dynohub question

[mikey3]

hi folks ,i,ve got a dynohub on my xtc and i,ve noticed that when i switch it on there is a buzzing/vibrating noise coming from it,and i can feel a vibration in my handlebars ,does anybody know what could be causing this? 

[john28july]

Hello,
I had a Shimano setup do this. After a couple of weeks it stopped doing it and appears fine. I never found the reason.
John. 

[freddered]

If I lift the front wheel up and spin it I can feel a slight vibration.  I assume it's the magnets passing each other.  At speed on the road I can hear a 'hum'.

I've done thousands of miles on it without problems.

[geocycle]

I notice a slight hum/vibration from my SON hub.  It's only obvious when freewheeling down hill on smooth tarmac when its switched on. I think it's the magnets as fred suggests and nothing to worry about.

[pdamm]

I have a SON front hub with over 20,000 km on it and have similar experiences to Freddered and Geocycle.  It is normal.  However on one occasion I noticed it becoming much worse.  It turned out that on the previous day I had taken the front wheel off and when I reinstalled it I neglected to tighten the front skewer enough.  The loose skewer allowed the hub to “rattle” in the front fork making the vibrations worse.

Peter

[Fred A-M]

Not sure what Geocycle means about the Son hub being switched on?   I wasn't aware that was an option, but presumably you mean the light, which wouldn't make any difference!  Unless I'm missing something!?  My experience is similar however, in that it's most noticeable on smooth tarmac, the vibrations coming through the fork and frame, but impact on speed is negligable and haven't really noticed any difference on tours other than peace of mind if it starts getting late! 

[geocycle]

Hi Fred a-m.  I meant that I've only noticed it when the light is switched on. Resistance increases when the light is on, see here:  http://www.vintagebicyclepress.com/VBQgenerator.pdf so it seems likely that it is linked to the hum.  I suppose it could be coincidence but I'd assumed it was something to do with the magnets in the hub.  Anyone know exactly how these work?

[freddered]

How a Dynamo works?

Either spin conducting wires so they pass through a magnetic field or spin magnets so the field passes through the wires.  Either way you induce a current into the wire

I assume the coils of wire are staic on the axle and the magnets are attached to the shell of the hub and do the spinning.

[jawj]

I've a Shimano dynamo hub (DH-3N71) that causes a definite juddering at very low speeds when I lift the front end and spin the wheel. Not exactly true-to-life test there so doesn't prove anything, so I'll just say that when actually riding the bike, I can't feel a thing.

I think I might remember once feeling a vibration when riding, but my memory's not what it was so I'm going to assume that if I once had a vibration, like John above, it's now gone.

I think we can conclude that nothing to worry about and it's all down to magnets and stuff and lay this one to rest.

Apart from one thing:

Either way you induce a current into the wire.

Is it just me or do other people believe that induction is actually magic...?