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  #1  
Old 01-14-2010, 12:40 PM
Chev
 
Join Date: Jul 2000
Location: Florida
Posts: 12
faulty alternator kill battery?

Re: '78 300d, 150Kmi DD

I recently had to replace my alternator (again) after 2 years on the previous AZone reman. (I know, I know... Bosch OEM is the preferred replacement), but since I originally replaced the one that's been in there since I bought the car in 1991, with an AZ part, ten years ago and it's warrantied for life, I couldn't help myself! If only they were self-installing...
Anyway, I'm already on that bandwagon.

After the previous alt failed ( 2 years ago) and was replaced, I also replaced the battery about a year ago.

Now with this third alternator-which charged at around 13.7-14.1 volts- last month the car again failed to start. I tried to charge the battery with my 10 amp charger. After an overnight charge, there still wasn't enough current to start the vehicle. I also noticed at that point that there was no apparent hydrogen outgassing.
I took it back to Interstate Battery, and they kept it for the long Holiday weekend-providing me with a loaner. They called, and told me that the battery had taken a charge and was ok, and we swapped the loaner.
Last night, I again had a nearly dead battery.

My question is this: if, as I suspect, one or more of the diodes were bad on the old (previous) alternator, can the resulting un-rectified electricity damage an otherwise good battery? I think it may be discharging internally.

I charged it overnight and I'm now showing voltages around 13.5-14 volts while engine is running, and do not have a charge warning light on the dash as I did when the previous alternators failed.

I've also checked to see if there is any major current drain with the key off, and, other than during the (wonderful Chrysler) A/C servo parking itself, there does not seem to be any major current flow. There is a small current drain, but I think it's just the clock. I'll find the appropriate fuse and see if I can eliminate that as a possible cause, next.

As a side question, are OEM diode packs still available for these, and where? I kept my first defective (original??) alternator rather than turning it in for core, in case OEM parts were available, and I wasn't satisfied with the AZ rebuilds. I used to diagnose and repair my Dodge Ram van alternators years ago, and parts were readily available back then, and it was really easy.

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  #2  
Old 01-14-2010, 12:53 PM
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Join Date: Sep 2006
Posts: 298
Quote:
Originally Posted by chev View Post
Re: '78 300d, 150Kmi DD

I recently had to replace my alternator (again) after 2 years on the previous AZone reman. (I know, I know... Bosch OEM is the preferred replacement), but since I originally replaced the one that's been in there since I bought the car in 1991, with an AZ part, ten years ago and it's warrantied for life, I couldn't help myself! If only they were self-installing...
Anyway, I'm already on that bandwagon.

After the previous alt failed ( 2 years ago) and was replaced, I also replaced the battery about a year ago.

Now with this third alternator-which charged at around 13.7-14.1 volts- last month the car again failed to start. I tried to charge the battery with my 10 amp charger. After an overnight charge, there still wasn't enough current to start the vehicle. I also noticed at that point that there was no apparent hydrogen outgassing.
I took it back to Interstate Battery, and they kept it for the long Holiday weekend-providing me with a loaner. They called, and told me that the battery had taken a charge and was ok, and we swapped the loaner.
Last night, I again had a nearly dead battery.

My question is this: if, as I suspect, one or more of the diodes were bad on the old (previous) alternator, can the resulting un-rectified electricity damage an otherwise good battery? I think it may be discharging internally.

I charged it overnight and I'm now showing voltages around 13.5-14 volts while engine is running, and do not have a charge warning light on the dash as I did when the previous alternators failed.

I've also checked to see if there is any major current drain with the key off, and, other than during the (wonderful Chrysler) A/C servo parking itself, there does not seem to be any major current flow. There is a small current drain, but I think it's just the clock. I'll find the appropriate fuse and see if I can eliminate that as a possible cause, next.

As a side question, are OEM diode packs still available for these, and where? I kept my first defective (original??) alternator rather than turning it in for core, in case OEM parts were available, and I wasn't satisfied with the AZ rebuilds. I used to diagnose and repair my Dodge Ram van alternators years ago, and parts were readily available back then, and it was really easy.
Is the voltage regulator part of that alternator?

Unrelated scenario, but this Summer I spent many hours diagnosing similar battery kills, starter solenoid destruction and high voltage. What I had assumed to be a faulty voltage regulator and rectifier was not the case at all. It was a tad bit of corrosion on the negative battery cable that was causing enough resistance to push the voltage up to a dangerous level. Snip and crimp and problem solved.
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  #3  
Old 01-14-2010, 01:07 PM
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The internal diodes are easy enough to check. While the engine is running, place a VOM in Volts AC across the battery terminals. It should be real low, less than 100mVAC. If you are getting 1VAC or higher then the diodes are suspect and will usually cause battery damage and the voltage regulator as well. Usually, you see a high DC charge voltage as well, when the rectifier diodes start to go bad.

As far as aftermarket diode packs, you might check with automotive electrical repair shops. They might sell you the diode packs. If you find one of these shops, it's just as easy to have them do the rebuild and I would have more confidence in their work than someone AZ uses. (After all, AZ is just looking for the lowest bidder with a reasonable amount of returns.)

From what you describe, I am still a little suspicious of the battery. It may have taken a charge but how low was it originally and how long will it hold that charge.
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84 300SD 350K+ miles ( Blue Belle )
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  #4  
Old 01-14-2010, 01:11 PM
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It seems to me that the battery is either not holding a charge or is being drained down. If you are getting a consistent charge of 13.5+V the it seems the charging system is not the issue.

I have had Autozone test my battery and tell me it was good when I fully charged it myself in the house, and then let it sit for 3 days and it couldn't hold a charge. Recharged it and took it to AZ. They told me it was good. I asked them to replace it under warranty anyways and they did. Problem was solved.

I also had a glow plug relay act up and my assumption is it took out my alternator and led to the above battery going bad through constant drainings.
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1998 E430
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  #5  
Old 01-14-2010, 01:17 PM
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Location: Tucson, AZ
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Quote:
Originally Posted by tr1cky View Post
Is the voltage regulator part of that alternator?

Unrelated scenario, but this Summer I spent many hours diagnosing similar battery kills, starter solenoid destruction and high voltage. What I had assumed to be a faulty voltage regulator and rectifier was not the case at all. It was a tad bit of corrosion on the negative battery cable that was causing enough resistance to push the voltage up to a dangerous level. Snip and crimp and problem solved.
+1 from me.

Battery cables and termination points are 95% of all charging/cranking problems. I've had a thousand people tell me, "It was the battery after all" when what they did was clean the cable ends when they installed the new battery and resolve the original problem.

A corroded ground will allow voltage to pass but will fail when amps are trying to be passed. I've always doubled the grounds on my diesels and used 1/0 cable for the starter feed. Ground one cable to the engine and run another from that ground spot to the body. Use a MINIMUM of 2 #8 gauge wires for the engine-body ground connection and I'd suggest using the same gauge battery cable as for the engine ground.

Any REAL auto parts place should either have the Bosch diode pack in stock or be able to order them (NAPA, Carquest, etc.). If nothing else, try to locate an automotive electrical shop who should be able to steer you in the right direction for availability.
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  #6  
Old 01-14-2010, 02:09 PM
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Quote:
Originally Posted by chev View Post
Re: '78 300d, 150Kmi DD

I recently had to replace my alternator (again) after 2 years on the previous AZone reman. (I know, I know... Bosch OEM is the preferred replacement), but since I originally replaced the one that's been in there since I bought the car in 1991, with an AZ part, ten years ago and it's warrantied for life, I couldn't help myself! If only they were self-installing...
Anyway, I'm already on that bandwagon.

After the previous alt failed ( 2 years ago) and was replaced, I also replaced the battery about a year ago.

Now with this third alternator-which charged at around 13.7-14.1 volts- last month the car again failed to start. I tried to charge the battery with my 10 amp charger. After an overnight charge, there still wasn't enough current to start the vehicle. I also noticed at that point that there was no apparent hydrogen outgassing.
I took it back to Interstate Battery, and they kept it for the long Holiday weekend-providing me with a loaner. They called, and told me that the battery had taken a charge and was ok, and we swapped the loaner.
Last night, I again had a nearly dead battery.

My question is this: if, as I suspect, one or more of the diodes were bad on the old (previous) alternator, can the resulting un-rectified electricity damage an otherwise good battery? I think it may be discharging internally.

I charged it overnight and I'm now showing voltages around 13.5-14 volts while engine is running, and do not have a charge warning light on the dash as I did when the previous alternators failed.

I've also checked to see if there is any major current drain with the key off, and, other than during the (wonderful Chrysler) A/C servo parking itself, there does not seem to be any major current flow. There is a small current drain, but I think it's just the clock. I'll find the appropriate fuse and see if I can eliminate that as a possible cause, next.

As a side question, are OEM diode packs still available for these, and where? I kept my first defective (original??) alternator rather than turning it in for core, in case OEM parts were available, and I wasn't satisfied with the AZ rebuilds. I used to diagnose and repair my Dodge Ram van alternators years ago, and parts were readily available back then, and it was really easy.
Just had almost the same experience you did. I have a Scanguage connected to my car, and about a week ago, the car started to show some erratic behavior. Instruments fluctuating, the red and green lights on my mirror would blink on and off when I first started the car. Well, the other night while driving back home, I noticed the voltage reading on my Scanguage take a nosedive, fluctuating between 12 and 10 volts. Got home o.k., and figured I would check it out the following morning. Next day, the battery was completely dead. Disconnected it, put it on a charger, and 24 hours later it was up to full charge. Reconnected the battery, and within 10 hours it was down again. One poster had mentioned the fact that the alternator diodes could fail, and cause a current drain via the casing. With the battery again connected, I disconnected the alternator battery connection, without the car running, with the key in the off position, and then intermittently touched the battery cable to the alternator post, creating small sparks as there was current passing through the alternator battery connection. Not only wasn't the alternator putting out its charge, but it was actually sapping the battery while the car was in the garage. Have a new one on order, and waiting for delivery of same. Good luck with your issue.....
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  #7  
Old 01-14-2010, 02:30 PM
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Just because there is 14V at the battery's terminals does not mean it is charging. Typically it is, but not necessarily.

You need to disconnect the battery cable and see if it will hold at least 12V overnight. Then reconnect the cable and see if has enough juice to crank the engine. Deep discharge can cause it to fail one of both these tests.
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  #8  
Old 01-14-2010, 03:27 PM
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Quote:
Originally Posted by patbob View Post
Just because there is 14V at the battery's terminals does not mean it is charging. Typically it is, but not necessarily.
Do you mean that the alternator could still be at fault? Or do you mean that the battery itself could still not be charging?

I would think the if I read 14Vs at the battery the alternator end of the system is fine.
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1998 E430
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  #9  
Old 01-14-2010, 04:13 PM
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Quote:
Originally Posted by Graplr View Post
Do you mean that the alternator could still be at fault? Or do you mean that the battery itself could still not be charging?
After a deep discharge cycle, the battery can have a high enough internal resistance that the alt will be supplying 14V at the battery's terminals (checked at fast idle), but the battery won't be taking on much, if any, charge. When you stop the charge cycle, and disconnect the battery cables, it will hold a terminal voltage of >= 12V for a while (if it doesn't, its really dead or probably wasn't fully charged), but will eventually drop below 12V. Typically, this happens in minutes to hours, but overnight is an easier time scale and a more definitive test. With any possible loads on the battery disconnected from it, it should be able to hold 12V terminal voltage before being reconnected to the system (and possible load). You can do this part of the test using a battery charger -- charge it long enough to be sure it is charged, then disconnect everything and see if it maintains >=12V overnight.

If it does, then you reconnect it to the car and see if it has enough charge, and low enoguh internal resistance, to actually start the engine. A fully charged battery that hasn't been run down by any loads overnight should be able to do that (duh). This part is best done in any season other than winter -- really cold temperatures can make the engine harder to turn over. Doing this in the really cold temperatures of winter is good test too, and if your battery can't do it, then you need a new one. However, the battery might be perfectly good, just too small to start the car under those conditions.

This test doesn't say much about the charging system itself, only that it isn't doing some things that will damage a battery.

Note: voltage reading are not absolute. +/- a few tenths of a volt are probably insigificant.
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  #10  
Old 01-14-2010, 04:51 PM
Chev
 
Join Date: Jul 2000
Location: Florida
Posts: 12
Gosh, I love this forum! Great replies and fast! Thanks, guys.

I've checked all connections for corrosion, looseness, etc. and all's ok.
It has been pretty cold here in North Florida these last couple of weeks, and that's probably exacerbating the issue. Since first post, I've checked the specific gravity, and all cells are > 3.0 except one which is a little more than 2.75.
I'll try Patbob's suggestion to disconnect the leads overnight and see if there is any drop in voltage in the morning.

I feel confident that I'm getting good charging. I think there is either something within the battery itself that is discharging it or that there is some "ignition off" drain. I'll have to replace the "meter protection" fuse in my volt ohm meter. I left it on 200ma scale to see if there was a drain on the battery with the key out, but the driver's door blew open and the dome light came on, which draws 650 ma and promptly blew the meter fuse... on the unprotected 10 amp scale, I see ~ .01 amp drain, which I think is the clock. I'll remove the car's fuse for that group of accessories and re-test when I can use the 200ma scale again.
I do know that the a/c servo will drain a good battery within a day or so if the motor cannot completely park the servo (those of you who don't have that device don't know how lucky you are). I've been through that situation before and now have one of George Murphy's aluminum body servo, and I can hear the servo motor park when the ignition is turned off.
Just wondered if anyone had seen a battery in a charging system which had (past tense) bad diodes. Thankfully AZ cheerfully replaced the alternator so I can't verify the diodes as the root cause of that alt failure. I want to resurrect my OLD, old alt when I find diodes for it, then I'll have a spare. Interestingly, the AZ rebuild was remanned by Remy of Delco-Remy fame (I believe) so I had some confidence in them.
I think ultimately the solution will be to convince the Interstate Battery people to pro-rate me a new battery, and I'm looking for documentation to support my theory. From their perspective, they charged it and "it works."

This is becoming a matter of pride, as my wife (2008 Honda Odyssey driver) says I'm delusional when I tell her what great cars these are... ok, it's 33 years old, and hasn't much paint left and has some rust, but I doubt her Honda will have much left after that much time. I sincerely believe these are the best automobiles ever made. Too bad I had to call her for a jump start last night.

Tnx again
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  #11  
Old 01-14-2010, 07:33 PM
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Quote:
Originally Posted by chev View Post
I'll have to replace the "meter protection" fuse in my volt ohm meter. I left it on 200ma scale to see if there was a drain on the battery with the key out, but the driver's door blew open and the dome light came on, which draws 650 ma and promptly blew the meter fuse.
Given the capacity of these batteries, a ~100ma draw shouldn't be running it down, not even overnight. That's only 1-2 amp hours, and car batteries typically have way more (can't remember exact.. 60? 80?).
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  #12  
Old 01-15-2010, 07:58 PM
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I worked for a battery company for a long time....

Here are some of the things I remember.

A FULLY charged battery will be about 12.72 volts, after standing overnight.
(that was the minimum voltage to ship a 'new' battery.

a little easier scale to remember is... (for used batteries)
12.6 = 100%
12.4 = 75%
12.2 = 50%
12.0 = it's 25%... but I"m going to call that, not charged, or 'bad'.

So.. charge your battery up.. let it sit overnight, then put a voltmeter on it.
Then use the scale above.

A battery will self discharge. The warmer, the faster.
At 80 (or so) I think it's about 1% a day.
so.... sitting for 30 days.. should never be a problem.
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  #13  
Old 01-15-2010, 08:13 PM
compress ignite's Avatar
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WAI (Wetherill Associates)

Uber electrics manufacturer/distributor.

You can contact WAIglobal as follows:
WAIglobal
Toll Free: 1-800-877-3340
Fax: 1-800-948-6121
Business Hours:
Monday - Friday, 8:15am - 5pm
E-mail: Info@waiglobal.co

I believe they are wholesale, "To the Trade", only.

But this is what they show for a Rectifier for a 1978 300D:
http://search.waiglobal.com/partsearch/partnum.aspx?part=IBR303-1

'Negative Diode:
http://search.waiglobal.com/partsearch/partnum.aspx?part=32-1040901

'Positive Diode:
http://search.waiglobal.com/partsearch/partnum.aspx?part=32-1040900

AND this lists ALL the parts for your Alternator that they carry:
http://search.waiglobal.com/vehiclelookup/bomsearch.aspx?search=bom&part=0-120-489-918
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Last edited by compress ignite; 01-15-2010 at 10:53 PM.
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  #14  
Old 01-15-2010, 08:30 PM
compress ignite's Avatar
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Rectifier MAY still be available from Mercedes ($$$$ ?)

'Playing around with the RU site and the EPC
the Mercedes part# "Might" be 000 154 82 16

http://www.detali.ru/cat/oem_mb0.asp?TP=1

http://epc.startekinfo.com/epc/subscribe.jsp

Ask Phil (@ top of page "But Parts"tab) if he can access the WAI or MB part.

(I can't remember the model designation for the '78 300D [If I ever knew it])
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Last edited by compress ignite; 01-15-2010 at 10:58 PM.
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  #15  
Old 01-15-2010, 10:44 PM
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Normally when a diode fails it goes open circuit so its unlikely to short & flatten the battery. If a diode fails you loose around 1/3 of your charging and so it would show as very slow charge. When it is suggested to clean a terminal, you need to remove it & clean the mating surfaces, not just the outside. Once clean a layer of grease all over the surfaces is required as well as making sure they are tight when put back together.
Bits can break off the plates of batteries and fall to the bottom of the cells, after a while this becomes an internal short & so the battery no longer holds charge. Any hard bump or knock can cause this eg hitting the curb when parking. Some 4x4 and heavy duty batteries are designed with more plate support to help prevent this.
If there is no external discharge and the battery is going dead after a day of sitting, it most likely has an internal short.
If you are having to change your alt every 2 years, unless you are very unlucky, it sounds like you have some other electrical problem.

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1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
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