Battery Drain

vaultsman

Well-Known Member
#1
Having been away for a couple of weeks, I came home and went to start Occie, my Series 2 3500S, only to find the battery was completely dead. No voltage reading at all on the multimeter.

Managed, to my surprise, to get it back to seemingly fully charged using the CTEK charger in Recondition mode. All was well for a couple of days but then, after another few days of non-use, the engine struggled to spin over.

Suspecting parasitic drain, I checked for it using the meter on the 10A range but could find no evidence of a drain. The battery was about 7 years old anyway, so I bought a new battery and fitted it, fully charged at approx 13V….with the same result, after 2 or 3 days of non-use the voltage had dropped to 12V and it was sluggish turning over.

Longish story shorter, I’ve found a 40mA drain across fuse #1 (Battery Control). Leaving the blade fuse out, the battery voltage has stayed at 12.9V for the last 4 days.

I’ve disconnected the boot lamp, time clock, interior light, cigar lighter & map light, and the LH horn so far…..but still the 40mA drain is registering across the fuseway.

I’ll do the RH horn when I’ve had this tea and warmed up a tad :), then as far as I can see from the WD that just leaves the horn switch and the terminal post.

Or am I missing something? Any ideas?
 

vaultsman

Well-Known Member
#6
Just the stereo head unit which is ignition controlled.

Hmm...but, from memory, I think there's a permanent live connection as well.
 

sdibbers

Well-Known Member
#7
Undo the + lead to the battery. Bridge with the ammeter between the lead and the batt terminal. (Make sure everything is off and the interior lights are off too).

Note the draw on the meter. Sub 35 milliamps is ok normally, higher suggests a parasitic draw. Now pull one fuse, check amps again. If it’s the same, replace fuse and pull the next one. Keep doing this across the fuse box. When you find the amps dropping to normal levels you’ve found the circuit containing the problem. If non of these change it’s suggests something without a fuse such as the starter, solenoid or alternator.

Hope that helps you some.
 

vaultsman

Well-Known Member
#8
Undo the + lead to the battery. Bridge with the ammeter between the lead and the batt terminal. (Make sure everything is off and the interior lights are off too).

Note the draw on the meter. Sub 35 milliamps is ok normally, higher suggests a parasitic draw. Now pull one fuse, check amps again. If it’s the same, replace fuse and pull the next one. Keep doing this across the fuse box. When you find the amps dropping to normal levels you’ve found the circuit containing the problem. If non of these change it’s suggests something without a fuse such as the starter, solenoid or alternator.

Hope that helps you some.

Yes, that's basically what I did to find the source of the drain although I always disconnect the negative to avoid the possibiilty of a short to the body.

The parasitic draw is 40mA across fuse #1.

Stan
 

vaultsman

Well-Known Member
#10
What’s on fuse 1 Stan? I have a sI so don’t know in sII cars. Also, 40mA is a pretty low drain.
Basically what I listed on my original post, mate.

Agree, 40mA is not a lot.......but it seems to be enough if the car's not in use for a couple of days or more. :)
 

ghce

Well-Known Member
#11
40mA whilst not sounding a lot is pretty significant especially if left like that for a week or 2, I always estimate that no more than 10mA should be drawn especially on a low tech car like a P6, in the big scheme of things 40 is too much.

One thing of note in flooded lead acid batteries is that the internal or self discharge is probably greater than that, with a battery of that age you would expect a self discharge rate of at least 120 or so mA, ie old batteries go flat faster than new ones.

This is generally caused by sludge and other contaminants causing internal current draw.

In the dim distant past I had got fairly anal about these things and fully charged (plus a bit) batteries then drained all the electrolyte, flushed the casings out then refilled with new acid at the correct specific gravity, helped significantly but you still are limited by the amount of sulfation and lead erosion or plate substructure that fails with time.

Graeme
 

ghce

Well-Known Member
#12
Just the stereo head unit which is ignition controlled.

Hmm...but, from memory, I think there's a permanent live connection as well.
Normally would expect memory circuit to take less than 1 mA, basically in the micro amp range however thats not to say that the stereo isn't a bit fritzy as I recall that the car factory radios that 90's Honda Civics used had a common fault where the stereo would draw quite large current after it was switched off causing the battery to flat pretty quickly.

Leaking electrolytic capacitors were at fault if memory serves me and these are in most stereos and often cause erratic faults and failures, so its a possibility.

Graeme
 

vaultsman

Well-Known Member
#13
40mA whilst not sounding a lot is pretty significant especially if left like that for a week or 2, I always estimate that no more than 10mA should be drawn especially on a low tech car like a P6, in the big scheme of things 40 is too much.

One thing of note in flooded lead acid batteries is that the internal or self discharge is probably greater than that, with a battery of that age you would expect a self discharge rate of at least 120 or so mA, ie old batteries go flat faster than new ones.

This is generally caused by sludge and other contaminants causing internal current draw.

In the dim distant past I had got fairly anal about these things and fully charged (plus a bit) batteries then drained all the electrolyte, flushed the casings out then refilled with new acid at the correct specific gravity, helped significantly but you still are limited by the amount of sulfation and lead erosion or plate substructure that fails with time.

Graeme
Thanks Graeme,

I'm far from au fait with all the technicalities :), but I did think the existing battery going completely flat may have knackered it, so I put a brand new one in.
At the moment I'm pulling #1 fuse while the car's stationary, and the voltage is still holding steady around 12.7V.
I just pop the fuse back in when I need to use the car......then I just need to remember to take it out again, which is far from a foolproof method these days. :LOL:
 

vaultsman

Well-Known Member
#14
Normally would expect memory circuit to take less than 1 mA, basically in the micro amp range however thats not to say that the stereo isn't a bit fritzy as I recall that the car factory radios that 90's Honda Civics used had a common fault where the stereo would draw quite large current after it was switched off causing the battery to flat pretty quickly.

Leaking electrolytic capacitors were at fault if memory serves me and these are in most stereos and often cause erratic faults and failures, so its a possibility.

Graeme
Thanks mate,

The stereo dates from 2008 when I put it in from new, I'll pull it and see what effect that has on the drain.

Stan
 

sdibbers

Well-Known Member
#15
So battery control would be the regulator for the alternator I’m guessing? I think on RHD cars that’s in the glove box right? Maybe try just unplugging that and see if your draw disappears?
 

vaultsman

Well-Known Member
#16
So battery control would be the regulator for the alternator I’m guessing? I think on RHD cars that’s in the glove box right? Maybe try just unplugging that and see if your draw disappears?
Thanks.
It's an integral regulator on the ACRs and, as Colin suggested above, I've unplugged the alternator but the draw's still there.
 

vaultsman

Well-Known Member
#20
Normally would expect memory circuit to take less than 1 mA, basically in the micro amp range however thats not to say that the stereo isn't a bit fritzy as I recall that the car factory radios that 90's Honda Civics used had a common fault where the stereo would draw quite large current after it was switched off causing the battery to flat pretty quickly.

Leaking electrolytic capacitors were at fault if memory serves me and these are in most stereos and often cause erratic faults and failures, so its a possibility.

Graeme
UPDATE:

Thanks for this, Graeme.

It is indeed the stereo that's causing the issue.
When I unplug it the current drain at the battery drops to 2 to 3 mA. :)

Stan
 
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