The Ossie motor

[Jimboot]

Ok Here is my thinking - A hub dynamo from shimano http://techdocs.shimano.com/media/techdocs/content/cycle/SI/HubDynamo/HB-NX22/20GED-DH-2N30-E_HB-NX22-EN_v1_m56577569830605425.pdf is rated for 6V 2.4watt. The fastest I've ever been on my mountain bike is 50kmh or 830m/minute. My wheel circumference is 205cm so my wheel would have to be doing around 4000rpm? I'm assuming the hub dynamo will reach top power before then. I can get my motor doing that at around 50mw. The current rotor has a lot more torque so I am hoping the dynamo will have a similar drag to my 12vdc motor that I had attached at 2500rpm. Just awaiting my dynamo May have to do some jiggery pokery to get the dynamo far enough away from the rotor mags so they don't interfere but I'm a bit excited

[gyulasun]

Hi Jim,

I was qurious to learn the efficiency of hub dynamos in general and found claimed efficiencies of about 62-65% as normal.

I try to follow your reasonings with the numbers on speed, circumference etc but I am puzzled    not good at such calculations.  I think it is not the best to start with your max speed (50km/h) because as I read most hub dynamos has a built in voltage limiter (and it is a power Zener diode with 7V or so to limit output voltage above a certain speed) so that the bulb(s) should not burn out.
So if you do not mind you could start with say 20km/h speed and calculate with it further on how the energy "budget" will look like?

I have not found any efficiency data for your hub type. In the data sheet you gave link to I see warning of electrical shock danger if you happen to touch the output wires and I am surprised if it produces much higher output voltage than 6V when the output is -say- unloaded?  Nevertheless  if the output can give shocks it may mean there is no any Zener voltage limiter inside?

Thanks,  Gyula

[Jimboot]

Hi Jim,

I was qurious to learn the efficiency of hub dynamos in general and found claimed efficiencies of about 62-65% as normal.

I try to follow your reasonings with the numbers on speed, circumference etc but I am puzzled    not good at such calculations.  I think it is not the best to start with your max speed (50km/h) because as I read most hub dynamos has a built in voltage limiter (and it is a power Zener diode with 7V or so to limit output voltage above a certain speed) so that the bulb(s) should not burn out.
So if you do not mind you could start with say 20km/h speed and calculate with it further on how the energy "budget" will look like?

I have not found any efficiency data for your hub type. In the data sheet you gave link to I see warning of electrical shock danger if you happen to touch the output wires and I am surprised if it produces much higher output voltage than 6V when the output is -say- unloaded?  Nevertheless  if the output can give shocks it may mean there is no any Zener voltage limiter inside?

Thanks,  Gyula

If it works happily at 20km/h then I should get charge at 1600RPM. VERY doable. The only question becomes how much drag is there.

[Jimboot]

A quick video update on my current rig. Just waiting for the dynamo. http://www.youtube.com/watch?v=CGGhk-jMPhc

[gyulasun]

hi Jim,

I'll keep my fingers crossed for your successful looping!

Will you use some extra mass on your present rotor and the would-be hub combination, I think here of a kind of flywheel effect whether it is needed to a certain degree, to store mechanical energy. I do not mean it is a must, just maybe, it all depends on total summed masses versus would-be "momentums".

rgds,  Gyula