Power consumption on a BKD 2.0TDI

[rabbituk]

For the past few months I've had a noise from the engine bay that I just kept ignoring. I thought it might be my turbo oil feed leak returning but oil consumption whilst not great, wasn't that bad. Then last week the over-running pulley fell off the alternator.



I sourced a new alternator and planned to fit it at the weekend. But not before I had to drive home 50 miles from where I was working on Friday. It was night so I needed headlights but they would only draw around 10A and so with a 70Ah battery I /thought/ it should be good for a few hours as long as I didn't have blowers, screen heaters or stereo running. I was very wrong. 'Managed about 35 miles towards home with 2 /cold/ starts before low battery light came on and then it died completely after another mile with the steering assist completely disappearing. So I understand now that the power steering is electric so that is probably consuming something but where does it all go? EPS motors online seem to be around 35A. Is EPS the biggest draw? What else might be significant. I think headlights are actually quite a small drain by comparison to other components. I'm curious to know what else there is. Any thoughts?

 

[NHN]

Headlights take a whack, xenon's specifically.

 

[Bloxham]

You can renew the pulley, no need to replace the whole alternator - you need the tools but they're cheap enough.

 

[NHN]

Tbh there's a guy on eBay that sells complete alternators, as new refurbed with new pulleys for very good prices.

Used several times & also clients, called mariusz iirc.

 

[paddy]

TBH a starter motor is basically a dead short and you had 2 cold starts but more importantly no top up charge between. the car prob has a 100a/h alternator which gives you a clue as to what the discharge could be on a bad day. The days of powering a 12v coil and set of points are long gone and you now have high and low pressure fuel pumps running constant as well as power steering and ECU's and ignition systems. Couple that with once the battery get below half charge you will be losing power anyway and chances are it would never hold the advertised 70a/h after a while in the first place i think you did well to do 35 miles.
As Nige says change the alternator or you will just be chasing the next problem in a few weeks time. Everything has a life and if the pulley went what are the bearings doing ?

 

[rabbituk]

I'd forgotten about the fuel pumps, too used to petrol carb engines. So at a rough guess, fuel pumps seem to be around 10A. So post crank running current draws are, I think:-
EPS @ 35A
2 x Fuel pumps @10A
Headlights total @ 10A
This is extremely rough but I'm just trying to satisfy my curiousity.

I agree that the battery depletion caused by the 2 cold starts must be significant.

I replaced the alternator with a second hand one because somebody was selling near where I worked. It cost £10 and took me about 1 hour to fit on Saturday morning. I did consider replacing just the pulley which would have been easier but I don't own the pulley tool so that would have meant a shipping delay. It's early days with this replacement alternator but I've done over 100 miles since and voltages seem okay. Also physically looks a lot cleaner than my old alternator for what it's worth. Nothing's shown up in the VCDS scan. Touch wood.

 

[paddy]

Lights are probably nearer 12-14 amp with tails , brakes , sides and dash but if your EPS is 35a then that explains it as the car is not going get that after just 2/3 drain on the battery. Remember it doesnt actually give 70 Amps for 1 hour then stop, it drops amps and volts as it goes. half way through that it will be capable of a lot less ie... the lights will get dimmer and dimmer, they will not just stop...