Alternator question and woe (W123)

pdrayton · #1 02-27-2007, 10:55 AM

I've been having alternator issues for a while now. At least I think they are alternator issues. This is what is happening/has happened. Any advice appreciated. I'm not sure if I should get a different brand alternator (Bosch) or try to find an electrical fault.

Symptoms:

Stock alternator bearings locked up, so being in a tight spot I through in a Worldwide 55A reman alt. from Advance Auto.

After a few months this reman alternator crapped out - wouldn't charge the battery - voltage would rise a little to about 12.5 at idle, and then drop about .5v as the revs increased.

Thinking it was a bum alternator, the store replaced it and the replacement is doing the same thing now after a few months of working fine. The voltage will sometimes suddenly go to 13.7v while driving and pretty much peg there until I restart the car at which point it may or may not go back up to 13.7. Normally it just does what I described above for the first reman alternator- 12.5v dropping to 12v or so at revs.

I have rewired the connections to the alternator. I have checked the grounding of the alternator - good.

Some other things which may or may not be relevant:

Voltage with car idling does not jump up when I systematically remove 1 fuse at a time. To me this means there is no short through a fused circuit that could be causing undue current drain.

A few weeks ago the radio would switch off whenever I opened the glove box! However, this problem has dissappeared by itself.

So I am not certain if there is a problem with my electrics, or these remans are poor quality.

I have been reading up on the AL69X 80Amp replacement for my car. It is a veg conversion (only draws an extra 7A at the moment - disconnected for the past few days to test the alternator without any extra load) and I want to put some more current drawing stuff on it . I'm just not sure how to rewire it - the 2 charging wires from the alternator go where? They seem to go through the firewall on the passenger side.

OH yes, another thing - when I turn the car off, the voltage at the cigarette lighter (where I monitor voltage) drops immediately to about 0.5v and then slowly drops to 0 over a minute or 2. Is this normal?

Thanks.

Magoo · #2 02-27-2007, 11:16 AM

Sounds like a ground issue to me. Did you check the battery ground cable at both ends? There are a number of equipment grounds inside the car as well.

pdrayton · #3 02-27-2007, 11:21 AM

Magoo, how do I check the battery ground at both ends? I don't understand that too well.

I did have a ground problem with the instrument console, but I fixed that. At least I thought so...

Knightrider966 · #4 02-27-2007, 11:23 AM

Try grounding the alternator to the negative ground terminal on your battery and see what happens. Also Ground your battery to your engine and your car body with new grounds and see if there is any improvement.

Knightrider966 · #5 02-27-2007, 11:27 AM

Quote:

Originally Posted by pdrayton

Magoo, how do I check the battery ground at both ends? I don't understand that too well.

I did have a ground problem with the instrument console, but I fixed that. At least I thought so...

The battery ground will be the negative terminal on the battery and the cable end where it is attached to the body and/or engine of the vehicle. Make sure you have a really good connection at both ends. Wire brush ALL connections and use some battery terminal protector on them. Grounding your alternator will boost your charging voltage if there is a ground fault in your car.

#6 02-27-2007, 12:25 PM

You should do a voltage drop test between the alternator positive and battery positive. This will prove or disprove the alternator connection to the battery. You can also even more easily do a voltage drop test between the alternator case and the ground terminal of the battery. Both of these should drop no more than a few tenths of a volt. If they do, find and repair the connection by doing the voltage drop test in smaller sections until you find the culprit.

Good luck,

pdrayton · #7 02-27-2007, 02:41 PM

Thanks chaps. I'll give it a go.

Larry - that's great advice - the kind you think "Oh that's a great idea! why didn't I think of that!"

I'll let y'all know what happens.

pdrayton · #8 02-27-2007, 05:36 PM

I did all that was suggested (at least I think so). Cleaned all posts and connectors on battery with wire brush. Same for power post that goes from alt. to Starter.

Also tested voltage drop - it was 0.02v across the board from the 2 alt terms to the post on the starter. I did this with a digital VOM with the ignition off. Also tested Ohms from battery negative to body - 0.02 Ohms or something small like that.

The alternator is pretty much behaving like it did before - voltage is below 13.7 volts with no load, and it drops 0.5v when the engine goes above idle. The voltage is a little higher - around 13.2v - I think becuase the battery is charging slowly (it's day so I'm not using my lights)

I/m thinking I should take the alternator back to the FLAPS and get a AL69X 80Amp bosch. I bet it will work fine. Unless I am missing something here - I don't see what a big current draw there could be. There was only .85amps being drawn with the ignition in the first position. I could try it in the second position, with the engine idling, but I don't think my VOM likes to read over 10A. Cheapie you know.

Any suggestions? Carry on looking for a bad ground or short. Or get a new alternator?

kerry · #9 02-27-2007, 05:52 PM

What about the voltage regulator? Did you change that when you installed the new alternator?

pdrayton · #10 02-27-2007, 05:56 PM

The voltage regulator comes with the alternator. I can't see that it was buggered from the beginning. Remember, this alternator has worked fine for a couple of months. I had an aftermarket extra 7amps drain on it. could it be it is a cheap rebuild and can't handle a little extra draw. It's worn out.

SD Blue · #11 02-27-2007, 08:04 PM

On mine, the large engine-chassis ground strap, by the starter, had worked loose.

Also, to check the alternator, check voltage DC and AC. Low DC volts point to a regulator and High AC volts point to the rectifier diodes in the alternator.

pdrayton · #12 02-27-2007, 08:52 PM

Check AC volts across B+ and ground? I never thought of that. Thanks.

The alt body shows ground at the negative battery terminal, i.e. it is grounded.

SD Blue · #13 02-28-2007, 09:05 AM

The alt. body may show ground, as mine did, and you might still have a ground strap problem. The scenario with mine was that the exhaust bracket where someone had attached the ground strap was loose. One time it would start and the next time not, flickering guages, intermittent voltage readings and these would happen only about every 2-3 days.

Also mentioned in a previous post, by someone who recently visited an alternator specialty shop, that they attributed many alternator diode failures to poor grounding.

pdrayton · #14 02-28-2007, 10:41 AM

AC volts at idle across the battery reads 28.9. With ignition off it reads 27.5v. Is that how it is supposed to be? Or am I supposed to disconnect the alternator? I heard that can damage the regulator

Jeremy5848 · #15 02-28-2007, 10:45 AM

Quote:

Originally Posted by pdrayton

AC volts at idle across the battery reads 28.9. With ignition off it reads 27.5v. Is that how it is supposed to be? Or am I supposed to disconnect the alternator? I heard that can damage the regulator

If you really have 28.9 Volts AC at the battery during engine idle, you have a failed regulator. That will damage the battery.

If you still have 27.5 Volts AC at the battery with the engine off then something is wrong with your measurement. Might you mean millivolts AC? Please check for us.

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