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Discussion Starter #1
Just moved the battery to the truck and installed a 3g
alternator.93 5.0 mustang.What should my volt readings be?
Here is what I have 13.69 with lights off at idle,12.70 with all lights on.
My truck runs 14.10 with lights on.With the car off, I read 12.28 at the battery.
 

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Battery should read 12.72 when new and fully charged, and surface charge removed. You can remove a surface charge by turning the headlights on gfor a minute, or letting the battery sit for a day after charging. With the surface charge still in it the battery could read anywhere from 13 to 13.8volts.

A starting battery that reads around 12.5volts is considered about 50% discharged for starting purposes.

As for a 3G's output. In all charging situations you want to see 13.8volts or higher. If the alternator is producing less than 13.8 it means it is being asked for more than its capaciy to produce, and you are causing damage to it. Bring it down to 13.2 for about 20 minutes and things will start to melt inside it. The 3G should read somewhere between 14.3 and 14.6 when things are going good. i.e. you are asking it for less than 80% of it's capacity at that rpm.

So you have a problem with your install. It looks like you are not getting enough power at idle. This could be for a couple of reasons. If you have an extremely high output alternator, its at idle charge could be effected (reduced), or a poor wind of the stator could cause it too. If you have a regular 3G I would guess you have gone with a power pulley type setup? You may just not be spinning the alternator fast enough at idle. You will want an alternator pulley about 2 1/2 times smaller than your crank pulley. I am thinking this is probably where your issues is. (guessing)

Another thing to look at is voltage drop down the charge wire. Do you have it going directly to your battery? Should be, and no place else. It maybe be undersized and that is why you are only seeing 14.1 volts max. How do a voltage drop test is described in a thread stickied at the top of this forum. I would do one on your alternator's charge wire,( and other places too). But start there.
 
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