Sturmey dynohub + Leds - Am I missing something ?

[Steve K]

I've built just such a light recently:

....<pictures snipped>...

Even though I'm using a cap, the light still flickers as can be seen in the video at the above link. In fact, I can't notice a different with or without the cap. Also, at most I only get a couple of seconds of (very dim) standlight function from the cap. Two factors come to mind here:

1. I used a common silicon diode bridge rectifier, not a Schottky bridge, so there are more voltage losses. This may prevent the cap from charging as high as it might at lower dyno-wheel speeds.

2. Since there is only one LED paired with the cap, there is not as much voltage present in the circuit as there might be with multiple LEDs in series. This may also be preventing the cap from charging as much as it might.

Thoughts?

hi Jim,

Don't worry too much about the diode choice. This is mostly a factor in how slow you can go and still get light, but there's not much other effect. Once you are at a modest pace, the dynamo is putting out full current and you have full voltage across your led.

Standlight design is an interesting area of study, and it's one place where you can improve over commercially available lights. However.... just adding a big cap isn't going to produce the best results. There was a good standlight thread a few months ago (might have been all the way back to December??). We discussed quite a variety of designs and the pro's and con's of each. Alex Wetmore ended up using one of the better designs, I think, and wrote it up on his blog(?)... my memory isn't that good.

In any case, do a search in this subforum for standlights, or for Alex Wetmore, and you ought to find it.

regards,
Steve K.

 

[syc]

Standlight design is an interesting area of study, and it's one place where you can improve over commercially available lights. However.... just adding a big cap isn't going to produce the best results. There was a good standlight thread a few months ago (might have been all the way back to December??). We discussed quite a variety of designs and the pro's and con's of each. Alex Wetmore ended up using one of the better designs, I think, and wrote it up on his blog(?)... my memory isn't that good.

It was this thread. It looks like if you don't want to build the Zetex circuit that Alex used pulling power off the supercap, you can just pick up a Micropuck. It seems to be (not coincidentally) almost identical to what Alex built up.