On Thu, 08 Dec 2011 11:14:27 -0800, Fred Abse
wrote:
On Thu, 08 Dec 2011 18:55:41 +0000, Ian Field wrote:
To my mind the inevitable clearance gap between the armature poles and the
magnet/field winding poles must make some difference to a transformer with
its alternating magnetic field in a closed core.
It will have the effect of increasing the reluctance, hence reducing the
flux in the core, hence the EMF per rad sec ^-1.
I recall, on a trip to the Hoover Dam power station, being told that by
reducing the alternator air gaps from (IIRC) 3/4" to 3/8", facilitated by
better bearings, they had got another 20% capacity.
Regarding the Sturmey Archer 'dynamo', the magnet is pretty crappy which
probably contributes to even more difference.
For 1936 magnet technology, it was pretty good. The Japanese, and Philips
Gloeilampfabrieken had a stranglehold on permanent magnet alloys, and a
lot of effort was being expended in catching up. Good job that the USA and
GB did make headway, before Holland was overrun, and Pearl Harbor. Of
course, the Japanese patents became void.
You can get Sturmey-Archer hubs with modern magnet materials,
improving the output. But, for Ian, his best bet would be FET
switching for the rectification. If he were clever he could even make
them regulating rectifiers ;-)
...Jim Thompson
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