Commodore VT ecotec Alternators keep dying.

[NickHidro]

Hi guys

I'm on my fourth alternator for my 98 VT ecotec in a year and it's failing on me again. They've all had issues with charging at too low a voltage (11.9V idle and around 12.9V at 2000rpm, then after a month or two even under load it is about 11.9V). So far I've all but the original have been bought from wreckers (with the second one being DOA so I don't really count that one) so it's perfectly possible that they've all just been broken but I find it strange that something that's usually as robust as an alternator is dying so often.

Do you guys think it could be something esle potentially damaging the voltage regulator everytime I swap it over? Has anyone had any similar experiences to this?

I should also note that after the second one died, I changed the pathetically small charge cable for a beefy 4 gauge one going straight from the alternator to the battery so I don't think it's the usual charge cable overheating issue. Also I have an aftermarket stereo installed but I'm not sure of the power draw it requires as it was from the previous owner.

Cheers for any help guys, it's greatly appreciated.

 

[Immortality]

It could be the charge sensing wire is damaged. There are 2 wires coming from the alternator regulator, one for the dash light and another to sense the battery voltage. Check this wire as it has a fusible link fitted. If this is suspect it can cause charging issues.


Have you tested the output voltage at the alternator or only the voltage at the battery? Check the voltage at the alternator between the alternator body and the positive output post. If this is greatly different to the battery voltage than there is a wiring/terminal issue in which case it would also be pertinent to also check all your earthing cables and connection points. Battery, chassis and block etc.

 

[greenacc]

If the wiring fix above doesn't solve it you might need to stump up for a new one. Get one on sale and it won't cost too much though I agree it's strange that two in a row would be bad but a VT alt would be pushing 20 years old now so not exactly new any more!

 

[NickHidro]

It could be the charge sensing wire is damaged. There are 2 wires coming from the alternator regulator, one for the dash light and another to sense the battery voltage. Check this wire as it has a fusible link fitted. If this is suspect it can cause charging issues.


Have you tested the output voltage at the alternator or only the voltage at the battery? Check the voltage at the alternator between the alternator body and the positive output post. If this is greatly different to the battery voltage than there is a wiring/terminal issue in which case it would also be pertinent to also check all your earthing cables and connection points. Battery, chassis and block etc.

I've tested all the voltage between the alternator housing and the positive battery terminal as well as just across the battery and at most I only ever see them differ around 0.2V so I'm guess that's fine.

It also turns out that the alternator is capable of supplying around 13.8V under no load when slightly warm, it's only when I turn up the Aircon, use the stereo and have lights on at night that it drops down to around 11V-12V (sometimes even 10.5V when slowing down to stop at lights upon which the stereo usually turns off).

I just took off the alternator and the regulator to have a look and it turns out the red wire coming from the regulator clip has had the insulation worn away and was exposed. I've patched that up but I figured I'd take a look at the regulator brushes to see how they were holding up and while I don't really know what properly worn out brushes look like, I'm guess mine aren't too new looking:



Would you say buying a new regulator might help? Or do you think the issue is still somewhere else?

Cheers for the help

 

[Immortality]

Those brushes are probably stuffed. I'd consider buying a whole new alternator. For the extra cost it's worth the peace of mind.

Sounds like the alternator is on it's last legs. With a few revs it should be supplying in excess of 14 volts (they are rated at 14.4 volts) and maintain that voltage even with a decent load on it.

 

[the_boozer]

its the groves in the slip rings that will determine weather or not replacing just the reg is a waste of time I'd put a new alternator on it and not ever touch it again. if the bushes spring in and out I think they aren't your problem I've found a lot less brush left than that