When It Rains, It Dies

[Third From Texas]

I've had this issue since I got the A1R.

All of my LMTVs were converted to dual battey as soon as they came into my possession. And I pretty religiously throw my battery disconnect every night. I've had no 12v vampiric drain issues as a result. If I forget and leave the batteries hot, after 3-4 nights if the truck isn't driven the 12v side will slowly slip into the low side (failing to start the truck and certainly causing some damage ton the battery).

But if I leave forget to throw the disconnect and it RAINS, the 12v battery will crater over night. I've never been able to identify what is getting wet and causing the 12v drain. I'm at a loss for how to locate the short (spraying water around on various locations has never resulted in any help). It has to be something exposed outside the cab. There's no water in the battery compartment, the NATO port, the battery diconnect box. I suspect the polarity protection as I park nose down on the driveway and water from the habitat lands between cab/hab. The only other culprit might be the starter (but I don't see any signs of water and being 24v I would expect to see both batteries discharging if so.) Where ever the short is it's isolated to the 12v system. It could very well be related to the typical 12v vampiric drain these trucks often suffer from.

Thoughts on how I might trace this?

*it rained for the first time in months here and of course I had left the batteries hot when I checked something the day before, so now I have killed a good 6TL battery (was down to 4v).

 

[Ronmar]

If it hasn’t set that low for too long, the battery may be recoverable, charge it. If I am recalling correctly the A1/A1R shouldn’t have a 12V vampire. The Vampire on the A0 is I believe from the 12V feed to the Vehicle Interface Module, and the WTEC3 transmissions don’t use that or 12V as far as I can tell. In the VIM that power is fed thru a fuse and on to the TCU and is the battery input(wires 136A and 136C). On the A1, wires 136 are 24V battery in…

i would put a volt/ohm meter set to measure current in series with the 12V battery connection(disconnect 12V lead, connect one meter lead to the cable end and one lead to the battery terminal). You can then measure the current flow out of the battery. Don’t turn on the ignition as the truck load may blow the meter fuse.

now start disconnecting leads and see where the current disappears. I would suspect the LBCD, so I would start there. That is also about the only thing that is going to get wet associated with 12V just setting in the rain… if the 12V load goes away when you disconnect the 12V battery lead on the LBCD, disconnect the 12V load side line(feeds to cab) and connect those two lines together, bypassing and completely isolated from the LBCD.

it could be you have something giving a path on or in the LBCD to ground, that gets worse when it gets wet. The LBCD not only has polarity diodes, it also has capacitors to absorb and dissipate the voltage spike caused when the alternator under full load is suddenly disconnected from the batteries that are overloading it… caps gone bad could cause the vampire as they are connected between 12V and ground…

 

[chucky]

No idea on water problem but on your battery fix i bought one of the noco g7200 12/24 battery charger and it pulse charges the AGM batteries back to life most of the time . Before i got my solar panels to charge the truck and house batteries i left the noco hooked up in the battery box . I have a on / off switch in the habitat for when i want to charge the 12 v side of the truck batteries so 1 day a week i let the solar top it off .

 

[GeneralDisorder]

Before you test for battery amperage draw make sure you pull all the circuit breakers in the M1079 van enclosure on the side of the blackout/emergency light panel. These power the relays that control the lights and they are energized even when the lights are off. There's a warning sticker to this effect but I didn't understand why till I rewired my fluorescent fixtures to 24v with LED tubes.

Beyond that - definitely check the operation of the LBCD and verify the connections at it's plug - the plug on the LBCD faces straight up towards the rain and mine had a cold solder joint that was completely disconnected. All the caps in mine were blown up and leaking badly.

FWIW - our trucks are basically identical so let me know if you need me to check anything you are unsure of. I have zero battery drain on mine and it routinely sits all weekend+ without being driven and I don't routinely flip the battery disconnect switch. I'm running the 4 battery system with fairly new 6TL's.

 

[Third From Texas]

If it hasn’t set that low for too long, the battery may be recoverable, charge it. If I am recalling correctly the A1/A1R shouldn’t have a 12V vampire. The Vampire on the A0 is I believe from the 12V feed to the Vehicle Interface Module, and the WTEC3 transmissions don’t use that or 12V as far as I can tell. In the VIM that power is fed thru a fuse and on to the TCU and is the battery input(wires 136A and 136C). On the A1, wires 136 are 24V battery in…

i would put a volt/ohm meter set to measure current in series with the 12V battery connection(disconnect 12V lead, connect one meter lead to the cable end and one lead to the battery terminal). You can then measure the current flow out of the battery. Don’t turn on the ignition as the truck load may blow the meter fuse.

now start disconnecting leads and see where the current disappears. I would suspect the LBCD, so I would start there. That is also about the only thing that is going to get wet associated with 12V just setting in the rain… if the 12V load goes away when you disconnect the 12V battery lead on the LBCD, disconnect the 12V load side line(feeds to cab) and connect those two lines together, bypassing and completely isolated from the LBCD.

it could be you have something giving a path on or in the LBCD to ground, that gets worse when it gets wet. The LBCD not only has polarity diodes, it also has capacitors to absorb and dissipate the voltage spike caused when the alternator under full load is suddenly disconnected from the batteries that are overloading it… caps gone bad could cause the vampire as they are connected between 12V and ground…

Oh mine has a 12v leak somewhere, trust me.

If I forget to throw the disconnect it will suck it dry after a few days.

Been this way since I brought it home.

But I'll run thru what you guys suggest,

Thanks as usual !