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

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I have a schmidt hub generator and I would like to use it to power a 3W
Luxeon Star, if possible two of them.

The Schmidt hub generator is a AC generator that is built into the
centre of a front bicycle wheel.  As the bike moves power is made.  It
is very efficent and quiet.
The schmidt hub generator is a constant current source ( approx 500ma )
but it varies in voltage ( 6v to over 30v ) as speed increases.

The Luxeon LEDs are high powered versions of LEDs.  To operate
efficently the 3W version requires 700ma-1000ma.  It will light with
less current but it is not as bright.  The voltage required is approx 3
to 4 volts.
The reasons these LEDs are better than standard halogen light bulbs are
that slightly more lumens per watt are made and that they have a longer
life..

A couple of people I have talked to have directly connected two 3W
Luxeon Star to either end of the AC supply so that one is on at a time
switching on and off very fast as the wheel spins.  I think the LEDs
are in series with another diode to protect them from reverse voltage.
This approach does not give a bright light as the current is too low.

I have tried connecting a LED dynamics 03021-A-E-700 puck regulator
across the generator and using this to drive a single 3W Luxeon Star.
The light was not too bright until I got above 20kph.  Then it was a
good brightness for about 10 seconds.  After this the puck regulator
exploded.  Presumably it was getting too much voltage.

What simple approach do you think would work for converting the
variable frequency and voltage of the generator to a constant current
in a suitable range to power the LED?
Would a puck regulator work, if I capped the voltage with a zener diode
or two?


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


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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:
http://www.leddynamics.com/LuxDrive/datasheets/3021-BuckPuck.pdf
suggests that you were pushing it pretty hard.  That 30VAC you
quote for the generator (vs 24vac rating) is prob about 42V peak.

Ed


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


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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:
http://www.leddynamics.com/LuxDrive/datasheets/3021-BuckPuck.pdf
suggests that you were pushing it pretty hard.  That 30VAC you
quote for the generator (vs 24vac rating) is prob about 42V peak.

Ed


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


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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

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



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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.

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

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



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<
http://www.enhydralutris.de/Fahrrad/LEDWerfer0402/BaronTD.gif

Guenther - KISS

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


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

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

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

Andreas

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


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


On Wed, 28 Sep 2005 19:51:02 +0000 (UTC), Nikolas Ojala
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No, it's an AC current source. As he says.

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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



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



Jasper Janssen wrote:
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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


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


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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

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



dvt wrote:
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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


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


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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

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



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

- Frank Krygowski


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


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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.
--
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