Quote:
Originally Posted by Bdc101
I came here to say this -- there is no way that the diamond fob is being charged when it is hanging from the key that's in the ignition. Wireless charging becomes completely ineffective when things are misaligned like that, or when they are a couple of inches away. I am guessing this fob has just been draining its battery, and the battery has lasted for however many years oldskewel has been doing this. After all, other manufacturers don't have wirelessly charged keys, and their fobs last many years without charging. (We had two Scion fobs which never needed battery replacements for the nine years we had the car.)
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Good info. When I'm back in there once the spare batteries arrive, I'll do some more careful testing, varying proximity and direction of the key coil, within the charging coil's field - both for the car ignition and the iPhone charging pad.
EDIT - the iPhone charger is a Belkin F7U027
https://www.amazon.com/Belkin-Boost-...075M59ZB7?th=1
https://www.belkin.com/us/support-ar...icleNum=274455
Based on my son's feedback, I really can't recommend it as an iPhone charger (too slow), but it most definitely charges my BMW keys.
Watching how it works, it does have a single green LED, that comes on briefly when the thing is plugged in. Then it comes on and stays on when an iPhone is placed on the surface.
BUT, when a key is put on the surface, the green LED will stay off, even though the key battery is being charged - confirmed with a voltmeter on the battery.
So I'm thinking this unit works by having a constant field out there, ready and scanning for any iPhones. Then when an iPhone is present and starts drawing power, it steps up to a fuller iPhone charging mode. True or not, the important thing for these BMW keys is that the
charger's LED-off state is still charging the key.
My test setup is pretty convincing. I measure the battery voltage directly on the key, after it has reached steady state, and observe how it will click up or not based on moving it around. For the charging pad, it was clearly going up at about 1 mV per minute, with a very steady mV reading.
EDIT - some quick followup testing with the iPhone pad confirmed about 2x-3x faster charging based on the orientation of the key - specifically, with the key pointing basically down toward the flat charger, so the key's coil axis was within about 15 degrees of vertical, it was 2x-3x as fast increasing in battery voltage, vs. the key laying flat on the charging pad.
And more careful testing in the vicinity of the ignition key coil: Right at the location where a diamond key would be maybe 5x what the charging pad did. Field strength drops off pretty quickly with proximity in all directions, either axially or radially from that point. And slightly affected by direction (whether the key's charging coil is pointed at the ignition key coil) as well.
So the basic conclusion is that the key fob arrangement is definitely worse than the diamond key location, but still enough to probably keep things alive, perhaps needing an annual boost, just as I have found over the years. Now knowing the charging pad works will make that a non-issue.
Swapping in the new batteries went pretty easily. I did tune up the prongs slightly with my Dremel tool to let it fit at the right height, but I probably did not need to do that. Splitting the case was very easy using a sharp bladed utility knife. Reassembling with super glue gel worked great. I had also previously reflowed the critical solder joints at the buttons, and of course the battery connections were re-soldered in.
I think one of the batteries I replaced was definitely on its way out. It maxed out at about 2.82V after solid charging. The other one maxed out around 3.00V, and was probably good - and in that one, the real problem was probably only a failed solder joint. But I replaced both batteries with the new ones I ordered, keeping the old ones for the retired parts museum.
I also definitively tested when charging occurs at the ignition key coil. I had read conflicting info on here whether it is activated when the key is OFF, ACC or ON.
With a voltmeter on the battery, I confirmed convincingly for my 2001 E53:
Charging is on when the key is in ON and also in ACC. No surprise in the ON, the ACC has been reported differently.
Charging also works when the key is in OFF (and still inserted in the ignition key cylinder) and the car has not yet gone into sleep mode. So it charges for about 16 minutes after the key is turned off. I had seen conflicting reports of this out there.
BTW, I know exactly when my car goes into sleep mode because I have a dash cam that runs off a power source that is similarly on when the car is in ON, ACC, or OFF-but-not-yet-sleeping. So I could see when the dashcam's green LED went out it marked the beginning of sleep mode, which also was the end of key charging.