay about the
same. Current should be somewhat dependent on engine RPM and accessories
that are on, voltage should go up to 27.6v (maybe slightly above) and
stay there no matter how fast you go. Have you had the generator apart
(or is it a new unit) and not polarized it? That's an often overlooked
step on VW's with generators, don't know if it's needed here.

Hope this helps. Keep us posted.

JIM :}
1967 M54A1

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