Alternator

[210bhp]

Hello electrical gurus,

I suspect an alternator problem and I have removed it complete with the fan housing from the RS.
Is there a definitive way of testing if it is functional with simple diagnostic equipment in situ (i.e. without dismantling it further)? I only have a simple test meter and normal tools, no electrical equipment as such.

Can anyone describe the step by step method I need to use if this is possible.

Thanks

Regards
Mike

[KS]

Do you have a copy of the proper Porsche factory workshop manual? If so, in there it tells you how to check the resistance etc through various parts of the alternator. That's how I discovered the fault with mine.

[210bhp]

Very helpful Keith thanks. I do have the workshop manual and I have flicked through the pages which seem to suggest,

I can test the function of the alternator in the car (but I've already removed it.......)
I can test the function with it out of the car with an oscilloscope (which I don't have)
I can test the various parts and functions with a test lamp if I dismantle the unit further.....


Is there a simple way of checking if it is kaput without dismantling?
Can you connect a battery, spin it in the housing for instance with an electric drill and do some simple tests with a multimeter?

Regards
Mike

[impmad2000]

Do you have a local alternator refurbishment/repair shop ? they may be able to do a quick test for perhaps a small charge.

[nj1052]

Yes you can just spin it up with a drill. I've done this several times. Just hook it up with a good battery with +ve to the output and the field exciter connection, -ve to the fan housing and off you go. As the alternator starts to generate you will feel the torque reaction on the drill. Connect a meter and you can see the voltage build up with rpm. Not super accurate but it proves it works.

Cheers

PS I use a mains powered drill as it needs higher speed than a battery one provides.

[Jonny Hart]

You can get the alternator tested and refurbed with new bearings, brushes, regulator (if applicable) to good as new for around £100. Hardly worth the bother of checking it yourself.

If you put it in for refurb, make sure the place has the means to mount it otherwise they will need the housing as well.

[210bhp]

Thanks Tim, NJ, and Jonny

At this stage I am trying to eliminate one thing at once and it would be nice to just check if I have a working alternator. It is newish (in road miles terms) so I am sure it doesn't need refurbed but I suspect damage. I have two or three spares but all are unknown as working so they don't help to eliminate the problem. I have gone through everything else (I think) so I'm down to a damaged alternator or an issue in the wiring loom.

Regards
Mike

[Lightweight_911]

Mike - what are/were the symptoms ?

[210bhp]

Red warning light on constantly (all of a sudden).

Batteries check
Battery terminal check
Battery earth check
Battery terminal clean check
Fan belt check
Gearbox earth check
Alternator earth check
Cdi box check
Regulator check
14 pinlug check
Starter motor live check.

Engine runs fine but tests show low or no charging. I want to know if the fault lies in the alternator or in the wiring/warning light. If I had a 'known' working spare I would be fine but I have 3 'unknown' alternators so I don't want to confuse matters (myself).

If you think I've missed anything please let me know.

Regards
Mike

[210bhp]

Thought you would like to know the fix for this problem.

Symptoms, red ignition light on bright, not dimming or flickering, constantly bright. 12 volts+ at both batteries with a test but absolutely no change when increasing the revs. Car runs fine and with a short test all electrics seem to work, lights,horn, blower fan etc.

As always it usually the simple things which are at fault. There is always a temptation to fear the worst.

Despite not knowing the condition of my spare alternators I thought it best to swop one into the fan and reassemble. Still trying to eliminate one thing at a time. Started up and the red light goes out completely, hurray! But within 30 seconds it's back on, boo! Just as bright as ever. There was a brief increase in the multimeter reading across one battery to 14 volts or so then back to 12.

Suspect both alternators or a lazy or non functioning regulator or the wiring (likely an earth strap) somewhere.

Decided to swop out the regulator for one of my spares but before I did I had a meeting with the local automotive electronics engineer and he confirmed it was unlikely to be the alternator, more likely the regulator or the batteries. Can't be the batteries I said, they are both showing a healthy 12.3 volts. That's not always a guarantee he said. When the batteries are put under load they won't charge if there's a fault like a dodgy cell.

Took the batteries to him for a load test and lo and behold, 12.2 volts on one and 12.3 volts on the other but applying a load and both went to zero (!) in a couple of seconds. There's your problem he said. The alternator can't charge anything that won't accept it.

Two new batteries fitted and the problem is solved. The simplest solution.

Regards
Mike

[bjmullan]

And now we have a car to take to Scilly

[Joelipol]

You can get the alternator tested and refurbed with new bearings, brushes, regulator (if applicable) to good as new for around £100. Hardly worth the bother of checking it yourself.

If you put it in for refurb, make sure the place has the means to mount it otherwise they will need the housing as well.

@JonnyHart you say you say you can get an alternator checked and rebuilt for a £100... whom might that be with?