1999 XJ 2.5TD charging problem

[amlav]

Originally Posted by Richard buttocks

yeah, dont do that.
Thats the worst advice ive seen on here in a while.

Why not . Please explain ??
What does happen when battery goes open circuit and alternator still charging ?
I'll answer that for you .
PCM does not pushes charging voltage above 14 V and car runs no problem.

As for no charge rate being under 13.6v, i guess you've never worked on late model cars that can drop the "charge rate" to battery voltage if the load on the battery is very low.
And please go find me a 2.4 diesel hilux that charges at idle...

Hilux's must be a different breed .
There is always a charging current going in to the battery to charge up
properly otherwise the plates would have only surface charge.
Therefore a battery needs 13.6 to 13.8v minim to charge.

Rather to just say "No , don't do that....worst advise and so on " explain your
assumptions .

Anyway...with battery cable disconnected briefly the alternator should push
14.1 volts (according to my DMM ). Tested myself .
Regards
Andrei

[M84AB1]

Alright guys,

I did some more tests and checks. Here is what I did and the corresponding results.

1. Brushes - Removed the back cover of the alternator (DENSO 38522261) which provided easy access to the brush holder. Brushes still have enough length to be pushing against the slip ring(s).

2. Rectifier Test - I saw a video online where a guy tests the overall diode voltage by using a digital multimeter (set in diode mode) and placing the positive probe on the alternator housing and the negative probe on the B+ terminal. Doing that, produced only 0.9V. Now for either a 4 or 6 diode setup I would expect to see more than that. Is this a good indication of a bad diode/rectifier?

3. Individual Diode Test - I then proceeded to test (what I think) are individual diodes, by doing a multimeter diode test between any one of the four screw terminals that go around the outside of the rectifier (see picture) and ground. Each produced a reading of about 0.54V

4. AC Ripple Test - Hooked my multimeter to the positive and negative terminals of the battery. Set it to AC and observed the ripple to be close to 1V at about 2,000RPM and 13.8V. From what I have read, it should not be this high, again hinting that indeed one or more diodes could be bad?

[amlav]

Diodes very rarely go open circuit . They are either Ok or shorted .
To avoid misleading reading the heatsink containing the diodes would have to be removed or disconnected from the alternator winding .
Simplest test for a diode is : with the multimeter set in diode or low ohms range probe the diode terminals . It should have a reading in one direction but no reading in the other direction . Thats about it ....
Don't worry to much about the ripple test ..Each silicone diode has a 0.6 Volt voltage drop or 0.2 Volts with germanium diodes and the battery acts as a sort of filtering device in the same time .Less internal resistance from battery allows for AC ripples to be more pronounced witch in turn would mean that battery is getting weaker and the chemicals on its plates are not reacting anymore 100%.
I still suspect your battery being all your headake .
Another thing is the type of battery used : old style lead/acid battery or lead/acid/calcium battery . The calcium ones require higher charging voltage 14 to 15.8 volts. Older cars charging system are set for lead/acid only .That made me worried a bit after I replaced mine but seems to be ok so far and it is always charged.

Regards,
Andrei

[M84AB1]

Ok guys, the problem is now solved. It was a faulty rectifier indeed.

the rectifier has 8 diodes, and on the new one I was able to measure about 0.45V across each and every one of them. The existing/old rectifier only measured voltage across 4 of the the diodes.

Furthermore, there was also obvious visual damage like corrosion on some of the diode leads..etc

The charging voltage is now regulated at any point (even at idle) between 13.9V and 14.2V

P.s. one thing I found crazy was, the rectifier cost me less than half the price, including delivery from the US than what it would have cost me to purchase here in Aus!!!

[Richard buttocks]

Shocking news.

are you surprised that it was cheaper?
The only thing our government doesnt tax us on is breathing.

[amlav]

Good news You got it fixed .
Must admit that corrosion was the last thing in my mind when I replied to your questions .
Comes to think of it my wife's Camry(2006) had the alternator winding ends
all corroded to the point that there was no continuity at joins .
I couldn't explain myself where or how the corrosion got there and assumed bad manufacturing or workmanship.
Engine bay was always clean and never had to wash that engine therefore no chemical reaction should have been the cause .Got me stumped .
Cheers,
Andrei

[layback40]

Originally Posted by amlav

Good news You got it fixed .
Must admit that corrosion was the last thing in my mind when I replied to your questions .
Comes to think of it my wife's Camry(2006) had the alternator winding ends
all corroded to the point that there was no continuity at joins .
I couldn't explain myself where or how the corrosion got there and assumed bad manufacturing or workmanship.
Engine bay was always clean and never had to wash that engine therefore no chemical reaction should have been the cause .Got me stumped .
Cheers,
Andrei

What happens when it rains heavy?