alternator....or?

[s2driveruk]

at idle, i seem to have a slight 'pulsing' effect on the lighting in the car (e.g. the interior light) and it is just about perceptable on the tail lights too.

The voltmeter in the car is holding pretty steady at idle but not sure what would be causing this...all seems fine at speed, just generally noticable when stationary.

I guess could be a tired alternator or bushings, regulator of possibly a poor earth somewhere.

Any ideas?

[Ian Simmonds]

It's probably the voltage regulator, if it packs up you'll get an uncontrolled output, which on ours set the ABS warning off and the volts meter go off te scale.. Shut it down straight away if it does... You don't want anything 'fried'....

[johne]

There's a lot going on for the alternator and its regulator at idle as it isn't turning fast enough to generate much electricity and is trying to keep that 2 volt difference between the battery 12 volts and the 14 or so volts of it's regulated output whilst at the same time the battery wants power to recharge, the car needs power to run and as the alternator tries to turn on it loads the engine which causes the engine to slow down until the ISV can do it's bit.

In short, it may well just be the way things are or your brushes are getting to the end of their life. Doesn't to me indicate imminent failure of the alternator.

John

[s2driveruk]

thanks guys, so it sounds like i might as well pull it out and get it off to a local refurb specialist to get everything checked over/rebuilt.

[johne]

Regulators (which come with the brushes attached) are cheap and easy to change in situ so you could give that a try first if you like.

John

[mcandmar]

I would try swapping out the regulator first, but could be a failed diode in the rectifier or winding inside the alternator.

[A1QSHIP]

With a digital volt meter set to A/C volts measure the voltage at the battery. With the headlights on & engine about 3,000 rpm you should see no more than 0.5 volts a/c. If more than that you have an alternator diode/rectifier problem.
HTH, Chris

[mcandmar]

I never knew you could do that, nice tip

[s2driveruk]

nice one will check later

[s2driveruk]

With a digital volt meter set to A/C volts measure the voltage at the battery. With the headlights on & engine about 3,000 rpm you should see no more than 0.5 volts a/c. If more than that you have an alternator diode/rectifier problem.
HTH, Chris

So just checked and its showing 0.02 so presuming its not that then. Will change the VR and go from there.

David

[AndyP]

So just checked and its showing 0.02 so presuming its not that then. Will change the VR and go from there.

David

Have you still got a 3B alternator? I have a 15v reg for this that I got from Jamo if you're interested?

[s2driveruk]

Yeah, I've also got the 15v VR...am wondering if its on its way out though the brushes dont look too bad...bit of corrosion on the tracks in place though.

Let me see if i can isolate that as the problem then i may take it from you. Don't remember the stock VR part number do you for the bosch unit? strggling to trace it

[AndyP]

The one I have came from here:-

http://www.woodauto.com/default.aspx

Sorry, don't know the Audi number.

[RS2junkie]

There's a lot going on for the alternator and its regulator at idle as it isn't turning fast enough to generate much electricity and is trying to keep that 2 volt difference between the battery 12 volts and the 14 or so volts of it's regulated output whilst at the same time the battery wants power to recharge, the car needs power to run and as the alternator tries to turn on it loads the engine which causes the engine to slow down until the ISV can do it's bit.

In short, it may well just be the way things are or your brushes are getting to the end of their life. Doesn't to me indicate imminent failure of the alternator.

John

John,

You again may be able to help me.

Had my alternator refurbished a while ago (bearings and bushes) and ever since the volts drop below 12v at idle, anything above idle and its back to normal (14v). Would you suspect the regulator ?. Is there anything else it could be ?

By the way, have ordered a new fan motor, (they are the same for LHD and RHD).

Thanks..

Paul

[johne]

"Volts drop below 12 volt at idle" - measured by what? If you mean as displayed on the in car voltmeter, then they are notoriously inaccurate.

As long as the voltage returns to around 14 volts once you're above idle and the ignition warning light isn't glowing red I wouldn't be concerned but the first step would be to measure the actual voltage using a decent digital voltmeter (DVM).

John