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Thread: Homemade LED bike light[ing]

  1. #1

    Default Homemade LED bike light[ing]

    Hey guys,

    First post! FWIW I'm in Australia at uni, studying things unrelated to electrickery.

    My current bike liight currently revolves around a Luxeon III I bought at jaycar (Australia).

    Currently there's a 6V lantern battery, 1.8 ohm 5W resistor and the Luxeon all in series.

    Under load my (new) lantern batteries drop to 5.3V, there's less than an amp flowing, I think more like 800mA. It certainly doesn't get hot, but then it is well heatsinked.

    I have the following questions:

    This new 2x bright Nichia innovation is impressive. I've never heard this 2x brightness mentioned WRT to luxeons though, are there 2x brighter luxeons around? How would I know which mine is? (I noted down the serial number on the back before the thermal compound went on)

    How hard is it reasonable to drive a this luxeon III when well heatsinked?

    This is the big question:

    I need some current regulation circuitry that I want to meet the following:
    - Over 70% efficent
    - Will operate in the voltage range 13.8V to 3V
    - Adjustable level of current regulation (say, 100mA - 1000mA, or maybe 1300mA?)
    - To power a white Luxeon III

    I would also prefer the following things, if possible/reasonable:

    - Some gauge, even if only 3 LEDs, of current draw (say red>1000mA, 1000mA>amber>700mA, green<700mA)
    - Some gauge of battery voltage, once again 3 LEDS would do
    - Adjustable level of current regulation (say, 100mA - 1300mA)
    - To power either a white or red Luxeon III

    I can solder, I should be able to manufactor a PCB at uni using the machine in the electrical engineering faculty (don't ask me what it is exactly...all I remember is a arm moving in 2 dimensions drawing the tracks).
    I also have plenty of time.
    The biggest obstruction is I want this done soon, so ordering parts from the US isn't really favourable.
    My jaycar store is the preferable source of components, www.jaycar.com.au.

    The following is on the path to a agreeable solution I suspect:
    MC34063 DC to DC Converter IC

    I know this is probably a old question, I did search. You guys use alot of jargon that is unique to you folks (fatman, uflex..etc..) that takes a bit of effort to work out.
    Links to information/previous threads would be greatly appreciated.
    As would links to circuit schematics
    Last edited by cold; 06-28-2006 at 01:17 AM.

  2. #2

    Default Re: Homemade LED bike light[ing]

    Quote Originally Posted by cold
    Hey guys,

    First post! FWIW I'm in Australia at uni, studying things unrelated to electrickery.
    I am in Australia also and am currently working on 'linear buck regulators' for LED's. That is where the Battery voltage is close to and above the Vf of the Leds. The regulator is IC controllered for varying brightness and other functions. The basic circuit has a voltage range of 16 to about 3volts but for high efficiency the battery voltage should be close to (and above) the forward voltage of the Leds.

    send me a private message if you would like to get in touch.

  3. #3
    Join Date
    Sep 2005

    Default Re: Homemade LED bike light[ing]

    Aussies everywhere! - which uni are you at? I'm based at University of QLD

    Having just finished the first prototype of a headlamp for MTB/ Adventure racing, i've been going through a similar thought process to you. My system uses a single 3W Luxeon and 18x5mm leds and will run off anything from 4.8-12V. After a lot of thought(and confusion) I've gone with off the shelf nflex driver from Taskled and am very happy. Basically it covers those input voltages and dimming you want, with the bonus of protection for reverse polarity and output short circuiting(really handy for newbies like me). They end up costing about $35AU and arrive within about 7days of ordering which is faster than I could print and solder a board.

    If you have any questions feel free to pm/email me, I don't as much as most people on this board but I've jumped through most of the hoops with sourcing parts in Australia.

  4. #4
    Flashaholic* Steve K's Avatar
    Join Date
    Jun 2002
    Peoria, IL

    Default Re: Homemade LED bike light[ing]

    Always nice to see someone playing around with bike lighting! I've taken a few shots at assorted bike lights myself.

    When I first looked at the On-semi 34063, it looked like a nice part. Simple, easily adapted to different designs, operates at low voltages, etc. Looking a bit closer at the circuit shown on page 7 of the datasheet, I see a problem. The use of cascaded drive transistor Q1 and Q2 means that you'll need 1.4v above the Luxeon voltage to make it work. Any less than this, and you can't turn on these two transistors. Assuming 3.7v for the Luxeon, you won't be able to run with less than 5v or so.

    I've looked around for buck regulators for this sort application, and never found anything that I was really happy with. In the end, I just made a linear current regulator, and powered the Luxeon with 4 NiMH cells. Under nominal conditions of 4.8v power, and Luxeon voltage of 3.8v, the efficiency is still 79%. As the battery voltage decreases, the efficiency increases. Best of all, the batteries can be used all the way down to full discharge (altho it's best to stop at 1.0 v/cell). I used a LM10 as the core of the regulator, and added an external mosfet as the pass transistor, a current sense resistor, and a couple of resistors to set the reference voltage. Pretty simple, cheap, and small-ish.

    good luck,
    Steve K.

  5. #5

    Default Re: Homemade LED bike light[ing]

    Ahh thanks for the replies .

    Working on in your spare time, or as a academic project?

    Excellent. I saw the nFlex before I posted...But for some reason didn't think of using it. I've since ordered/paid for one from George. We shall see how well it goes.
    I'm in Darwin, CDU, the institution formally known as NTU (...annoying politics.)

    Steve K:
    Input absorbed! This nFlex board was one of the more pricy options ($30USD,40AUD). I'm not entirely willing to spend that again for the back light, and head lamp (time will tell how much I like the nFlex) so cheap options are very much favoured.

    I have to find a reflector yet. Right now I have a hugely wide beam (80 degrees) that dimly lights up everything.

    My end aim of all this is to have:

    A front light with a broad beam (1 Luxeon III seems enough)

    Headlamp with a tight beam (No idea what LED here yet. A Luxeon V is awfully pricy)

    A red backlight that is highly visible from anywhere in the 180 degrees behind me (Maybe a red Luxeon I star and a side emit sandwiching a piece of Al)

    Yeah, I know. No normal person needs to put this much time into bike lighting. But hey, I'm on holiday .
    Last edited by cold; 06-29-2006 at 11:13 AM.

  6. #6
    Join Date
    Jan 2006
    State College, PA

    Default Re: Homemade LED bike light[ing]

    Hey cold, another erstwhile biker here.

    You might consider swapping the luxes around - the V will be floodier, just due to the design, while the smaller phosphor of the III makes it easier to focus tightly.

    Whatever you do, make sure the heatsinking is good. In motion airflow helps a lot, but you don't want things to overheat if you have to stop and wait for someone, or change a tube or whatever.

    For the rear light, a red luxI is perfect. There's no need to get fancy, a simple 2 AA holder and dropping resistor should still give lots of light - a 2.2 ohm, 1/4 watt resistor should give you 250 mA at the LED, decreasing as the batteries fade, but that'll be plenty of light. 1.5 ohms will give you 350 mA, but that's a lot of light.
    If you want it to flash, that's a little more complex, but you could easily mod a standard blinky taillight.
    I'm not sure I'd bother with optics, just use a lambertian lux behind some sort of diffuser, to make a bigger light source.

    For experimenting, a simple resistor can be pretty efficient, as long as the battery voltage is close to the vF of the LED. They're also cheap and remarkably tolerant of reverse voltage and open circuits...
    I use the calculator at http://led.linear1.org/1led.wiz, but it's a pretty simple calculation.

    Anywho, good luck with it all - the nFlex should serve you well. I truly believe the LED is the way to go for bike lighting - HID is great, but the $100 bulb is a bit of a turnoff. Bikes crash, y'know.


  7. #7
    Join Date
    Apr 2003
    Ulm, Germany

    Default Re: Homemade LED bike light[ing]

    Regarding the red LUX I as rear light: I've built a few (the fourth is just on the bench, waiting for the rack so I know how to drill the holes for the mounting screws) rear lights from a standard bike rear light (b&m XS - go to www.bumm.de if you need to know how it looks), an aluminium rear plate (also serves as heat sink - not that you'd need it), a red LUX I and an elliptical Fraen optic. With the elliptical optic, you'll get a light emitting area close to 1" diameter and have the light bundled in the vertical so you don't waste too much for the planes and hedgeh^h^h^h^h^h^hsnakes. If you intend on riding with other people behind you, 50 mA is plenty, 30 mA well sufficient (I'm using something like 30 mA on the recumbents where the following rider - my wife - is more or less eye in eye with the light and 50 mA on the normal bike where she's out of the main beam). 250 would be almost sufficient to cause lasting eye damage to the driver of any vehicle following you...

    As to the front light - I definitely don't like circular symmetric beams for the main lights, so I'm using converted b&m 'Lumotech's in front.


  8. #8

    Default Re: Homemade LED bike light[ing]

    Quote Originally Posted by cold
    Working on in your spare time, or as a academic project?
    A spare time project, it is up and running now with a 25mm x 25mm double sided PCB + the FET I am using it to run 6 x 3W Leds (3 sets in parallel each set 2 in series). I was inspired (and assisted) by George after using his D2Dim board, but wanted to add current limiting as well as level control.
    Currently working on removing the external switch for a completely sealed unit.

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