Altinator is good but wont charge battery
#1
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Altinator is good but wont charge battery
ok so i put the volt meter on my battery with the car off and i get 12.5volts, then i turn the car on and test @ the battery and i get less than 12.5 volts. this tells me the altinator is not working. so i took the altinator off and got it tested at two different auto parts stores and it works like new... so why does my battery not charge? my voltage gauge on the dash is always discharging never charging. is there a fuse or a fusible link that i need to change to get power form the altinator to the battery?
1981 corvette 4 speed w/383 stroker
1981 corvette 4 speed w/383 stroker
#3
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#4
How old is this said alternator?
I would double check the battery with the car off to be sure you aren't getting a false read. (I've had it happen after attempting to jump a car. Battery showed full charge from the jump but had a bad cell and wasn't working. Didn't figure that out until after the tow.) Then check the cords for any wear or breaks from the battery. If everything looks good then bite the bullet and replace the alternator.
Good luck.
I would double check the battery with the car off to be sure you aren't getting a false read. (I've had it happen after attempting to jump a car. Battery showed full charge from the jump but had a bad cell and wasn't working. Didn't figure that out until after the tow.) Then check the cords for any wear or breaks from the battery. If everything looks good then bite the bullet and replace the alternator.
Good luck.
#5
Drifting
On an 81 the charge wire off of the alternator should go directly back to the battery.
If you look in the battery compartment there will be a wire coming off of the positive terminal that goes to a junction block.
Check that wire for a blown fusible link, or a bad connection at the block.
If you look in the battery compartment there will be a wire coming off of the positive terminal that goes to a junction block.
Check that wire for a blown fusible link, or a bad connection at the block.
#6
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ok so i put the volt meter on my battery with the car off and i get 12.5volts, then i turn the car on and test @ the battery and i get less than 12.5 volts. this tells me the altinator is not working. so i took the altinator off and got it tested at two different auto parts stores and it works like new... so why does my battery not charge? my voltage gauge on the dash is always discharging never charging. is there a fuse or a fusible link that i need to change to get power form the altinator to the battery?
1981 corvette 4 speed w/383 stroker
1981 corvette 4 speed w/383 stroker
#7
Safety Car
The alt should put out 14.2 volts.
Either the battery has a dry cell or the alt is about to give up.
1: start the car and take a screw driver and touch the back bearing with the tip of the screwdriver and if its magnetized the alt is charging.
2: while running unhook the negative battery cable from the battery post, if car stays running the alt is good.
3: hook up your meter to the battery and start the car and while its cranking the meter goes down to around 9 volts the battery has a dry cell.
4: replace alt and batt and be done with it.
Either the battery has a dry cell or the alt is about to give up.
1: start the car and take a screw driver and touch the back bearing with the tip of the screwdriver and if its magnetized the alt is charging.
2: while running unhook the negative battery cable from the battery post, if car stays running the alt is good.
3: hook up your meter to the battery and start the car and while its cranking the meter goes down to around 9 volts the battery has a dry cell.
4: replace alt and batt and be done with it.
#8
Race Director
Sounds like you might have a problem in the exciter circuit.
Try this very simple test,connect a standard 12v test light like the picture.
If this makes the alternator start charging , your exciter circuit is open.
Try this very simple test,connect a standard 12v test light like the picture.
If this makes the alternator start charging , your exciter circuit is open.
#9
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On an 81 the charge wire off of the alternator should go directly back to the battery.
If you look in the battery compartment there will be a wire coming off of the positive terminal that goes to a junction block.
Check that wire for a blown fusible link, or a bad connection at the block.
If you look in the battery compartment there will be a wire coming off of the positive terminal that goes to a junction block.
Check that wire for a blown fusible link, or a bad connection at the block.
#11
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I had the same situation. With mine (1980), there are two wires going under the battery box/compartment. If you look under the car there is an aluminum shield which these wires rest. Somehow my wire was skinned and arching? I put 2 new alternators on which continued to show discharging before I found the chaffed wire. Fixed the wire and it seems to be charging now.
#12
Race Director
Put a voltmeter across the battery terminals when it is running and if it reads 14-14.5V go out and buy a new battery they only last 4-5 years nowadays, if your lucky. The Chineseium in them breaks down faster than a few years ago
#13
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Either the battery has a dry cell or the alt is about to give up.
1: start the car and take a screw driver and touch the back bearing with the tip of the screwdriver and if its magnetized the alt is charging.
2: while running unhook the negative battery cable from the battery post, if car stays running the alt is good.
3: hook up your meter to the battery and start the car and while its cranking the meter goes down to around 9 volts the battery has a dry cell.
1: start the car and take a screw driver and touch the back bearing with the tip of the screwdriver and if its magnetized the alt is charging.
2: while running unhook the negative battery cable from the battery post, if car stays running the alt is good.
3: hook up your meter to the battery and start the car and while its cranking the meter goes down to around 9 volts the battery has a dry cell.
thanks for the tips, i will try these things this week and let you guys know if it helped me narrow down my charging problem... thanks for the help, gotta love this forum
#16
Just in case this helps anyone else out, i changed my globes out for SMDs and a week later my car was struggling to start. Apparently Field windings according to the wiring diagram are charging through the globe so the SMD/LED in the battery / Alt light was stopping the batter from being charged !!! who would of thought.. Took SMD bulb out and put old style bulb in and i now have 14.35volts back at the alternator not 12v with the SMD led ...