Alternator warm and buzzing when car is off
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TECH Apprentice
Joined: Jan 2015
Posts: 313
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From: Austin area
Alternator warm and buzzing when car is off I've read a LOT of threads on various forums about this with out a definitive answer. I'm hoping someone can at least point me in the right direction, or give me some guidance on where to start.
First off, here's the layout:
LS3 and 4L75e from BluePrint Engines with CVF front end accy drive
New American Autowire harness
LED bulbs everywhere (taillights, turn signals, courtesy lights, etc.
Battery to LS ECU - 4ga wire through a circuit breaker
Battery to starter - 1/0ga wire through 250amp fuse
Starter to alternator - 4ga wire
Alternator - one wire, but there is a rectangular plug on it. I believe it is a GM CS130 style
Issue - I was getting a battery drain that would kill the battery in a couple days. I happen to be under the hood the other day and I noticed the alternator was warm and there was a buzz coming from it when the engine was off and the car was cool (was sitting for a while).
Troubleshooting steps:
- Took out fuses one by one, and checked the alternator...still buzzing
- Grounded the alternator with another wire (small gauge though)
Weird thing:
- I accidentally brushed the ground wire across the + wire on the alternator (I know, I know) and the buzzing stopped. WTF?!?!?
Possible things I think I need to try:
- Wire the alternator as a 3 wire (hook up the P L S F wires)
- S to the Batt + at the PCM
- L through resistor to ignition? (this is a question)
- F to GEN wire coming from the ECU (BluePrint uses the GM connect and cruise harness and instructions)? (this is a question)
- Connect a 4ga wire from the alternator to the + on the ECU
- Willing to try anything else
Thanks all,
Jim
First off, here's the layout:
LS3 and 4L75e from BluePrint Engines with CVF front end accy drive
New American Autowire harness
LED bulbs everywhere (taillights, turn signals, courtesy lights, etc.
Battery to LS ECU - 4ga wire through a circuit breaker
Battery to starter - 1/0ga wire through 250amp fuse
Starter to alternator - 4ga wire
Alternator - one wire, but there is a rectangular plug on it. I believe it is a GM CS130 style
Issue - I was getting a battery drain that would kill the battery in a couple days. I happen to be under the hood the other day and I noticed the alternator was warm and there was a buzz coming from it when the engine was off and the car was cool (was sitting for a while).
Troubleshooting steps:
- Took out fuses one by one, and checked the alternator...still buzzing
- Grounded the alternator with another wire (small gauge though)
Weird thing:
- I accidentally brushed the ground wire across the + wire on the alternator (I know, I know) and the buzzing stopped. WTF?!?!?
Possible things I think I need to try:
- Wire the alternator as a 3 wire (hook up the P L S F wires)
- S to the Batt + at the PCM
- L through resistor to ignition? (this is a question)
- F to GEN wire coming from the ECU (BluePrint uses the GM connect and cruise harness and instructions)? (this is a question)
- Connect a 4ga wire from the alternator to the + on the ECU
- Willing to try anything else
Thanks all,
Jim
I would measure voltage between the ground on your battery and the body of the car for a start.
The only thing on the alternator that I would think that could cause a noise are the brushes. Something could be sucking power through the alternator or have a short in such a way that the only path to ground the device can find is backward through the power wire to the alternator. (A problem like this could bypass the fuses if there is a short to a hot battery wire.)
I doubt this is an alternator problem.
The only thing on the alternator that I would think that could cause a noise are the brushes. Something could be sucking power through the alternator or have a short in such a way that the only path to ground the device can find is backward through the power wire to the alternator. (A problem like this could bypass the fuses if there is a short to a hot battery wire.)
I doubt this is an alternator problem.
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
Likes: 127
From: Austin area
I would measure voltage between the ground on your battery and the body of the car for a start.
The only thing on the alternator that I would think that could cause a noise are the brushes. Something could be sucking power through the alternator or have a short in such a way that the only path to ground the device can find is backward through the power wire to the alternator. (A problem like this could bypass the fuses if there is a short to a hot battery wire.)
I doubt this is an alternator problem.
The only thing on the alternator that I would think that could cause a noise are the brushes. Something could be sucking power through the alternator or have a short in such a way that the only path to ground the device can find is backward through the power wire to the alternator. (A problem like this could bypass the fuses if there is a short to a hot battery wire.)
I doubt this is an alternator problem.
assume unhooking the battery makes the chattering stop, right? If so, I'd next measure voltage between the power wire on the alternator and the body when the chattering is happening. If you see voltage, then trace it back to the source.
If you don't see voltage, (and the alternator is chattering without power) then I would see an exorcist.
If you don't see voltage, (and the alternator is chattering without power) then I would see an exorcist.
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
Likes: 127
From: Austin area
assume unhooking the battery makes the chattering stop, right? If so, I'd next measure voltage between the power wire on the alternator and the body when the chattering is happening. If you see voltage, then trace it back to the source.
If you don't see voltage, (and the alternator is chattering without power) then I would see an exorcist.
If you don't see voltage, (and the alternator is chattering without power) then I would see an exorcist.
Joined: Nov 2001
Posts: 34,643
Likes: 2,571
From: Schiller Park, ILL Member: #317
So you might need that exorcist after all! Either that, or for some reason it's pulling more power than it should be (hence the buzzing and heat) - like what wssix99 mentioned in post #2 above.
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From: Bossier City, Louisiana
I'm thinking one or more bad diodes are blown towards ground in the rectifier portion of the alternator. Get the alternator "load tested" at a well equipped auto parts store and I will bet that it fails the "ripple test" while spinning on the bench at the store.
Rick
Rick
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Verdad Gallardo I was hypothesizing a fault or short in the wire between the alternator and battery, but supposed there could be a problem with the alternator. (That could be the source of heat and this backward flow of power.)
Scratch my comment about measuring voltage to the body. That's not going to prove anything (and a fault in the main cable is going to be unlikely) - but it would be helpful to know if unhooking the battery stops the chatter. Then - if the chatter continues, we think of exorcism. (Disconnecting the battery should indicate if power is flowing backward to the alternator while it is chattering.)
Great point. I can't imagine what else would allow power to flow the wrong way through the part.
Scratch my comment about measuring voltage to the body. That's not going to prove anything (and a fault in the main cable is going to be unlikely) - but it would be helpful to know if unhooking the battery stops the chatter. Then - if the chatter continues, we think of exorcism. (Disconnecting the battery should indicate if power is flowing backward to the alternator while it is chattering.)
Great point. I can't imagine what else would allow power to flow the wrong way through the part.
I would be more concerned with the heat. In electronics heat is indicating a large power draw or a short (extreme power draw). I would think something inside the alternator is shorting out as pointed out above.
Another test to try:
- Disconnect battery after running the car. (I assume this stops the buzzing.)
- Let everything cool.
- Hook up the battery and see if the alternator heats up. (Without starting the car and rotating the engine.)
^ If the alternator heats up on a cool car, this should indicate a bad rectifier.
- Disconnect battery after running the car. (I assume this stops the buzzing.)
- Let everything cool.
- Hook up the battery and see if the alternator heats up. (Without starting the car and rotating the engine.)
^ If the alternator heats up on a cool car, this should indicate a bad rectifier.
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
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From: Austin area
Yes, with a one-wire setup there will always be voltage at the alternator. The downside is exactly what you are experiencing (albeit not on the same scale) - battery drain when the vehicle is not in use. I have a 1-wire setup on my '71, but I rarely use the car so I keep the battery disconnected when not in use. Otherwise, it will drain the battery after a couple of weeks (not a couple of days as you are seeing), and there is no buzzing or warmness of the alternator in my case. The quick battery drain might be due to a weak/old battery, but you shouldn't be getting a buzzing sound at the alternator just from applying field voltage full-time (only consequence would be, as mentioned above, quicker than normal battery drain).
So you might need that exorcist after all! Either that, or for some reason it's pulling more power than it should be (hence the buzzing and heat) - like what wssix99 mentioned in post #2 above.
So you might need that exorcist after all! Either that, or for some reason it's pulling more power than it should be (hence the buzzing and heat) - like what wssix99 mentioned in post #2 above.
The other thing I'm going to do is run a separate ground to the case of the alternator. An ohm meter shows no resistance from chassis ground to the alternator case. But the FEAD is powder-coated, so it's possible it is grounded, but once things get warm, there is resistance not fully grounding the alt.
I'm thinking one or more bad diodes are blown towards ground in the rectifier portion of the alternator. Get the alternator "load tested" at a well equipped auto parts store and I will bet that it fails the "ripple test" while spinning on the bench at the store.
Rick
Rick
I was hypothesizing a fault or short in the wire between the alternator and battery, but supposed there could be a problem with the alternator. (That could be the source of heat and this backward flow of power.)
Scratch my comment about measuring voltage to the body. That's not going to prove anything (and a fault in the main cable is going to be unlikely) - but it would be helpful to know if unhooking the battery stops the chatter. Then - if the chatter continues, we think of exorcism. (Disconnecting the battery should indicate if power is flowing backward to the alternator while it is chattering.)
Great point. I can't imagine what else would allow power to flow the wrong way through the part.
Scratch my comment about measuring voltage to the body. That's not going to prove anything (and a fault in the main cable is going to be unlikely) - but it would be helpful to know if unhooking the battery stops the chatter. Then - if the chatter continues, we think of exorcism. (Disconnecting the battery should indicate if power is flowing backward to the alternator while it is chattering.)
Great point. I can't imagine what else would allow power to flow the wrong way through the part.
Another test to try:
- Disconnect battery after running the car. (I assume this stops the buzzing.)
- Let everything cool.
- Hook up the battery and see if the alternator heats up. (Without starting the car and rotating the engine.)
^ If the alternator heats up on a cool car, this should indicate a bad rectifier.
- Disconnect battery after running the car. (I assume this stops the buzzing.)
- Let everything cool.
- Hook up the battery and see if the alternator heats up. (Without starting the car and rotating the engine.)
^ If the alternator heats up on a cool car, this should indicate a bad rectifier.
Voltmeter shows ~14v. I finished the car about 3 months or so ago. This is a new alternator that came with the crate engine.
The short of your battery on the positive terminal indicates a bad alternator, but the battery test is a clean way to confirm. (I would have expected your battery to go completely dead if it shorted, right?)
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
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From: Austin area
It would be good to do a proper disconnect of the battery so you can 100% confirm if electricity is flowing backwards through the alternator. If it is, the alternator needs to come off. The alternator should be a one-way street and the diodes in the rectifier enforce this convention. (You won't be the first person to have a "new" alternator be bad out of the crate/box. You wouldn't be the 1000th, either. Its very common.)
The short of your battery on the positive terminal indicates a bad alternator, but the battery test is a clean way to confirm. (I would have expected your battery to go completely dead if it shorted, right?)
The short of your battery on the positive terminal indicates a bad alternator, but the battery test is a clean way to confirm. (I would have expected your battery to go completely dead if it shorted, right?)
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
Likes: 127
From: Austin area
I had a chance to take the car out yesterday. Sure enough, the issue came up again. After parking it and turning it off, I let it cool. Once cool, I went out and checked. The alternator was buzzing and warm. I removed the cable from the alternator battery post. The buzzing stopped and it cooled off. I re-connected the cable and still no warmth or buzzing. What does that indicate?
I also though of something else. The cable from my alternator is connected to the starter along with a cable from the battery. Most diagrams I see send the alternator cable to the fuse box. I have a separate cable from the battery to the LS ECU and fusebox. Would that matter? Also, as far as I can tell with a multimeter, the alternator is grounded. Should I attach a separate large ground cable to the alternator? I have 1/0ga grounds from battery to chassis, battery to body, chassis to engine and chassis to grounding post in the passenger compartment for everything in there.
Thanks,
Jim
I also though of something else. The cable from my alternator is connected to the starter along with a cable from the battery. Most diagrams I see send the alternator cable to the fuse box. I have a separate cable from the battery to the LS ECU and fusebox. Would that matter? Also, as far as I can tell with a multimeter, the alternator is grounded. Should I attach a separate large ground cable to the alternator? I have 1/0ga grounds from battery to chassis, battery to body, chassis to engine and chassis to grounding post in the passenger compartment for everything in there.
Thanks,
Jim
Maybe it is heat related? Does this only happen on long drives? What about short drives? Just running the engine for a minute in your driveway? (For other tests, I would disconnect the battery for convenience and try hooking it back up as the alternator cools down to see if it might be dependent on the temperature of the alternator.)
Thread Starter
TECH Apprentice
Joined: Jan 2015
Posts: 313
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From: Austin area
Maybe it is heat related? Does this only happen on long drives? What about short drives? Just running the engine for a minute in your driveway? (For other tests, I would disconnect the battery for convenience and try hooking it back up as the alternator cools down to see if it might be dependent on the temperature of the alternator.)
Joined: Nov 2001
Posts: 34,643
Likes: 2,571
From: Schiller Park, ILL Member: #317
I had a chance to take the car out yesterday. Sure enough, the issue came up again. After parking it and turning it off, I let it cool. Once cool, I went out and checked. The alternator was buzzing and warm. I removed the cable from the alternator battery post. The buzzing stopped and it cooled off. I re-connected the cable and still no warmth or buzzing. What does that indicate?
At this point, it sounds to me like an internal alternator problem that is excited by operation/heat, and then continues until it's isolated from power. Sounds like disconnecting it effected a 'reset' of some sort. Too bad you don't have another alternator lying around to swap out for a test, that might be all that's needed. Some good test ideas posted by wssix99 above too.