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From: Keith Wootten
Subject: Re: Drive white leds from bicycle generator
User-Agent: Turnpike/6.02-U (<7r9OMDU2ooRJCQmjnYJxyjtHfm>)
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Date: Thu, 21 Nov 2002 13:18:05 +0000
NNTP-Posting-Date: Thu, 21 Nov 2002 13:18:55 GMT
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In message <firstname.lastname@example.org>, GéWé
>How can I drive 20 white leds from a 6V 3W (AC) bicycle generator
>(dynamo)? Output voltage of the dynamo varies with cycling speed. How
>can the light output be at maximum at a low cycling speed, and remain
>constant with increasing speed (= increasing voltage)?
The dynamo's unloaded output voltage will be quite high - 0-30V for
0-20mph has been quoted for one popular bottle dynamo. They're more
like constant current generators, really.
Make five full-wave bridge rectifiers using LEDs, and put a small
current limiting and balancing resistor, say 10 ohms across each bridge
'output'. This effectively gives you two series connected LEDs in each
direction sharing a resistor. The two pairs of LEDs light on alternate
Connect these bridges in parallel. Connect them to the dynamo through a
series resistor, try 10 ohms first and adjust as necessary for
This won't keep the output constant, but it's simple. I haven't tried
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