minisystem
Newly Enlightened
- Joined
- Jul 12, 2011
- Messages
- 96
(hopefully not too off topic...)
The last couple of days I've been getting some performance data from my GH-6 Sturmey Archer dynohub (which I've become unhealthily obsessed with lately). I've got it set up in a motor-driven testing rig (more on that later...). I think I've sorted through just about everything that's been written about the GH6 online, including some insights from the (legendary) Jobst Brandt. To summarize, the GH6 can put out about 1.8W, supposedly reaches its rated output at about 20 kph/12 mph and has a saturation current of around 300 mA (6V @ 0.3A = 1.8W). One often discussed issue with the GH6 is the 20 pole Alnico ring magnet which can lose what little magnetism it has if the armature is removed from its centre without a keeper. It has also been said that this magnet can become weaker over time. My hub is a 1966, so an aging magnet could definitely be messing with power output. My testing suggests that my particular hub isn't saturating until 30+ kph.
This preamble brings me to my question: it seems like machining a simple adapter would allow the ring magnet to be replaced with a series of more powerful rare earth block magnets. This is kind of what I have in mind: http://www.etotheipiplusone.net/pics/pq2/pq2_54.jpg
Would replacing the old Alnico magnet with modern rare earth magnets in this configuration result in a significant increase in power output? Any obvious pitfalls I'm missing?
The last couple of days I've been getting some performance data from my GH-6 Sturmey Archer dynohub (which I've become unhealthily obsessed with lately). I've got it set up in a motor-driven testing rig (more on that later...). I think I've sorted through just about everything that's been written about the GH6 online, including some insights from the (legendary) Jobst Brandt. To summarize, the GH6 can put out about 1.8W, supposedly reaches its rated output at about 20 kph/12 mph and has a saturation current of around 300 mA (6V @ 0.3A = 1.8W). One often discussed issue with the GH6 is the 20 pole Alnico ring magnet which can lose what little magnetism it has if the armature is removed from its centre without a keeper. It has also been said that this magnet can become weaker over time. My hub is a 1966, so an aging magnet could definitely be messing with power output. My testing suggests that my particular hub isn't saturating until 30+ kph.
This preamble brings me to my question: it seems like machining a simple adapter would allow the ring magnet to be replaced with a series of more powerful rare earth block magnets. This is kind of what I have in mind: http://www.etotheipiplusone.net/pics/pq2/pq2_54.jpg
Would replacing the old Alnico magnet with modern rare earth magnets in this configuration result in a significant increase in power output? Any obvious pitfalls I'm missing?