Converting Old Light To LED - HELP!

[Road Master]

Hi! I have this old bicycle light that was originally chrome but now is rust and was powered by two D size batteries that are now shorted out. But it has a nice switch and a glass lense - I'm a sucker for old lights with glass lenses. Somewhere in RRBBO5 a builder converted a light to LED but was using a 9 volt battery. I went to Wally World and couldn't find any LED flashlights that were powered by a 9v. I don't know if it's a custom build or if it's something that is available. If anyone knows of this system or any other system that is easy and econmical to use - no funky batteries, preferably something rechargeable (anything smaller that a D?), please let me know. I appreciate all comments and ideas - I need this for my build. Thanks alot. Robert (Road Master)

 

[Ratfink1962]

well you could use one of those cheapie led flashlights that take 3 AAA batteries (4.5 volts) and hook it to a 9v battery with a limit resistor.

Ohms law... Voltage divided by current = resistance

Since I dont know the design current of one of those, just use 30mA as a starting point since that should be in the ballpark.

so 9v divided by 30mA = 300 ohms

Run down to the radio shack and grab a few resistors from 300 ohms to say 100 ohms. then hook the highest ohm resistor you have in series with the LED light, if its not bright enough, switch it out with a lower value resistor until you get it where you want it.

The best way would be to actually measure the current with a digital volt/ohm meter at the original 4.5 volts, then use the current reading plugged into the formula (at 9v) to get you actual resistor rating.

Or... you could search for some of those LED's that have a built in resistor made to work at different voltages, pricier but it may save you a little hassle.

 

[icyuod2]

most of the bling for cars at walmart will run off a 9volt battery.

i'm using 2 red leds to light up my buildoff skull light.

its a 2 light car alarm set. it also includes the wiring/hardware to switch from flashing light to constant light.
its a cheap easy way to go and they have practically every color light you can imagen.

 

[XC204]

I use 3 watt led's on all my lights you can get a 1watt or 3 watt at menards they use 3 AAA cells find one that has a battery holder 3 batterys side by side as they are small use the flash light gutts. The led in mine is epoxyed to the 1/4-20 bolt the plastic led optics glued to the led then inserted from the front side of the reflector nut and washer hold it in place of orig bulb holder batterys set behind reflector and I wired a sm toggle switch to the light back.

By xc204 at 2009-08-18

By xc204 at 2009-10-01

 

[No Talent Clown]

http://www.plasmaled.com/

 

[Road Master]

Hi Guys! Thanks for all the different ideas - I guess there's more than one way to LED a light. I didn't see any kind of lights with batteries in a side by side holder which is why I was asking about a 9v to begin with. I have 2 headlights on my build and I may end up converting both even though the one works fine as is. I'm afraid the two different kinds of light will annoy me. Thanks again for all the tips.

 

[Bigcam59]

I've been using cheap dollar store reading lights, the ones with a bendable neck. Once you cut the neck you have a nice LED bulb with a reflector and the wires already connected. I've also used dollar store LED flashlights. They're cheap enough to experiment with. 8)

 

[Bigcam59]

I've been using cheap dollar store reading lights, the ones with a bendable neck. Once you cut the neck you have a nice LED bulb with a reflector and the wires already connected. I've also used dollar store LED flashlights. They're cheap enough to experiment with. 8)
viewtopic.php?f=3&t=22740#p233920