E9x vehicles don't have always-on power sockets, partly to preserve battery life.

 

My only beef with the E90 is the lack of an always-on power socket. I'd love to learn about some aftermarket add on, and the tie point into the electrical system to provide one always-on power socket.

 

• Find an empty slot in the fuse panel that is always on. Seems there are several.
• Place an appropriately sized fuse in it.
• Pull a line from the outlet side of the new fuse using a fuse tap.
• Pull the fuse in the current power socket slot out and overload it so it blows.
• Place a fuse tap on the outlet side of the old socket fuse.
• Place the blown fuse back in the slot it came from.
• Connect the two fuse taps together with a jumper wire.

This would accomplish what you want. The lighter socket would now be always on. Would cost just a few bucks.

The blown fuse in the current socket should prevents backfeeding the back side of the ignition circuit and protect the rest of the car's wiring. You do need to be concerned that the wiring upstream of the new fuse may not be rated for the load that can now be imposed on it.

 

I agree that losing power to an accessory outlet when parked is an inconvenience. My IPOD in the center console is an example. But, a device left plugged into an "always-on" 12v outlet might prevent the car from going to "sleep", thus creating a significant battery drain issue. That would, IMHO, be more inconvenient and expensive than finding an alternative to needing to charge gadgets when parked.

 

I agree that losing power to an accessory outlet when parked is an inconvenience. My IPOD in the center console is an example. But, a device left plugged into an "always-on" 12v outlet might prevent the car from going to "sleep", thus creating a significant battery drain issue. That would, IMHO, be more inconvenient and expensive than finding an alternative to needing to charge gadgets when parked.

So does someone know that an E90 has some new 'battery drain issue' associated with a need for 'sleep' mode, which did not exist in all prior generations of BMWs?
I have never had power outlets be disconnected from power in any vehicle I have owned in 45 year of car ownership..., including 6 different BMWs, the first car that I encountered with interrupted power to outlets was my wife's 2007 Toyota and is a pain in her a$$ for keeping her Bluetooth handsfree charged!

Zooks527 solution is a nice one -- if the 'lack of sleep' issue is not present. If you plug in a self-regulating device which monitors its own charge state and then stops charging, is there some issue within the car itself caused by its 'not going to sleep'?!

fdriller9's solution does not address the desire to have power on to charge devices like portable GPS or Bluetooth devices overnight, for example.

 

Here's an option. Pin 13 in the radio harness of all e9x is a remote turn on lead. Normally it's used for aftermarket amps.

Using a wire tap, extend that wire, fused with a 1A fuse, to the glove box. Pick up a Bosch relay, and use the wire from pin 13 as a trigger. Grab power using a fuse tap from the glove box.

The way this remote lead behaves is that it's only on when when car is "awake". When you leave your car unattended for about 15-30 minutes (depending on if you locked the car or not), pin 13 will shut off. This will cause the relay to turn off as well. When you unlock or open your doors, pin 13 will turn back on, and supply power to whatever you want.

You can remove the original circuit for the 12v socket (remove the fuse from the fuse panel), and wire the relay to the socket instead. It will remain powered with the vehicle running and behave as I have described above.

This is your safest bet to prevent excess current draw when the car is off. There are other circuits within the fuse panel that behave this way as well and if you can find them, all you need is a fuse tap.

 

If you leave accessories charging overnight, you will kill the battery and need a jump start in the morning.

If you plan on charging accessories while the car is off, invest in a higher capacity, deep cycle battery. Otherwise, you will wear out your original battery quickly.

These cars periodically wake themselves from sleep mode to do self checks and monitor systems. This will drain the battery over the course of a month or 2.

I don't know why you would need a nav unit to be charged while the car is off. You power the nav off the car when you driving don't you?

 

OK, so my understanding from your reply is that the current cars wake themselves from sleep to do self checks and monitor systems...Which self checks are going on, and why are these needed if the car is not in use? I'm trying to understand why these more current cars (than my E46) have some magical new requirements to check themselves if no one is in the car and the ignition is off!

As to why you need a nav system charged, I merely used a nav system as one example of what you might need to charge. My wife has a Bluetooth handsfree speaker/mike so she can answer a call or place a call in her car without violating California vehicle code, and it needs charging for several hours to fully charge its battery. Given the difficulty that many folks have had in pairing BMW Bluetooth to their phones, it is easily understood that someone might NEED to use an add-on Bluetooth rather than to try to pair and use the BMW feature! And drawing 0.5A for 12-14 hours (assuming -- wrongly-- the add-on Bluetooth didn't stop drawing power at full charge rate) only amounts to 6-7A drawdown.

 

I'm not sure of all the self tests that wake the car but the IBS constantly monitors the SoC, or State of Charge of the battery. If the threshold falls below a certain level, the BSD will wake the DME so it can shut off accessory circuits to conserve battery power.

By wiring a line directly to the battery and leaving it always on, the IBS will see excess current draw and wake the DME to turn convenience features off such as heated seats or steering wheels, welcome lighting, comfort access, etc.

 

Thanks for info about what's happening. Sounds like I will consult my very long time Service Advisor (asst mgr of Service) and see what he says about connecting per Zooks527 method, to add a supplemental power outlet that never powers off, for the purposes of low rate USB charger devices to charge its battery, given a 70-90 AH battery rating and only about 6-7A draw down (assuming it actually drew 0.5A for all the 12-14 hour time -- which it wouldn't).