4a parasitic drain c180 2004

[zxcvbnm]

I have a c180 2004 (possibly w203?)

I changed the battery at Christmas because it went dead in cold weather and had trouble getting it back up.

Since then it has been harder to keep the new battery charged. There seems to be plenty of voltage when driving and it seems to finish a journey with more charge but then drifts down. Then last week, parked in hot sun, it decided it was unhappy and went into "alternator error go to workshop" and limp mode at 30mph with all electrics disabled. It then put out 17v on the way home, which probably didn't do the battery any good. On getting home it would still start but by the next morning the battery was dead. I jumped it and once jumped it was perfectly happy which suggests it was just the battery being a bit low that bothered it not the actual alternator? I had to disconnect the battery to get it to trickle charge.

I put a multimeter on it today between the negative and the battery terminal and it read between 3.2a and 4.2a which is presumably about 40w. I pulled virtually every fuse out in the engine bay, the passenger side and the boot. None of them seemed to help. I did not remove all the square cube block things plugged into the fuse panels. This presumably means it is drawing 40w which seems alot. Where is it going? I left it for half an hour on the multimeter in case something would go to sleep but it stayed at around 4a. Which explains why I struggled to charge the battery.

Any ideas? Taking it to the garage is the obvious but it would be nice to have an idea of what is wrong first. What can draw 4a without an obvious fuse?

I don't really know what I am doing so easy answers if possible please... Starting to wonder if its time to scrap it. Still drives very nice but...

Thanks

 

[Blobcat]

Hello and welcome,

Faulty regulator pack on the alternator can give a high current draw and flat battery overnight.

 

[Flyinspanner]

As above, if the rectifier pack is failing it can allow current to flow back through it when ‘off’ - that may also explain the 17v when running?

get the alternator tested asap. (Search for any alternator specialists or Bosch service centres near you?)

 

[pgh13]

Couple of checks at home... At 4A the alternator may feel warm. You could also try disconnecting the alternator, after first disconnecting the battery. Then reconnect the battery and see if the current has dropped to a low value

 

[s5tuart]

Depending on the meter you are using, I’m not sure you can see current draw just by measuring across the + and - terminals…….

 

[s5tuart]

ps. Most service places can check the battery for you for free. That’s where I would start.

 

[alexanderfoti]

100% alternator regulator, combined with your 17V charging voltage

 

[zxcvbnm]

Thank you for your ideas. It seems the alternator or regulator is most likely.

I didn't check the load positive to negative, I put the multimeter between the negative terminal and the negative battery clamp/cable in 10a mode.

If the car is happy with the battery voltage then it seems to operate OK? Its when it thinks the battery is a bit low then it throws a fit. I'm not sure if the 17v was due to the regulator or if limp mode and no electrics just disabled it.

I had the battery tested briefly at kwik fit for free and they said looked fine to them. Its quite a smart bosch one. I thought it might all just be a dud battery but the fact the car is draining four amps when off does rather suggest it may not be the batteries fault it is not holding up. Of course 17v may not have helped now.

I measured the voltage while driving by a cigarette lighter plug in gadget that is not perfect but actually fairly close.

Annoyingly I went out this evening with a basic infrared thermometer but the car only asked for 1a and after 30 seconds went down to 0.2a. Why? Does it only go wrong when its warm in sunshine, not on a cold evening? Or did I knock a connection poking the regulator with my hand. Or is there a regulator fault that's intermittent?

I did not realize the regulator could drain power even when off. Is there an easy plug somewhere that would disable it?

Thanks again

 

[Blobcat]

Thank you for your ideas. It seems the alternator or regulator is most likely.

I didn't check the load positive to negative, I put the multimeter between the negative terminal and the negative battery clamp/cable in 10a mode.

If the car is happy with the battery voltage then it seems to operate OK? Its when it thinks the battery is a bit low then it throws a fit. I'm not sure if the 17v was due to the regulator or if limp mode and no electrics just disabled it.

I had the battery tested briefly at kwik fit for free and they said looked fine to them. Its quite a smart bosch one. I thought it might all just be a dud battery but the fact the car is draining four amps when off does rather suggest it may not be the batteries fault it is not holding up. Of course 17v may not have helped now.

I measured the voltage while driving by a cigarette lighter plug in gadget that is not perfect but actually fairly close.

Annoyingly I went out this evening with a basic infrared thermometer but the car only asked for 1a and after 30 seconds went down to 0.2a. Why? Does it only go wrong when its warm in sunshine, not on a cold evening? Or did I knock a connection poking the regulator with my hand. Or is there a regulator fault that's intermittent?

I did not realize the regulator could drain power even when off. Is there an easy plug somewhere that would disable it?

Thanks again

Depends on where the alternator stops as it might only be one of the diodes that has failed. Get the alternator off and tested/repaired/refurbished at a specialist