Thread: D2a TD5 - low voltage when driving - sick battery or alternator?

At the moment this charging problem I have is intermittent.
When the red battery warning light comes on I get a reading of under 12v But when the light is off I get a normal voltage reading, I can rev the guts out of the motor ( Not something I like to do) and it will start to charge correctly again But it will drop out again quickly.
The alternator is nice and clean so that is why I am assuming that worn brushes/regulator are the culprit and not contamination.
I ordered a new set of brushes/regulator yesterday and have just received a call letting me know they have arrived so I will head into town to pick them up so that I can do the repair.
I will post the results of this when I have completed the repair

If you get a red warning light on the dash that should indicate a failing alternator. When the alternator on our D1 300Tdi was failing the tacho would stop and the red light would be on.
If the battery is starting the vehicle OK then it should be OK.

Success

It took me a while with my fat fingers and dodgy eyesight But I persevered and got the job done in about 2 hrs
The job really wasn't that difficult and the brushes were cheap at under $20 for Genuine Bosch brushes So if you have a similar problem and you can do a bit of soldering work then give it a go, Much Much cheaper than getting this done at a workshop

Voltage reading before the repair
alt.jpg

New brushes fitted

alt3.jpg

Voltage reading after the repair
alt1.jpg

good work

Originally Posted by Eevo

good work

I followed Bee utey's instructions in this thread that made the job Sooooooo much easier, Much obliged Bee utey
Alternator brushes, D2 V8

I will remove, clean and double check all the terminals and earth connections over the weekend when time allows.

Charged it again on the Ctek charger on Recon Mode last night. Disconnected the battery as the SLS kept intermittently running the pump every 2-3 seconds (even when the SLS fuse and relay were pulled I could hear a solenoid or relay clicking as it attempted to run it).

Reconnected it this morning, engine started well as always, vehicle charged at 13.9 initially for the drive to work and dropped down to 13.7 by the time I was at work. So seems to be running well there.

Of note is that when stopped (i.e. engine at idle at traffic lights/intersection etc) this drops down by at least 1 volt, i.e. down to 12.7 while sitting there. I doubt that illuminating the brake lights is enough to cause such a large voltage drop so assume it's the lower engine RPM. A blip of the throttle immediately increases the voltage. Is this normal for the alternator on the TD5 to drop down so much at idle or is this a sign of it being well worn and faulting?

td5 alternator | eBay seems that replacement TD5 alternators with what I assume to be a vacuum pump on the front are available new starting at $299.00. Maybe worth me considering as just replacing the bushes will still leave old bearings, rectifier and vacuum pump which could cause future issues. At 270,000km with what I believe to be the original alternator it's had a pretty good service life.

AFAIK the battery itself, at rest, will never be higher than 12.7v

http://www.mmbalmainauto.com.au/PDF/..._batteries.pdf

Originally Posted by 87County

AFAIK the battery itself, at rest, will never be higher than 12.7v

http://www.mmbalmainauto.com.au/PDF/..._batteries.pdf

that makes sense as all my deep cell batteries have a voltage of 12.7-12.8 when fully charged