Charging problems

[Avocet]

Well, it finally happened! Having never let me down, my 30 year old Alfa 164 finally arrived home last night on the back of a recovery truck...

I'd driven up to Glasgow (about 150 miles) in the morning. No problems. On the way home, I'd got about 70 or 80 miles and noticed the voltmeter (yeah, remember when cars had voltmeters?!) was showing about 13 volts. About 10 miles further on, it was showing 12. Normally, it sits just over 14.

Another 10 miles after that, it was showing 11 volts and I was getting worried because I was going to have to turn the lights on soon!

I just got over the border at Gretna and I was down to 10 volts. The ABS light came on. (At NO POINT in all this, did the alternator light come on)! A mile or so later, I lost the speedometer and rev counter. Anyway, I JUST managed to get off the motorway and up the sliproad, but the first set of lights I stopped at, the engine died (not even enough to run the fuel pump). Obviously, no chance of a re-start.

Looking at it this morning, (it's been on the battery charger all night) it starts and runs fine, still no alternator light, but isn't charging. It's a pretty ordinary Bosch alternator. I have a good 12 volts on the heavy cable at the back of the alternator and a good engine earth. The battery is in the boot, but I can't find any significant voltage drop between it and the front of the car. However, there's a thin green wire which pushes on to a spade terminal on the back of the alternator, at which I'm only getting 7 or 8 volts. I'm guessing that's the wire that feeds the field coils? I'm a bit of an electrical numpty, so I could be talking rubbish here! I tried running a wire direct from the battery positive to that spade terminal to put 12V on to it, but the alternator still won't charge. That's me out of ideas now!

 

[Burnerman]

Time for a replacement, I'm afraid......probably the voltage regulator that is goosed inside the alternator, giving the spurious reading.
John

 

[Spark123]

The small green could be just for the warning lamp in the instrument pod. It is more likely to be an alternator fault.

 

[Astra99]

Does the alternator light come on with the ignition on but the engine not running? If it does not, then the alternator cannot get the excitation voltage to start it charging. Reasons for the lamp not to illuminate (when it should!) are a blown bulb, worn-out brushes in the alternator or a defective diode pack or voltage regulator. If you ground out the small green wire, the alternator warning light should come on. Unless it's just worn-out brushes, a replacement alternator might be the best option.

 

[Avocet]

Thanks everyone. Well, that turned out to be probably the easiest job I've ever done on the car! I can take the regulator (complete with brushes) off the alternator in situ. Once it was off, it was pretty obious wha tthe problem was!

I had a spare alternator and the brushes were good in that. Swapped it over and all fine again, charging at 14.2 Volts.

 

[Burnerman]

Nice one!
Wondering what state the slip rings are in though......in my very few excursions into an alternator I've found the slip rings to be in a surprisingly poor state
John

 

[Avocet]

Nice one!
Wondering what state the slip rings are in though......in my very few excursions into an alternator I've found the slip rings to be in a surprisingly poor state
John

The one that the good brush was running on was fine. Nice and shiny and not much of a lip on it. This is a "new old stock" alternator that I got for £35 on eBay a couple of years ago, so it's only done 10,000 miles (...supposedly...)! Looking at it, I think I was "had" because the lip is not as bad as the lip on my 130,000 mile one that came off the car, but it's not THAT much smaller! I think I just got a "second-hand-but-very-clean" one...

The ring that the broken brush had been running on, had a small clean patch where you can just see that a tiny fraction of the brush surface was still touching it, but the rest was dull. However, being the bodging git that I am, I wrapped some wet-or-dry paper round the end of a stick, poked it into the hole where the brushes went, and started the engine... (And a few seconds later, it was quite impressively shiny again)!

 

[Mottie]

You can’t beat that satisfying 'dog with 2 dicks' feeling when you fix a potential aggro fault on your own car for nothing.

 

[fixitflav]

Thanks everyone. Well, that turned out to be probably the easiest job I've ever done on the car! I can take the regulator (complete with brushes) off the alternator in situ. Once it was off, it was pretty obvious what the problem was!

Well done!
Interesting that the brushes look different. The shorter (looking) one isn't stuck in the holder by any chance? If they're both free to move they should wear at the same rate. Different on the early Lucas alternators which had face-type sliprings, the outer one wore quicker for obvious reasons. Usually lasted about 80000 miles, and at that point could swap them over as a stop-gap.

 

[ericmark]

One brush always wears more than other, that is standard, to do with one being positive and other negative. Lucky with the Bosch easy to change. The warning light comes one before starting as the current flows through it to start the charging process, it is just as important to check it comes on before starting and goes off after starting. If you had banged alternator with screwdriver handle it would have likely got you home.

 

[fixitflav]

One brush always wears more than other, that is standard, to do with one being positive and other negative.

Interesting, I hadn't heard of that, and can't think of any reason polarity would affect brush wear. Not that that proves anything.

Years ago I used to repair alternators and sell them part-exchange, mostly Lucas with face-type sliprings. I still have 2, a Ford and a Delphi from a Renault, both substantial mileage. Conventional sliprings. I had a look at the brushes and one is a little shorter than the other on both, whether that's due to polarity I wouldn't like to say.

 

[ericmark]

Electron flow neg to pos so yes even when not like Lucas always one wears more than other, but with Lucas 17ACR etc, battery sensed OK but machine sensed would burn a hole through centre of slip ring.

 

[fixitflav]

Electron flow neg to pos so yes even when not like Lucas always one wears more than other

I'm sure you're right, but I still don't see why. Which brush wears quicker, the one with electron flow from brush to slipring, or the other?

battery sensed OK but machine sensed would burn a hole through centre of slip ring.

I've seen a few of those, with a hole drilled right through the central slip ring. I just put it down to old age! (the alternator's, not mine).

 

[ericmark]

I'm sure you're right, but I still don't see why. Which brush wears quicker, the one with electron flow from brush to slipring, or the other?

I've seen a few of those, with a hole drilled right through the central slip ring. I just put it down to old age! (the alternator's, not mine).

Never bothered to work it out as to which wears most pos or neg, but with Lucas and centre hole on slip rings, only a problem with machine sensed, I assume it switches off/on faster so seems it is switching off on rather than steady current which causes the wear.

 

[fixitflav]

with Lucas and centre hole on slip rings, only a problem with machine sensed

Scan of both types attached. Perhaps part of the explanation is that the voltage at the Zener diode is steadier coming from the battery.