Bicycle headlight from old mobile phone. What type of light?

Factual Questions
1

My idea is to convert my old mobile phone into a headlight for my bicycle.

This will make recharging easy since I have three of the same old phones, giving me a couple of spare batteries and rechargers. The batteries are a 7.2 v Li ion.

I intend to pull the guts out of the phone and use the battery connecters to provide the power to a light that I will fit into the body of the phone. Then rig up a bracket to mount the light on the handlebar.

What is the best light to use for this sort of battery? Bright LED’s, halogen, something else?
Is it dangerous - can I inadvertantly blow up the battery?
Do I need any special circuitry?

I can recharge every day, so the power does not have to last long, but the brighter the light the better.

2

Seems like a lot of work, since a headlight wouldn’t cost more than twenty bucks.

3

With regards to LEDs, yes, yes, sortof.

LEDs have no internal resistance. Put that across a LiIon batt pack and the pack will heat up and cause problems. If the cells burst open, emergency room type problems. LEDs need a resistor in series to handle this. (Some come with one builtin.) But no Radio Shack LED is going to do you any good. Bright LED packs are still something of a specialty item.

I know how to do that sort of stuff and it still doesn’t seem worth it…

4

You need to design and build a circuit that prevents overcharging and over-discharging. The phone has one built in, but it’s part of the circuit board. This would be a difficult project - if you value your time at all, it’s much better to buy a high-end commercial light.

Also, there isn’t much energy in a cell phone battery. The battery in mine is 3.6V 630mAh. That’s less energy than a single rechargeable AA battery.

5

This basic rechargable 2.4 watt Halogen bulb is $69AUD - expensive enough.

A good 10-watt wide-angle halogen bulb light is expensive - $185.

This 30 watt bulb is very bloody expensive - $419.

I want a very bright light and dont feel like spending lots if I can do it myself.

From ftg’s post, it looks like a halogen would be best. If I use a 6 volt 15 watt halogen light would I have to do anything to avoid annoying things like explosions?

6

OK you have convinced me. I forgot about the charging circuit. Thanks.
Just seems like such a waste of good batteries and powerpacks.
Oh well, I’d better start saving.

7

I’ve actually used one of these. Unless you’re really stuck on a halogen bulb these are adequate unless you want to blind oncoming traffic.

8

I just got one of those led jobs, and its great–especially for the weight.
I once had a critical performance demand that I filled with a rechjargable 12 volt battery from radio shack ($25.00) meant to back up home alarm systems.

I strapped that to my luggage rack and ran wires to automobile halogen driving lights from aftermarket store (you could just as well simply buy a raw headlamp and fabricate a mounting to comport with your bike)

serious visibility, HEAVY battery…

I like my 4 AA cell led better.