Dynamo hub neo conversion again

[gotwind2]

This is something i have been trying to improve for over 5 years, I think it's time to give up, Hugh Piggott told me as much, years ago.

It's the bicycle dynamo hub, 'dynohub' made by Sturmey Archer in the U.K. shortly after the second world war - I don't think it has much of a presence in the U.S, although there are modern day variants, Shimano e.t.c

I put together a page on my website, just because I like it, and it reaches 6v cut-in at only 60 rpm.

http://www.gotwind.org/diy/Dynohub.htm

I have always wanted to convert the 20 pole ceramic ring magnet to a more modern Neodymium arrangment, the alternatot is a single phase claw pole arrangment.

Twenty N/S/N e.t.c N45 Neodymium poles were carefully arranged, and the stator inserted. The air gap was large, 3mm, but I don't think that mattered from my findings.

The cogging was horrendous, as expected, I was seeing a noticeable increase in voltage from the added flux, but the stator became saturated, as Hugh suggested, max current 0.5A.

I attempted to skew all of the magnets by approx 20 degrees to reduce the cogging, but it had little effect.

I think I will have to shelve my ideals of making the old dynohub into a suitable small wind alternator - It was good fun trying however :-)

Ben.

[hiker]

found one like that on a old raliegh bike[50s-60s]]--even at walking speed the light was bright.

nice little alts...

[Flux]

These machines are reactance limited, it's more or less inherent in the design. It was a particular virtue for a cycle dynamo before electronic control. They just hit constant current and that prevented the bulbs blowing.

You can reduce the effect of reactance a bit and possibly delay its onset by saturating the iron circuit but you are on a looser from the start. Stepper motors and many transverse flux machines suffer from the same problem.

I admire your patience but the original Alnico magnet ( not ceramic) was not really the limiting factor.

I suspect that with a force commutated rectifier and a tracking buck converter you could overcome some of these limitations but the problem with cogging, single phase and keeping iron loss reasonable in a bigger version remain.

Flux

[gotwind2]

Thanks Flux for the feedback.

I appreciate I'm fighting a loosing battle with these Dynohubs.

I just have a childhood fascination with them, I saw one coupled to the 3 speed sturmey archer gearbox at the London science museum physicaly cut into a sectional view when I was about 10 years old, and loved them ever since..

A gearbox and generator in something the size of a large coffee cup, amazing, and that was the 1950's

The Alnico magnet is another interesting cast magnet that I was unaware of, thanks for correcting me, Wicki has an interesting piece on these magnets.

http://en.wikipedia.org/wiki/Alnico

Ben.

[mehall]

Hi Ben,

I'm interested in these old dynohubs too, not really for wind power, but it would be great to get even a little more power from them when using them for their original purpose.

Can you advise

(i) whether you felt that you got more power from the unit with the new magnets, and what voltage was achieved at the 0.5 Amp maximum?

(ii) which make and model the magnets are and where they may be purchased.

(iii) What cogging means (I've not heard of this in relation to electromagnetics before)

Regards,

Matt