[Si]

Help - quick Q about Alternators (sorry my questions are never actually quick!)

I dowt this exact question has been asked so i hav'nt done a search..yet, but

How far do you think i'd get with a dodgy alternator? I've had the battery on charge for about 18hrs overnight aswell, i need to do a 11 mile trip across town.

Been having a few problems and it's either the loom or alternator.

On wed took the car out for a quick run for the first time since i put the new engine and box, i'd had a few problems caused by a missing earth but the car ran fine when i took it out.

The next day it would'nt start, cranked but no spark, i managed to drain the battery so i put it on charge overnight.

Just tried to start the car and although it was slightly sluggish it started & idled/reved OK, seems fine again.

With the engine running battery shows 12.46v and 12.66v with the engine off, I get 12.44v at the B+ on the alternator and about 12.5v on the D+.

So I think the problem is either with the D+ wire which may have come loose somewhere in the loom or the alternators dead, i've got another one but need to run the car tonight, so will i make it?

 

[trackside]

If the alternator is giving you a voltage it should be charging - are you sure the battery is not the problem?

 

[Si]

battery

It could be, i've been swapping between 2 different ones so i've always got a charged backup, i'll have to try charging the one i had in yesterday and see if it holds a charge.

I checked the battery before connecting it up and it was at just over 13v, with it connected it was lower so maybe i've got a short somewhere causing it to drain.

If the batterys got enough power to crank the starter it should be able to produce a spark should'nt it?

There's always a chance that it would'nt start yesterday because the LT/HT leads were damp but i did'nt have time to check.

It's great that it's starting again but a bit of a bugger when you don't exactly know whats up! I don't want to conk out half way across the city.

 

[Si]

No charge warning light

It's not comming on atall, is there an easy way to check if the bulbs OK, or have i got to pull the dash apart?

 

[ShadowWorks]

With your engine running your battery should show 14.4 volts for 30 seconds and then roll back to 13.2 at the least, noway should it go down to 12.6, thats what a good battery should float at, remember that a battery just starts the car and provides storage for current, it makes no power at all, its sounds to me like your battery is not being charged and your alternator is only producing trickle current, I would recommend you check the alternators bushes, the wiring and take it from there, you wont get more than 8 miles from a ok battery before your cars electrics say bye bye and bring you to a rapid stop.

 

[Si]

battery

Just checked the battery again, it's at about 12.9v with the engine off.

Going to look at the warning light now.

 

[Si]

This is soooo weird?????

OK so firstly i checked the warning light, with it connected to the alternator, nothing on any ignition setting, took the connector off and touched it to the alternator case, this time the light is lit when i turn the key.

Is'nt that supposed to mean the Alternators gone?

So as i said the battery voltage was at 12.9v with the engine & electrics off, I thought gone on i'll try and make it accross town, i can always leave the car at my mates house and return with a freshly charged battery if it's looking dodgy, took a digi multimeter with me (also drove with no lights/did'nt open window or listed to stereo)

When i got there I checked the voltage of the battery again, 13.2v this time, and when i got home, 13.4v.....so what's going on?

It looks like the alternators gone but the battery is still charging????? Uhhhh?

 

[ShadowWorks]

Electrical gremlines!

Its working intermittently thats the worst kind of fault cos if you show anybody it will work and one your on your own it plays up.

There are alternators on Ebay from donar cars, you can get it for a tenner

I dont recommend driving your battery into the ground, lead acid batteries never fully recover once you pan cake them, its just the way it is, nicads and most modern batteries work in the opposite fashion.

I would be point my finger at your alternator and shaking my head right now, but one thing, did your alternator work before? or is it from the donar car?

 

[john-w]

Make sure you have the earth wire between the alternator & ground, the wire should be near the oil pump housing. Quick test for the alternator, park the car up against a wall, turn on the headlights & let the car idle, now blip the throttle, you should see the lights brighten up if the alternator is charging.

 

[cdaly]

i checked the warning light, with it connected to the alternator, nothing on any ignition setting, took the connector off and touched it to the alternator case, this time the light is lit when i turn the key.

Pull the voltage regulator from the back of the alternater {2 screws} and inspect the state of the brushes. If they're fine {you can get replacement brushes from Saab for about a fiver}, check the alternator ground wire.

 

[Si]

Alternator

The alternator followed the engine, i think the bearings on the older one may be a bit noisy but i did'nt have a charging problem, i might just swap out the regulator and see if that makes any difference, also going to check the battery again and see if it's drained much overnight, if so i guess a short is causing the problem.

The alternator earth strap is fine & securley attached, may replace some from teh engine to bulk head though as they are looking a bit corroded.

Cheers for your input anyway, i'll get there soon hopefully!

 

[ShadowWorks]

For the time it takes put your old alternator on and see what happens, its less tinkering about than find the culprit which will be something tinny anyway.

Like your regulator or bushes or diodes?