On 07/03/17 04:22, Jeff Liebermann wrote:
On Mon, 6 Mar 2017 17:04:13 +1100, James
wrote:

On 06/03/17 12:26, Jeff Liebermann wrote:

Well, let's do some arithmetic. If your dynamo is rated at 3 watts,
and your lighting is rated at 70 lumens/watt, then the most you can
perhaps deliver is 210 lumens. 6 watts will get perhaps 420 lumens.
Usually, it's less as the losses accumulate. Rectification losses,
optical losses, heat degradation, and connector losses all conspire to
produce lower output.

We know that a 3W dynamo is quite capable of delivering more power than
3W, once the bicycle speed increases. 6W from a 3W dynamo is quite
achievable, and the retardation torque drops off as speed increases too.

Maybe:
http://www.myra-simon.com/bike/dynotest.html
See "Electrical Output" graph.

Kinda looks like all of them will sorta deliver 2.5 watts before the
core saturates (to provide some level of voltage regulation). Further
down the page is a "Low Speed Power" graph, which shows that most can
produce 2.0-2.5 watts at 10km/hr. One could assume that the dynamo
will deliver 4.0 watts, but that would require buying one of the few
better (hub) dynamos listed, and riding at 25-30km/hr (15-19mph).

If I were designing or sizing a lighting system suitable for my slow
style of "cruising", I would use the worst case 10km/hr (6mph) and 2.0
watt figures.




Back to electrical engineering school for you, Jeff.

--
JS