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Alternator at fault?
https://forums.tipec.net/viewtopic.php?f=25&t=12212		 Page 1 of 1
Author:  swallowtaillee [ Wed Jan 18, 2012 9:55 pm ]
Post subject:  Alternator at fault?
hello! my first post for my first porsche! haha. go easy on me!

i have a 1985 944 - square dash. the other day after a long drive, i turned the car off and the battery light stayed on with the key removed- but the light went out when i started it and remained off whilst driving.

a couple of days later the light came on and stayed on while driving, but voltage was still good - drove round for a week with no issues (other than the battery light constantly on), light went out when i turned the car off unlike the time before.

Its like what ever was causing the light to come on when the car is off has switched around and now is causing it to stay on whilst running rather than off.

then tonight, the battery light doesn't come on at any time, and the alternator stopped charging resulting in voltage dropping until the car cut out.

just wondered if anyone has had the same problem its obviously something to do with the alternator, i have checked the belt and connections. all fine. i was thinking that it could be the voltage regulator as i have read on another forum that they can make the battery light stay on when the car is turned off and key removed - also could this be causing the symptoms to switch around as such??

any help or advice would be greatly appreciated!! :D

thanks guys!
Author:  ChrisM [ Fri Jan 20, 2012 11:54 am ]
Post subject:  Re: Alternator at fault?
I have a similar problem with mine. No solution ad yet, but I think its a bad earth or loose connection.

In my case revving the engine hard clears it somtimes it moving the car. I'm not convinced that the light going out always means you're getting a charge. We did put new connections on the wires by the brake servo which improved the voltage, but hasn't solved the light issue.

My money is on an earth.
Author:  tr7v8 [ Fri Jan 20, 2012 12:19 pm ]
Post subject:  Re: Alternator at fault?
In simple terms your alternator is knackered!
What is happening is that the light staying on points to a regulator fault & not coming on not charging could be either regulator or a sticky brush. Personally I'd get the alternator to a good autoelectrician to test/strip & overhaul.
Author:  ChrisM [ Fri Jan 20, 2012 12:42 pm ]
Post subject:  Re: Alternator at fault?
I've tried three alternators now. All the same.
Author:  swallowtaillee [ Fri Jan 20, 2012 12:51 pm ]
Post subject:  Re: Alternator at fault?
thanks for your help and advice! i want to rule everything else out before getting a new alt. cheapest ones i have seen are like £350-£400!!!!!#

think im gunna try trace the wiring as the red cable that connects at the alternator has got hot an melted the sheaving which would suggest there is too much resistance causing it to get hot. i think its probably going to be where the cable is bridged at the starter under the car.

i took the alternator out and stripped it down, all looks good but could still be the voltage regulator.

also took all the dash out last night as i read on another forum that if the bulb is blown to the battery light the trigger wire which runs through the bulb wont trigger the alternator to start charging! rubbish design! anyway bulb was fine! :(
Author:  tr7v8 [ Fri Jan 20, 2012 1:15 pm ]
Post subject:  Re: Alternator at fault?
ChrisM wrote:
I've tried three alternators now. All the same.

Have you checked the battery supply & earth leads? Also I cannot remembe if this is externally sensed or internal but I assume the ignition warning light is OK? As it maybe a part of the alternator sense circuit.
Author:  tr7v8 [ Fri Jan 20, 2012 1:17 pm ]
Post subject:  Re: Alternator at fault?
swallowtaillee wrote:
thanks for your help and advice! i want to rule everything else out before getting a new alt. cheapest ones i have seen are like £350-£400!!!!!#

think im gunna try trace the wiring as the red cable that connects at the alternator has got hot an melted the sheaving which would suggest there is too much resistance causing it to get hot. i think its probably going to be where the cable is bridged at the starter under the car.

i took the alternator out and stripped it down, all looks good but could still be the voltage regulator.

also took all the dash out last night as i read on another forum that if the bulb is blown to the battery light the trigger wire which runs through the bulb wont trigger the alternator to start charging! rubbish design! anyway bulb was fine! :(

Worth finding a decent auto electrics place & getting them to test it on the rig.

As for externally sensed through the ignition warning light :P You'll hate more modern cars then where the ECU controls charge current.
Author:  ChrisM [ Sun Jan 22, 2012 8:15 pm ]
Post subject:  Re: Alternator at fault?
Well my (or at least one) problem has been traced to a faulty relay for the rear heated screen. It was permanently live, even when turned off.

It also seems my cooling fan switch has a mind of it's own.

For another problem please see my thread about a missing relay :) viewtopic.php?f=25&t=12229
Author:  ChrisM [ Sun Feb 12, 2012 5:44 pm ]
Post subject:  Re: Alternator at fault?
bit of a thread resurrection, but we've found the real cause of this problem, on my car at least.

Even after disconecting the rear screen the throttle still needed a "blip" to make the battery light go out. Then a couple of weeks ago the clutch slave cylinder went and the car has been off the road until todaymwhern we changed it.

In the process of changing it the starter motor had to come off, and to cut a long and slightly frustrating story short is turns out that there is a wire from the alternator to the starter and the connector on it was hanging by a thread. Taking the starter off to change hte cylinder finished it off.

It remains to be seen what happens from a really cold start, but the light has gone off every time so far!
Author:  tr7v8 [ Sun Feb 12, 2012 6:33 pm ]
Post subject:  Re: Alternator at fault?
That wire is probably the sense wire & because the alternator couldn't see the charge because of the high resistance would have caused probs. Worth noting for future reference that this alternator is externally sensed.
Author:  ChrisM [ Sun Feb 12, 2012 7:03 pm ]
Post subject:  Re: Alternator at fault?
tr7v8 wrote:
That wire is probably the sense wire & because the alternator couldn't see the charge because of the high resistance would have caused probs. Worth noting for future reference that this alternator is externally sensed.


It's a really thick wire, so must carry a lot of load! Same thickness as the lead from the battery to the starter.

Is it possible that the charge to the battery is routed via the starter? When we tested the chage at the alternator the alternator was kicking out good voltage, but none of it was making it to the battery, which was running at just under 12v according to our battery tester.
Author:  dirty hands [ Sun Feb 12, 2012 7:06 pm ]
Post subject:  Re: Alternator at fault?
hi jim ,it wasnt the blue sensor wire,it was the main voltage wire (red),that was at fault with chris,car i believe at27yrs old its had quite a bit of current go through it! must have been just touching and when loaded up broke its contact...could be one to remember for the future ...regards phil
Author:  Richy_S [ Sun Feb 12, 2012 9:59 pm ]
Post subject:  Re: Alternator at fault?
Glad you have fixed the problem but reading the above seems a bit over complex.

The alternator will develop a voltage and the charging current(limited) will depend on how much the battery draws.

The output for the dash lamp is just that, coming on when there is a differential in voltages.

Rich
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