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Old 12-22-11, 11:21 PM   #1
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Dynamo lighting circuit with standlight and flasher: finished prototype

I just finished a prototype of a circuit I've been working on for several months. I want to retrofit a selection of vintage lamps with modern LEDs with standlight capability as well as the option to flash. I breadboarded it, had a PCB made and just finished soldering the parts on last night. The circuit charges a supercapcitor which powers a LED boost driver when stopped to provide anywhere from 2-5 minutes of standlight (depending on flash setting). A 555 timer provides the blinking option.

A couple of pictures:

The PCB is about 1.6" in diameter.

To fit the LEDs in the lamps I've made an E10 bulb with a copper heat sink:

I have yet to install the whole contraption on a bike yet, but it seems to be working well on the bench. The schematic is here.

The only issue is that the 6.8V Zener diode that regulates the input voltage gets very hot while in flashing mode. During the off cycle it clips the dynamo output and shunts its current. Kind of wasteful, but easy to implement. It's a 5W Zener, so it should be able to handle the dynamo output with the load disconnected, but I'm still a little worried about it. At some point I'd like to implement a kind of charge pump that stores the dynamo output during the off period of the flash and adds a burst of current during the on period. No idea how to do that though...

Last edited by minisystem; 12-22-11 at 11:28 PM. Reason: didn't finish!
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Old 12-23-11, 07:15 AM   #2
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Cool, look forward to some photos and vids once you have it working...I've got a an old schwin I want to try this on and I want to possibly use it to change the light on my 1980 honda CT 110, which uses a generator, and the light sucks.
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Old 12-23-11, 07:46 AM   #3
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Your worries about the zener could be a problem. A dynamo *can* produce more than 3W. On a fast descent, it could produce substantially more.

I'm not an electrical engineer and I only glanced at your circuit but I'd want to turn the driver on and off with the 555 rather than shunting with the zener. In the meantime, it'll probably work just fine in steady mode.
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