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Old March 6th 17, 09:10 PM posted to rec.bicycles.tech
David Scheidt
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Default More About Lights

Frank Krygowski wrote:
:On Monday, March 6, 2017 at 1:37:23 PM UTC-5, AMuzi wrote:
: On 3/6/2017 11:22 AM, 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.
: I don't know about currents but 6V 4W bulbs for standard
: dynamo systems have been around for twenty years and some
: customers like them. I don't know if the dynamo drag is
: noticeably greater.

:6V 4W? I'm aware of 6V 3W bulbs, which are (or were) used mostly with bottle
:dyno systems when driving a headlamp but no taillamp. They were an alternative
:to 2.4 W in front and 0.6W in back.

:I'm not aware of any common use of 6V 4W bulbs.

It's a standard lantern size.

But all of a sudden Igor Stravinsky shows up with bag of psilocybin
mushrooms and a chainsaw.... -- Jens

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