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  #16  
Old 10-17-2011, 08:42 AM
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Originally Posted by chetwesley View Post
Thanks,

I will see if I can get a new regulator locally tomorrow. There is a re-builder not very far from where I live.

When I measured the voltage, I had the probes from my multimeter wedged by the bolts of the clamps, but I think I also read the same while directly touching the battery posts with the clamps connected.

I am glad I only fried what I did. I guess one has to use more caution when taking advice.

If I measure resistance from the engine to body, what would be a reading that would tell me it is suspect/poor connection? Probably anything over an ohm? Or even less?
Using a booster cable apply one clamp to the negative post and the other end to a good connection on the engine duplicates a good ground circuit temporarily. Usually the starter being able to function indicates the ground is reasonable. Perhaps not good enough though.

A better test might be a resistance check between the negative battery terminal and the alternator frame. It should be zero ohms. If not clean the connections on the ground straps and check it again. Reading the voltage between the negative terminal of the battery and the engine when cranking the starter is yet another way. Voltage drop should be minimal but I might suspect a very small amount indicated like 1/4 volt perhaps. This is because of the very heavy current flowing through the ground connections and the thickness of the ground strap. The chance of a problem is increased by the age of these cars. Not that there is a problem present in the ground circuit on your car. It is just something to check just in case.

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  #17  
Old 10-17-2011, 08:59 AM
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Originally Posted by Codifex Maximus View Post
My suggestion was to only *test* the alternator output with the battery disconnected. If the battery was bad, it would effect the voltage readings of the test.

Absolutely DO NOT drive or run the car with the battery disconnected as shorts could and probably will occur.

I have performed this same test for many years - over 30 at least with no ill effects to any car I've ever owned. However, I would not rule out the possibility that the battery might provide a load for the charging system in the event of an overvoltage condition.

Now, if the Voltage Regulator is defective which, after testing, sounds like it is, the battery would have little to do with any over voltage condition. I agree damage could occur to electrical systems due to a faulty regulator.
Untold thousands of people do this and usually get away with it. It is just sometimes they do not. On a newer car it can be a major disaster sometimes.

When you are a good samaritan and boost a car it may also cost you dearly. I am not sure of the actual why of it but it is a fact. Theoretically it should not happen but it does. Not caused by reverse polarity boosting either.

If I agreed to boost your car I would just tell you to keep the key off and let my alternator and battery bring your battery charge level up. Takes a little more time but we will both drive away. Usually both of you will as well if you crank the engine while boosting. There will just be a time that one or the other of you may not.
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  #18  
Old 10-18-2011, 01:25 AM
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Just an update - I replaced the voltage reg and at last check, it was reading about 12.9V with car off, and 13.6 ish with it running. I am still getting a slight drop in voltage with revving the engine (like .2v), but maybe this is normal?

I'll keep watching it and keep my battery charger in my trunk just in case...

Also, it was no one's idea but mine to drive with the battery disconnected. Stupid, yes, but a lot of things you only realize were stupid in hindsight.
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  #19  
Old 10-18-2011, 06:03 AM
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That's good news. It sounds like the new regulator is working.

[Old-timer Rant Mode On]
The old-timer way to monitor the charging system was by a zero-center ammeter.
- Amps out of the battery, needle deflected to the negative side, it's discharging.
- Amps into the battery, needle deflected to the positive side, it's charging.
- Zero amps in or out, needle centered, battery is charged and just floating along.
Ammeter installation costs more, and was all too often misinterpreted, so we got voltmeters. We might as well have an 'idiot light' or "Check Engine Now" warning.

[Old-timer Rant Mode Off]
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  #20  
Old 10-18-2011, 11:24 AM
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Quote:
Originally Posted by chetwesley View Post
Just an update - I replaced the voltage reg and at last check, it was reading about 12.9V with car off, and 13.6 ish with it running. I am still getting a slight drop in voltage with revving the engine (like .2v), but maybe this is normal?

I'll keep watching it and keep my battery charger in my trunk just in case...

Also, it was no one's idea but mine to drive with the battery disconnected. Stupid, yes, but a lot of things you only realize were stupid in hindsight.
Not stupid. Your approach was based on fokelore. Many will still do it and get away with it. After the first time it does not work out.They never will again. Thank yourself it was not a three year old car. So not all that bad really.
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  #21  
Old 10-18-2011, 11:32 AM
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Quote:
Originally Posted by chetwesley View Post
Just an update - I replaced the voltage reg and at last check, it was reading about 12.9V with car off, and 13.6 ish with it running. I am still getting a slight drop in voltage with revving the engine (like .2v), but maybe this is normal?

I'll keep watching it and keep my battery charger in my trunk just in case...

Also, it was no one's idea but mine to drive with the battery disconnected. Stupid, yes, but a lot of things you only realize were stupid in hindsight.
I think the small voltage drop at higher revs might be normal. The alternator is putting out a lot more current at higher revolutions so any point of resistance in the system may drop a little more voltage across it.

You may want to remove and clean all grounds and battery terminal clamps in the primary battery alternator circuit. Clean them and apply a little dielectric grease of just grease and reconnect. Refreshing old grounds is not a bad ideal anyways as I have seen it improve other things. Cheap preventative maintenance as well.
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  #22  
Old 10-27-2011, 11:32 AM
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Update to this.

Last night I drove home in the dark, lights on radio blasting.

Then after I parked it I went to start it again to test out this weird clutch problem I am having and battery was too low to turn starter fast enough.


MORE:

I charged the battery overnight.

As I was driving on the freeway today, I noticed the battery light pulsing on and off at roughly 2 pulses per second fading in and out. The faster the RPM, the brighter it pulses. At idle speed, I don't see it.

I checked voltage at idle and it is normal - about 13.5V ish - so can I assume the alternator is working weakly at high RPMs?

Does the battery light actually warn you that the alternator (not the battery) is weak?


So my problem persists. It has been a little over a week since replacing the voltage regulator, which doesn't appear to be the problem. The battery has worked for numerous starts since then, but had apparently gotten weak from the long drive with the headlights on and weak charging.
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  #23  
Old 10-27-2011, 12:27 PM
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What's the age and tension on your belt? Something is causing the alt to not keep up with it's duty under hard load.

It could be failing contacts or pulley in the alternator. Could be that one of your other pulleys is seizing up and causing drag/slap in the belt. Do you have A/C or power steering that you notice dropping functionality at speed?

If it was me (read I'm not familiar with that chasis and have another car I can drive) I'd take the belt off. See if it's worn, how the tension is. Are any of the pulleys sticking or binding? There's a place near me that can bench test alternators. Southern electronics, they do radios and speedometers and soldering, but they can bench test an alt under different loads.

Good Luck!
-Dave
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  #24  
Old 10-27-2011, 12:36 PM
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FIRST... which car are we dealing with?

it sounds like your alternator is worn out. as mentioned though, the belts could be slipping. (TD would have dual belts, 240D would have single belt on alt.)
if you have dual belts, they need to be a MATCHED set from the same box!
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  #25  
Old 10-27-2011, 01:11 PM
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240D.

The alternator was rebuilt in July. I would need to double check, but pretty sure I remember seeing that the belt was replaced with it. A mechanic did it, as I was on a trip out town with the car when it failed.
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  #26  
Old 10-27-2011, 01:30 PM
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Charge the battery overnight, then load test it. Voltage doesn't tell the whole story. If you don't have a load tester, you can measure voltage at the battery while cranking: shouldn't drop below 10 or 11.

Cables need to be clean and tight at the battery, body ground, and starter.
A weak point in the wiring is the connector which plugs into the vr at the alt. Check that the three connectors in the plug aren't loose.

Like has been said, the vr has to have a clean ground at the alt.
If all of these things are ok, and the belt is tight and not worn out, the issue might be a diode or wire in the alt itself.

I bet the battery is weak.
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  #27  
Old 10-27-2011, 01:41 PM
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I brought the battery in to be tested at the place I bought it.

They said it would be 45 min to test it, but after about 10 they said it was fine.
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  #28  
Old 10-27-2011, 02:18 PM
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Checking for adaquate belt tension is easy. Just reach in with the engine off and see if you can turn the fins of the cooling fan on most alternators. If you can at all the belt or belts are too loose or worn out.

Usually when a belt wears heavily it may contact the bottom of a pulley groove. When this happens it cannot gain side traction. This said usually loose belts like to squeel under heavy electrical load just after you start up and pull away.

Unfortunatly a lot of rebuilt alternators are also suspect. Do you still have any warranty left on yours? I would give it one more chance before calling it probably intermittent. Cleaning and treating all the relavent connections first.
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  #29  
Old 10-27-2011, 06:02 PM
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i've recently had charging problems with both my 240Ds and after having alternators pulled, tested OK, batteries pulled, charged, tested OK, i found each to be a wiring problem. on both cars, it would sometimes charge fine, sometimes battery light would flicker, sometimes be off but then not enough juice to start,etc..
so once you have your alternator and battery tested and they are OK- maybe look into the wiring--

on one car it was the positive cable going from the battery to the starter. it looked fine from the outside, i repeatedly cleaned the battery terminal,etc. but once i just took it completely out it was obvious that the wires INSIDE the battery terminal were way nasty. the were corroded and probably making partial intermittent contact.. replace that cable and everything works great ever since.

on the 240D, it was a longer process of testing every wire,and i thought at first changing the regulator had solved the issue, but finally found it to be the wireharness on the back of the alternator- same thing, it LOOKED ok on first look, and made a tight connection, and even tested OK when probing in there with a volt meter. i finally just cut it out and seeing out of the vehicle - the inside of the connectors were very corroded and worn- and again making intermittent contact, sometimes partial contact where i'd get some charge, but not full, etc.. i replace the harness with new standard wire quick connectors and it works great now, everything charges as it should. my thread on it has pics of the connectors i used. if you already have connectors as i did, it was a quick, easy, inexpensive piece of the puzzle to rule out, and for me it happened to be the culprit.

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