Battery not charging

[valleyautos]

Hi

 

Having a problem with my 1.9 tdi the battery is not charging i have changed the alternator for a know good one and the battery put has made no change still not charging anyone any ideas.

 

Thanks

[Gaz]

Is it not charging, or is the battery not accepting charge.

 

Have you charged the battery - as in overnight with a trickle charger?

 

Have you had the battery checked?

 

Any lights on your instrument cluster?

 

Any error codes or 'alternator workshop' messages (or similar)?

 

Gaz 

[jimbof]

These cars are quite heavy on their batteries (mine is on it's 3rd battery now at 8 years old), so perhaps it just needs retiring.

[CRC]

Placing a volt meter across the battery terminals will tell you a lot.

 

Look at the voltage reading when not running, then cranking, then ticking over, then being gently revved.

 

Not sure about the Superb alternator, but, in general, if an alternator is not charging then it's often the "brushes with voltage regulator" that's the problem and they're not that dear.

 

Effectively, the regulator regulates the voltage and hence current that is being applied by the brushes to the spinning coils fixed to the spinning shaft. The solid state regulator controls the output from the alternator by the controlling the input to the spinning coils, the current being much smaller on this side of the fence.

 

Normally, the "charge" light on the dash is just a bulb that lights when the voltage at the ignition switch (the battery) is not equal to the voltage being generated at the alternator.

[rotodiesel]

I can't agree that these cars are heavy on batteries - I changed mine after 9 years' use on an AWX engine without any failure whatsoever. I did this just as a precaution as I had had my money's worth and a failure would cost me more than the residual value of the battery. I fitted another Varta, of course.

 

The Valeo alternators are more reliable than the Bosch which suffer from water ingress to the regulator. Either will run to a high mileage before needing brushes or bearings.

 

The real killer on the B5.5 is the sprag clutch in the alternator pulley. It's very prone to fail and can sometimes slip, giving a baffling "no charge" to a good alternator, simply because it's not being fully driven. Broken sprag pulleys have also been known to make an excursion through the radiator.

 

On any diesel B5.5, change the sprag pulley after about 80k miles.

 

rotodiesel.

Edited 3 April, 2014 by rotodiesel