Auto-elec question - standlby / leakage current from batteries

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.

Reply to
Dennis
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Dennis Inscribed thus:

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

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Best Regards:
                     Baron.
Reply to
Baron

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).

Reply to
Dennis

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

Reply to
Rheilly Phoull

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hould

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.

Reply to
kreed

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

Reply to
Dennis

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
Reply to
John G

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

Reply to
Rheilly Phoull

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.

Reply to
Dennis

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

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

Reply to
Dennis

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That is indeed correct. Thank you for picking that up.

acurate ? :)

Reply to
kreed

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.

Reply to
Metro

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

Reply to
Dennis

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Yes, it could be something that pulls a significant load, but intermittently.

Reply to
kreed

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

Reply to
Metro

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.

Reply to
Dennis

8> It's intriguing................

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.

Reply to
Metro

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...

Reply to
Dennis

Nothing you've said indicates definitively that the batteries were fully charged to start with. Were they? How do you know?

Reply to
Clifford Heath

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.

Reply to
Dennis

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