John Halliwell wrote:
> In article <[email protected]>, Peter Clinch
> <[email protected]> writes
>> You don't really switch them off or on in the usual sense, you either
>> draw current from them or not. If you draw current there's more drag
>> than if you don't. With the best hub, the SON, there is not much
>> more
>> drag than a conventional hub when they're "off", and not much more
>> when "on". The Shimanos at half the price aren't as good, but
>> they're still pretty good and there's not particularly perceptible
>> drag on a utility bike.
>
> Thanks to all.
>
> There was me thinking you'd lock the coils and magnets together
> somehow to turn it off! Am I right in thinking the 'additional'
> resistance is related to the current drawn, if so are there limits
> (do they come in various wattages)?
Yes, the pedal resistance comes primarily from the current drawn.
Pretty much every generator(*) conforms to a German specification; this
being 6v and fairly high lighting levels from quite low speeds. They are
constant current devices, limited to 0.5amp, which ensures that a total of
3W of bulbs stays illuminated. (either 3W front alone, or 2.4W front plus
0.6W rear).
Both the Schmidt and the more expensive Shimano can generate a lot more than
6v, whilst still limited to 0.5amp constant current (so won't blow a normal
single light setup).
Both can deliver 12V at higher speeds. So, its possible to wire two bulbs
in series to double the illumination. Usually this is done by manually
switching in a second 3W headlamp at higher speeds. There is a special
Schmidt headlamp for this purpose with a capacitor included which helps its
operation, though any lamp will work if wired correctly.
Alternatively, both SolidLights and Inoled offer LED lamps which
automatically increase the illumination as the voltage rises. Neither of
these suppliers are particularly cheap.
I find a hub with a single 3W bulb is adequate for 20-25kph on unlit rural
roads with no moon. But, its underpowered for 35-40kph.
Twin lamps or the newer LED options give more illumination.
> If touring, would it be possible to connect one up to some kind of re-
> charge system to provide battery lighting when camping?
In principle yes.
In practise it could be a complex circuit as the voltage goes up/down, but
the current stays constant. Further, its AC from the generator, not DC.
I'm sure someone will have done it before.
Might be cheaper/easier to strap a solar recharger to the top of your
luggage and use that instead ?
(* there are some sidewall models which conform to a 12V specification, but
I don't think any hubs do yet).
- Nigel
--
Nigel Cliffe,
Webmaster at
http://www.2mm.org.uk/