[Vwdiesel] 89 Jetta D phantom voltage update

[James Hansen]

There is approximately a volt drop across the alternator diodes when you
have a hooped one.
Your alternator is not working correctly.
I suggest it has a couple things wrong, like a bum diode, and brushes are
not brushing.
To test for diode failure, remove the wire from battery to alternator. (yeah
I was the guy that mentioned it)
Put a current meter between the wire you removed, and the battery.  Never
mind voltage, look for current draw.
If there is a bad diode, it will pull an amp or two with the engine off.

Secondly, to hit 12.7 on starting, and slowly climb to a higher voltage over
time is not how it works.  The alt should hit 13.8 to 14 right off, no
climbing, if the battery is low, you can hear them charge with a slight
whirr and it will warm up fairly quickly.  Your description indicates it is
probably just charging enough to keep the light off, which is peanuts.
Usually on a bosch, it's the brushes that wear out, and just lets the
electrons dribble through.

If the car has a/c it has a 90 amp alternator which should charge like a hot
damn, audibly whirr and drag the idle down a couple hundred rpm when
charging.  If it isn't doing that, it just isn't charging.
-james




-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com] On
Behalf Of Doyt W. Echelberger
Sent: May-28-11 5:56 PM
To: vwdiesel at audifans.com
Subject: [Vwdiesel] 89 Jetta D phantom voltage update

In early May I asked for help understanding an apparent  battery drain, and 
several of you replied with advice. Here is an update:

I made sure I didn't park it with the key in the ignition, Loren.

It is a base model and doesn't even have a trunk light, Sandy.

Like Scott Kair, I have no idea about how to boost the charge rate, which 
seems functionally inadequate because at times the battery ends up unable 
to crank over the engine.

Someone suggested disconnecting the blue wire from the alternator, but that 
didn't seem to change anything so I reconnected it. I really didn't 
understand how that was going to make the problem go away, but am
interested.

OK, here are some facts: With the engine idling, the alternator starts 
charging with a voltage of 12.7 and this slowly climbs to 13.7 over about 
20 minutes with the car just sitting there idling. That is a test 
situation, and I usually just get in the car and drive it. It doesn't idle 
much except during the test.

With the engine off, the key out, and all other wires (2) disconnected from 
the positive battery terminal, I got an 11.85 constant voltage by inserting 
a volt meter between the red wire that serves the headlights, brake lights, 
cabin lights and radio.

I then sequentially pulled and replaced every fuse and relay in the fuse 
panel, with no flicker of the 11.85 voltage.

When I applied the brakes, the volt meter jumped to 12.80 (max battery 
voltage). Got the same voltage jump when I switch on the headlights or the 
radio.

I then replaced the volt meter with a 10 watt DC bulb (out of the dome 
light) and it didn't glow. I assumed the volt meter would have still read 
11.85 volts but I didn't have enough hands and alligator clips to verify it.

All I can think of that would behave that way (voltage but no current) is a 
circuit that is charging a condenser.

-----------------][-----------------  and then I don't know why it isn't 
full battery voltage. 11.85 is about a volt less than full battery voltage.

Also, it is possible that all the above information has nothing to do with 
the battery ending up not charged.

OK, I got practical and used a charger and brought the battery to full 
charge, and then drove the car mostly on short trips around town for about 
10 days. It started fine and ran the lights and radio and wipers a few 
times, and then I drove the car for two hours on a long trip,  and near the 
end of the journey the red dash battery warning light came on, and when I 
tried to start it after a layover, it didn't turn over the engine. Had to 
jump it....then it ran OK. (I now carry a jumper battery in the 
trunk.)  So, back on the big wheeled fleet charger and ready for another
cycle.

Also, a few hours ago I wired a Sears 1.5 amp  battery maintenance charger 
(from another Jetta now deceased) into the 89's battery circuit and plugged 
it into the wall. The green "charging" light came on and the "fully 
charged" light isn't on. So, that's where things are at the moment.

Maybe this story will strike a familiar note with someone and will point 
out the magic button that makes it all work reliably for at least a few 
months at a time. Until then, the phantom electrical consumer (?) will have 
to deal with the Sears charger, and perhaps the emergency jump start 
battery in the trunk. Diesel on.....   Doyt





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