Discuss Alternator Problem Advice needed in the Auto Electrician Forum area at ElectriciansForums.net

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Hi Everyone!!

I need some serious advice please

History: The Car was working fine and there was no electrical problems
Had to repair the alternator / PAS mounting bracket and after putting it all together I accidentally put the battery warning light cable onto the W terminal and it did not show charging voltage when we started up. it did fluctuate between 12v to 14.2V .... realizing something was wrong i checked the cable and corrected my error
Then i took the alternator apart and checked everything - regulator, stator and rotor and everything checked out with a fluke digital multimetre. we thought the only thing that could have blown was the voltage regulator and replaced that this evening...
and now we are even more confused as it will not go above 12.2v and will not charge
my Red battery charge light is constantly on.
Now: ......there looked like a slight fray in the battery charge light cable in the engine bay just before the alternator (it was only giving 1.4v on the volt meter) so i cut it and tested that i was now getting 12.4v to it and I even took the other end of the alternator and tested its resistance and it was fine i rejoined the cable back up and tested unconnected and and still got 12.4V
then tested that the alternator casing was earthed and it was with no resistance!
Took the battery cable off the alternator and off the battery and tested resistance and that was fine ( less than 1 ohm)
thinking we have solved the problem with it being the poor wire connection we put everything back together and founds ourselves back at sqaure one .... no charging and if i measure from the alternator case
When i put the volt meter on the battery light cable when it is connected to the alternator it only shows 1.4v
we are completely stumped here HELP!!!
 
If it is an old car the lamp is in the excitation wire. If this is damaged the alternator will not charge . You may of damaged the diodes.
If there was no electrical problems why did you touch the alternator.
 
If it is an old car the lamp is in the excitation wire. If this is damaged the alternator will not charge . You may of damaged the diodes.
If there was no electrical problems why did you touch the alternator.

the bracket of the alternator broke and it had to be replaced ....
 
Hi,your readings on the charge light wire,both connected and disconnected,seem OK,you may have a faulty alternator.
 
I am happy to accept that the alternator is broken but I would like to know why .... I have two alternators (both lucas A127) and have stripped and fully tested the stator, the rotar, the rectifier and have renewed both regulators on both and it is still not right... I have tested for Resistance on the 3 stator windings and they came back as per spec in the manual... there is no short to ground ...

the Rotor has been tested and there is no short to ground and the resistance of the winding to the slip rings are in Spec and has good resistance

The rectifier (I have 3 separate ones) and are all coming back with the same results... they all check out right with the Dioid tester..

I have purchased 2 new voltage and replaced it and still no luck!

Im stumped cause I do not want to go and buy a new Alternator and then find out there is something else wrong...
 
alternators may have issues if they were contaminated. slip rings and brushes tend to be the trouble spot for this.
Oil contamination can leave a residue from the brushes that under heat creates something like varnish that will increase in resistance and causes charging issues.
cleaning them with a good quality contact cleaner can help, oil contaminated brushes should be replaced.
testing the diode pack should be done in a good auto shop, they can test the alternator with the proper equipment
 

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