How do you charge a key fob

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

BMW E90 Key Fob Charging at Home?

BMW suggests leaving the key inside the car in position 1 for 24hrs to wireless charge the key, but this isn't an option if you live in an apartment and don't have a garage. I'm trying to figure out how to charge the key from a home outlet and purchased an Adafruit Induction charging set to play around with. It's nice to have a fully charged key so you have a nice and long operating range. Sometimes after a while of not much driving you'll find the key range getting shorter and shorter. Some say they've had luck with certain toothbrush chargers but I wanted to do some more research.

So as I understand the receiving end usually handles all the voltage regulation and protection in this sort of setup. With stronger inductive coupling I should get more current draw from the transmitting end and faster charging.
I found that the circuit drew the most current when the key was placed with the roundel facing the inductive charging loop. (about 75mA over the idle current) I'd be interested to see how the coil is positioned within the inductive charging assembly in the vehicle itself to compare. Has anyone taken one apart to see the insides of one? Maybe I'll just buy an old one off of eBay to satisfy my curiosity.

The Panasonic VL-2020 battery used in these has a capacity of 20mAh and standard charge current of only 1.5mA, so you should be able to hit a full charge in well under 20hrs.

Last edited by Yangorang; 12-15-2018 at 06:43 PM..

Lieutenant General

Drives: 325xi 06 wagon MT

Join Date: Jan 2010

Location: Santa Cruz, Ca

Any inductive charger should put something in it.

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

So out of curiosity I took apart an ignition assembly from an old E90 and you can see the coil windings under the cover. You can see the little tiny coil within the key will line up inside of the bigger winding within the ignition housing when inserted.

I'm not sure using a toothbrush charger would be the best thing....with that sort of setup you'd get a very weak coupling with the winding in the key and also you'd probably be heating up all the other pieces of metal within the key as well like the battery and ICs.

Lieutenant General

Drives: 325xi 06 wagon MT

Join Date: Jan 2010

Location: Santa Cruz, Ca

Ok why not make one out of the part you removed .
Taking the keyfob apart to charge the battery seems
like a big PINTA.
What about wireless cell phone chargers.
These may not be ideal charger but they are enough
to tell if the battery will accept a charge before trying
to replace it.
If there was a signal strength meter to read the rf output
that would be another indirect way of measuring battery
strength without disassembly.

Also the picture of the fob tells me to be more effective
you want the inductive antenna end of the fob down in the
the receptacle end of a toothbrush charger.

https://www.wikihow.com/Charge-a-BMW-Key

Last edited by ctuna; 12-22-2018 at 03:47 PM..

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

Yup that's exactly what I'm going to do....figure out which pins are power from WDS and hook it up to a power supply....looks like BMW has it made so the coils will line up perfectly when the key is inserted. I was able to get the part for less than $20 so it's just one of those little things for me to tinker with.

Lieutenant General

Drives: 325xi 06 wagon MT

Join Date: Jan 2010

Location: Santa Cruz, Ca

Any way of knowing what the frequency and amplitude of the
charger should be would be one of my questions?

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

The ignition module itself should just take a standard 12V DC power and I won't have to worry about the details as it should just charge my key properly like it would in any car.

As far as what AC freq/magnitude is driving the transmission side of the coils I really wouldn't be able to tell. I don't have a oscilloscope to measure it with, but I could try to tear the ignition module down further when I have some time to see if any components/ICs are recognizable.

Lieutenant General

Drives: 325xi 06 wagon MT

Join Date: Jan 2010

Location: Santa Cruz, Ca

It might be speced somewhere.
Worth a google search
and a search of the training pdf's and https://www.newtis.info/tisv2/a/en/

Enlisted Member

Drives: BMW E90 330i 2005 Automatic

Join Date: Jan 2019

Location: United Kingdom

This used to work perfectly on the E46 (diamond) keys so I don't see why this can't work with the E90 keys...

I brought a key back from the dead on the old E46...

Lieutenant

Drives: TiAg e91, r53 Cooper S, e28 M5

Join Date: Jan 2019

Location: Santa Barbara/Modena

Quote:

Originally Posted by BimmerLad

This used to work perfectly on the E46 (diamond) keys so I don't see why this can't work with the E90 keys...

I brought a key back from the dead on the old E46...

Yes, I have done the same thing with my Mini R53 key which is like the e46 key.

Yeah shouldn't need to be exact, you just need to get the key in the general area.

I have brought 2 keys back from the dead leaving them on my sonicare toothbrush charger for a day or two

Enlisted Member

Drives: BMW E90 330i 2005 Automatic

Join Date: Jan 2019

Location: United Kingdom

Quote:

Originally Posted by dakine_surf

Quote:

Originally Posted by BimmerLad

This used to work perfectly on the E46 (diamond) keys so I don't see why this can't work with the E90 keys...

I brought a key back from the dead on the old E46...

Yes, I have done the same thing with my Mini R53 key which is like the e46 key.

Yeah shouldn't need to be exact, you just need to get the key in the general area.

I have brought 2 keys back from the dead leaving them on my sonicare toothbrush charger for a day or two

Exactly that! Although I did "alternate" the side of the key that does the "stump" on the charger each day. sure it had next to no effect mind!

I did also notice a good overnight blast greatly increased the working remotes range too

luckily my E90 has CA so nice old fashioned replaceable batteries here

__________________

Current Car:
BMW E90 MY2005 330i Automatic

Previous Car:
BMW E46 MY2001 316ti Manual

Lieutenant

Drives: TiAg e91, r53 Cooper S, e28 M5

Join Date: Jan 2019

Location: Santa Barbara/Modena

Quote:

Originally Posted by BimmerLad

Exactly that! Although I did "alternate" the side of the key that does the "stump" on the charger each day. sure it had next to no effect mind!

Yeah, I honestly don't think it matters. On my old e46 and on my r53, if you just get the key in the general area of the ignition lock and it starts dinging, which makes me think that the chime and charging is based on the proximity of the key to the ignition lock.

Quote:

Originally Posted by BimmerLad

I did also notice a good overnight blast greatly increased the working remotes range too

This is also very true. The range on mine had decreased to maybe 6 meters or like 20 feet. A day or two on the charger and they are back to 30 meters or more.

I think that the induction charger in the steering column may be getting weaker over time.

First Lieutenant

Drives: '11 E93 M3 6MT, '08 E92 335Xi

Join Date: Jan 2019

Location: Southington, CT

when I purchased my E46, the 2nd key had been in the owners drawer for 9 years and was dead..... I put a battery charger on the car's battery and put the key in the ignition in the "on" position overnight. Worked like a charm after that recharge

__________________

Lieutenant Colonel

Drives: '05 E90 330i Manual

Join Date: Aug 2010

Location: Cape Town, South Africa

I've always cycled my keys to keep them charged, and so far, both my cars, 14 and 15 years old, still have both of their original keys in perfect working order!

Quote:

Originally Posted by pedro2u

when I purchased my E46, the 2nd key had been in the owners drawer for 9 years and was dead..... I put a battery charger on the car's battery and put the key in the ignition in the "on" position overnight. Worked like a charm after that recharge

That's a nice stroke of luck!

__________________

BMW E90 330i (M) '05 (His) | (Hers) BMW E46 320i f/l (M) '03

Registered

Drives: BMW E90

Join Date: Sep 2019

Location: Netherlands

@ Yangorang, have you found out which pins in the keyfob lock have been used for the 12V DC power. I have a spare lock here and would also like to make a charging units as i have several keys that are not being used for weeks at a time

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

I don't remember 100% for sure, but if I recall correctly I think what I found out after digging through WDS was that this ignition module is actually not taking 12V and rather it is getting the RF sent to it from the CAS. I think I had taken out the PCB in that ignition module and found there were no ICs of any sort.

I ended up hooking up an adafruit wireless charging emitter to it but I really have no idea whether it actually works. Unfortunately I don't have an oscilloscope to check on things so I sort of gave up this project.

Brigadier General

Drives: 2007 E92 335i

Join Date: Aug 2012

Location: GTA - Greater Toronto Area

Quote:

Originally Posted by Yangorang

I don't remember 100% for sure, but if I recall correctly I think what I found out after digging through WDS was that this ignition module is actually not taking 12V and rather it is getting the RF sent to it from the CAS. I think I had taken out the PCB in that ignition module and found there were no ICs of any sort.

I ended up hooking up an adafruit wireless charging emitter to it but I really have no idea whether it actually works. Unfortunately I don't have an oscilloscope to check on things so I sort of gave up this project.

Nonetheless thank you for your initial efforts on identifying all of the charging components.

Quick question, have you opened up the key fob itself and if yes how did you glue it back together afterwards?

Second Lieutenant

Drives: 2008 BMW 328xi

Join Date: Aug 2013

Location: Chicago, IL

I haven't pried my own key fob apart since I had found plenty of pictures online for what it should look like inside. From what I had seen on BMWGM5's instructions it does look like it is basically just pried apart and super glued back together.
https://www.bmwgm5.com/kf_repair.htm

Registered

Drives: BMW E90

Join Date: Sep 2019

Location: Netherlands

I have opened the fob, but over here we can buy an empty housing that snaps together and isn't glued. So to repair no problem just a new housing

Lieutenant

Drives: '07 335xi 4D AT

Join Date: Jan 2017

Location: Seattle, WA

The solution is to put the fob in the ignition and drive the car. If it doesn't hold a charge after, then you need to replace the battery; not try to rig some external charging system.

Cheapskate

Drives: 2018 440i / 2010 X5

Join Date: Aug 2016

Location: Cincinnati

Quote:

Originally Posted by ewicky

The solution is to put the fob in the ignition and drive the car. If it doesn't hold a charge after, then you need to replace the battery; not try to rig some external charging system.

So how do you replace the battery? My car has been giving a low battery warning for some time now, and I've been driving it too and from work for several days. I don't understand why it would ever show the warning if the car is supposed to charge it when I'm driving, so I actually assumed maybe the charging coils in the ignition switch were bad. I replaced it a few month ago so considering getting a warranty replacement through FCPEuro.

__________________

Quote:

Originally Posted by umizoomi

As long as 3-pedals are an option, I will exercise my right to suffer the handicap and indignity of slower shifts and reaction times.

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Lieutenant General

Drives: 325xi 06 wagon MT

Join Date: Jan 2010

Location: Santa Cruz, Ca

Does a key symbol appear with the warning if not
its the main battery for the car.

Two kinds of key's 1) Comfort Access key has a replaceable battery .
2)Non comfort access key does not .(at least by the average person)

Last edited by ctuna; 01-10-2020 at 01:28 PM..