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Flat battery, v. high current drain - Fuse No. 8 under bonnet. Water pump continuous...

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Newbers
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Flat battery, v. current high drain - where to start?

Post by Newbers » Thu Nov 02, 2017 6:27 pm

Yes seems like a great price. I actually couldn't believe how difficult it was to find an ammeter that could handle that sort of current (DC) - or that I've managed all my life without one....

I happen to be working from home tomorrow so if it comes earlyish I should be able to have a quick play.

To test the alternator and starter I guess I can just clamp this round each of the red wires in turn (which if engine is not running shouldn't be carrying any current). No need to disconnect any wires (unless I find something untoward.)
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Flat battery, v. current high drain - where to start?

Post by ph001 » Thu Nov 02, 2017 6:48 pm

Yep, you got the right idea. Of course do the battery first just to confirm what that actual drain current is. The car will still go into 'sleep' mode if you lock it with the boot open and it will kill the boot light as well if you give it 30 mins or so.
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Flat battery, v. current high drain - where to start?

Post by Newbers » Thu Nov 02, 2017 7:06 pm

I'm going to be really upset if there is a problem with my heated seat. :(
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Flat battery, v. current high drain - where to start?

Post by TonyP » Thu Nov 02, 2017 7:56 pm

Grr, looked at the clamp meter earlier, £20, get the call to pick my son up from the bus stop, now £27 odd quid. :x

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Flat battery, v. current high drain - New info...

Post by Newbers » Thu Nov 02, 2017 8:19 pm

£7 taxi fare!
Last edited by Newbers on Fri Nov 03, 2017 6:24 pm, edited 1 time in total.
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Flat battery, v. current high drain - where to start?

Post by Newbers » Fri Nov 03, 2017 6:06 pm

Bit of an update. Big thanks to ph001 - ammeter arrived this morning courtesy of Amazon.

V. pushed for time today but couldn't resist a quick test. Firstly testing at the battery (with boot light on) current draw was 18.8Amps (more than twice my estimate which suggests battery was in better condition than anticipated when fitted, worse when checked and perhaps the drain reduces over time).

I've then checked a few accessible cables under bonnet. I haven't been able to tie this down too much but i'm getting nearly 15A at the fuse box under the bonnet. (See pics). Also I can hear a high frequency buzz near the front of the engine. I don't think it was the alternator but near by. Sounded a bit like a whirring pump (oil pump?) but it was a bit noisy outside so hard to tell. I'll find a metal rod to use as a stethoscope and see if I can narrow it down. Meanwhile any suggestions?
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Flat battery, v. current high drain - New info...

Post by Magicarcher » Fri Nov 03, 2017 6:12 pm

Newbers wrote: Thu Nov 02, 2017 3:06 am What do you think of this? https://www.ebay.co.uk/itm/Sealey-Curr ... 487b142aa4
If you already have a multimeter you can buy leads that do the same thing with your multimeter.
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Flat battery, v. current high drain - New info...

Post by Magicarcher » Fri Nov 03, 2017 6:20 pm

Newbers wrote: Fri Nov 03, 2017 6:06 pm V. pushed for time today but couldn't resist a quick test. Firstly testing at the battery (with boot light on) current draw was 18.8Amps (more than twice my estimate which suggests battery was in better condition than anticipated when fitted, worse when checked and perhaps the drain reduces over time).
Is this with ignition off? That is colossal I would expect this to be less than 100mA (you need to give a short delay after ignition off as some ecus may initially draw higher current then go to sleep).

If it is with ignition off I would recommend pulling all the battery fed fuses one by one each time returning and see if you can find a single fuse that causes it to drop considerably. By looking at the fuse diagram you ill be able to narrow down the issue.

I did a post with all the fuses and if they were ignition/aux/battery fed if it helps.

viewtopic.php?f=2&t=99155&p=1451269&hilit=fuse#p1451269
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Flat battery, v. current high drain - New info...

Post by Newbers » Fri Nov 03, 2017 6:26 pm

Yes it's with the ignition off
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Flat battery, v. current high drain - New info...

Post by Newbers » Fri Nov 03, 2017 6:31 pm

I remember seeing that post and thinking it as very community spirited of you but that I didn't need it! Does that refer to the internal fusebox?

I only recorded substantial load from one of the red cables off the battery. I suspect this one heads to the small junction box on the bulkhead then to the fuses under the bonnet. I guess the other feeds the internal fuses. I could be wrong but I suspect my problem is under the bonnet and could be a faulty relay which is not turning off something in or around the engine.
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Flat battery, v. current high drain - New info...

Post by Ducklakeview » Fri Nov 03, 2017 6:37 pm

You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

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Flat battery, v. current high drain - New info...

Post by Newbers » Fri Nov 03, 2017 6:50 pm

Ducklakeview wrote: Fri Nov 03, 2017 6:37 pm You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

Mike
Agreed. All the same there are a lot of electrons hustling their way down that conduit!
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Flat battery, v. current high drain - New info...

Post by Ducklakeview » Fri Nov 03, 2017 6:57 pm

Newbers wrote: Fri Nov 03, 2017 6:50 pm
Ducklakeview wrote: Fri Nov 03, 2017 6:37 pm You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

Mike
Agreed. All the same there are a lot of electrons hustling their way down that conduit!
You can't trust ANY part of that reading, there could well me 15ma going through there...

Mike

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Flat battery, v. current high drain - New info...

Post by ph001 » Fri Nov 03, 2017 9:59 pm

Not quite how it works. Clamp ammeters work on magnetic field, so if you have say 10A flowing down one conductor and then 10A flowing in the return then the mag fields cancel out and the net result is zero. This is why you don't get a reading clamping around 3-core mains cable for example.

In a car, it's unusual to run a separate 0v cable as chassis is 0v anyway so they tend to just terminate locally to chassis. I suspect that current is genuine so now it's just a case of trying to isolate.

OP, have you had a good feel around the fuse box for anything getting warm as previously suggested?
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Flat battery, v. current high drain - New info...

Post by jamesditchy » Fri Nov 03, 2017 10:18 pm

I had the same issue, turned out to be the nav drive constantly searching for the disc after key was removed. I ran a separate live back to the fuse board connected to a circuit which is only live once ignition is on and its been fine since.
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