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Can you build a key charger?

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D4dawg

Can you build a key charger?

Post by D4dawg » Wed Aug 16, 2017 11:20 pm

Bmkeys full refurb
Case battery and key cut for peanuts
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RickRob
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Can you build a key charger?

Post by RickRob » Thu Aug 17, 2017 7:53 am

I don't recall reading any previous posts about keys failing due to lack of charge.

Over what period of time is the recommended 30 hours - monthly, weekly (daily :P )?

There's no way that mine is being charged for 30 hours a week, yet I have had no issues in my 3+ years of owning the Zed.
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Can you build a key charger?

Post by obewan » Thu Aug 17, 2017 8:02 am

RickRob wrote: Thu Aug 17, 2017 7:53 am I don't recall reading any previous posts about keys failing due to lack of charge.

Over what period of time is the recommended 30 hours - monthly, weekly (daily :P )?

There's no way that mine is being charged for 30 hours a week, yet I have had no issues in my 3+ years of owning the Zed.
Same here, I reckon 3.5/4.0 hours a week tops on average
Although I make sure I alternate the keys
Interesting thread though, keen to see the results :thumbsup:
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Can you build a key charger?

Post by mmm-five » Thu Aug 17, 2017 8:50 am

I don't think I've used my 2nd key more than once a year, so will have to check it's still working. It was working last time I tried (probably before Christmas).

The 1st key is in the car for about 12 hours a week though, and is still fine after 9 years and 143,000 miles.
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Can you build a key charger?

Post by ph001 » Thu Aug 17, 2017 9:44 am

Can anybody confirm if the battery in the key fob is definitely 12V? Seems more likely it's a 3.6v lithium, in which case you would be looking at a 5v charger so the basic wireless phone chargers should work.
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Can you build a key charger?

Post by Mangozac » Thu Aug 17, 2017 10:37 am

ph001 wrote: Thu Aug 17, 2017 9:44 am Can anybody confirm if the battery in the key fob is definitely 12V? Seems more likely it's a 3.6v lithium, in which case you would be looking at a 5v charger so the basic wireless phone chargers should work.
It's definitely not 12V, but either way the supply voltage of the charger is irrelevant for an inductive charging system.
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Can you build a key charger?

Post by ph001 » Thu Aug 17, 2017 11:09 am

Yeh, I suppose as it's really down to the turns ratio of the coil in the charger and the pickup coil in the key. But then the coupling will be so poor it might be pretty much irrelevant as long as the induced voltage on the key is above 4V or so.
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Can you build a key charger?

Post by Ducklakeview » Thu Aug 17, 2017 11:49 am

ph001 wrote: Thu Aug 17, 2017 9:44 am Can anybody confirm if the battery in the key fob is definitely 12V? Seems more likely it's a 3.6v lithium, in which case you would be looking at a 5v charger so the basic wireless phone chargers should work.
Just tried my key on the wireless desktop charger here - Nada..

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Can you build a key charger?

Post by jabber » Thu Aug 17, 2017 11:52 am

Ducklakeview wrote: Thu Aug 17, 2017 11:49 am
ph001 wrote: Thu Aug 17, 2017 9:44 am Can anybody confirm if the battery in the key fob is definitely 12V? Seems more likely it's a 3.6v lithium, in which case you would be looking at a 5v charger so the basic wireless phone chargers should work.
Just tried my key on the wireless desktop charger here - Nada..

Mike

I used my toothbrush charger to do mine but had to resync both keys to get it to work
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Can you build a key charger?

Post by Mangozac » Thu Aug 17, 2017 9:36 pm

If you can't find a spec for the inductive charging frequency then the way to find out how to drive the coil is to stick a wire loop into a spectrum analyser and measure it next to the keyhole on the steering column. I have such equipment but I would need to find time to do it :/
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Can you build a key charger?

Post by Dablk » Thu Aug 17, 2017 9:42 pm

Is the frequency dictated by the the coils? Or the charge going thru them? Or both?

I plan on using a s/h coil of an e46. Basoaccly the whole barrel unit. It's just how to drive it I don't understand.

Ac or dc current and how much.
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Can you build a key charger?

Post by Dablk » Thu Aug 17, 2017 9:43 pm

On the transmitter that is.
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Can you build a key charger?

Post by GuidoK » Thu Aug 17, 2017 10:15 pm

Dablk wrote: Thu Aug 17, 2017 9:42 pm Is the frequency dictated by the the coils? Or the charge going thru them? Or both?
Neither.

The coil will pick up most frequencies but some will give a higher efficiency than others.
But as I wrote, the coil is handling a duplex signal (both the charge energy and the transponder data) so there is some active filtering.

Chances are that the coil in the key is not used for transmitting transponder data, but the coil in the lock is used for recieving it (at least, thats what BMW WDS tells us)
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Can you build a key charger?

Post by markeg » Thu Aug 17, 2017 10:18 pm

GuidoK wrote: Thu Aug 17, 2017 10:15 pm Chances are that the coil in the key is not used for transmitting transponder data, but the coil in the lock is used for receiving it (at least, thats what BMW WDS tells us)
+1, when my car goes into the dealer, the key is read by the dealer to retrieve service data etc.
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Can you build a key charger?

Post by buzyg » Thu Aug 17, 2017 10:42 pm

In six years of week end driving. My key has always remained charged. My wife's key did lose it's marbles once. So I went through the reboot procedure with both keys, plus a couple of trips out & soon had it working fine again. It has never done it again & that key only see's the car ever few months. :D
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