No EE background. Suggest a smoothing cap?

Thread Starter

frascati

Joined Jun 1, 2010
37
Nominal 6v magneto trail bike system. Measured 4vac ~ 16vac. 40w max output. Unrectified, unregulated.

Considering these LEDs for headlamp duty
http://www.google.com/url?sa=t&rct=...S39zYl3UX0vqC1HNg&sig2=L5P81vaIAZnRDZXBDFlmxQ
XMLBWT-00-0000-000HT20E7
XMLBWT-00-0000-000LT40e4
XMLBWT-00-0000-000LT50e4
XMLBWT-00-0000-000HT30E7

This full wave rectifier
http://www.digikey.com/product-sear...ng=en&site=us&keywords=GBU10A-BPMS-ND&x=0&y=0

This DC/DC regulator
http://www.digikey.com/product-sear...g=en&site=us&keywords=NE12S0A0V06PNFA&x=0&y=0

I've tried to decipher smoothing cap formulae on line but it's over my head. Please suggest an appropriate DigiKey part number?

Thanks so much.

Frascati
 

RichardO

Joined May 4, 2013
2,270
You can't power an LED directly from a generator. You have to have something to limit the current to the LED. In low power LED circuits this is normally just a resistor.

In high power applications, you need a switching regulator to get any efficiency. If this is a bicycle light then you have to remember that any energy lost is supplied by your legs.

Other requirements that you must consider are:
Higher currents do not produce proportionately higher brightness.
The LED brightness decreases with temperature.
The LED will need lots of heat sinking to keep it from getting hot.
Optics are important to get the light where it is needed.
The optics are not 100% efficient.

In practice, I needed about 15 watts of input power to get 450 lumens which is about the same as as 30 watt incandescent light bulb.
 

SgtWookie

Joined Jul 17, 2007
22,230
Don't try to change from an incandescent to an LED; your electrical system isn't set up for that. It works fine as it came from the manufacturer; keep it that way.
 
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