Alternator not charging

[Johan]

I've recently rebuilt my alternator, since it was not charging enough. I replaced the brushes, the diod trio and the regulator.
However, it still ony gives 12.2 volts (BAT and ground around idle), or 11.8 when I use headlamps.
What more can I do? Should I just go for a new unit?

 

[brusso]

Oh I can tell you some horror stories about charging system tail chasing. I think, if you put on a new unit, you will still have the same readings. It sounds like you are familiar with the alt, or you wouldn't have tried the rebuild. I think that you may have a degraded ground (bad neg bat cable). To check this is not too hard. I assume that you have a multimeter? With the car running and maybe the headlights on, measure the voltage drop across the neg bat cable. In other words, set the meter for dc volts and put one lead at each end of the neg bat cable. Don't worry about reading pos or neg volts, it doesn't matter. You shouldn't get anything more than .1 or .2 volts. The same can be done for the pos batt cable for that matter. The point is is that there is a series resistance that is causing a voltage drop.

I had one that started fine, all of the accessories worked well, power windows were fast, ect... but the voltage read across the batt was 13.2 volts. Checked the battery cables, using the ohms mode, and had 0 resistance. When I ran the car and checked the cable (neg) with the volts mode I had a one (1) volt drop. Replaced cable and wellah 14.2 and better running accessories.

 

[Robin7TFour]

have you considered a bad stator or the windings have gone bad. check for continuity between the 'legs' of the windings. good luck

robin

 

[brusso]

have you considered a bad stator or the windings have gone bad. check for continuity between the 'legs' of the windings. good luck

robin

Good point!

 

[Johan]

Thanks for the replies.

Brusso, the 12.2/11.8 volts is between the BAT connector on the alternator (not the battery) and ground. Even if the ground strap is bad (wich may very well also be the case), this shouldnt affect the reading when you measure on the alternator itself?
I have 12.3 Volts between the poles of the battery when running at idle (should be higher?)
When checking the battery cables, where do you measure? Can you reach the place where the ground strip is connected to the frame from inside the car, or where does it connect?

/Johan

 

[JohnZ]

Sounds like the internal regulator isn't working, or isn't getting a sense signal. You should read 14.0-14.5 volts across the battery terminals at 1500-2000 rpm if it's charging.