Auto-elec question - standlby / leakage current from batteries

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I've a problem with a truck failing to start after 5 days sitting idle -
completely flat batteries, no ignition lights, no "click-click-click",
nothing.


The electrical sytem is supplied by 2 x 12V batteries. These are 21 plate,
800 CCA big lead acid units, each larger than a large 4WD battery. The
charging system works fine with over 28V at fast idle, and around 26 at
idle. It starts fine after a couple of days sitting idle.


I've measured the standby current draw from the batteries with everything
switched off at around 150mA. As far as I can tell the standby current
mainly goes into the remote entry system and a 24/12V converter.

From my rough reckoning, 5 days @ 150mA = 120 x 0.15 = 18A.hr which should
have bugger all effect on such large batteries.


Comments or suggestions???

Thanks.



Re: Auto-elec question - standlby / leakage current from batteries
Dennis Inscribed thus:

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Could be silt buildup in the bottom causing discharge internally.  I've
seen similar batteries have had a couple of inches of thin sludge
material sat in the bottom.

If that is the case and they are of the type that can be disassembled,
then they can be drained, the plates lifted out and flushed with water
before reassembly with new acid and recharged.

HTH

--
Best Regards:
                     Baron.

Re: Auto-elec question - standlby / leakage current from batteries

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Thanks for the suggestion Baron - pretty unlikely in my case as the
batteries (& the vehicle) are only a few months old.

I also make a point of keeping the tops of the batteries clean to prevent
possible discharge through the crap that collects there (especially in damp
conditions).



Re: Auto-elec question - standlby / leakage current from batteries
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I guess mebbe you should disconnect the batts and see if the problem
does exist in the batteries themselves. If it does then it should be a
warranty situation ??

Cheers ...... Rheilly

Re: Auto-elec question - standlby / leakage current from batteries

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Good point - I was working on the assumption the batteries were ok.
thanks.



Re: Auto-elec question - standlby / leakage current from batteries
Another thing I forgot was dont rely on the alternator to charge the
batteries after they are flat (unless you are doing 12hour runs for a
couple of days) To recharge 2 large batteries needs putting them on a
decent charger until the electrolyte shows fully charged.
If you were just doing an hour or two that would not charge them and
give the symptoms you describe.

Cheers ...... Rheilly P

Re: Auto-elec question - standlby / leakage current from batteries

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I'll do that, I took it for a 40 minute run, but as you say that probably
hasn't fully charged the batteries up. Cheers.



Re: Auto-elec question - standlby / leakage current from batteries
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150ma @ 24v  sounds a bit high to me for standby on such a system.

You might have to start pulling fuses and finding out exactly where
all this current is going to.
Put an amp meter across the supply, and pull the fuses one at at
time.  IF there is any drop after
pulling a fuse, then you have to follow down the line and see what is
on that fuse.
It is possible that this load comes from more than one source.


I would also look at anything added to the system (after market
accessories, or recent work done).
There was a recent story in Silicon Chip about a car that had had
driving lights added, controlled by a
automotive relay.  This relay failed and was replaced.  This caused a
problem similar to yours

The problem turned out that the new relay had a slightly different pin
out to the old one, and this resulted
in the dashboard switch directly switching the lights, and the relay
coil held on constantly - slowly flattening
the battery.






Re: Auto-elec question - standlby / leakage current from batteries
kreed expressed precisely :
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Whatever you do DO NOT put an amp meter across the supply.!!!!

In series with the supply is OK but ACROSS will destroy the meter and
depending on it size maybe splash you with sparks.

It would be good if advice here was acurate.

--
John G



Re: Auto-elec question - standlby / leakage current from batteries

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I have enough trouble keeping a fuse in my DMM as it is!   :)

I'm sure kreed's comment just came out wrong.



Re: Auto-elec question - standlby / leakage current from batteries
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That is indeed correct. Thank you for picking that up.


acurate ? :)



Re: Auto-elec question - standlby / leakage current from batteries

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Just a thought . Any clocks or timers hooked up/? Is there a back-up alarm
battery for you security flat and attempting to charge continuously. Any GPS
type that regularly transmits  reports. You never know. Silly things cause
silly faults.



Re: Auto-elec question - standlby / leakage current from batteries

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No GPS or alarms. Vehicle has 3 ECU's, a couple of 24/12V converters and a
remote access door controller. Leakage current drops back in steps to around
150mA then seems to be stable. I've decided to take it back to the
manufacturer Monday and let them sort it out.....

thanks



Re: Auto-elec question - standlby / leakage current from batteries

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I'll bet it's something silly albeit annoying. Let us know the outcome. It's
intriguing................



Re: Auto-elec question - standlby / leakage current from batteries

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Will do.

The manuf has told us that there is a "spare always on tail light" that
should have had the supply fuse removed. This sounds very odd, and would not
explain the total flattening of the batteries over 4 or 5 days as the static
leakage current is only ~ 150mA. For what it's worth, the vehicle starts off
as a bare FD230 truck chassis and is fited with coach body + some
electrics/hydraulics.




Re: Auto-elec question - standlby / leakage current from batteries
 >> I'll bet it's something silly albeit annoying. Let us know the outcome.

8<- - - - - - - - - -  - - - - - -  - - -- - - - - -

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Agree very odd. Did you find this ' tail light ' and the fuse for it?
 I have mentioned you prob to a couple of auto mates. They're mystified.



Re: Auto-elec question - standlby / leakage current from batteries

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No, I left it for the guys who built it. We pick it up later this week. I'll
let you know what they say...



Re: Auto-elec question - standlby / leakage current from batteries
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Nothing you've said indicates definitively that the batteries were fully charged
to start with. Were they? How do you know?

Re: Auto-elec question - standlby / leakage current from batteries

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You are correct, mitigating factor is that vehicle had been running ok for 5
weeks, albeit it only stood idle for 2 day weekends.

I gave it an 18 hour battery charge prior to returning it to the
manufacturer.



Re: Auto-elec question - standlby / leakage current from batteries
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Yes, it could be something that pulls a significant load, but
intermittently.


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