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

On Wed, 28 Sep 2005 19:51:02 +0000 (UTC), Nikolas Ojala
wrote:
In rec.bicycles.tech wrote:

The schmidt hub generator is a constant current source ( approx 500ma )
but it varies in voltage ( 6v to over 30v ) as speed increases.

1) The hub generator, which is essentially an AC voltage source.

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

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.

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

Jasper Janssen wrote:
On Wed, 28 Sep 2005 19:51:02 +0000 (UTC), Nikolas Ojala
wrote:
In rec.bicycles.tech wrote:

The schmidt hub generator is a constant current source ( approx 500ma )
but it varies in voltage ( 6v to over 30v ) as speed increases.

1) The hub generator, which is essentially an AC voltage source.

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

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.

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.

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

wrote:
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.

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

dvt wrote:
wrote:
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.

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'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

wrote:
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.

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

dvt wrote:
wrote:
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.

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.

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

- Frank Krygowski

Quoting dvt :
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?

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.