You are reading a single comment by @moth and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
@moth
They now have a shop where you can buy the lights (£200 for a full set - ouch!), and more interestingly a patent published:
full text translated to english: http://www.google.com/patents/WO2013004320A1?cl=en
key image: http://worldwide.espacenet.com/publicationDetails/biblio?CC=WO&NR=2013004320A1&KC=A1&FT=D
It's both cleverer and simpler than i'd imagined.
According to their patent, they can reach 60%: 1.2W of electrical power for 2W of braking at 20km/h, and because they seem to be using the pair of LEDs as their rectifier they are about as efficient as they can be converting that to light. They claim the system works up to 10mm from the rim (although presumably the above power requires closer operation).
Having the magnets rotate with the rim (with some slip) means that they aren't creating the full eddy current brake effect, and by using rare earth permanent magnets they get away with all the big air gaps. (Air gaps are bad when you're making your field with coils, because air's low permeability means you need more current and so more resistive losses to make the same field strength in air compared to iron. But with permanent magnets there's no on-going energy cost for the field. The air gaps clearly harm power output, but i think have only second-order effects on efficiency.)
I'm a bit dubious about their installation design, but i think they have a great product idea there.
As for my initial speculations that their system might just use coils with no magnets and on it's industrial applications to train braking, well, the Japanese are ahead of me: https://www.jstage.jst.go.jp/article/rtriqr/50/3/50_3_173/_pdf