Not charging at idle.

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LivewireBlanco

LivewireBlanco

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So I've noticed my '71 Dart isn't charging at idle. It isn't until I'm above 1000 rpm that I'm charging at 14 volts. Is this a voltage regulator or alternator issue?
 
13.5-14 volts is what it should read at the alternator. Could be a diode going, start it up...then pull the positive cable and see if it still runs.
It's never a bad idea to loosen and retighten the screws that secure the voltage regulator.
Try that.
 
Put a meter on the battery and slowly bring off idle. See what/ when it comes up. Could be a number of things.......poorly rebuilt alternator, dirty slip rings/ poor/ worn brushes, someone may have put a larger pulley on the alternator, on and on. Alternator could have internal problems, bad stator or diodes, or even a partially shorted rotor

Did this just start happening, or what?
 
I run around 12 volts at idle too on my cars, one with FITech. I don't think you have an issue. All of my cars have volt gauges.
 
67Dart273 said:
Put a meter on the battery and slowly bring off idle. See what/ when it comes up. Could be a number of things.......poorly rebuilt alternator, dirty slip rings/ poor/ worn brushes, someone may have put a larger pulley on the alternator, on and on. Alternator could have internal problems, bad stator or diodes, or even a partially shorted rotor

Did this just start happening, or what?
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No, it's been doing this for as long as I' e had it running. Ever since you helped me install a relay to help with my voltage drop issue through the bulkhead. The alternator is a rebuilt one from autozone less than a year old.
 
LivewireBlanco said:
Does it die if left idling for too long?
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hmm, never had that happen , but it would take a really long time for that to occur, assuming a fully charged battery. I once drove my 66 charger with the alternator field wires unplugged, not very far but car got very sluggish, once home and tried to start it again it would not start, battery dead,, thats when I found the field wire had slipped off the alternator connection.
 
Some model alternators simply won't "kick in" well at idle. This is complicated by the fact that rebuilders get sloppy and put the wrong rotors into the wrong stator, and come up with a poor performing unit. Also, some alternators are better at low speed. The so called "squareback" ones generally are better, and in particular I believe it's the 45 amp rated on is particularly good.

Actually, "back in the day" this was common. If you can round up another alternator cheap, even a used one to try, that might be worth a shot. Frankly most of us lived with it and didn't give it much thought

It also might be that you have a small capacity battery, and the load on it when not being charged causes it to drop sooner than a more robust design. This can be a just-plain small light battery, one that is aging, or one that has something defective
 
LivewireBlanco said:
The alternator is a rebuilt one from autozone less than a year old.
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That does not guarantee that it is a good alternator. As others have said above, the round backs are more prone to this. The diodes are easy to check if you have a multimeter and are comfortable opening it up.
 
If its dropping from 12.5 to 12.0 Volts then the battery is discharging.
That's a little different than not charging.
Is there anything drawing power on your setup other than ignition?
At what rpm does the system voltage start to rise above battery voltage?
 
LivewireBlanco said:
So I've noticed my '71 Dart isn't charging at idle. It isn't until I'm above 1000 rpm that I'm charging at 14 volts. Is this a voltage regulator or alternator issue?
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Are you measuring the voltage with a proper Voltmeter or are you relying on the gauge in the car?
 
Mattax said:
If its dropping from 12.5 to 12.0 Volts then the battery is discharging.
That's a little different than not charging.
Is there anything drawing power on your setup other than ignition?
At what rpm does the system voltage start to rise above battery voltage?
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About 1100 rpm is when it gets up to 14 volts using an aftermarket volt gauge installed. It's never died on me but it's gotten to about 11.9 before at night with lights on. I guess I'll keep an eye on it. If not I'll swap out the alternator since it's a lifetime warranty. It's a square back model.
 
LivewireBlanco said:
About 1100 rpm is when it gets up to 14 volts using an aftermarket volt gauge installed. It's never died on me but it's gotten to about 11.9 before at night with lights on. I guess I'll keep an eye on it. If not I'll swap out the alternator since it's a lifetime warranty. It's a square back model.
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Here's the part that makes it hard to judge. We don't know whether the battery is charging or not.* If this right after starting, it certainly is charging and that could be sucking a bunch of power. Once the battery is fully charged, then the only thing drawing power is ignition and field.

Chrysler expected a '37 Amp' roundback to supply a minimum of 23 amps at 15 Volts at 1250 rpm.
At 1100 rpm a '60 amp' square back should easily supply the 5 amps at 14 Volts needed for igntion and field.

Get the battery charged and measure the voltage at the alternator output and you'll have a better sense of whether the alternator fully working.
Here's a photo sequence showing the current demand of a battery needing recharge.
You can see a battery's state of charge is a big variable.

*assuming no ammeter.
 
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