LED voltage question...

Okay -- I'm a road biker, and I tend to do a fair amount of night riding. Actually, by "fair amount", I mean "I've been nearly run off the road too many times to not have good safety lighting." My issue is this: I recently bought a cheap light (the Sigma TriLed), but the battery housing is a bit bulky, and it attaches to the bike awkwardly. The light is normally supplied by three AA batteries, but I'd like to use a cheap rechargable lithium I have as a spare for my digicam - they're rated at 3.7v and 850mAh (don't worry -- I didn't pay this much).

My big questions are:
1) Is this safe? eg. will I blow up the battery or the LEDs?
2) Is it worth it? The size difference will be dramatic, but will that coorespond to battery life?
3) Is it smarter to just use a larger capacity battery?

Okay -- thanks for reading the long post. Sorry I'm such a noob, but I guess I should have really taken more physics classes while in college!

From looking at some internet pics of the light, the 3 AA's are in parallel. So that means the electronics are working off of 1.5 volts and not 4.5 volts. I would say that 3.7 volts (actually 4.2 fresh off a charger) is going to fry something in there, either the LEDs if direct driven or the electronics (if it has any).

Morelite said:

From looking at some internet pics of the light, the 3 AA's are in parallel. So that means the electronics are working off of 1.5 volts and not 4.5 volts. I would say that 3.7 volts (actually 4.2 fresh off a charger) is going to fry something in there, either the LEDs if direct driven or the electronics (if it has any).

Click to expand...

I haven't seen any pics of the innards of the Sigma, but it makes no sense to wire the batteries in parallel when it is so much more of a pain to boost 1.5v to 3.5v than it is to put in a resistor or a current regulator to bring the 4.5v down.

RB, you need to measure, if you can, the voltage going into the light - if it is 3 or 4 volts, then the batteries are wired in series - which is how 99.9% of the world would do it. Also, if the Sigma works off NiMH rechargeables, then that is almost a guaranteed thing.

AND, if NiMHs work with your light, then the voltage of the LiIon is close to 3 AA rechargeables so it should be safe, and well within the amperage required by the 3 LEDs.