I believe mine is around the 14V range. 

14.3-14.5 at idle...taurus 3g alternator.  I was having the exact problem you mention.. 12.5 at idle..as soon as i hit gas it flew up..my idle speed was way too low..i have it set to 900 ish rpms..my cam likes that and so does my alternator

btw 13.5 sounds too low... id question the alt working properly with that voltage

Last edited by jeremy (6/07/2013 8:34 PM)

The 3G doesn't put out full voltage (14.5) at idle.......Unless an exciter is wired to it. Otherwise it don't really start genning till bout 2k RPM.
IIRC the green/red will work as the exciter.

Tubo
3G in Miss May and the 73 Vert

I think you're pulley on you're 3g is too large to spin the alt all the way at idle. if its 12.5v at idle its not charging, mine did this too so i found a 2" pully to get it to charge at 600rpm steady 14v unless all my stuff is on then 13.5v

I jumped it up to 3.5K and I still never got more than 13.5V in fact the voltage didn't change with the RPMs other than the initial jump.  I am sure it will work fine I just wish I was getting a little more juice out of it.

Daze if turn everything on lights, radio ect. load up the alternator, if it holds at 13.5 volts I don't think you have a problem. Maybe change pulley size to help at lower RPM's. If you think there is still a problem you could change the internal regulator. If all works well the lower charging voltage may actually be easier on the system. Battery may last longer.

Daze wrote:

The volt meter is good, no issues there.  The voltage does drop when things are turned on...  I guess I need to test it again, but before I do I need to make sure the battery is fully charged.  This car has been sitting for about a year.

Daze, I'm about to do the 2g to 3g Alt upgrade on my fox, and have been reading that the 3G alt needs a 4 gauge ground wire from the block to the chassis ground where the battery pigtail connects.  Hows the condition of your battery cables?  Do yiou have a 4 gauge pos wire thru a mega fuse to the battery?

Daze wrote:

if you put a volt meter on the battery terminals what kind of a reading do you get??  At idle I am getting about 12.5V and then when I give it some gas it jumps to 13.5 and holds there.  I know the alternator is working but I also know older alternators can go as high as 14.5V so I am just wondering what the normal range is for the 3g

Daze,  I'm starting to think your alternator is too small. I put a 3G on my 66 Mustang and it puts out 14.5 VDC from idle on up. I bought a new in the box 135 amp alternator for a 93 Taurus. I bought the connectors from Ron Francis. His connectors take the green wire with red stripe from the stock voltage regulator for exitation. The alternator bolted up with the stock mounts and the stock belts. If you are not measuring 14+ volts, then 1) your battery is shot, or 2) your alternator is too small, or 3) you have a tremendous electrical load somewhere in the system.
 

14.5v at idle, w/ an electric fan set on kill and all the lights on!