Charging System Problem - Voltage Drops
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Date: 2020-08-05
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Comments and reviews: 10
Jay
To me it looks like that remanufactured alternator may be working as designed, but it may have actually been a mislabeled look-alike designed for a lower amperage car. It's still a supplier problem, and ultimately your parts store needs to take responsibility for their supplier, as they kindly did in your follow-up video. My own guess is that few other mechanics would have noticed the insufficient amperage output problem like you did - you're a great mechanic - thumbs up to you! Don't feel too bad that you melted your voltage clamp/probe, I have done that before too! Those cheap air cooled alternators get HOT, much hotter than the engine. I learned the same lesson the other day, melting a scope probe on the V+ terminal of an air-cooled alternator. I suspect those fancy water cooled alternators last longer, and wouldn't have melted your clamp, but of course they are expensive and harder to replace. I enjoy these newer alternator systems which don't actually turn on the alternator until after the car is started. That reduces the mechanical load on the starter, and the peak current requirements of the battery, both of which which can be especially useful in cold weather. Some of these intelligent charging systems also back off on the alternator voltage after the battery is charged, so the battery doesn't get overcharged, which can confuse you trying to diagnose a problem like this. Again, FANTASTIC video for anybody who wants to learn about alternators!
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To me it looks like that remanufactured alternator may be working as designed, but it may have actually been a mislabeled look-alike designed for a lower amperage car. It's still a supplier problem, and ultimately your parts store needs to take responsibility for their supplier, as they kindly did in your follow-up video. My own guess is that few other mechanics would have noticed the insufficient amperage output problem like you did - you're a great mechanic - thumbs up to you! Don't feel too bad that you melted your voltage clamp/probe, I have done that before too! Those cheap air cooled alternators get HOT, much hotter than the engine. I learned the same lesson the other day, melting a scope probe on the V+ terminal of an air-cooled alternator. I suspect those fancy water cooled alternators last longer, and wouldn't have melted your clamp, but of course they are expensive and harder to replace. I enjoy these newer alternator systems which don't actually turn on the alternator until after the car is started. That reduces the mechanical load on the starter, and the peak current requirements of the battery, both of which which can be especially useful in cold weather. Some of these intelligent charging systems also back off on the alternator voltage after the battery is charged, so the battery doesn't get overcharged, which can confuse you trying to diagnose a problem like this. Again, FANTASTIC video for anybody who wants to learn about alternators!
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RusH
I hope u respond knowing this video is old but anyhow wen i connect the positive battery side and positive post on alternator on just idle i get. 05-. 07 i rev engine and it goes to. 18-. 25 so do i have a problem on positive side or no? Cause when checking voltage im getting 10. -9. vlts whether im checking just battery pos&neg or neg battery to pos on alt i kno its brand new battery that sat for long time in back seat never charged and after swapping out what i thought to be bad alternator and battery with junkyard alternator and this new battery i had but never installed those are my reading on my meter any thoughts oh and neg battery to alt housing at idle is. 07 and stays. 07 wen engine is revd please help
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I hope u respond knowing this video is old but anyhow wen i connect the positive battery side and positive post on alternator on just idle i get. 05-. 07 i rev engine and it goes to. 18-. 25 so do i have a problem on positive side or no? Cause when checking voltage im getting 10. -9. vlts whether im checking just battery pos&neg or neg battery to pos on alt i kno its brand new battery that sat for long time in back seat never charged and after swapping out what i thought to be bad alternator and battery with junkyard alternator and this new battery i had but never installed those are my reading on my meter any thoughts oh and neg battery to alt housing at idle is. 07 and stays. 07 wen engine is revd please help
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Dano
Probably the third time I've watched this video. Most people don't realize the alternator is supposed to put out ample current at idle WITH LOAD. They just give the car gas and everything is okay. And as long as it starts every time that's all that matters. Wonder why your headlights dim, wipers slow down and heater fan slows, then when you take off everything's good? That's cause at idle your car is demanding more current than the alternator can put out until you speed up and increase RPM. How many DIYers actually do all this testing when they replace an alternator? Probably less than half. They install it and see 14+ volts charge and call it good. You should do some testing.
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Probably the third time I've watched this video. Most people don't realize the alternator is supposed to put out ample current at idle WITH LOAD. They just give the car gas and everything is okay. And as long as it starts every time that's all that matters. Wonder why your headlights dim, wipers slow down and heater fan slows, then when you take off everything's good? That's cause at idle your car is demanding more current than the alternator can put out until you speed up and increase RPM. How many DIYers actually do all this testing when they replace an alternator? Probably less than half. They install it and see 14+ volts charge and call it good. You should do some testing.
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Highly
Good point about wiring resistance and voltage drops. An old motorcycle I had years ago had a crappy headlight. When I measured running battery voltage versus voltage right at the headlight bulb, I can't remember the exact number, but it was a lot! It had very thin gauge wiring.
To solve this, I used the headlight wires to trigger relays. I had a heavy wire right from the battery, to the relays, from there to the headlight. This nearly eliminated the voltage drop, and made the headlight much brighter.
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Good point about wiring resistance and voltage drops. An old motorcycle I had years ago had a crappy headlight. When I measured running battery voltage versus voltage right at the headlight bulb, I can't remember the exact number, but it was a lot! It had very thin gauge wiring.
To solve this, I used the headlight wires to trigger relays. I had a heavy wire right from the battery, to the relays, from there to the headlight. This nearly eliminated the voltage drop, and made the headlight much brighter.
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David
Good troubleshooting. Vibration may have caused the adapter failure. When the alternator is removed it is a good time to clean the mounting area and bolts to get a good ground. You didn't show a voltage drop test from the alternator case to the block.
At a cold start up in cold weather the alternator out voltage would be increased, a cold battery gives less current out but it also won't take as much current in.
Good video.
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Good troubleshooting. Vibration may have caused the adapter failure. When the alternator is removed it is a good time to clean the mounting area and bolts to get a good ground. You didn't show a voltage drop test from the alternator case to the block.
At a cold start up in cold weather the alternator out voltage would be increased, a cold battery gives less current out but it also won't take as much current in.
Good video.
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Edie
having this on 91 4. 3 s10 pickup. everything is nice but when it gets warm the volts play around it jumps up and down the gauge but it never dies. starts up every time. just no battery light when starting but a flickering one once it gets up to temps. i put two alternator on from autozone both valucraft and they both went to shyt in a four day span. grounds are good and exciter is okay. two wire alternator.
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having this on 91 4. 3 s10 pickup. everything is nice but when it gets warm the volts play around it jumps up and down the gauge but it never dies. starts up every time. just no battery light when starting but a flickering one once it gets up to temps. i put two alternator on from autozone both valucraft and they both went to shyt in a four day span. grounds are good and exciter is okay. two wire alternator.
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Jeff
With so many changes to the amps being used, one thing I learned to do was all ways check the size of
the drive pulley on the old alt to the replacement. if the pulley is smaller, it will change the rpm on how fast a alt turns, which affects amps being put out a idle speed with a load. please comment.
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With so many changes to the amps being used, one thing I learned to do was all ways check the size of
the drive pulley on the old alt to the replacement. if the pulley is smaller, it will change the rpm on how fast a alt turns, which affects amps being put out a idle speed with a load. please comment.
reply
Daniel
We only want simple quick diagnose explaining function specs of good or bad problems created by bad alternator. Problems that cause alternator to go bad. Making a video on random car has little value. Not interested in a Mayberry episode. Get to the point we want to know and understand alternators.
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We only want simple quick diagnose explaining function specs of good or bad problems created by bad alternator. Problems that cause alternator to go bad. Making a video on random car has little value. Not interested in a Mayberry episode. Get to the point we want to know and understand alternators.
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Feeney's
Thank you for this video. After watching this video. A day later I had the same issues on a 2001 Mack truck. Day cab. Voltage drop the ground side and found I had a 2 volt drop. Turns out I needed to build a ground Cable and the truck ran great and the alternator was charging he batteries.
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Thank you for this video. After watching this video. A day later I had the same issues on a 2001 Mack truck. Day cab. Voltage drop the ground side and found I had a 2 volt drop. Turns out I needed to build a ground Cable and the truck ran great and the alternator was charging he batteries.
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moomike
You are willing to swap the alt out 5 or 6 times to find a good one? Never heard of anyone who does that. Testing between swaps who pays the labor? Or do you eat it? Seems if they were that much trouble you'd just go the new route from the get go.
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You are willing to swap the alt out 5 or 6 times to find a good one? Never heard of anyone who does that. Testing between swaps who pays the labor? Or do you eat it? Seems if they were that much trouble you'd just go the new route from the get go.
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