79 corvette high alternator output
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
Well I tried another new battery with no change. I ran the brown wire direct to the battery with no change. I purposely drained the battery down a bit to see how alternator reacted and voltage went to 15.3v then as battery charged it settled back to 14.7v within a few minutes. sure would like to see a little lower voltage but at this point not sure how to get there.
Last edited by Dave Witman; Jun 20, 2020 at 09:56 AM.
Le Mans Master
Joined: Dec 2006
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The voltage found in the main power wire (electrical harness) is used by the alternator to REGULATE its output voltage. The lower the voltage it detects, the higher the output voltage. If that were not the case, alternators wouldn't have REGULATORS built into them.
So, If your battery is fully changed and the alternator is sending 14.5-15.0 volts to it all the time, your battery will boil over and be "toast" in short order.
Le Mans Master
Joined: Dec 2006
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Well I tried another new battery with no change. I ran the brown wire direct to the battery with no change. I purposely drained the battery down a bit to see how alternator reacted and voltage went to 15.3v then as battery charged it settled back to 14.7v within a few minutes. sure would like to see a little lower voltage but at this point not sure how to get there.
Clean all your positive wire connections.
If you have that stupid starter harness plug, see if it's burnt..
Mine went ape, and I found that plug burnt. I hard spliced it and things settled down.It's 40 years old. Time to do a little housekeeping.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
OK i went for a 30 min drive came bad and meter shows 14.17 . So looks like problem solved just needed a longer drive to charge battery i guess. I did check gounds and added star washers way back we this started and did see a .2v drop which brought me done to 14,7. then changed regulator. But i never drove it just idle.
Race Director
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What brand regulator and part# did you use?
With the engine running and the voltmeter set to AC voltage do you get any reading at the main output wire on the alternator?
With the engine running and the voltmeter set to AC voltage do you get any reading at the main output wire on the alternator?
Last edited by MelWff; Jul 3, 2020 at 06:15 PM.
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Joined: Apr 2007
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From: South Western Ontario
The voltage found in the main power wire (electrical harness) is used by the alternator to REGULATE its output voltage. The lower the voltage it detects, the higher the output voltage. If that were not the case, alternators wouldn't have REGULATORS built into them.
So, If your battery is fully changed and the alternator is sending 14.5-15.0 volts to it all the time, your battery will boil over and be "toast" in short order.
Yes, the alternator has a REGULATOR. It is set to REGULATE to a FIXED voltage, possibly with some temperature compensation. The REGULATOR measures the output voltage of the alternator and REGULATES the voltage to it's fixed set point.
The REGULATOR does NOT measure the open circuit, no load voltage of the battery when the engine is running and the alternator is working. It's impossible to measure 12.7V at the battery when both the alternator output and battery voltage are being held at about 14.7V by the alternator. This means your chart giving the open circuit battery voltage vs battery charge is useless when discussing how an alternator works. Good info about a battery, but knowing what's in the chart is utterly useless when measuring the charging voltage of an alternator.
Last edited by lionelhutz; Jun 20, 2020 at 04:05 PM.
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I'm thinking you need to go to "Mad Electrical's" web site and read all about the differences between one wire and three wire Alternator's. VERY good information on there site.
one major point everyone is missing here is Amps. Voltage regulated at 14.5 volts is perfectly normal. But how many Amps are being pushed at the battery? 14.7 volts and .005 amps will never boil your battery and take a long bloody time to charge it. Right after you start your car, your amps will shoot up to 20 or more to charge the battery, then slowly settle down to maybe 1. Remember when cars had amp meters???
one major point everyone is missing here is Amps. Voltage regulated at 14.5 volts is perfectly normal. But how many Amps are being pushed at the battery? 14.7 volts and .005 amps will never boil your battery and take a long bloody time to charge it. Right after you start your car, your amps will shoot up to 20 or more to charge the battery, then slowly settle down to maybe 1. Remember when cars had amp meters???
Team Owner
Joined: Jan 2006
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From: Crossville TN
The BATTERY establishes the voltage in the SYSTEM, not the alternator. The alternator merely replenishes depleted battery charge. But, the voltage coming out of the alternator is REGULATED depending on what level of charge is in the battery. Alternator voltage and battery voltage are two different things which are interconnected. Battery voltage is the 'driver'; alternator [output] voltage is the 'follower'.
P.S. Your battery gauge measures BATTERY voltage. You have no meter on the alternator output to see what it's doing...unless you connect a VOM to it.
P.S. Your battery gauge measures BATTERY voltage. You have no meter on the alternator output to see what it's doing...unless you connect a VOM to it.
Last edited by 7T1vette; Jun 21, 2020 at 12:50 AM.
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From: South Western Ontario
The BATTERY establishes the voltage in the SYSTEM, not the alternator. The alternator merely replenishes depleted battery charge. But, the voltage coming out of the alternator is REGULATED depending on what level of charge is in the battery. Alternator voltage and battery voltage are two different things which are interconnected. Battery voltage is the 'driver'; alternator [output] voltage is the 'follower'.
The gauge isn't a battery voltage gauge or an alternator output gauge. The gauge is simply a volt meter that reads the voltage of the electrical system under the dash.
Face it, you're giving the cars electrical system characteristics that don't exist..
Le Mans Master
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If you start the car and unplug the alternator, the system will gradually decrease in voltage till the ignition fails.
If you start the car, and disconnect the battery, it will run until you turn the engine off.
If you start the car, and disconnect the battery, it will run until you turn the engine off.
Team Owner
Joined: Jan 2006
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From: Crossville TN
Piffle....
I believe that I erred on how the battery gauge is wired in the system. It is wired to detect the alternator voltage, so that the driver can see it is charging properly. Otherwise.....
I believe that I erred on how the battery gauge is wired in the system. It is wired to detect the alternator voltage, so that the driver can see it is charging properly. Otherwise.....
Last edited by 7T1vette; Jun 21, 2020 at 01:55 PM.
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From: South Western Ontario
Yet, you still called it a battery gauge....
How exactly does the alternator know when the battery has reached fully charged? Post an actual technical explanation of how it accomplishes this feat.
How exactly does the alternator know when the battery has reached fully charged? Post an actual technical explanation of how it accomplishes this feat.