Alternator/electrical question
Thread Starter
Intermediate
Joined: Jan 2004
Posts: 42
Likes: 0
From: Arecibo P.R.
Alternator/electrical question
Hello,
I finally got all 4 headlights, wipers and taillights working on my '70. I did a quick alternator check by simply disconnecting the battery and the car keeps running just fine. However, if I turn all 4 headlights on AND the wipers, while the batery is disconnected, the car dies. If the battery is connected everything works fine. Obviously, the alternator doesn't produce enough for that load at idle. But if I accelerate it just a bit it keeps working. My question is: Is that somewhat expected from an old alternator or do I have to run and get a new one? Could it be something else besides the alternator? I need to take it out and have it checked at the auto parts machine, but that won't happen in the next few days. For what it's worth, the alternator is the one that came with the car when I bought it, almost 15 years ago. so it is at least that old.
Any comments?
Thanks,
Ismael
I finally got all 4 headlights, wipers and taillights working on my '70. I did a quick alternator check by simply disconnecting the battery and the car keeps running just fine. However, if I turn all 4 headlights on AND the wipers, while the batery is disconnected, the car dies. If the battery is connected everything works fine. Obviously, the alternator doesn't produce enough for that load at idle. But if I accelerate it just a bit it keeps working. My question is: Is that somewhat expected from an old alternator or do I have to run and get a new one? Could it be something else besides the alternator? I need to take it out and have it checked at the auto parts machine, but that won't happen in the next few days. For what it's worth, the alternator is the one that came with the car when I bought it, almost 15 years ago. so it is at least that old.
Any comments?
Thanks,
Ismael
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Thats not really a valid test. If you have a voltmeter, connect it to the alternator with everything hooked up normal and then turn on all the lights etc, the alternator should still be putting out over 13v. If it does not, then you have a problem. You can also take the alternator to some parts stores and have it checked, they have a load testing gizmo to do that with.
Disconnecting the battery removes the reference voltage that the regulator in the alternator uses to set the output voltage, so testing without it is really pointless. Reving the engine with the battery disconnected will make the voltage from the alternator go very high very quickly and can fry parts.
Disconnecting the battery removes the reference voltage that the regulator in the alternator uses to set the output voltage, so testing without it is really pointless. Reving the engine with the battery disconnected will make the voltage from the alternator go very high very quickly and can fry parts.
Burning Brakes
Joined: Feb 2006
Posts: 1,024
Likes: 1
From: AL
you may have to get one now that you have disconnected it while the engine was running; in fact i'd go ahead and get it checked now.
after you get the alternator checked, if it is not sufficient to handle the load at idle, you have several options. the first is to correct the high resistance wiring issues all old cars have (you must first identify these). then you can place high load items on relays. do a search and you will find much info in past threads as well . . .
edit: i must type too slow!!! (twice today)
after you get the alternator checked, if it is not sufficient to handle the load at idle, you have several options. the first is to correct the high resistance wiring issues all old cars have (you must first identify these). then you can place high load items on relays. do a search and you will find much info in past threads as well . . .
edit: i must type too slow!!! (twice today)
Thread Starter
Intermediate
Joined: Jan 2004
Posts: 42
Likes: 0
From: Arecibo P.R.
Thats not really a valid test. If you have a voltmeter, connect it to the alternator with everything hooked up normal and then turn on all the lights etc, the alternator should still be putting out over 13v. If it does not, then you have a problem. You can also take the alternator to some parts stores and have it checked, they have a load testing gizmo to do that with.
Disconnecting the battery removes the reference voltage that the regulator in the alternator uses to set the output voltage, so testing without it is really pointless. Reving the engine with the battery disconnected will make the voltage from the alternator go very high very quickly and can fry parts.
Disconnecting the battery removes the reference voltage that the regulator in the alternator uses to set the output voltage, so testing without it is really pointless. Reving the engine with the battery disconnected will make the voltage from the alternator go very high very quickly and can fry parts.
Thanks. I just did that test and this is what I found with everything connected:
idle, no load (headlights off / wipers off) 14 Volts
Idle with only one of the loads (either headlights or wipers) 13.5 ~ 13.7 volts
idle with both headlights and wipers on: 12.6 Volts
if I rev the engine ever so slightly it comes back up to 14 Volts.
I'll take it out and have it checked in a few days or so.
Thanks,
Ismael
