Hub dynamo producing less power overtime?

asolodin

Newly Enlightened
Joined
Jun 8, 2012
Messages
1
Hello, I bought a pre-built wheel with shimano DH-3D71 dynamo hub back in 2010 time frame. I since put on maybe 15-20k miles on it with different lights. Overtime the hub developed a clicking sound, but up until last year seemed to work fine with the Philips dynamo light, which was ALWAYS on, as in daytime running light of sorts. The light was always bright and provided very good lighting in the dark. Last fall I noticed that at full speed the brightness was significantly lower, to the point where it was barely enough to see my way in the dark. I thought the problem was with the light, so I got a 6V AC wall power block which I hooked up to the light to test it and lo and behold the light was super bright again. I also cleaned all contacts but it didn't help. My conclusion is that the hub is simply not producing enough power any more for some reason. Has anyone experienced this? Is there any solution other than replacing it?

Thank you
 

znomit

Enlightened
Joined
Aug 1, 2007
Messages
979
Location
New Zealand
I thought the problem was with the light, so I got a 6V AC wall power block which I hooked up to the light to test it and lo and behold the light was super bright again.

The light won't necessarily behave the same with a dyno vs wall wart power source. I'd still be inclined to blame the light rather than the hub.
 

broadgage

Enlightened
Joined
Nov 23, 2007
Messages
442
Location
Somerset UK
Do these in fact have brushes, or diodes ? Despite being called dynamos, my understanding is that they are in fact miniature permanent magnet alternators with an AC output to the lights, no diodes needed. The winding is on the stator, with the magnets on the moving part so no brushes either.

I suppose that the magnets could lose their effectiveness in time, but have never heard of this happening.
 

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