Bicycle light, usb-charger help

[barughy]

Hello,
I have a bicycle dynamo (40% efficeiency, 6v/3w) that I want to charge my bike lights (which is a converted 12v Remington electric shaver, with rechargable batteries - powered by 3 LEDs in parallel)
The voltage going to the LED's is 4.8v, if I've used the multimeter correctly.

I also have a car USB charger with built built-in fuse protection, it converts 12-24v to a 5v charge, which I want to use to power my phone. I'm not sure if it will be able to using a bicycle dynamo.

I dont know much about electronics and what I do know I've learnt myself over the last few days. I'd be grateful if I could get some advice on what what I need to make it all come together and not blow my face off, wreck my phone, or cause a problem with the batteries.

So do I need to build a regulator and if so, how would I go about doing that?
The LEDs work fine and haven't blown (yet) but I'm not confident I have the right voltage going through them (it seems high) so what resistor would you suggest?

If I've missed out any glaring issues you think I should resolve as well then please dont be shy in elightening me.

Thanks.

 

[shokjok]

I've had that experience before, with a bike light glowing brightly that it burnt out at night. I now use battery-powered lights. The solution is a crowbar circuit, if you want to charge your phone off the dynamo. Most cellphones will take a 4.8VDC feed from a car plug ( regulated), but for your bike idea a low voltage may not adequately recharge your phone. The LEDs will still glow, while the extra feed recharges your phone battery. Too low a voltage from the dynamo may justify adding a small disc battery to the crowbar output to increase the voltage to the phone. I don't have such a circuit.

 

[ben7]

You could use a buck/boost regulator to power your stuff.

E=IR
2=.02*R
R=100

So you would need a resistor of about 100Ω for each LED, using a power supply of 5V.
The resistor goes in series with the LED.

Oh and your dynamo is rated at a 6V output so no you won't be able to use the USB charger thing.
Maybe it will be possible to use a Low-Drop-Out V-regulator.

-Ben