Originally Posted by
minisystem
Another good point. The Supernova standlight is pathetic and I'm not crazy about the Edelux's either. The taillight is significantly better, perhaps because of the way red light is perceived or the efficiency of the LEDs? Having been experimenting with standlight designs, it seems to me the reason standlights are so dim is that the super capacitors that run them are expensive and big. In order for a small/cheap supercap to power a standlight for a reasonable amount of time, the current has to be kept low. My DIY standlight is very bright, but it uses an $8 supercapacitor that wouldn't fit in an Edelux or any of the B&M headlamps.
In my DIY dynamo system, I've also had issues with the standlights. One of the problems with capacitors in general is that none are perfect; they all have an Equivalent Series Resistance value. They also have low operating voltages, requiring several to be run in series to build up the required voltage rating. According to my calculations, the ESR on my supercaps (2x Panasonic 20F, 2.7V, for 1 XP-G LED), the voltage drop induced by the supercaps is sufficient to actually dim the LED-this has to do with the Current vs Voltage curve of an LED, which is basically exponential. When running on low current (about 2.8V for 500ma), a difference of -.3V (for 2 capacitors with 300mOhm ESR) puts the LED wayyyy in the low range of its output. I haven't gotten around to splicing in a multimeter to check the current as I ride (project for this weekend), but I'm pretty sure this is why I have disappointing performance on my light when the standlight capacitors are installed.
Low-ESR supercaps are typically (one or both
more expensive or lower capacity. I've just got my hands on a few 10F caps that have only a 26mOhm ESR, I'll be trying those on my backup system soon.
I know this is the Cold Fusion/Free Energy of dynamo lights, but I'm also working on a dynamo buck regulator. I'll let you guys know how that goes.