Skippy Blue
Member Since: 28 Oct 2007
Location: Hampshire
Posts: 35
  
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Puzzled by this... my key fob battery has nearly died, can only open door at very close range, and getting a new one under warranty. here is the puzzle - how does the battery get recharged in the ingition - there seems just to be the key isself- i.e no way of making a full circuit ?
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 5th Apr 2008 10:52 pm |
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simon
Member Since: 11 Jan 2005
Location: Shropshire
Posts: 18296
 
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The key is metal - it conducts a current - that goes into the battery 
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| 5th Apr 2008 10:55 pm |
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ianv
Member Since: 20 Dec 2007
Location: Bungendore, New South Wales
Posts: 338
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Understand the question,
I've looked at mine as well, yes there is primary contact via the key itself but where does the earth side come from?
 TDV6
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| 5th Apr 2008 10:59 pm |
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simon
Member Since: 11 Jan 2005
Location: Shropshire
Posts: 18296
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Why does it need an earth ?
Its fully isolated once inserted.
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| 5th Apr 2008 11:02 pm |
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xtc
Member Since: 27 Mar 2007
Location: Hampshire
Posts: 1072
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It's charged by induction.. Small coil in the fob and one near the ignition lock. Works like a transformer. Same as charging an electric toothbrush!  Off Roading is OK.... But I'd rather be Boating!
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| 5th Apr 2008 11:03 pm |
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Bodsy
Site Sponsor
Member Since: 06 Nov 2006
Location: In the Clubhouse
Posts: 21361
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Must be something about the time of night, I was about to reply to state the same re toothbrush  Bodsys Brake Bible
D4/D3 Remote FBH heat kits
BAS Remaps/ EGR Blank
Transmission Flush
Software updates/enabling
Clock/ SNOTM /3Flash / 4x4Info /BT Update /Service Reset/Error Codes / Gearbox Reset
See It Here
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| 5th Apr 2008 11:06 pm |
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Bodsy
Site Sponsor
Member Since: 06 Nov 2006
Location: In the Clubhouse
Posts: 21361
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Some of our boffin researches had been looking into how you can charge something by radio waves....... Cool stuff! Bodsys Brake Bible
D4/D3 Remote FBH heat kits
BAS Remaps/ EGR Blank
Transmission Flush
Software updates/enabling
Clock/ SNOTM /3Flash / 4x4Info /BT Update /Service Reset/Error Codes / Gearbox Reset
See It Here
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| 5th Apr 2008 11:07 pm |
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Martin
Site Admin and Owner
Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18507
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Simon, it'd need an earth to complete the circuit otherwise a current cannot flow! 06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
Any issues with the site let me know!
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| 5th Apr 2008 11:07 pm |
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Skippy Blue
Member Since: 28 Oct 2007
Location: Hampshire
Posts: 35
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clever stuff these toothbrushes !
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| 5th Apr 2008 11:09 pm |
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simon
Member Since: 11 Jan 2005
Location: Shropshire
Posts: 18296
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Martin wrote:Simon, it'd need an earth to complete the circuit otherwise a current cannot flow!
Not always... the induction of current in a toothbrush has no conductive parts so no earth or live.
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| 5th Apr 2008 11:09 pm |
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Hobgoblin
Member Since: 15 Nov 2007
Location: As always, in the sh*t, it's only the depth that varies
Posts: 1445
 
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This may seem a bit far fetched but it is correct, believe it or not it is charged by induction loop, in other words effectively it is charged by radio waves and the metal of the key IS the earth, it is also being considered for the charging of mobile phones while in vehicles so that you can leave the phone in your pocket and as well as connecting to the vehicle for hands free use it will also charge the battery of the phone, but they haven’t worked out the earthing yet. I'm not as good as I once was........but I'm as good once as I ever was.
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| 5th Apr 2008 11:14 pm |
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xtc
Member Since: 27 Mar 2007
Location: Hampshire
Posts: 1072
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Bodsy wrote:Must be something about the time of night, I was about to reply to state the same re toothbrush
Must be a $hite night on the telly!  Off Roading is OK.... But I'd rather be Boating!
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| 5th Apr 2008 11:14 pm |
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AndrewW
Member Since: 06 Aug 2007
Location: Saddleworth
Posts: 2302
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Hobgoblin wrote: but they haven’t worked out the earthing yet.
No earthing required. The primary loop produces a changing elecromagnetic field which induces a (charging) current in any (suitably coiled) conductor to charge the battery. They do it on loadsa things from toothbrushes (v.s.) to pacemakers and artificial hearts.
The interesting question is why/how they bother to produce an AC supply from the car's DC supply, as inductive phenomena  are AC based.
How long does a key have to be operational to stay charged? What about SWMBO's key that never (hopefully) gets used? if I use it, the seat zooms up to the steering wheel and the mirrors point at the floor!  2006 D3 finally swapped for a 2016 D4 Graphite in Graphite grey. No mods
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| 6th Apr 2008 12:04 am |
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Hobgoblin
Member Since: 15 Nov 2007
Location: As always, in the sh*t, it's only the depth that varies
Posts: 1445
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Interesting.
But I have found the 'Key Memory' as far as the D3 is concerned to be  , only seems to remember the last position used irrespective of the key used, with the Jeep, althought the car itself is a load of the memory function works great. I'm not as good as I once was........but I'm as good once as I ever was.
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| 6th Apr 2008 12:24 am |
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