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  1. #1
    Scott n4zou's Avatar
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    Dynamo powered 3-watt LED flashlight.

    After purchasing a cheap Schwinn dynamo light kit I found the head and taillights to be of poor quality with the taillight bulb blowing only after 2 hours of use. You can't use the headlight without the taillight as that will cause an over voltage condition thus blowing out that bulb quickly. I ride after dark a lot so I thought the dynamo lighting system would save mounting costs for AA batteries for my Mag-Lite 3-watt LED flashlight. After looking for dynamo light systems on the Internet I discovered this link.
    http://www.pilom.com/BicycleElectron...moCircuits.htm

    After looking at the designs I thought there was too much complication involved in trying to use an unregulated AC power source with voltage and current sensitive LED's like the Luxeon 1 and 3-watt LED's. I thought it would be much better to feed the LED lights with a regulated power supply. Granted, using a regulated power supply is not going to be as efficient as the circuits shown but I did not want to burn out my LED's while miles from home in the dark. My main purpose was to build a robust and reliable power supply using the Schwinn bottle dynamo. I consequently designed and tested such a system.

    I wanted the components to be easy to obtain and cheap. I consequently chose the 317-voltage regulator circuit. This adjustable voltage regulator has been around for many years and is still being used in consumer products. Everything for the circuit can be purchased in a Radio Shack store. Here is the circuit diagram.

    I had a Mag-Lite 3-watt flashlight so that's what I wanted to use. It uses 2 AA batteries so the voltage regulator needs to prevent the voltage from exceeding about 3 volts DC. A combination of 220 and 330-ohm resistors provides a regulated 3.1 VDC no load output, which is close enough. A voltage reading of 2.5 VDC with the Mag-Lite flashlight loading the circuit is just fine. I drilled a small hole in the flashlight battery cap and used a section of fiberglass tent pole from a cheap tent to fabricate something to replace the batteries. Medical tape is used to hold it centered in the battery compartment.


    Testing was performed on a bicycle with 700c wheels. I performed the test by getting out and doing a 30-mile run on an MUP (multi use path). The flashlight will start illuminating at 3 MPH pushing the bike but will not provide enough light to see where you're walking; oncoming traffic will be able to see the light. At 5 MPH riding on the bike the flashlight is providing the same amount of light as batteries that are near the end of their charge. At 8 MPH the flashlight is providing its maximum light output and is the same as fresh batteries. No problems were encountered with the flashlight, dynamo, or circuit.

    This circuit will operate with hub dynamos as well, as the flashlight retains its on/off switch so no external switch is required. Here is a photo of the installed dynamo powered flashlight.

    Note the use of an amber blinkie up front and a red blinkie is used as a taillight as well. Considering they run for 200+ hours on 2 AAA batteries each and don’t turn off when you must stop the bicycle it’s a safety feature you really need instead of depending on dynamo powered lights that quit when you stop.

    The flashlight must be insulated and cannot short to the bicycle frame as this would short out the power supply. The reason for this is the dynamo is grounded to the frame so half the AC power provided from the dynamo is on the frame of the bicycle. All you need do it use a plastic clamp between the flashlight and handlebar solving that problem.
    Last edited by n4zou; 09-03-07 at 01:26 PM.

  2. #2
    I am the Eggman Mooo's Avatar
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    Cool!

  3. #3
    Senior Member Fibber's Avatar
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    Thinking back to the dynamo I had in the '60, it put serious drag on my bike at anything more than 10-12 mph. How is this little Schwinn unit? Do you 'feel' it much?

    Otherwise, agree - nice job.

    What is the current output? Wondering if you could drive the 3W Luxeon head from one of the Element flashlights? I posted the link to Sam's Club two pack of these flashlights a few days ago on the "Is 4 one watt LEDs......" question.

  4. #4
    Scott n4zou's Avatar
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    Quote Originally Posted by Fibber View Post
    Thinking back to the dynamo I had in the '60, it put serious drag on my bike at anything more than 10-12 mph. How is this little Schwinn unit? Do you 'feel' it much?
    I never considered using a dynamo myself from my experiences of trying to use one when I was a kid. Back then they were terrible with lots of drag. I remember it was like peddling up hill all the time. A friend purchased one of the Target Schwinn dynamo kits and let me know the drag was not even noticeable after a few minutes of riding. I consequently purchased one myself and was impressed myself with just how little drag was produced by this modern dynamo. I actually enjoy getting out and riding at night with the dynamo engaged knowing I am not burning up batteries in the process.
    Quote Originally Posted by Fibber View Post
    Otherwise, agree - nice job.
    Thanks!

    Quote Originally Posted by Fibber View Post
    What is the current output? Wondering if you could drive the 3W Luxeon head from one of the Element flashlights? I posted the link to Sam's Club two pack of these flashlights a few days ago on the "Is 4 one watt LEDs......" question.
    This dynamo like just about all dynamos are designed to power either a single 6-volt 3-watt bulb in the headlight or a 6-volt 2.4-watt bulb in the headlight and a 6-volt .6-watt bulb in the taillight. This equates to about 500mA or .5 amps. The goal is to load the dynamo with 3-watts so the voltage is at or just below 6-volts. My Mag-Lite flashlight draws 350mA so I think it's really rated about 2.5-watts so Mag-Lite rounded it up to 3-watts so it would sell well. I'm not concerned too must as everything works just fine as it is with plenty of light output considering I'm using a dynamo. The problem with using the Mag-Lite flashlight is it's rated to only use 3 volts! It would burn out if I run more than 3-volts DC into it. Considering it also draws less then 500mA the unregulated dynamo is going to pump more than 6 volts into it with too much current as well. That's where the voltage regulator works to keep that from happening. Any voltage produced higher than 3 volts is going to be converted to heat and blown off via the heat sink tab on the voltage regulator. No additional heat sinking is required on the tab of the regulator if the current differential is below 200mA.
    A real 3-watt LED is going to draw more than 500mA so technically you would not need a voltage regulator to use it with a dynamo but your still going to need to convert the AC voltage produced by the dynamo to DC for use with the LED and this is going to slightly reduce the current available for the 3-watt LED. The work around for this starts getting complicated as can be seen in this circuit for using 3 1-watt or a single 3-watt LED with a dynamo.

    I just wanted to keep everything simple and easy. Using an off the shelf flashlight and electronic parts from Radio Shack allows just about anyone to copy this project.
    Last edited by n4zou; 09-08-07 at 09:29 AM.

  5. #5
    Senior Member Fibber's Avatar
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    It is interesting that Mag-Lite powers their "3 watt" LED with two AA batteries (3v assuming alkaline cells). I wonder what emitter they are using, and what voltage / current it is rated at for strong output and long life? At 3v and 350ma, I'd call it a 1+ watt emitter. Are you sure that is all it is drawing?

    Other possibility for you would be to run two lights in series to make use of all of the 6v output.

    By comparison, the Element "3 watt" flashlight uses three AAA batteries (4.5v assuming alkalines). The emitter is a III on the star backing. According to the Philips/Luxeon spec sheet, the emitter does best in 1000ma (1 amp) configuration with 3.75v applied. So that is technically closer to 4 watts consumed to get the rated 70-80 lux output. To drop the overvoltage one would assume that there is either a puck regulator or a resistor in there, but if there is, it is well hidden and not obvious. As an experiment, I threw in three Everyready AAA NiMh 850ma rated rechargeables, and the light output compared very favorably to the other light running the alkalines. Yet now we only have 3.6 volts applied, and presumably less available current.

    If I do decide to harvest the emitter and optics from two of these for a homebrew project, I will have to pay attention to applied vs rated voltage. Using the AC dynamo as a 'charger' (like an automotive alternator) with full bridge rectifier and maybe the LM series regulator as you showed to supplement a battery pack was what I had in mind.

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    It looks great. and I like the idea from above poster about putting in a rechargeable battery although I have no idea if thats feasible.

  7. #7
    Scott n4zou's Avatar
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    Quote Originally Posted by Fibber View Post
    It is interesting that Mag-Lite powers their "3 watt" LED with two AA batteries (3v assuming alkaline cells). I wonder what emitter they are using, and what voltage / current it is rated at for strong output and long life? At 3v and 350ma, I'd call it a 1+ watt emitter. Are you sure that is all it is drawing?
    That’s what my meter is telling me but considering how hard it is to read current accurately the 350mA reading I get is most likely not correct. This reading was obtained when checking the current draw with two fresh AA batteries. I think it's very close to 500mA when using the dynamo and bridge rectifier circuit. I tried using the flashlight without the LM-317 voltage regulator and found it came close to loading down the dynamo enough to keep the voltage below 3-volts DC. This was when using just a bridge rectifier and capacitor with just the Mag-Lite flashlight. I had a Cyclocomputer hooked up so I could read the wheel speed and at 8 MPH the dynamo with bridge rectifier and capacitor could easily exceed 3 volts output to the flashlight if a were to exceed that speed. There are times I am exceeding 25 MPH so without the LM-317 voltage regulator the LED and chip in the flashlight would have burned out. With the dynamo loaded with 3-watts of filament bulbs (original configuration) the illumination and dynamo output would peak at 12 MPH. I didn't want to find out just what the peak voltage would have been with the LED flashlight and end up burning it up. That’s something else that makes me think my current measurements are off. There is a buck boost LED driver chip driving the LED in the 2 AA version of the Mag-Lite flashlight. I tried to dissemble the flashlight to find out just exactly what they're using. They did very well when assembling this flashlight to prevent anyone from doing that without destroying it in the process!
    Quote Originally Posted by Fibber View Post
    Other possibility for you would be to run two lights in series to make use of all of the 6v output.
    I don’t want to do that! I want it as simple and uncluttered as possible.
    Quote Originally Posted by Fibber View Post
    By comparison, the Element "3 watt" flashlight uses three AAA batteries (4.5v assuming alkalines). The emitter is a III on the star backing. According to the Philips/Luxeon spec sheet, the emitter does best in 1000ma (1 amp) configuration with 3.75v applied. So that is technically closer to 4 watts consumed to get the rated 70-80 lux output. To drop the overvoltage one would assume that there is either a puck regulator or a resistor in there, but if there is, it is well hidden and not obvious. As an experiment, I threw in three Everyready AAA NiMh 850ma rated rechargeables, and the light output compared very favorably to the other light running the alkalines. Yet now we only have 3.6 volts applied, and presumably less available current.
    I tried rechargeable batteries in my Mag-Lite as well. That’s when I figured out they had a chip in there somewhere. It ran just fine for 15 minutes and then shut down. I reloaded with alkaline batteries and it worked fine for the remaining 20 miles back home. When I got home I checked the rechargeable batteries, which showed 80% charged. The chip shut down due to the lower voltage supplied from the rechargeable batteries.

    Quote Originally Posted by Fibber View Post
    If I do decide to harvest the emitter and optics from two of these for a homebrew project, I will have to pay attention to applied vs rated voltage. Using the AC dynamo as a 'charger' (like an automotive alternator) with full bridge rectifier and maybe the LM series regulator as you showed to supplement a battery pack was what I had in mind.
    I've been playing around with some rechargeable batteries as well. I found that by just placing 2 AA ni-mh rechargeable batteries between the bridge rectifier and the flashlight the batteries act as a voltage regulator and prevent the voltage to the flashlight from exceeding about 2.8 volts. Whats very interesting is the fact that it made no difference if the batteries were at full charge or completely dead. The only problem is the current produced; well over the 180mA suggested charging rate printed on the side of the batteries! I am in the process of ordering a 1.5-watt star LED from mouser.com and a few 1N5818 diodes and capacitors as well to start playing around with the circuits here.
    http://www.pilom.com/BicycleElectron...moCircuits.htm
    I don't think you really want to "harvest" parts from perfectly good flashlights when you can get emitters from mouser.com.
    Just go to www.mouser.com and enter the mouser part number
    859-lopl-e011wa that is a 1.5-watt star mounted LED for $4.96. Be sure and click page 84 for even more choices including 3 and 5 watt LED's.
    Last edited by n4zou; 09-09-07 at 09:14 AM.

  8. #8
    Scott n4zou's Avatar
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    Quote Originally Posted by remsav View Post
    It looks great. and I like the idea from above poster about putting in a rechargeable battery although I have no idea if thats feasible.
    The rechargeable batteries are very feasible but keep in mind the time it takes to charge them. It takes 4-6 hours even at the 500mA maximum "rapid" charge rate! Unless your going to be on a tour lasting several days or a week, way out in the "jungle or outback" where you cant purchase batteries, and donít mind "dragging" batteries day and night to charge them, I'd just put up with the lights going dead at stops and use Blinkies on the handlebar and rear rack!

  9. #9
    Senior Member Fibber's Avatar
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    The reason I am considering "harvesting" is driven by price and convenience. By the time you price up the delivered cost of two Luxeon III Star units, the reflector & lens, and aluminum forward shell, you are pretty close to the Sams Club asking price of $29. And they throw in 6 batteries to boot!

    The reason I am looking at using a pair is to fashion the final pattern. I could 'tune' one for wide, and one for narrow, place two side by side for wider spread, or stage them near/distance. Not sure what will be best for casual road riding. But two give me the option to play with arrangements.

  10. #10
    Scott n4zou's Avatar
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    I was riding through the local college campus via the MUP and this guy noticed the circuit board connected to my bottle dynamo and wanted to know all about it. I described the LM-317 regulator circuit shown in this thread. He tells me he's working an electrical degree and said I didn't need the regulator or the capacitor. All I needed were two NiMH rechargeable batteries across the bridge rectifier to regulate both the voltage and current for my 2 AA flashlight and 5,000 MCD taillight. When I got home I tested his design and he was correct! I subsequently tried a 3-battery setup with a 3 battery LED light and the 3 batteries regulated the voltage and current perfectly as well. I subsequently have built the circuit and have been testing it. It's great! I did 30 miles and my lights never went out at any stops and I even walked my bike up the very steep hill home with both the flashlight and taillight working fine. I've even ridden around with the switch open recharging the batteries as I ride. At no time can the dynamo put more than 500mA across them or exceed the voltage required for recharging them. I tested the current for the LED's and found that he was correct. The LED's take what they need and the batteries sink the excess current for recharging them. It's doesn't get any better than this!
    I've found that the dynamo starts recharging the batteries at 8 MPH with the LED's turned on. With dead batteries the LED's will illuminate at 5 MPH. I started a test run with dead batteries just to make sure the LED's would still work with discharged batteries and they work exactly the same as the LM317 regulator circuit with no batteries.
    Here is the circuit and short information he made for me.

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    Thats great! ... I did wonder about the rechargeable battery in the set up, since all the dynamo flash lights comes with nimh batteries built in... thought maybe overcharging was a concern. You should make a video and put it on youtube.

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    Scott n4zou's Avatar
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    Quote Originally Posted by remsav View Post
    Thats great! ... I did wonder about the rechargeable battery in the set up, since all the dynamo flash lights comes with nimh batteries built in... thought maybe overcharging was a concern. You should make a video and put it on youtube.
    I donít know how good a youtube would be as the lights are on all the time, stopped or not! It's just like powering the 3-watt Mag-Lite flashlight on batteries except they're being recharged when you're riding above 8 MPH, which is very easy to do. All the video would show is a guy riding around on a bike with his lights on. My average speed is 14 MPH so the flashlight is using 350mA; 30mA by the taillight, and the remaining 120mA is recharging the NiMH batteries. I've started disengaging the dynamo from the wheel when riding up inclines and then re-engaging it on the flat or downgrade. I got home last night and noted the batteries were at 90% charge. So far the batteries are holding up pretty well even doing that. Doing that got me an extra 2 MPH average speed increase. I remembered having an old solar panel and dug it out of a box. I hooked it up to the batteries and parked the bike in the sun. The panel started pumping 275mA into the batteries and in 2 hours the batteries were back to 100%. I am going to be going on a week long tour and will take the solar panel with me so I can recharge the batteries during the day without resorting to the dynamo for charging. Here is a photo of the solar panel sitting on the front rack.

    Ignore the 12-24 volt label on the panel. There was a boost circuit board connected which went bad and thatís the reason it found it's way to a dumpster. I retrieved that panel and removed the boost board and now have a free solar panel that runs about 5 unloaded volts in bright sun, just right for charging my NiMH batteries!

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    I like the solar panel . Hey can you show a closer photo of the set-up for the rectifier and the switch? I've got couple of D size Ni-Cad that I want to hook up to the Bell dynamo that I just bought. I figure a picture is worth a thousand words .

  14. #14
    Scott n4zou's Avatar
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    Quote Originally Posted by remsav View Post
    I like the solar panel . Hey can you show a closer photo of the set-up for the rectifier and the switch? I've got couple of D size Ni-Cad that I want to hook up to the Bell dynamo that I just bought. I figure a picture is worth a thousand words .

    The rectifier is located on a terminal board under the switch. It's tiny so you'll need to look close! That’s the smallest bridge diode matrix Radio Shack sells. About the batteries, you must use batteries with solder tabs! If you hit a bump and a battery gets loose the dynamo will pump 500mA and maximum voltage into your LED's. A cheap dynamo may only kick 9 volts into them but a good hub dynamo could produce up to 15 volts quickly burning out your LED's. If you look closely at the photo your see the batteries wrapped in black electrical tape and wires firmly locked down in the white terminal strip. When I build my final version all that ugly stuff will be gone. All you will see is a project box with a switch clamped to the rack. My final version will be this circuit.

    The LED drivers will automatically shutdown the LED and disconnect the batteries when the rechargeable batteries are dead. This way I don’t need to worry about manually opening the switch at stops if I've been running on the batteries with too little charging, like needing to stop often in town, climbing a very long and steep hill with the dynamo disengaged, or riding very slowly. Even with dead batteries the lights will start working again as soon as you start moving. Switch S2 in the circuit is for use with hub dynamos and is not required for bottle dynamo's, just disengage the dynamo from the tire when S1 is open, unless you need rapid battery charging.
    Last edited by n4zou; 09-21-07 at 10:21 AM.

  15. #15
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    Quote Originally Posted by n4zou View Post

    The rectifier is located on a terminal board under the switch. It's tiny so you'll need to look close! Thatís the smallest bridge diode matrix Radio Shack sells. About the batteries, you must use batteries with solder tabs! If you hit a bump and a battery gets loose the dynamo will pump 500mA and maximum voltage into your LED's. A cheap dynamo may only kick 9 volts into them but a good hub dynamo could produce up to 15 volts quickly burning out your LED's. If you look closely at the photo your see the batteries wrapped in black electrical tape and wires firmly locked down in the white terminal strip. When I build my final version all that ugly stuff will be gone. All you will see is a project box with a switch clamped to the rack. My final version will be this circuit.

    The LED drivers will automatically shutdown the LED and disconnect the batteries when the rechargeable batteries are dead. This way I donít need to worry about manually opening the switch at stops if I've been running on the batteries with too little charging, like needing to stop often in town, climbing a very long and steep hill with the dynamo disengaged, or riding very slowly. Even with dead batteries the lights will start working again as soon as you start moving. Switch S2 in the circuit is for use with hub dynamos and is not required for bottle dynamo's, just disengage the dynamo from the tire when S1 is open, unless you need rapid battery charging.
    Thanks for the photos, I'ven't converted to LED yet, still using the original bulbs that came with the dynamo. I guess I'll have to do some reading on diodes ,rectifers and regulators to figure out how to set up the battery charger correctly. Def ntly post the pic of the final setup.

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