Alternator woes!!

[shepster]

Started getting the battery light come on during a trip to Sheffield yesterday, but only when revs were over 3000.

This morning I checked the belt wasn't slack and no obvious wiring issues, all seemed fine, the charge rate altered in accordance with the light coming on so I know it is a true lack of charge issue.

I went to GSF for a new voltage regulator, out of desperation I might add, only to find this one didn't appear to work at all as the batt light stayed on at all times.

I then put the old one back and went about my journey further oop North, initially the light stayed off even at 3000 revs plus but as the journey went on the revs needed to be dropped lower to keep it off and eventually gave up altogether and stayed on at all revs.

I eventually got back home and tried another regulator which was a known worker and went out for a drive, all was well for around 30 mins of 3500 revs driving and then the same happened again with the light only going off when the revs drop below 3000.

I doubt I've got 3 duff regulators so I'm guessing something in the alternator itself is at fault, anyone had any similar issues?

Cheers in advance.

[Mocki]

I would say the armature is at fault, did the brushes have any evidence of heat or damage when you took them out ?

[CovKid]

To rule it out, pop the end cap off (two screws) and clean the armature as well as giving the contacts on the regulator a slight 'twang' to get a better connection.

[shepster]

Cheers lads,

Been a strange one this, Kev had a spare so I put that on and still the same so assumed the van at fault but to make sure kev took them both to a local re-furb place for testing.

His spare was proven to be faulty BUT mine was ok? as a double check Kev put my 'good' one on his van and after a short while got the same symptoms as I did, he then took it back to the repair place for them to take another look.

In the meantime I fitted kev's now repaired one on my van and it seems ok, I've yet to take it for a run but initial signs are showing it's charging.

The repair place have been back in touch and say they still can't find anything wrong with mine so the jury's still out.

I'll keep you informed.

[kevtherev]

I would say the armature is at fault, did the brushes have any evidence of heat or damage when you took them out ?

The alternator gets hot very quickly Steve.
The ign. Lamp glows at around 2500 rpm then blinks fully on at just over 3k rpm.
Charge then stops.
The arm is bright and seats very tightly on the regulator.
I thought that maybe the arm is faulty internally.
Anyone have a link to a breakdown of internal components.?

spotted this in my research

All the ignition switch does is to supply a small energising current to the alternator via the warning lamp. Once modern alternators are charging they supply their own energising current, so the ignition switch no longer plays any part in the operation.

If you turn the ignition off you also remove the supply to all the other ignition fed instruments. The alternator tries to supply them by pushing current back up the warning lamp wire and through the warning lamp. This normally causes the warning lamp to light up. This is also why an old/worn ignition switch can cause the warning lamp to glow. However on a boat there is often not enough load on the "ignition" circuit for this to become apparent.

It was also noted than some people have "got away" with disconnecting the load from an alternator. There are a number of reasons for this.

On a modern alternator it is likley that you have a surge quench zener diode so that when the voltage surge (and thus current surge) starts to develop as the load is removed the zener opens at a predetermined voltage and quenches the surge by "short circuiting" it to negative. The problem is that some zeners fail under fault conditions so it is not a good idea to rely upon it.

and warm alternators..

That sounds like current flowing through the field coil. from one of the diodes failing, or is your ignition switch stuck on? If so, the charge warning lamp would be lit unless, even worse, it has shorted out. The bulb is supposed to allow a small current to flow in the field coil to energize it before the engine starts.

Shep have you ever disconnected the batteries while the engine is running?

[shepster]

No.

[kevtherev]

Thanks for the update