E30 Zone

I'm having some alternator issues, it doesn't seem to charge the battery until I blip it past 3k revs.

The engine dies if I take the negative cable off the battery when running, but if I rev it past 3k and then take the neg cable off it continues to run.

I've also tried 2 good batteries with no change. Replaced the alternator carbon brushes and cleaned contacts with no change.

You guy think its time for a replacement alternator?

does your battery light appear on the dash when you switch your ignition on ?

It comes on at ignition position 1, then goes out when I start the car.

The abs light comes on every now and then too, which I know if a weak voltage symptom.

You could put a new one in? Or get a second hand working one from here - £20 - £30. It might be better to diagnose the problem properly (I wouldn't bother personally if your sure it's the alternator) and one of the boffins could help you with that.

Is the Fanbelt tight?

Chances are that one of the diodes on the D+ output is duff, putting a huge ripple on the supply to the regulator and confusing it.

TPS - alternator belt is new and tight.!

Brian - I don't know what the 'D+output diode' is. I'm assuming its a component within the alternator?

Im guessing a swap is needed, I have a replacement on its way.!

I have had this issue on other cars whereby the thin wire "exciter wire" as I have heard it referred to as is faulty e.g. broken/poor connection so it would be worth looking over the wiring as they often run close to hot areas of the engine they can become brittle or melt etc...

I also read bosch alternators are self exciting... Brian what do you know of this chap?

So Bosch alternators, self exciting?

mcbonio wrote:Ok so pulled the injectors out today, they look like this;

See the one on the end, the little yellow cap on the end is missing half.! Could this be the cause of my problems?

It won't affect the charging.

Ben

Sorry Ben, posted my other problem on this page....

mcbonio wrote:I also read bosch alternators are self exciting

Kinky!

If the battery light is doing its stuff, there's nothing wrong with the 'exciter' circuit, and in any case, the relevant wire goes nowhere near anything hot on an E30.
Diode I refer to is an internal part of the alternator, and while it can be changed, it's more cost effective and easier to replace it with the whole unit with a second hand one, and fit your new regulator pack to it.

Cheers Brian,
I should have the new alternator on tuesday, I'll fit the alternator with new brush pack and report back.

Just so I can understand, why does my faulty alternator begin and then continue to work once its been spooled up fast?

The output from an alternator is not DC. (A very good reason why you should NEVER disconnect the battery on a running engine - especially if revving it to, say, 3k+!). It consists of three overlapping half sine waves at 120 degree intervals - an approximation of DC, and close enough for the average meter not to show any variation.
With a diode down, one of the half sine waves will be missing, so the voltage will drop to just about zero for a fraction of every turn of the alternator, which is what I suspect is upsetting the regulator. When the revs are increased, there's still the drops to zero, but the time between them is reduced, along with the time the regulator has to respond to them. A bit like if you drive fast enough over pot holes, you don't go right down into them.

I see what you mean, more info here;

Battery reads like this when I start it;

Battery voltage at idle - 11.8v
Battery voltage at idle after the 3k rev blip - 13.9

It then stays at the correct voltage until I shut the engine off. The alternator needs kicking into life with a good rev...

Ok swapped the alternator out today, car is working great. No more intermittent ABS light, no more dim lights and almost stalling when putting the clutch in. The car is very perky indeed.!

I had noticed the copper 'barrel' which the carbon brushes ride against had worn 2 deep grooves. I think possibly the alternator was just very worn.

Only remaining issue is now that the battery has been disconnected few a few days, the rev gauge, eco gauge and temp gauge are all flickery and dancing around again, I've reset the service indicator and all green lights remain on, so can't be SI batteries as they are only a couple of months old. Very frustrating.

Ok I've just fixed this ongoing jittering, inaccurate rev gauge, eco gauge and temp gauge issue. I read you can reset the whole cars electrical system and adaptive by disconnecting the battery and joining the 2 cables together, set ignition to position 2 and leave for 10 mins.

I did this and it worked, my gauges are working. The engines is also 20% perkier and more power, smoother idle too.