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-   -   Alternator stops charging (http://forums.pelicanparts.com/porsche-911-technical-forum/1009651-alternator-stops-charging.html)

DaddyGlenn 10-06-2018 05:56 AM

Alternator stops charging
 
I’ve done a search but did not find anything helpful. I’m sure it’s out there, just can’t find it.

Here is my situation. 1978 911sc, battery is a couple years old, alternator is much older (12 years w/internal regulator). I drove from Pittsburgh to Indianapolis without a problem, then on to St. Louis the next day. Still no problem. The car sat in STL for a few days while I attended a conference and fired right up on Thursday morning when I headed to Florida.

In the afternoon I stopped at a rest stop in north Georgia and there wasn’t enough battery to start it back up. Multimeter showed just under 10 volts at the battery. I found the battery negative ground wire was a tad loose and tightened it up. AAA was called and 3 hours later, got the car jumpstarted. I drove to a nearby auto parts store and had the battery tested. Battery was good but needed a charge.

It was only about 15 minutes of driving to get to the auto parts store but the battery had enough juice to start the car without any problem. I drove another 15 minutes and stopped for the night. Hoping the problem was the loose wire.

The next morning, the battery was showing 11.8 volts and the car started easily. I continued south. Shortly after crossing into Florida, my radio would not stay turned on. This had happened the prior day before I found the issue. So I took it as a sign the electrical issue was back. I powered off the vent fan and unplugged my phone from the charger to save power. With a lot of drafting of 18 wheelers, I stretched that tank of gas and made it to my destination (Melbourne, FL) 3 hours later.

Generator light only came on when first starting the car. Other than the radio not staying on and my phone not charging like normal, there were no indications of a problem. I can only correlate the issue with running duration of 4-5 hours and heat. Both days were cool in the morning when I started out but got really hot.

Question ... is the alternator failing when it is hot, a typical failure mode?

I have ordered a rebuilt Bosch alternator to be delivered Monday and hope to be driving back to Pittsburgh on Tuesday. I just need to boost my confidence that replacing the alternator will solve the issue.

woland 10-06-2018 06:22 AM

Extremely hot and cold temperatures can affect the battery, not the alternator.
In case of alternator fail, red light stays
Had similar issue ten years ago all sudden, and simply replaced the brushes
Never again had problems with battery charge.

http://forums.pelicanparts.com/uploa...1538835456.JPG

Targalid 10-06-2018 06:43 AM

If you have a voltmeter, diagnose the problem by testing the battery voltage with the engine running. Should be about 14 volts if the alternator is working. If it is not charging, likely your 40 year old alternator needs repair.

Alfasrule 10-06-2018 06:54 AM

I start my cars turn every thing on fan lights etc. As it's running I disconnect the battery. If the car dies your alternator is in need of repair. 9 times out of 10 it's the module which contains the brushes and the regulator ~$70.00. 2 nuts to replace it.

The alternator should supply the necessary current to run the car without assistance from the battery. After the car starts the battery's function is a big capacitor.

timmy2 10-06-2018 07:10 AM

Check the battery voltage while running to see if the alternator is charging, 11.8 volts in the morning is possibly a failed or failing cell.

Hawkeye's-911T 10-06-2018 08:04 AM

Quote:

I start my cars turn every thing on fan lights etc. As it's running I disconnect the battery. If the car dies your alternator is in need of repair.
I seem to recall reading somewhere if one disconnects the battery while the engine is running, you'll basically crater your alternator.
Is this factual or not? Maybe I could be misinterpreting a 'tongue-in-cheek' remark.

Cheers
JB

geoff_68s 10-06-2018 08:56 AM

Quote:

I seem to recall reading somewhere if one disconnects the battery while the engine is running, you'll basically crater your alternator.
I've read this too, on the colour wiring diagrams that our host used to host. In the lower right corner of the diagram, at least for my '68, it reads:

IMPORTANT -- Disconnecting of the battery with running engine results in immediate destruction of alternator.

Given that that's on the factory wiring diagram, I'd be inclined to believe it. I don't know if it applies to the more civilized SC, though, maybe their regulators are different.

DaddyGlenn 10-06-2018 10:25 AM

Update:

Battery showing a little over 10 volts and will not start the car. Jump started it and measured 12.8 volts with car running at 2k rpm.

Rebuilt Bosch alternator is scheduled for delivery on Monday.

Based on comments above, I suppose a loose battery cable could have damaged the alternator.

If all goes well, Iíll be on the road to PGH on Tuesday.

Alfasrule 10-06-2018 11:21 AM

It does not, it takes 1 second. If the alternator is malfunctioning it will stall immediately. No harm to anything. Running the car without the battery connected I understand, but this is only a test procedure I've used for decades, Old cars as well as new.
We all use pretty much use the same brand of alternator in both cars as well. Why mess with perfection?

midnight911 10-06-2018 09:34 PM

these are useful. i have them in my cars. my 911 started showing 12.x and 11.x volts. Indeed the brush was gone. replaced the VR and back at 14+V when running. some people also have these to monitor voltage surge which results in battery explosion.

https://www.amazon.com/s/ref=nb_sb_ss_i_1_13?url=search-alias%3Daps&field-keywords=volt+meter+cigarette+socket&sprefix=volt+ meter+ci%2Caps%2C227&crid=1O6JBYDB6FMKQ

Tori 12-12-2018 06:48 PM

Quote:

Originally Posted by DaddyGlenn (Post 10207137)
Update:

Battery showing a little over 10 volts and will not start the car. Jump started it and measured 12.8 volts with car running at 2k rpm.

Rebuilt Bosch alternator is scheduled for delivery on Monday.

Based on comments above, I suppose a loose battery cable could have damaged the alternator.

If all goes well, Iíll be on the road to PGH on Tuesday.


So how about an update buddy ???

7783911 12-12-2018 07:47 PM

did you by any chance change your dash bulbs, if so, your charging lamp may be a culprit as its not generating enough in the circuit to trigger the exciter?

Tori 12-12-2018 09:36 PM

Quote:

Originally Posted by 7783911 (Post 10282529)
did you by any chance change your dash bulbs, if so, your charging lamp may be a culprit as its not generating enough in the circuit to trigger the exciter?

Hold the phone..... is this a thing? I just changed my dash bulbs to LED and am having charging problems. I did not change my idicator bulbs, only the illumination bulbs.

7783911 12-13-2018 03:55 AM

if you dont have the cprrect current flowing through the alt lamp. it can impact the current to the exciter and you dont get charging..ask me how I know after converting to LED!

ossiblue 12-13-2018 06:29 AM

Quote:

Originally Posted by Tori (Post 10282556)
Hold the phone..... is this a thing? I just changed my dash bulbs to LED and am having charging problems. I did not change my idicator bulbs, only the illumination bulbs.

Yes, it is a "thing", but it only applies to your alternator warning lamp, not the dash illumination bulbs that are there to light the face of the gauges. You may, however, have mistakenly put a LED into the socket for the alternator lamp and that could have accounted for your problem. Or not.

Tori 12-13-2018 07:06 AM

Quote:

Originally Posted by ossiblue (Post 10282796)
Yes, it is a "thing", but it only applies to your alternator warning lamp, not the dash illumination bulbs that are there to light the face of the gauges. You may, however, have mistakenly put a LED into the socket for the alternator lamp and that could have accounted for your problem. Or not.

Thanks for the confirmation, that is what i expected. I 99% sure i didn't get a bulb in the wrong spot as i had an extra left over (Carmagic kit comes with a spare bulb) and the illumination is even throughout the face.

I will still pull the gauge and investigate however.

DaddyGlenn 12-14-2018 03:34 AM

Sorry guys. Alternator arrived and was installed. Made the trip back from FL to PA with no further issues.

Had I been home when it happened, I would have tried replacing just the voltage regulator on the alternator first. But given I had to get back, replacing the whole unit was the quickest and easiest way to go.


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