Normal Voltage
Team Owner
Joined: Sep 2003
Posts: 20,170
Likes: 672
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
13.2-.7 is normal at cruise. (+or- 0.3)
It will drop at idle. Not to worry
After the car sits a while you may see the low 14's as the alt is trying to charge the batt.
It's best to have the battery fully charged or use a float charger to prevent premature alt and batt failures
Also always measure and compare voltage with a hand held VOM.
Don't trust the instrument panel to give c\accurate reading unless you have compared first.
.
It will drop at idle. Not to worry
After the car sits a while you may see the low 14's as the alt is trying to charge the batt.
It's best to have the battery fully charged or use a float charger to prevent premature alt and batt failures
Also always measure and compare voltage with a hand held VOM.
Don't trust the instrument panel to give c\accurate reading unless you have compared first.
.
Last edited by JrRifleCoach; Feb 2, 2013 at 05:18 PM.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Yep...'coach is right.
Mine charges at 14.3 the first few minutes after start up, then settles to the 13s when moving....as low as 12.1 with everything ON at idle.
That being said, these things are famous for electrical issues and charging is not immune.
You can show a low charge when there is absolutely nothing wrong except for dirty connections at the alt and the alt to battery cable. Even a dirty cable on the starter will lower the amount of actual charge that makes it thru the system.
Mine charges at 14.3 the first few minutes after start up, then settles to the 13s when moving....as low as 12.1 with everything ON at idle.
That being said, these things are famous for electrical issues and charging is not immune.
You can show a low charge when there is absolutely nothing wrong except for dirty connections at the alt and the alt to battery cable. Even a dirty cable on the starter will lower the amount of actual charge that makes it thru the system.
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
My 85 runs 13.5 volts normally, with a/c or lights 12.6 both 12.4 prolonged Idle is a problem. Can occasionally show low volts when it dips below 600 rpm with everything on, but voltage is well up at 700rpm. I have the 86-91 alternator, it is only a 105 amp as to the 140 amp 85 alternator.
But the larger 85 alternator doesn't fit under the hood with the supercharger mounting.
The battery is just there for starting power, if it cannot maintain charge above 12.6 volts the alternator is not able to charge enough for the load. Larger capacity alternator is the best way to go.
But the larger 85 alternator doesn't fit under the hood with the supercharger mounting.
The battery is just there for starting power, if it cannot maintain charge above 12.6 volts the alternator is not able to charge enough for the load. Larger capacity alternator is the best way to go.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
When you're driving you are not measuring the battery voltage -- you're measuring the alternator output voltage. That varies with the voltage regulator (all parts have a tolerance and this is no exception) in the alternator and is generally around 13 volts. The voltmeter will show a red warning light at the bottom if it's bad. The dash is smart enough to switch to the voltmeter if it is bad so you can see the problem.
You measure the battery voltage with the engine OFF.
You measure the battery voltage with the engine OFF.
