Shimanon Hub Dynamo

brompting · June 2007

Hi Tinkerers,

I am building a front wheel with a Shimano Hub Dynamo, DH (dynamo hub?) 3R40. This one has a hollow axle for a QR and pick-up for the Roller Brakem (what's the use of the QR, but that is not the isue here).

I notice it is not free turning, of course the magnets you will say. But I went to several shops to give the front wheel of new bicycles with a Hub Dynamo a swirl. They all turn with almost NO resistance. I quickly put my Hub Dynamo in a rim with twelve spokes, even then it was VERY difficult to make the wheel turn! I loosened up the Left Hand cone, no difference at all.

I must say all the wheels I have tried are a different type of Shimano Hub Dynamo. I got mine from a whole-sale shop and I doubt wether they really now their hubs. I can always return the hub. But I would be thrilled that with your help I could outsmart [;)] the guys at the whole-sale-shop.

There used to be a "Mister Shimano" at the importer. But I could not get him on the phone. I do not know if he is on leave or they send him on riterement and did not replace him.

Hope you could help, Brompting

A Brompton by any other name, should it not ride as smooth

amaferanga · June 2007

The cheap shimano dynamo hubs are always "on". The good ones, like the Ultegra quality hub, can be switched "off". If you've got one of the former then there'll be more resistance than with the later (when the later is "off").

More problems but still living.....

Anonymous · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by amaferanga

The cheap shimano dynamo hubs are always "on". The good ones, like the Ultegra quality hub, can be switched "off". If you've got one of the former then there'll be more resistance than with the later (when the later is "off").

More problems but still living.....
<hr height="1" noshade id="quote"></blockquote id="quote">

Rubbish! When the lamp load is connected, you will feel the extra resistance. When the lamp load is disconnected, the resistance will be much less.

Are you sure your roller brake isnt engaged, or needs adjusting?

amaferanga · June 2007

Its not rubbish actually. I have both a cheapo shimano dynamo hub (NX22) and the ultegra dynamo hub (DH-3D70). There is no noticeable difference in the resistance with the cheapo hub when the light is disconnected. With the ultegra hub there is a huge difference when the light is disconnected. My dynamos don't have roller brakes.

More problems but still living.....

Anonymous · June 2007

I have the 3N71, and its not noticeable when riding on it. However, Im talking about spinning the wheel by hand and noticing the frictional difference.

campagman · June 2007

I have an ultegra dyno hub. When I first recieved it I tried to turn the spindle by hand and like you say it is surprisingly difficult. When you build the wheel up and fit it into your bike you will not be able to notice anything at all. It is just the magnets and rotor passing each other.
Ultegra hubs cannot be switched off either but you will also not notice any difference between light on or off.

remember to keep pedalling in circles.

wotbus@ · June 2007

[:)] What's all this ON/OFF stuff.

Surely the physical resistance of any dynamo remains constant if the distance between the magnets and rotor remains the same! When the light is switched off, current is still being generated but simply not used.

Not a wind up, honest [;)]

Anonymous · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by wotbus@

[:)] What's all this ON/OFF stuff.

Surely the physical resistance of any dynamo remains constant if the distance between the magnets and rotor remains the same! When the light is switched off, current is still being generated but simply not used.

Not a wind up, honest [;)]
<hr height="1" noshade id="quote"></blockquote id="quote">

Thats the difference between an EMF (electro motive force) and a voltage. Voltage appears when current flows. Google up on back-emfs if you want to learn more.

wotbus@ · June 2007

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by xroads

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by wotbus@

[:)] What's all this ON/OFF stuff.

Surely the physical resistance of any dynamo remains constant if the distance between the magnets and rotor remains the same! When the light is switched off, current is still being generated but simply not used.

Not a wind up, honest [;)]
<hr height="1" noshade id="quote"></blockquote id="quote">

Thats the difference between an EMF (electro motive force) and a voltage. Voltage appears when current flows. Google up on back-emfs if you want to learn more.
<hr height="1" noshade id="quote"></blockquote id="quote">

Thanks xroads - that was a real trip down a dusty memory lane. The only thing I really remembered was my science teachers name LOL. Can I assume then, more load (or any) is placed on the dynamo - harder it is to turn?

Shimanon Hub Dynamo

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