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Here are some awesome LEDs

Discussion in 'Electronic Design' started by Doug Goncz, Feb 4, 2004.

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  1. Doug Goncz

    Doug Goncz Guest


    From down under, with stamps all over it, comes a package from Oatley
    Electronics containing four 1 watt white LEDs and four lenses. Each LED is
    about the usual size but is heat sinked to a disc about the size of an American
    nickel. Quite heavy.

    Each is rated 3.6 VDC, and a whopping 350 milliamps. I have a 15 V regulator on
    my bicycle. Let's see, that's 2 x 7.2 or 14.4 volts for the LEDs off of 15 from
    the regulator.

    What are the efficiency tradeoffs between a resistor and a constant current
    source? Is it better to use a constant current incandescent lamp as a source in
    this application, or a semiconductor solution? I suppose the semiconductor
    would be more efficient but the lossy lamp gives some light which counts toward

    I calculate a 43 ohm, 6 watt resistor. Did I get it right?

    What's the most efficient setup for these LEDs in series or even parallel, with
    the given source, 15 V, capable of 5A. (It also runs an inverter)? Do I need to
    evaluate the performance of the regulator at 350 milliamps?

    My intuition is that these 4W of LED lighting should be the equivalent of 16W
    of incandescent, assuming they do about as well as fluorescents. With the
    lenses, I should have plenty of light forward with a mere twitch of the pedals.

    Is the right resistor calculation 0.6 V / 0.35 A = 1.7 ohms, 1/4 watt? That is
    acceptable on efficiency.

    Should I further heat sink the 4 LEDs side by side on a 1/8 or 1/16 inch thick
    aluminum base about 6x1 inches, forming a chassis with more structure
    supporting the lenses and enclosing the system?

    My physics project at NVCC:
    Google Groups, then "dgoncz" and some of:
    ultracapacitor bicycle fluorescent flywheel inverter
  2. Ian Stirling

    Ian Stirling Guest

    They don't.
    They are about the same efficiancy as halogen lights.
    About the only advantage is shock resistance and life.
  3. Syd Rumpo

    Syd Rumpo Guest

    Another particular advantage for a bicycle is that the LEDs will still
    show white at low power input when an incandescent lamp will be
    glowing a very inefficient dull yellow or red.

    Up to a point, a bicycle dynamo behaves more like a constant current
    source than a constant voltage source, so you *may* be able to
    dispense with any current limiting or regulation.

    Your 15V and 5A sounds either wrong or very hard to pedal, unless
    that's 15V open circuit and 5A short circuit.

    A 3W dynamo - which many are - would probably allow you to use three
    of these LEDs in series. I'd try it, slowly at first, and with an
    ammeter in series. Substituting a suitable zener might be a good idea
    for a first try if you're nervous, and 11V high power types are
    readily available.
  4. Doug Goncz

    Doug Goncz Guest

    Thanks, Ian and Syd.

    I asked too many questions. I will share more of what I know.

    A 48T cog on the rear wheel of my bicycle drives and 11T cog on a Kollmorgen
    Servo Disc motor. Analysis in Mathcad shows that should be 96T, and I can make
    that soon. Any way, this is the road-coupled generator/motor. It's potential is
    proportional to road speed. It can output 275 mechanical watts at rated 41V,
    8A. Decent efficiency.

    What I found in the analysis that is just plain stunning is that on a one
    hundred foot plus descent of Apex Circle near here, about a tenth of the
    available potential energy is converted to kinetic energy. Much is lost to air
    friction. But some nearly 1/4 is quickly pumped into my storage medium of
    choice, ultracapacitors. A couple of watt hours. There is a longer hill

    The Ke of the motor is 12.1 V / 1000 rpm, so it can generate around 30 volts
    with a 96 tooth gear on a descent. So there's plenty of power to illuminate
    scary descents. I'm working on storing it for use to power lighting. It is of
    use on the long climb back up Apex Circle. In this application, it is pretty
    efficient, way up there. I have a post to sci.physics.research to illuminate
    the difference between positive and negative traction power and current flow.
    There is a four quadrant efficiency graph I can't get to. With this graph,
    which must make sense of the two contradictory quadrant, I can get a mean
    efficiency. Right now, I pick traces off the energy graph and compute the
    potential energy of the descent and the energy picked up by the capacitors.
    About 25%.

    Now the other motor generator is planned only for continuous lighting. It has a
    Ve of 37V/1000rpm, an 8 tooth pinion, and a 48 tooth driver on the cranks. So
    at a leisurely pedaling speed of 60 rpm we have 60*48/8 = 60*6 then
    360*37/1000=about 12 volts for the taillight, a bright JC Whitney red LED
    marker light. The low power front light isn't figured out yet. I have a four D
    cell, 16 white LED flashlight coming, and the four white high power LEDs with
    their nice little assymetrical condensor lenses. I have a 6V converter from TI
    sample service that's a fat TO-220 package and this will provide 6V, 1.5A. I'm
    sure I can make the output 9W and another 3 for losses using the pedals. I need
    a 12V regulator for the taillight.

    The 15V, 5A converter is for powering a 150W sine wave inverter, one or more
    dimmers, and two 20 W dimmable fluorescents. That's for the scary descents and
    for making maximum use of the energy in the caps. The inverter will run from 15
    to 10 V At 12.75 V it beeps. Does that explain the 15V 5A 75W plus losses
    figure? It's not coming from the pedals. The idle consumption of the inverter
    is 6W. If I go back to my "modified square wave" inverter and use diodes to dim
    the fluorescent tubes, the idle will go down and the adjustment of light level
    to surroundings will be less distracting.

    I don't know the thermal time constant of my Servo Track armature but I know
    the coupling. It's an ironless armature PM disc motor. Fits nicely mid frame.
    But will it handle the downhill pulse? We'll have to put in a Freon and see if
    it boils.

    It really blew my mind getting ahold of the Runge-Kutta solver. I leaned a lot
    about what can be expressed in differential form and what cannot. The variables
    in my RK model are position along the track, speed, charge on the cap, and
    voltage on the cap. I guess charge isn't needed as it does not appear in the
    other three.

    Altitude is an external function used in computing the force balance. It's the
    "survey" of altitudes along the position line, by linear interpolation. Slope
    refers to altitude. Rider power is constant assuming perfect gearing. Wind drag
    is computed iteratively over a few simulations The torque at the motor provides
    the other element of force. All these sum, then divide by mass to produce
    acceleration, the first derivate of speed, which itself is the first derivative
    of position, thereby defining position, that is, progress along the course.

    The literature that came with the four LEDs does say heat sinking extends their
    life. The right resistor really is 15V-14.4V = 0.6V, divided by 0.35 ma max is
    1.7 ohms min., about 1/4W added to four watts plus is an acceptable efficiency.
    We'll just have to see how hot the heat sink gets, and how quickly. I'm
    putting an ammeter port on the chassis to monitor current. What I'd like is a
    1/4W resistor with a heat sink interface so I can measure the total heat up of
    the heat sink, including heat from the resistor. A milled slot between the two
    center LEDs might provide good coupling with heat sink paste. I need some 1 1/2
    inch OD clear plastic tube for my D cells so the spacing between LEDs can be
    just more than that. The tubing segments will support the lenses at a fixed
    distance from the LEDs and allow light not lensed to escape to some use as a
    side marker for oncoming traffic.

    A 3W dynamo provides 6V. I don't think that power level is more than a marker
    light on a bike, not suitable for navigation. I don't think they are safe.

    There's a new, small, brushless/senseless Sanyo hub motor coming out that would
    get the motor mount out of my frame and let me build a cleaner system. It's
    rated 200W. They don't say if that's mechanical output or battery consumption.

    In some of the simulations, with a precharge as if ten cycles had been
    completed, the equipped bicycle wins out by hundreds of feet over a few laps.
    We'll see what the actual bike is capable of.

    I'm looking for two things in a bicycle headlight: output and an adjustable
    beam pattern to adapt to changing conditions.

    I've got a four watt six volt fluorescent ready for the front (remember my post
    about the Avon Skin Spec UV light conversions? They didn't work out. It has to
    be button started. You can't just have it come on line whenever power is
    available. Too bad. Nice reflector.) The little 4W light has esentially no
    refector. It's a first gear, difficult terrain light.

    ..>From: Syd Rumpo
    Yes, I'd to try like a non-dropout regulator.

    I'm building a parallel/series relay PCB to allow energy capture at low speeds,
    too, such as just pedaling on flat terrain in first gear, when the rider has
    capacity to spare.
    Yes, but this is by choking the output of an AC dynamo with its own inductance.
    I can do better.

    My physics project at NVCC:
    Google Groups, then "dgoncz" and some of:
    ultracapacitor bicycle fluorescent flywheel inverter
  5. N. Thornton

    N. Thornton Guest


    I dont know quite what your 15v supply is, but the odds are its not
    that brilliantly stabilised. Running the LEDs with a 0.6v drop R will
    give you wild current variations and probably kill the LEDs.

    Better to series parallel the LEDs to 7.2v and use a series dropper
    for them. A bulb would be best, 8v 700mA, or in the real world 6v
    700mA plus a 2v R drop. Use 2x 2v drops, one in each series chain for
    good current sharing.

    But with a bulb driving the LEDs you have no advantage: when the bulb
    goes your LEDs go out.

    Best way is a switched mode constant currant source, but much more
    complex. Just use a halogen light.

    Regards, NT
  6. Chris Hodges

    Chris Hodges Guest

    If these are the ones I think they are then the efficiency is better
    than halognes (though nowhere near as good as fluorescents), and much
    better than "ordinary" incandescents. For a torch (bike lamp) type
    application you may well end up with noticeably more light for the
    same battery consumption than halogens. Not a factor of 4 though.

  7. Syd Rumpo

    Syd Rumpo Guest

    On 05 Feb 2004 13:27:43 GMT, ( Doug Goncz )

    Strewth. Nurse!
  8. Ian Stirling

    Ian Stirling Guest

    Not even a factor of 1.5.
    Krypton torch bulbs are surprisingly good lumen-wise.
    They produce a lot of light by trading off life for light.

    Halogen bulbs are around 15lm/W, the white luxeon star LEDs are at
    the most 23lm/W. (IIRC) and down to around 13lm/W.
  9. Jim Yanik

    Jim Yanik Guest

    ( Doug Goncz ) wrote in

    How much did you pay for them?
  10. Jim Yanik

    Jim Yanik Guest

    I checked their site myself,and their price is $14 AUS.and they're
    currently out of stock.

    BTW,I believe 350ma is a MAX rating(not to exceed),their nominal op level
    is 300ma.
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