Battery LED light DC-AC conversion

[Stradageek]

I still find myself accumulating dead battery powered LED lights, mostly from bikes I renovate for a local charity. Many of them are the 4xAAA battery variety and are very bright when working. The deaths are caused, invariably, by control circuit corrosion, not LED failure.

My wife's town bike has recently had an upgrade to a dynohub but I wanted to run LED lights to avoid bulb failure - and I'm a cheapskate!

Rear lights are easy, a cannibalised red LED, 300 Ohm resistor and a diode, it flickers nicely at low speed.

For the cannibalised front LED I built a simple diode plus Zener voltage limiting circuit. My big mistake was to assume that 4xAAA means that I need 6V to drive the LED. After blowing up a couple of LEDs I checked the voltage drop across the control circuit of a working LED light to find that the LED itself runs on only 3V.

So the latest incarnation is: Red LED, 300 Ohm 0.25W resistor and 1N4001 diode in series, White LED, 1N5334B Zener in parallel, 1N4001 in series. Both are bright and flicker nicely at low speed.

As for proven long term reliability.......

[rjb]

Nice
I use full wave rectification using 4 diodes in a bridge. I save old led gu10 bulbs which fail due to the electronics failing. The leds are often perfectly ok. I throw the electronic module away and add the rectifier giving me a nice front light. Ive also used pound shop rear leds with an added resistor to limit the voltage.
viewtopic.php?f=5&t=116628&hilit=Gu10+Free


This site here provides a wealth of ideas. http://pilom.com/BicycleElectronics/DynamoCircuits.htm :

BTW how are you finding it down south now.

[Stradageek]

Love the GU10 idea, must try that next

Really looking forward to exploring Devon but delayed by house selling/buying ATM.

Cheers for asking

[rjb]

Mr16's or Mr11's work straight out of the box on a dynamo. They have the rectification built in so keeps life simple.
Finding red ones may be tricky so you will need a dropper resistor and some form of rectification if using a standard bike rear led.