13 replies to this topic

[lam]

So...

I got in my car to drive home from work and noticed the alternator light didn't come on. It started fine but as the journey went on the battery started draining until it conked out completely with a flat battery.

I assumed a loose connection was the cause but couldn't find anything.

Any ideas?

Thanks.

[dave21478]

check the bulb hasnt blown - it forms part of the charging circuit.

[cobblers]

If the alternator light itself blows, the alternator won't charge. Sounds stupid, but the alternator needs the a small current to excite it to get it going. Sometimes the will self-excite if you rev them to high heaven, but generally not.

If you have a voltmeter, turn the ignition on and check the voltage at all three terminals of the alternator plug. They should all read approx 12v. If the small wire is 0v, your bulb has blown.

EDIT: Forgot to mention, Check this with the ignition on!

Edited by cobblers, 07 December 2009 - 06:32 PM.

[lam]

Nope, not the bulb. Tried the working one from the oil light in it and it didn't work (and vice versa - tried the alternator bulb in the oil one and it worked fine).

Any other suggestions?

[cobblers]

What voltage does the alternator output when it's running?

[lam]

If you mean on the battery voltage reading, once I jump start it begins around 10 and slowly drops down again. Like I said it's just not charged/charging. Apologies if that's not what you meant, I'm not the most mechanically minded.

What I can say is I just had the breakdown fella have a look who told me the alternator was fine, no issues (it's fairly new so didn't think it was that anyhow). He was pretty useless though and the best he could suggest was 'some fault in the electrical circuit'...

Edited by lam, 07 December 2009 - 07:05 PM.

[welshdan]

is your fanbelt still there?

[lam]

Yep, the fanbelt is present and running fine.

[lam]

Anyone??

I'm in a real dilemma with no real answers.

[tommy13]

Pull the plug from the rear of the alternator. With a voltmeter or test lamp, check the large terminal is live as the wire from this should be connected to the battery live.
With the ignition on, using a short piece of wire, connect the small terminal to earth and see if the ignition warning lamp comes on.
If both these tests are OK then the alternator is at fault.

[dklawson]

As a footnote to Tommy's suggested tests above, do NOT unplug the alternator from the loom with the engine running. Only unplug the alternator with the engine OFF.

As he suggested, with the ignition on, you should find voltage between earth and each of the pins in the alternator plug. If you do not find voltage on each of the pins in the plug, you have a problem somewhere other than the alternator. If the big wires are not "hot" they may be broken in the plug or on their far ends (check the starter solenoid in particular). If the small wire does not have voltage on it, look for issues both at the alternator plug AND perhaps at the ignition switch. When the ignition switch is in the run position, power is supposed to flow from the switch, down a white wire to the warning lamp, then from the lamp along the small wire (brown/yellow ?) to the alternator plug.

If you find voltage on all the alternator plug wires, look for problems IN the alternator itself.

[Lukes_mini]

I had this same problem last month with my mini. It turned out to be where the wiring loom went past the starter motor wiring it had worn throught the little brown/yellow wire which is the exciter wire for the alternator on my mini. I replaced this bit of wire and has solved the problem.

[lam]

Hey Luke, that's exactly what it was! All fine now, thanks for your help everyone...

[mini_mad69]

Im having a charging problem with my car.
Firstly checked all wires, found a small one in the alternator to be loose, so re-attatched it, all earths are in perfect condition.

Ignition on I get the red light, engine on, red light goes out. Battery won't charge though. Which led me to the battery being at fault. Although if I leave it on jump cables from another car it will charge up lovely.

If I run the car with nothing on, it will charge up a little bit. So If I go for a drive with nothing on, the car will charge up a little and be able to start itself again.


Edit: It's a 1985 mini, it's got a pug306 diesel battery

Edited by mini_mad69, 08 December 2009 - 10:26 PM.