DIY - E65 E66 Converting 12VDC outlet to constant power for trickle charger - Bimmerfest - BMW Forums

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Old 04-17-2016, 06:29 PM
rippjd rippjd is offline
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Location: Charlotte, NC
Join Date: Apr 2006
Posts: 371
Mein Auto: '05 745i / '10 X5 35d
DIY - E65 E66 Converting 12VDC outlet to constant power for trickle charger

My E65 is not my daily driver at the moment, so it sits in a garage most of its life connected to the BMW trickle charger. I have the Comfort Access option and those handles are known to short internally, drawing excessive current. Other modules many not go into sleep mode, so there are multiple reasons for excessive current draw and a dead battery may result. A trickle charger is needed.

I prefer to use one of the cigarette lighter sockets for this purpose, however these 12VDC outlets are all disconnected from the battery after 60 minutes of no activity. They have a dedicated relay (K31) which is powered by the "Consumer Circuit - Body" or "VA-K" coming from the Power Module. Specifically, VA-K comes from PIN 17 on the 32 pin connector of the Power Module. Normally the VA-K shuts down after 60 minutes, though you can use NCSExpert to change the shutdown time. In the Power Module look for "VAK_IRUHE_ZEIT". Default data is 3C HEX (60 DECIMAL), another option is 10 HEX (16 DECIMAL). I coded mine to 10 HEX (16 minutes) as VA-K draws almost 1/3 Amp, which I don't need every time the car is woken up. You could create a custom value, that is longer than 60 minutes, though I'm not sure about indefinitely.

Alternatively you can move the physical "battery switch" in the trunk to OFF, then ON, then OFF, then ON within 2 seconds and VA-K will stay on until you cycle the ignition on. See the PDF below. There are 3 things I don't like with this method.
1. You are powering multiple devices, especially the power hungry relay (it gets warm to the touch), for weeks at a time if you want the trickle charger to stay connected. Once the battery is charged most of the current output by the trickle charger goes to just powering this relay.
2. If the trickle charger gets bumped or turned off and doesn't output any current you will run down the battery as VA-K draws almost 1/3 Amp
3. If you turn the ignition on to do coding or diagnostics, this re-sets VA-K to normal operation which means you have to remember to open the trunk and do the OFF - ON - OFF - ON procedure.

There must be a better solution...

Studying relay K31 and the wiring diagrams I realized this light green colored relay has 2 outputs which are switched on (closed) when VA-K is on. BMW has a different relay (orange color) that has 2 outputs, but one that is switched on (closed) when it gets power and the other switched on when the relay has no power. Perfect.
Remove the glove box, swap in the orange relay (# 12-63-1-742-690) and now the rear outlet on the left side of the center console is connected to the battery only after VA-K shuts down (60 minutes for normal coding, 16 for my car). And the relay draws no power. And I don't have to mess with the battery switch. If I get in the car and start it, while forgetting the trickle charger is connected, no big deal. The car is awake with VA-K on and my trickle charger is electrically disconnected. This rear left outlet even has it's own fuse, #32.

Note: when I first installed the orange relay my setup was "backwards". The rear left had power when the car was awake, the other 3 (rear right, center console and passenger footwell) only had power after 60 minutes of sleep. I think BMW wired it wrong. I unbolted the fuse block, removed all fuses from the section having fuse #31 and #32, removed the lower half of terminals, slid the blue secondary lock over one notch, pulled all 4 contacts and swapped the contacts going to fuse #31 and #32. I really recommend the special tooling to remove these contacts - it's much easier than trying to do it with toothpicks (my old method). After I swapped these two wires, then it worked correctly.

Note 2: if you turn on the ignition with the glove box removed you will log a fault due to the glovebox knee airbag being disconnected.

Note 3: when re-installing the glovebox I use one of those spring loaded "pick-up" tools to hold the bolt head and get the threads started.
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Attached Files
File Type: pdf Note on Charing Batteries - E65.pdf (102.6 KB, 83 views)
2005 745i Individual

E65/E66 Parts for Sale:
Alpina Type 743 Front Spoiler complete retrofit kit (new in box) $1200

Last edited by rippjd; 04-27-2016 at 06:41 PM. Reason: added detail to title
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