Overcharging battery causes?

[~SlideWays~]

I'm running in the engine (4agze) on my Trueno before a retune next Thursday. All of a sudden it has started over charging.

I thought it must be the voltage regulator but I swapped it with one from a spare alternator, just the regulator since he alt has a broken pulley.

Put it back together and no change, voltage goes to 18v+.

So I thought maybe its just another dud regulator.

I tried another one which I know worked on an old 4age years ago. But it's still overcharging.

Is there anything else it could be? Can the alternator itself be stuffed? Otherwise it ran fine since I drove it yesterday but at night with headlights on it didn't have the warning light since it must have been just below the warning level, unfortunately it killed the battery.

[Mr Revhead]

You have confirmed charge rate with multimeter?

[~SlideWays~]

You have confirmed charge rate with multimeter?

Yep, also getting dash lights at anything over idle which goes away if I turn the headlights on high beam.

[Mr Revhead]

Just checking, thats extent of my sparky knowledge!

[gepsk8]

warning light on dash works? check it has two power feeds and warning light circuit at alt, and sometime bad earth issue, thru mount and block.
or could be another internal issue inside alt.

[matt dunn]

Uplug the 3 pin plug and there should be 12v on all 3 wires with a multimeter and the key on.

If there is 3 powers then it is in the alternator, usually the rectifier has one diode out to make them overcharge.

[jondee86]

I think that there is a voltage sensing wire up the alternator to
give it battery voltage as a reference, so that it knows how much
(at what rate) to charge. If thats not hooked up I believe the alt
will overcharge.

Cheers... jondee86

[matt dunn]

Actually been thinking about it more.

If you are actually getting 18 volts from the alternator the only culprit is the rotor inside the alternator itself is shorted.

Nothing in the wiring can cause it to go that high.

Normal charge is between 13.8 and 15.0 depending on the actual regulator,
incorrectly wired they will overcharge but to a maximum of 16V,
then the internal circuits in the regulator will stop it there no matter if the sensing wire is connected or not.


To get 18V the rotor is shorted so the regulator cannot control the voltage.
If you have the proper 4AGZE alt with the heavy bearing and the long shafted rotor from the AE92 or AE101 GTZ,
then it is a common problem with them.

They dont interchange with the NON gze ones and the rotors a specific to that model.

[~SlideWays~]

Actually been thinking about it more.

If you are actually getting 18 volts from the alternator the only culprit is the rotor inside the alternator itself is shorted.

Nothing in the wiring can cause it to go that high.

Normal charge is between 13.8 and 15.0 depending on the actual regulator,
incorrectly wired they will overcharge but to a maximum of 16V,
then the internal circuits in the regulator will stop it there no matter if the sensing wire is connected or not.


To get 18V the rotor is shorted so the regulator cannot control the voltage.
If you have the proper 4AGZE alt with the heavy bearing and the long shafted rotor from the AE92 or AE101 GTZ,
then it is a common problem with them.

They dont interchange with the NON gze ones and the rotors a specific to that model.

I think this is probably the explanation since I tried three different regulators on the same alternator. I thought that a faulty regulator was the only reason it would over charge.

Late last night I put a known good regulator (which was one of the three I tried) onto a spare alternator which I haven't used before and a quick check with revs to 3000rpm it did not give a warning and the factory gauge looked to be around 15V.

I couldn't test it any more than that because it was 11pm and the garage is directly below our bedroom and the wife was asleep...I hope anyway.

I'll test drive it tonight and hopefully it is sorted.

Good to know that the alternator rotor itself can be another cause rather than just the voltage regulator.

I think I'll get the old one rebuilt anyway just as a spare.

Thanks for the info guys, I was ready to start tracking all the wires looking for a short or bad ground.

Fingers crossed its sorted with test drive tonight.