by Burgerman » 06 Oct 2020, 18:17
For the last 13 years I get a steady stream of people emailing me or mentioning on here, that they suffer battery discharge problems when they dont use a mobility modified van such as the various rollx/braun/vmi etc converted vehicles.
Mine is the same. I tried all the battery drain fixes, investigations, and the results were complex. With no distinct pattern. So.. In an attempt to fix this, I fitted a 50 watt solar panel and charge controller set to 13.8V in winter and 13.4V in summer. Its a 90% success but the battery drain still exceeds the drain from the van in winter 3 months. Not enough daylight hours to keep up... So its a case of being great over the spring, summer and autumn, and connecting a maintainance charger over november, december and january.
However we are in october, and I just noticed my battery was down to 11.8V (80% discharged) when measuring recently. So this battery drain is not consistent. So the solar cant now keep up ALL of the time even in early october. So now I got more angry.
Its been to my freindly auto electrician many years back who stuck it on some fancy monitor over 24 hours that records the diacharge current and obviously it behaved perfectly so nothing to fix. So now I decided to do it myself. Want a job done right? As usual, DO IT YOURSELF!
So I measured the current all the various vehicle modules and systems draw when the van is asleep overnight. My fluke meter can LOG and GRAPH everything in volts, amps, resistance, frequency, peak values, ac/dc compunents on the systes etc over a 24 hour period. And it was rather odd. And very confusing. The overall picture was a 5A plus drain the moment you close a door and lock the van. That drops in stages to 127mA eventually, after 5 to 15 mins.
But thats not the end of it. After a few hours (2 to any - it seems that it can be any period) it starts taking an additional 1.2Amps. For 1 minute, and then graduall drops away again. And then repeats this every 3 to 5 mins from then on.
Tried disconnecting the computer in the rear of the van that controls doors/ramp etc. That removed 10mA. And made no difference to the overall picture.
Tried pulling all the fuses. One different one each night a year back. NONE of them apeared to make a blind bit of difference. ALONE and I wasnt testing overnight. And I did this a year previously. But I noticed one thing at the time. The body control module fuse (Called a BCM fuse) stopped all the key fob buttons and so remote locking, as well as interior lights, central locking, and dashboard clocks, and engine from working. Its a tiny current that goes through this 20A fuse. I measured it. The BCM fuse when removed, meant that the van drew just 30mA from the battery once everything was closed up, locked, and then had the fuse pulled in that order. I have no engine bay switch or light. So can leave that up when testing.
So that super expensive hard to change BCM is CAUSING the battery pulse drain, that randomely appears. And when disabled drops the vans parasitic drain from 127mA to 30mA...
I suspect that the module itself isnt faulty. I suspect the way that the vans wiring and door closing/locking mechanism works in conjunction with the stock wiring upsets the BCMs many voltage and other sensors and it keeps waking up. And shutting down. And thats the cause of the non starting dead battery issues.
Now doing all that is too much trouble every time you want to park up for more than 2 to 3 days.
So I did the following.
Bought a fuse... And used sidecutters to remove the two blades and the fuse wire part. And I soldered a 2 core 1 meter long cable to these legs. And plugged it in where the BCM fuse would normally go.
On the opposite end I fitted a 20A switch. A waterproof one.
I drilled a hole in the plastic above the radiator, where the bonnet/hood metal release lever lives.
Here I fitted the switch. And routed the wire back to the fusebox.
You can reach in with a finger and flip that switch easily with the hood/bonnet lid shut.
So now if I plan to not drive the thing the next day, I get out, shut doors, and use the remote for the central locking to lock the van. Then I go to the front before going into the house and flip the BCM switch. Thats the same as pulling its fuse.
That reduces battery drain to a low 25 to 30mA. Thats good enough to park up for: 68Ah, or 68,000mAh.
That 30mA drain means then 68,000 div by 30 = 2167 hours. Or 90+ days.
Now, instead of dead in days or a week depending on that pulse discharge thing, we get 3 months parked. Lets say after 2 months it should start fine.
Now, remembering that I have solar too, that means that it should always stay between 95 and 101% charged regardless on month or season.
So if you are having issues, fit a switch on the BCM fuse (applies to MOST modern cars/vans) and switch it OFF when leaving your vehicle for more than a couple of days. Your battery will last years longer and you will be far less likely to suffer the no start dead battery syndrome.