Battery issue…alternator/generator?
12-28-2022, 12:49 PM
#16
I've seen it written (maybe in Leffingwell's 911 Buyer's Guide?) that alternators last about 40K miles. I've replaced mine once in about 55K miles of ownership.
I wish I was well-prepared enough to have purchased one of those cigarette lighter voltmeters. Instead, I used what I had, and used speaker wire to connect my voltmeter to the battery, then wedged the voltmeter on top of my dashboard.
As others have said, at rest (engine off) a battery should sit at around 12.4-12.7 volts. While idling, maybe around 13 volts. The voltage should increase with engine rpm, if the alternator's working, but should then be limited by the regulator to prevent your electrical system from seeing too high a voltage and frying stuff. So while driving around (or revving the motor in neutral) you should see about 14-14.5 volts. If you're seeing 16-18 volts, that's not good (bad regulator?).
I wish I was well-prepared enough to have purchased one of those cigarette lighter voltmeters. Instead, I used what I had, and used speaker wire to connect my voltmeter to the battery, then wedged the voltmeter on top of my dashboard.
As others have said, at rest (engine off) a battery should sit at around 12.4-12.7 volts. While idling, maybe around 13 volts. The voltage should increase with engine rpm, if the alternator's working, but should then be limited by the regulator to prevent your electrical system from seeing too high a voltage and frying stuff. So while driving around (or revving the motor in neutral) you should see about 14-14.5 volts. If you're seeing 16-18 volts, that's not good (bad regulator?).
12-29-2022, 09:00 AM
#17
Rennlist Member
The voltmeter is a good idea for these cars because the only warning you get when the alternator craps out initially is a very brief light flicker, which you probably won’t notice. I now carry a portable battery pack which enables me to clamp on to the drained battery and then drive for a considerable distance.
01-01-2023, 07:15 PM
#18
Thank you for all of the constructive input. I really enjoy and appreciate this community. It turns out it was the alternator. Had it replaced and all works fine now. Thanks again for all the help.
Best wishes and HNY!
Best wishes and HNY!
01-05-2023, 09:10 AM
#21
Rennlist Member
I had the same problem
A few months ago, I acquired a 1985 wide body cab. At the time, the dealer said he put a new battery in the car because the one that was in the vehicle was the wrong size. The car has been running fine. Yesterday, I go start the car and there is a “click” when I turned the key and the battery is dead. I look at the batter an it has handwritten “03-14” on the top. I don’t know if that means it is old (from March 2014) or something else. So, I get a jump, and drive to an auto parts store to replace the battery. When I go inside to see if they have the right battery, I leave the car running because I am afraid if I turn it off, it won’t re-start. The store has the correctly battery, so I go back outside to turn off the car, and the car has quit running! The key is still on, but the car is dead. I put in a new battery and the car starts, no problem.
So, my best guess is that the battery may have been fine, but that the alternator/generator was not charging the battery. I am guessing that the car ran on the battery until the battery was exhausted and just quit. I intend to drive the car to my mechanic to have him check it out, but would be grateful for your thoughts/input. What do you think is wrong?
As always, thank you to those who respond!
So, my best guess is that the battery may have been fine, but that the alternator/generator was not charging the battery. I am guessing that the car ran on the battery until the battery was exhausted and just quit. I intend to drive the car to my mechanic to have him check it out, but would be grateful for your thoughts/input. What do you think is wrong?
As always, thank you to those who respond!
Last edited by alfetta; 01-05-2023 at 09:13 AM.