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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > AUDIO/VIDEO + BLUETOOTH + Electronics/Alarm/Software > BMW E90 Key Fob Charging at Home?



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      12-15-2018, 06:37 PM   #1
Yangorang
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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..
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      12-15-2018, 08:39 PM   #2
ctuna
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Any inductive charger should put something in it.
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      12-22-2018, 12:36 PM   #3
Yangorang
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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.
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      12-22-2018, 12:47 PM   #4
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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..
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      12-22-2018, 04:41 PM   #5
Yangorang
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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.
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      12-22-2018, 08:52 PM   #6
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Any way of knowing what the frequency and amplitude of the
charger should be would be one of my questions?
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      12-22-2018, 11:29 PM   #7
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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.
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      12-22-2018, 11:48 PM   #8
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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/
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      01-02-2019, 08:40 AM   #9
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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...
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      02-08-2019, 06:54 PM   #10
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Quote:
Originally Posted by BimmerLad View Post
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
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      02-08-2019, 06:57 PM   #11
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Quote:
Originally Posted by dakine_surf View Post
Quote:
Originally Posted by BimmerLad View Post
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
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      02-11-2019, 01:15 PM   #12
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Quote:
Originally Posted by BimmerLad View Post
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 View Post
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.
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      08-07-2019, 08:49 PM   #13
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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
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      08-08-2019, 03:58 AM   #14
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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 View Post
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!
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