AC version of BuckPuck with dynamo

[FrontRanger]

I'm contemplating using an AC version of the Luxdrive BuckPuck (3023-A-E-xxxx) to power one or two Cree XR-Es with my Shimano DH-3N71 hubdynamo. Searching through earlier threads on this forum revealed that others had thought about using an AC-input-compatible BuckPuck with a dynamo, but I didn't find any threads where someone said they've actually done it. So has anyone tried this?

Thanks,
Stephen

 

[rideatnight]

I had thought about it, but then after a lot of research I found out that you don't need a current controlling device when using a dynohub. I use the Shimano hub you mention, a shottky-diode full wave rectifier (look it up on wikipedia, great diagram) and two cree XR-E Q5 bin LEDs in series. The hub keeps the current at 500ma, with the voltage only increasing with speed until you reach 500ma. If you're going to use this off-road, a smoothing capacitor of 4700 uF across both LEDs will eliminate some flicker at lower speeds (6-8 mph).

Above 10 mph, my light is brighter than the NiteRider HID light on high, with a more natural color.

If you try it, let us know how it works out!

 

[FrontRanger]

I had thought about it, but then after a lot of research I found out that you don't need a current controlling device when using a dynohub. I use the Shimano hub you mention, a shottky-diode full wave rectifier (look it up on wikipedia, great diagram) and two cree XR-E Q5 bin LEDs in series. The hub keeps the current at 500ma, with the voltage only increasing with speed until you reach 500ma. If you're going to use this off-road, a smoothing capacitor of 4700 uF across both LEDs will eliminate some flicker at lower speeds (6-8 mph).

Above 10 mph, my light is brighter than the NiteRider HID light on high, with a more natural color.

If you try it, let us know how it works out!

Yes, thank you, rideatnight. I know about that type of arrangement. It sure is a happy coincidence that classical 6V-3W hubdynamos happen to source ~500 mA, a value that happens to be in the useable range of most modern high-power LEDs.

But I want the capability to drive the LED(s) at a current that's greater than 500mA. A simple transformer placed before the rectifier could accomplish this by scaling up the current and proportionally scaling down the voltage. But this is inefficent because the diodes now drop the same voltage at twice the current, so I rejected that. I also would like to able to dim the lamp. These two features are driving me toward the BuckPuck. The only modification I foresee is the addition of a typical BJT-and-Zener-diode clamp at the input, since I don't know the input impedance and user "Martin" has just shown us what kind of voltage a dynohub can produce unloaded. Luxdrive hasn't replied to my emails, but I'll probably just try it anyway. If I do, I will indeed post the results.

 

[PhxCycler]

I don't have an answer to your question, but have you seen this thread?

http://www.candlepowerforums.com/vb/showthread.php?t=174557

There are some great circuits and idea in there.

 

[Martin]

Stephen,
a long time back I experimented with switchmode designs for dynamo lights but because of the losses involved, I could never get near the optimized rectifier circuits.
If you still want to do it, you need to modify the switchmode regulator so that it does NOT deliver a constant current to the LED but instead draws a constant current from the dynamo and delivers whatever power results to the LED.
As you do this you will learn that you need a buck which limits your low-speed performance. You control this by not using a full wave rectifier but a voltage doubler instead. The doubler halfs your diode losses which is nice. However , the high speed end of the range punishes you with a huge input voltage at a controlled current and trying to cope with this you sacrifice efficiency over the most-used middle range. Alternatively, you add a pretty good amount of circuit complexity.
If it is possible to modify the windings of the dynamo, this would get you where you want to be a little easier. I was always hoping someone would try that.
Don't miss the link that PhxCycler has posted.