Flat Battery Investigations

ulfilias · #1 22nd August 2013, 01:58 PM

Hi Guys,

Been running my 2000 S8 for a good few years now and after an initial fault where i'd wired the aftermarket stereo to leave the BOSE amp on i've had very little problems with the battery and starting.

However after working on the car for a month or so and moving it in and out of the factory at work, I had a dead battery issue. We charged it up and I went on a run up to leeds and the next morning it was flat. Went with the theory that the battery was a few years old and flattening it a few times and it had a memory and a new battery was in Order.

Fixed the prob for a few weeks. Cue a trip to Germany where I left the car for a few days and flat battery

The alternator will run the car fine as I found out when i loosly connected the negative lead went over some bumps, got home, stopped the engine and dead car!

So I've picked up a blade fuse tester (£12 ebay, you pull the fuse, place in socket, put tool in slot and read ampage) and have just gone through all my fuses. Took about 30mins but was easy to do. Igition off and key removed. Drivers door open. I got 5 fuses with some draw, mainly 0.02-0.05, though one at 0.35 and the stereo one in the boot at 0.15 (sat nav is always on). Checking them with me locked in the car and most of the low figure ones dropped to zero.

However the 0.35 one still seemed high. It's Yellow 4. The description reads "Air Conditioning/Intake blower, Auxilary Heater receiver, Multifunction Steering wheel, Instr. Cluster, Solar roof, Park aid"

Any ideas on what to check in that lot or if this is normal ???

Lee

Delboy · #2 22nd August 2013, 02:37 PM

Seems a bit suspect, the 0.35 amps sounds quite low but I don't know the capacity of your battery.

Have a look at this to determine if it would be enough to flatten your battery in the time frame you mention.

If you have access to a large amp meter put it between the battery and main feed to see total draw to determine if something else wrong.

Once you know your total draw you will be able to determine if the battery is U/S

PsYcHe · #3 22nd August 2013, 02:41 PM

Do you have a solar roof? If so, then there may well be current flowing over that fuse.

ulfilias · #4 22nd August 2013, 03:49 PM

Hi There,

I got a new battery about 3 weeks ago, so i'm certain it isn't that. I have a multimeter which I was tempted to see what the draw was with everything off, ie just to check is there is a short to ground.

Seem to recall it is this one

http://www.advancedbatterysupplies.c...attery019.html

Also while I drove the car for 30mins to get to where I left it, it had been on my drive unused for a few days too as I have a second car for back-up/commuting.

I'm guessing most peoples Yellow 4 fuse isn't on a 0.35amp drain when the car is off ???

Goran · #5 23rd August 2013, 09:49 AM

If its any help I measured my old S8 (FL) current draw with everything shut off, key out, at 0.24A (in the battery compartment, multimeter in series with battery)
Get yourself one of those clamp amp meters so you dont have to keep disconnecting the battery to put a standard multi meter in series. I need to get one too.
http://www.tmart.com/Mastech-Ms2001-...r_p144098.html
(make sure sensitivity is enough for low currents)

If you already measured it to be 0.35A, that shouldn't be high enough to kill a 95Ah fully charged battery in a week.
95x0.8/0.35 = 217hours, or 9 days to go down to 20% capacity.

Although its 0.35A is a bit high, have you run a VCDS auto-scan with everything switched on including the radio? Radio will sometimes only show speaker-to-ground errors if its switched on whilst you scan it.

Also, some cars apparently go into sleep mode 15~20 minutes after the key is out, so may be worthwhile measuring current draw again to see if it reduces.

notorious · #6 25th August 2013, 08:23 PM

0.35A is a bit high.

I've got 0.13A total drain at battery terminals. Still too high IMHO. About half of that is stereo one in the boot (car is RNS-E upgraded), the rest is "Yellow 4", plus very minor current in "Brown 1" and in "Brown 3".

I measure at battery terminals. Lock car and wait for 3 minutes when RNS-E goes to sleep.

I'm very interested to know how your "Yellow 4" investigation will finish.

Any 3rd party electrical equipment installed?

I'd like to recommend this battery isolator switch: http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=230825055786
Very convenient to quickly connect/disconnect battery. In disconnected mode just connect tester to measure drain current.

In terms of clamp meter the one that Goran recommend will be too rough to measure mA currents. I'd go for this one: http://astore.amazon.com/m0711-20/detail/B001TCWL1E

http://astore.amazon.com/m0711-20/detail/B001TCWL1E

Goran · #7 26th August 2013, 09:48 AM

Sergey is right, go for a better meter. I have been investigating which one to buy, apparently Kewtech and Fluke are amongst the best. Here is a Kewtech meter that looks good available from a UK store.

http://www.tec-supplies.com/products...a+clamp+meter/

or here

http://www.test-meter.co.uk/products...c-clamp-meter/

there is a more expensive one that also measures true rms current for AC circuits, I'm leaning towards it as it could be useful for circuits around the house.

http://www.test-meter.co.uk/products...c-clamp-meter/

here is another UK shop with a wide selection. Watch out for the AC only ones, there is a lot of them and they wont measure DC.

http://www.testermans.co.uk/clamp-meters

notorious · #8 26th August 2013, 02:14 PM

I'm looking at this one from FLUKE: http://www.testermans.co.uk/clamp-me...0Clamp%20Meter

Clamp detaches to access awkward places in car.

But currents are measured with accuracy of 1 digit after decimal point...

graynada · #9 27th August 2013, 06:27 AM

Quote:

Originally Posted by ulfilias

I got a new battery about 3 weeks ago, so i'm certain it isn't that.

I would never be certain a new battery isn't faulty. I have seen many occassions where new batteries have been bad.

Either get it tested at your friendly local motor factors or test it yourself by with enginge off put as much load on, lights, fans, heated rear screen/seats etc and seeing how quickly the voltage on the battery drops.

Goran · #10 27th August 2013, 10:13 AM

Quote:

Originally Posted by notorious

I'm looking at this one from FLUKE: http://www.testermans.co.uk/clamp-me...0Clamp%20Meter

Clamp detaches to access awkward places in car.

But currents are measured with accuracy of 1 digit after decimal point...

Good idea, never thought it may be tricky to get the standard meter into awkward places. Shame about the 0.1A accuracy, but I guess its close enough. Who cares about 0.05A