> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Jonathan Hallameyer
> Sent: 16 November 2009 12:52
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Batteries in fast-charging "Faraday" flashlights
> 
> Ive seen both, the real shaker flash lights use a supercap to hold 5v
@
> 1farad or so, and have a bridge rectifier from the coil etc.. like you
> would
> expect.
> 
> The knock offs from china contain a coil of magnet wire, just one
layer
> typically, which in the one Ive seen both leads were soldered to the
same
> pad on the pcb, and there was still 4 diodes, hooked up to nothing,
and 2
> 2032 coin cells stacked where the cap would go. The knock off ones are
> cheap, the legit ones are pricy, as you would expect.  (guess that
super
> cap
> and all that copper for the coil adds up...)

Some of the knock offs have a slug of mild steel instead of a magnet as
well.  Then again a proper magnet isn't going to do much if the coil
goes nowhere!

I have a semi-knock off torch at home, it has a proper coil and some
kind of supercap, but performance is dismal; many minutes shaking gives
useful light for maybe 20-30 seconds, then it rapidly falls off.  Not
surprising once you check the circuit as the LED is connected straight
across the supercap, no kind of current limiting or regulation so once
the voltage falls below the LED's Vf, it goes out

Also there is no protection for overvoltage on the supercap.  I tried
shaking the torch for quite a long time with the LED switched off just
to see what would happen, but the cap voltage would never go much more
than about 6v. I guess the leakage becomes so high it limits its own
voltage?

Regards

Mike

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