[Vwdiesel] Battery Charging Question

[Nate Wall]

My thoughts:

Sounds like you have a low amperage voltage drain.

DO NOT RUN THE VEHICLE W/ the battery disconnected.  It may ruin the alternator
diodes. Start it and let it idle w/ the alternator light on (don't increase the idle
to excite the rotor windings to start it charging) and turn the interior light on.
Watch the light very closely (at night is best). Rev the engine to start the
alternator charging.  If the interior light gets noticeably brighter, you're charging
fine. Try it again w/ the headlights and blower fan turned on after starting, but
before blipping the throttle to activate the alternator.  Interior light still
brightens and stays bright at engine idle after the throttle is blipped, its charging
w/ a load and is o.k.

I had the same thing happen you described. Tried to return the new battery, but they
refused it after they load tested it. In my case, the trunk light was staying on
because the plastic strip w/ the light switch dipmle was missing (A-2 Jetta) and I did
not have the switch pushed in into its detent. (Also, the interior light delay circuit
might have had a short in it leaking current, this was hard to tell, since it was on
the same circuit (capacitor possibly) as the trunk light. I clipped the lead in the
interior light bulb holder that enabled the delay. This also prevented me from leaving
the light on overnight, thinking it was on because of the delay and walking away, and
it now goes out when the door is closed.). Indications were the trunk light bulb was
blackened badly from being on all the time, and a 50 or so MA draw w/ an amp meter. It
was enough to produce a tiny visible spark on the neg battery post when touching the
cable to the post. Again, in the dark will show up better.

"Duncan L. Forbes" wrote:

> Hey gang,
>
> I have a question that is along the same lines as the thread Jon started
> last week with his battery issues with his van. I just caught up on that
> thread as I was away from my computer for the week as my daughter was ill
> and in the hospital.
>
> I have an 18 month old battery (purchased 02/01). This past week it failed
> to have enough juice 3 times to turn over the car. After each time I jumped
> the car and ran it for awhile to recharge the battery. All three times the
> next time I went to use the car, dead battery again. The battery was still
> under full warranty so I replaced it yesterday. Car started fine after new
> battery yesterday and again this morning. However, the shop that sold me the
> battery tells me that my old battery is charging fine and that they want the
> new one back. They say I probably have a charging system problem.
>
> So I figure I have possibly one of four problems,
>         1. bad battery (the shop simply hooked up a charger to it,
>          they did not run any real tests on it, heck I could have done that)
>         2. electrical fault draining battery (this would not shock me as I have
>            old wires whose casings are flaking off and could be grounding out)
>         3. charging system problem (alternator is 18 years old with 200K miles on
> it)
>         4. battery was drained so low that it required more recharging time than I
> gave it
>            (it was an expensive 720 Amp Interstate battery and I may have
> underestimated
>             what it needed to be able to recharge)
>
> Does this sound right?
>
> If so is there a way to test these things without a multimeter? I broke mine
> by accident  and the budget is tight for replacing it right now.
>
> I was thinking that with the engine running I could disconnect the battery
> leads and see if I still had power to the system. Would this work? I know
> that the diesel doesn't need a battery to operate (besides cranking the
> starter and heating the glow plugs). Would this accurately show me that the
> alternator was producing charge if say my headlights were functional with
> the battery disconnected?
>
> I know I really need to replace my multimeter and test the system properly,
> but until the end of month it won't be happening. So if anyone has any quick
> and dirty ideas to lead me to a correct diagnosis of the problem I would
> appreciate it.
>
> Duncan
>
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