Low voltage AC ( Schmidt hub ) to constant current ( luxeon star )

a cheap ordinary diode bridge would double the current (average, not peak) improving brightness with little impact to load terminal voltage (min speed to light it). It won't be full brightness, but much closer.

Putting two Luxeon LEDs in series at one bridge output should light them both as bright as with one, but you'd need more speed to light them both fully.

BTW, data on the page:

suggests that you were pushing it pretty hard. That 30VAC you quote for the generator (vs 24vac rating) is prob about 42V peak.

Ed

a cheap ordinary diode bridge would double the current (average, not peak) improving brightness with little impact to load terminal voltage (min speed to light it). It won't be full brightness, but much closer.

Putting two Luxeon LEDs in series at one bridge output should light them both as bright as with one, but you'd need more speed to light them both fully.

BTW, data on the page:

suggests that you were pushing it pretty hard. That 30VAC you quote for the generator (vs 24vac rating) is prob about 42V peak.

Ed

It doesn't go to 30V unless it's unloaded. Loaded with the designed-for

6V/3W lightbulbs it only goes to 7 or 8V.

Jasper

I would embed your LED light in the middle of a Schottky diode bridge, so that it gets forward biased regardless of which way the alternator output is going.

You say that the Schmidt generator is a constant current device, with a current limit less than what your LED lamp requires. If this is true, you don't need any kind of regulator, the generator is doing it for you.

I don't have first hand knowledge of these items; I'm just taking your word for their characteristics.

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

Guenther - KISS

22 Sep 2005 03:32:42 -0700, snipped-for-privacy@linuxufo.com:

Wrong. 3W-Luxeons work most efficent at about 10-50mA. Efficiency decreases significantly with increase of current - especially if cooling is less than perfect.

The difference is not as high as you would expect: Try it out!

Andreas

Assuming, that is, it's got a load with the proper resistance (or impedance).

Standard load is a lamp (or pair of lamps) designed to have 12 ohms resistance when carrying the standard current of 0.5 amp. That's your

6 volts, 3 watts. If you present the generator with, say, 24 ohms resistance, and spin it fast enough (say, 14 mph?) it still puts out very close to 0.5 amp, but generates 12 volts to do so. This is how I run the second headlight on my generator set, in series with the first.

If you give it essentially infinite resistance (an open circuit) a generator can produce high voltages indeed! How much, exactly, depends on the design of the generator.

- Frank Krygowski

I suppose that you would need these four things series connected:

1) The hub generator, which is essentially an AC voltage source. 2) A switch to turn the light ON/OFF 3) A choke. I suppose that an iron powder would be ok. I can't give the exact design parameters, because I don't know all the components, especially the generator. The choke (an inductance) is needed to limit current at high speeds (higher frequencies) so that you don't accidentally destroy the LED. 4) Two (2) parallel LEDs connected opposing directions.

You could build the circuit and test it first with low speeds. Use a multimeter to measure current while on the test ride. If the inductance is not big enough, increase the number of winding turns. Some iterations may be needed, but as you see, active components are not absolutely necessary.

Disclaimer: I haven't tried this circuit by myself, so I don't know how well (or badly) it works.

Nikolas Ojala

--
Home page:     http://www.iki.fi/no 

Static truth is dead truth and only 
dead truth can be held as a theory.

No, it's an AC current source. As he says.

Bike generators, including the SON, usually have a built-in choke, they saturate the core. That way the voltage runs from about 4 to 7 volt going from 7 mph to essentially infinity.

Jasper

I've got a simple on-off (SPST) switch in parallel with the second headlight. When closed, it shorts out that headlight to take it out of the circuit. So the generator sees only one bulb at low speed, and lights it up perfectly.

I leave the switch closed almost all the time. Opening the switch allows current to flow to the second light, a sort of "high beam" that I use mostly on descents - and, frankly, just because I like playing with it. ;-)

BTW, I plan to replace the switch with a three position, "center off" selector switch. Each side will be in parallel with one of the headlights. This will allow me to select the left headlight, the right one, or (at high enough speed) both lights. It will also give me a quick solution if I should blow one bulb.

The setup I use now works well with my Soubitez roller (or bottom bracket) generator. It would also work with a hub generator, and (I believe) with the FER 2002 spoke driven unit. From what I hear, it wouldn't work with most bottle generators. Their smaller roller diameters require more tangential force to turn, and they'd slip under the increased load of the two lights.

- Frank Krygowski

Let me see if I have this straight. You have two headlights connected in series. Neither headlight gets bright until somewhere around 14 mph. Is that right? Or do you have something more complex so the first light gets bright at slow speeds, while the second kicks in at higher speeds?

I know the 14 mph number is just a wild guess, but I used it to simplify my question.

--
Dave
dvt at psu dot edu

OK, I got it now. I know you're a bit of a simpler is better kinda guy, and I didn't imagine you had some electronic circuit switching on the second headlight when the generator was up to speed.

--
Dave
dvt at psu dot edu

Not that I haven't thought about it! But it was hard to see how that would beat a switch.

- Frank Krygowski

Quoting dvt :

The normal arrangement is that the secondary headlight has a switch on it that makes a short across its terminals; dynamo headlights sold as secondary have a fitted switch with this effect. For example I've got for our tandem a 2.4W Lumotec Oval Plus as a primary and a Schmidt E6-Z as a secondary; the Oval's wider beam is slightly more useful for low speed maneuvering and the E6's tight beam more useful at high speeds.

In practice the two-light speed is around 10-12mph such that you only need to switch the secondary off to climb steep hills.

--
David Damerell  Distortion Field!
Today is First Gouday, September.