Power P7 flashlight with Dynamo hub?
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Power P7 flashlight with Dynamo hub?
I have a two cell (18650) P7 flashlight and a one cell P7 flashlight. Both throw great light, though the 2 cell is bulky for a bike light.
I'm currently getting a Sturmey Archer 6v 3watt hub wheel for a new bike. My question is - could a P7 be adapted for use with the dynamo? The 18650 are nominal 3.7v.
Would a dummy battery connected to the hub work? Could the 18650 be wired in parallel - and be kept charged up while moving while providing a stand light?
What's horribly wrong with my reasoning (I suspect the P7 draws too many watts)?
I'm currently getting a Sturmey Archer 6v 3watt hub wheel for a new bike. My question is - could a P7 be adapted for use with the dynamo? The 18650 are nominal 3.7v.
Would a dummy battery connected to the hub work? Could the 18650 be wired in parallel - and be kept charged up while moving while providing a stand light?
What's horribly wrong with my reasoning (I suspect the P7 draws too many watts)?
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It's not that the P7 requires too many watts, it's that it requires too few volts and too many amps.
As for charging lithium cells from a dynohub, I guess it could be done, but not at the same time as powering lights.
A single 18650 can (theoretically) output 2.5A for one hour @ 3.7V - to recharge it from a 3 Watt source would require the full (high speed) output of the hub for maybe 4+ hours, depending on the losses in the charging circuit.
As for charging lithium cells from a dynohub, I guess it could be done, but not at the same time as powering lights.
A single 18650 can (theoretically) output 2.5A for one hour @ 3.7V - to recharge it from a 3 Watt source would require the full (high speed) output of the hub for maybe 4+ hours, depending on the losses in the charging circuit.
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In any case it would be inefficient, it would be far better to use some LEDs in series.
The P7 is 4 LEDs in parallel.
The MC-E LED can be series or parallel, so would be a better choice.
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you could use a switching regulator, and saying that glosses over a lot of complications. And that would be a lot of work for not much gain. The MC-E is a much better choice.
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Could you mod the P7 and rewire them in series? Or is is just easier to buy loose LEDs?
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Seems like there are at least 3 companies that make multi-emitter LEDs that can be run in series, so Seoul is missing out. There are MC-E flashlights, not sure how hard it is to convert them to series configuration.