I'm looking for any suggestions on something I might have not thought of checking. I have a 1974 412 wagon that doesn't appear to be charging properly. First clue was that the battery would suddenly poop out so that it couldn't crank the starter. Second clue was that with motor running I was only reading around 11.85 volts at the battery posts, whereas I believe I should be getting around 14v when charging system is OK.
First I checked all the charging system wiring to ensure that it hadn't been hacked by a PO. No problem there. Then I did the alternator check where you disconnect the VR, connect 12v to the DF (green) wire, start engine and quickly check voltage at the battery. A-ha, now I'm getting 15v off the alternator. So the alternator is good and the VR is bad, right?
I just put on a brand new VR (substitute Bosch #0 192 062 007 if you're keeping score), started engine, and I'm STILL getting only 12v at the battery posts. I'm taking in the battery tomorrow to be tested in case there may be an internal problem there. Otherwise I'm out of ideas--looks like the alternator and VR are both good separately, but not together.
Anyone have a suggestion on another test procedure I should try? Assuming the new VR is not defective, could the alternator still be the culprit anyway?
Charging system malfunction
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JohnConnolly
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Charging system malfunction
the most important thing is making sure you are getting 12V to the field terminal on the alternator. Without a field current, you have no magnetic field, and no charging.
john
Aircooled.Net Inc.
john
Aircooled.Net Inc.
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Marc
- Moderator
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- Joined: Thu May 23, 2002 12:01 am
Charging system malfunction
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by JohnConnolly:
<B>the most important thing is making sure you are getting 12V to the field terminal on the alternator. Without a field current, you have no magnetic field, and no charging.
john
Aircooled.Net Inc.</B><HR></BLOCKQUOTE>
`zactly. The aluminum housing of an alternator doesn't hold much residual magnetism so they can go dead after only a few days of sitting idle. The field current is delivered through the warning light bulb's filament => no warning light = no charging.
<B>the most important thing is making sure you are getting 12V to the field terminal on the alternator. Without a field current, you have no magnetic field, and no charging.
john
Aircooled.Net Inc.</B><HR></BLOCKQUOTE>
`zactly. The aluminum housing of an alternator doesn't hold much residual magnetism so they can go dead after only a few days of sitting idle. The field current is delivered through the warning light bulb's filament => no warning light = no charging.
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Chris Hobbs
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- Joined: Sat Mar 23, 2002 12:01 am
Charging system malfunction
I decided to pull out my clock pod and check the alternator light and - lo! - it had apparently burned out in the last couple of weeks. Put in a new bulb and it remained on while car was running. Ran a multimeter to DF and D+ and found only around 1-2 volts there. So I'm guessing that the alternator was fried after all.
The DPO used to run a CB radio in the car and it looks like he rearranged the wiring so the charging system could handle the load without overstressing the alternator - not!
Anyway, later on I went to the VW show in Sevierville TN and picked up a used alternator at a good price, so I'm going to give that a try...and make darned sure the wiring is un-hacked this time.
[This message has been edited by Chris Hobbs (edited 10-12-2002).]
The DPO used to run a CB radio in the car and it looks like he rearranged the wiring so the charging system could handle the load without overstressing the alternator - not!
Anyway, later on I went to the VW show in Sevierville TN and picked up a used alternator at a good price, so I'm going to give that a try...and make darned sure the wiring is un-hacked this time.
[This message has been edited by Chris Hobbs (edited 10-12-2002).]