Alternator?
Thread Starter
Intermediate
Joined: Jan 2021
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From: SW Florida
Alternator?
I replaced my battery 2 months ago. Today I went for a ride in my 78 and after I parked the car it wouldn't start up. I jumped the battery and it started. Could it be the alternator or something else?
Safety Car
Joined: Dec 2012
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From: Summerville SC
Ok. First question is why did you replace the battery? Was it dead.? Did you check the alternator voltage which should be between 12.5 and 14? That would have been the first thing I would have checked. You probably need to have a plan on what to check before you start randomly replacing parts. Because there are a lot of reasons the battery might be dead. Follow a plan and this forum will help you
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Step one. with engine running, what does your volt gauge read? what happens when you turn on the headlights and step on the brake? let us know those readings.
Le Mans Master
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Bad battery- will make the alternator work too much-possible damage-shorten its life.
Bad alternator will not charge the battery- continual drain on the battery will damage it- lifespan will be effected.
Parasitic drain- will wipe out the battery and then possibly damage the alternator.
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I just had this issue. The alternator would put out 12.9 volts. It was enough to keep the car running but not charge the battery. I would say if the alternator isnt putting out more than 13 volts it needs to be checked. Mine failed all tests at OReillys. New 12SI solved all my issues. Its a PowerMaaster and it says right on it to make sure the battery is at full charge before installing and running the engine or it will cause the alternator to fail. And alot of the alternators I’ve bought lately all had a max RPM rating on them as well. I Believe my last one failed from high RPM
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Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
And, a poor GRD connection will keep a battery (good or bad) from charging properly. There has to be a complete circuit for the ALT to work its magic.
A poor GRD, could be the original fault here.
A poor GRD, could be the original fault here.
Race Director
Joined: Mar 2017
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From: Virginia
I just had this issue. The alternator would put out 12.9 volts. It was enough to keep the car running but not charge the battery. I would say if the alternator isnt putting out more than 13 volts it needs to be checked. Mine failed all tests at OReillys. New 12SI solved all my issues. Its a PowerMaaster and it says right on it to make sure the battery is at full charge before installing and running the engine or it will cause the alternator to fail. And alot of the alternators I’ve bought lately all had a max RPM rating on them as well. I Believe my last one failed from high RPM
If an alternator diode fails internally, not only won't it charge properly, it can drain the battery quickly. In C2s, it can even cook the wiring (there are fusable links in C3s to prevent this).
But all of this is easy to diagnose with a multimeter, and cheaper than throwing parts at the problem! Let us know what you find out.
Thread Starter
Intermediate
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From: SW Florida
Yes, battery was 4 years old and they normally last 3 years in the Florida heat. When I replaced the battery 2 months ago, I pulled into a parking lot, went for a drink, and when I came out the car would not start. Jumped it to get it going. Went to my mechanic and he said battery was dead.
So the other day, I went to a restaurant and parked the car for the valet. He came to me 5 minutes later and said the car is dead. Again, I jumped the battery and it started right up.
The one thing that was in common both times this happened is that I was running the A/C. Don't know if that has anything to do with it, but I could see the voltage drop below 13 to about 12 or so.
I've only had the car a few months, so I don't know how old the alternator is. Replacing it is a small cost. At least then I will know it's new.
So the other day, I went to a restaurant and parked the car for the valet. He came to me 5 minutes later and said the car is dead. Again, I jumped the battery and it started right up.
The one thing that was in common both times this happened is that I was running the A/C. Don't know if that has anything to do with it, but I could see the voltage drop below 13 to about 12 or so.
I've only had the car a few months, so I don't know how old the alternator is. Replacing it is a small cost. At least then I will know it's new.
Racer
Joined: Apr 2001
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Great advice from all. In addition when re reading your original post you state you put a new battery in 2 months ago and just took a ride. I read that as no ride for 2 months. When buying a new battery many times they are not fully charged, that could be the simple answer here. A battery tender would be a great and cheap investment for any collector car driven infrequently.
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Beginning to wonder if you have a huge parasitic draw when the vehicle is left unattended.
You can run a test on that with a Volt / Ohm meter between the POS battery post & cable.
Meanwhile, I think I would disconnect the NEG cable and see if it starts in a couple days. This would eliminate a possible parasitic draw.
You can run a test on that with a Volt / Ohm meter between the POS battery post & cable.
Meanwhile, I think I would disconnect the NEG cable and see if it starts in a couple days. This would eliminate a possible parasitic draw.
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potentially he may have a parasitic draw. But only throwing 12 volts with Air Con on says his Alternator and or wiring is not up to the task. I would be installing a new Charge wire from Alternator to Starter with a new fusible link or good blade type fuse as the original wiring was marginal when new and has degraded with age. A new 100 amp Alternator and checking the block to frame ground and frame to battery ground.