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Thread: Will a current regulator perform well with a dynamo hub?

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    Default Will a current regulator perform well with a dynamo hub?

    So I'd like to have a commuter light using a dynamo hub and a single Cree/Seoul running at up to 1A. Will a current regulator perform okay with the pulsed current coming from the hub, or will there need to be a cap placed across the two dynamo leads? I've seen a couple diagrams that would mean I could make my own, but I'm wondering if there's an easy one-piece solution.

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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Your dynamo will only provide 0.5 A, not the 1 A you hope for.
    However since you will have about 6 Volts available, you could drive two LEDs in series with different optics (one for proximity lighting and the other for distant lighting). The only other thing you will need is a bridge rectifier. No need for a current regulator. KISS.

    You can find a lot of information on this forum : http://lists.topica.com/lists/bikecu...t=12093&sort=d
    Last edited by Calina; 04-11-2007 at 05:14 PM.
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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    If you want to had a standlight (useful), things are not so simple anymore.

    Have a look at these sites for more info : http://www.pilom.com/BicycleElectron...moCircuits.htm

    http://www.nscl.msu.edu/~daniel/regulator.html#lgtlnk

    http://i17.tinypic.com/4brqkgh.jpg

    http://www.myra-simon.com/bike/tips.html
    Last edited by Calina; 04-11-2007 at 05:10 PM.
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    Default Re: Will a current regulator perform well with a dynamo hub?

    so why do you need to use a bridge rectifier? do these dynamos put out ac? and if so, why not use the ac? seems to work for me, at slow speeds the led flashes, at hight speeds the led flashes become to frequent to notice. im using a cree xr-e on a 6v 3w dynamo. is that a bad idea? what benefits would adding a bridge rectifier give me? thanks for the info!

    p.s. if they are ac, why dont they make permanent magnet dc dynamos?

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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Dynamo are AC devices.

    Your set up works but I think there is a danger of harming the LED with reverse current if you don't have at least a zener diode in the circuit. Also with a direct drive set up, you are only using half of the power available and as such generate only half of the light you could get. The bridge gives you access to all the power and the light would not flicker. If you add a capacitor the light level should be very constant.

    What dynamo and light do you use? How is you light beam (considering it is only half of what it could be)? What optics do you have? How do you use the light (city roads or dark trails, be seen or lighting up the road, commuting on a regular basis or occasional use only or ...)?

    I'm not sure why they don't make DC generators. My guess is that this would imply a more complex design (brushes etc.) that would be more expensive and not as reliable.

    With two LEDs you could use one phase for each light and not even use a bridge (just put a couple of zeners to prevent reverse current damage). Your lights will still ficker at low speed though.

    Let me had that I'm no expert on the subject but I tried a few things, read a lot about it and did managed to learn a little.
    Last edited by Calina; 04-11-2007 at 07:39 PM.
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    Default Re: Will a current regulator perform well with a dynamo hub?

    What a current regulator will do on a dynamo will depend on a lot of things, including (but not limited to) the exact circuit used, cable length, temperature, phase of the moon and water level on the Thames (only slightly exaggerating here).

    Basically, what would most likely happen is this:
    - a step-up-converter will see a low voltage at startup, so it will try to draw a lot of current in order to create the voltage necessary to drive the LED. The generator can't supply this current, so the generator voltage will drop even more... and you'll end up in a more or less stable state where the generator will deliver its full current at or around the startup voltage of the converter, not really much power in total.

    - a step-down converter will only start to work when the generator voltage has risen over the LED voltage. If the regulator then switches off the current path, the input voltage from the generator will rise. This will lead to a shorter duty cycle on the input and a further rise in the generator voltage... if you're lucky, you'll end up in a stable state below the maximum input voltage of the regulator. More likely, you'll end up in a stable state with a blown regulator.

    BUT: your generator already IS a current regulator, although it's (most likely) set at 500...600 mA. Use it and a bridge rectifier to power a couple of LEDs in series, that's the easiest and most reliable solution. Anything with electronic regulation usually isn't worth the (huge) effort.

    Regarding the question of DC generators: yes, they'd be more expensive, less reliable and basically not needed. On the other hand, a hub generator with external magnet control (don't know the english word for it, same technology as a car alternator)....

    Bye
    Markus

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    Why only one emitter?
    Most any dynamo can power up to 3 and will not give more than 600 mA.

    Use some good rectifier and emitter in series --> working




    You can also move to the "better than possible" solution by using the MOSFET-Rectifier (using 2 IRF7319 Mosfets instead of very bad rectifier or just bad schottky-diode rectifier. The light using the MOSFET already works, when there is not even a glow from the other ones: at walking speed)



    if interrested, there is onyl one thing to consider: at least ONE emitter must be totally free (not in series with a gold cap capacitor for a standlight)

    Then, if You absolutely have to use one emitter only, get Yourself a good Lux V (they are very cheap now) and insert it into an exisiting, cheap bike front light:


    comparison Lux III / Lux V / tri-Cree bikelight


    If You want an automatic switching from low speed (2 emitters, giving light while walking already, with the MOSFET of course) to high speed 3 led (or 4 if Your dyno is strong enough), use this circuit here:

    pic shows "SSC P4", I used Crees, doesn't matter
    Last edited by yellow; 04-13-2007 at 02:15 AM. Reason: minor punctuation errors
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Quote Originally Posted by yellow
    Why only one emitter?
    Most any dynamo can power up to 3 and will not give more than 600 mA.

    nice work yellow...

    but FYI,

    from my dynamo hub, I get 12.8w peak...into 3 series LEDs...up to 1150ma peak...using a series bi-polar cap before the bridge ref...in fact by changing the size of the cap you can get different power curves, for on-road I use a flatter curve peak of 910ma into 3 series cree LEDs...but with more boost down the bottom, so insted of the peak (1150ma) @ 40km/hr, you get a peak of 910ma @ 27.5km/hr...for off road racing I use, a bigger cap again...& get peak of 670ma @ 19km/hr...but as it is a flatter curve, I get only a 90ma variation, between 18km/hr & 30km/hr...so it looks pretty much the same, for most for the ride...

    the bi-polar cap before the bridge ref, is the best one to start with...4 diodes & 2 caps...thats it...easy to make...custom curves...gives you the best results for the least work...as I ride home @ night my average speed is 25-30km/hr... & its nice to know that my dynamo light is pumping out 500-600lm!! ....once you get that going... add a low boost voltage doubler switch (two more caps)...or switch in different curves...all good fun...and easy to do to get ya started...


    their are many ways to do it...this one is just one of them...

    Best

    Ktronik
    Last edited by ktronik; 04-12-2007 at 04:39 AM.

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    from my dynamo hub, I get 12.8w peak...into 3 series LEDs...up to 1150ma peak...
    ...4 diodes & 2 caps...thats it...
    what is Your dynamo model?
    (I come to similar Amps, but with a Lightspin, not with a hub -> and Your hub wont be affected by dust, rain, ..., as my dyno. Did not know these hubs could give more than 600 mA

    2nd thing: are You talking about a "voltage doubler" here?
    Good at very low speeds, less useful at high
    (btw: thats why I like the mosfet and the automatic switching circuit I posted, light even earlier than with doubler)

    find some ideas here. german site, but the pics speak for themselves:
    http://www.led-treiber.de/html/dynamo-treiber.html

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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Markus, Yellow and ktronic thank you for the great info.

    It is too bad that it is so hard to find good dynos in North America. The choices are very limited; it is either low hand or top quality from a few specialized shop; nothing in between. I'm especially thinking about AXA HR, Nordlicht and a few others, just unavailable here.

    Dynamos are not very popular with cyclists on this side of the pond. That is too bad, they don't know what they are missing.

    Yellow, what is the light you modified? Is it a Lumotec?

    I still think two separate units with different optics are more flexible. What do you thinK?

    Aren't the dynos over heating when they are pushed at more than 0.5 A?
    Last edited by Calina; 04-13-2007 at 05:38 PM.
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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Yellow,

    On the first circuit, I guess K1 is the lamp and K2 is the power source.
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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

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    K1 is AC input from Dynamo and
    K2 is positive and negative output
    the general idea of the mosfets is, that they do not have the voltage drop a schottky- or other rectifier have. Thus light at much less speed.
    Some guy here had boards made, but I dremels the ones showed and they work, so ...

    PS: light modded is a cheap (€ 10,--) headlight,
    AXA HR is mounted on my dads bike and I dont like the model. Sure its cheap-to-medium (about € 25,-- here I think) but that "wheel" running on the tyre keeps cracking.

    more pics, that automatic switching circuit + the 1F/5V Gold Cap all fit inside and there is almost no sign of the mod (when the light is not running at night) Its another version of a cheap Bike-headlamp


    2 heads might be easier to focus.
    With that Tri-Cree I filed the heatsink that all the emitters are not parallel with the axis, makes a triangular shaped output (but much file work)

    want an idea for a tail light?
    (normal rectifier absolutely enough at that currents. + I had to add a 10 ohms resistor between that 5V regulator and the Leds)
    directly under that "+ 5V", between "+" of the capacitor and the led

    again: cheap tail-reflector (€ 1,--), opened, put circuit inside, pyramids of reflector over emitters dremeled away, closed. Almost no sign at all of the mod from the outside
    Last edited by yellow; 04-12-2007 at 04:26 PM.

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    Default Re: Will a current regulator perform well with a dynamo hub?

    Quote Originally Posted by Calina
    Dynamo are AC devices.

    Your set up works but I think there is a danger of harming the LED with reverse current if you don't have at least a zener diode in the circuit. Also with a direct drive set up, you are only using half of the power available and as such generate only half of the light you could get. The bridge gives you access to all the power and the light would not flicker. If you add a capacitor the light level should be very constant.

    What dynamo and light do you use? How is you light beam (considering it is only half of what it could be)? What optics do you have? How do you use the light (city roads or dark trails, be seen or lighting up the road, commuting on a regular basis or occasional use only or ...)?

    I'm not sure why they don't make DC generators. My guess is that this would imply a more complex design (brushes etc.) that would be more expensive and not as reliable.

    With two LEDs you could use one phase for each light and not even use a bridge (just put a couple of zeners to prevent reverse current damage). Your lights will still ficker at low speed though.

    Let me had that I'm no expert on the subject but I tried a few things, read a lot about it and did managed to learn a little.
    hi and thanks to everyone for the advice. feeling a little "in over my head" at the moment, im not great with circuit diagrams. i see now why i need to use at least a bridge rectifier, basically to convert the negative portion of the wave to positive right?

    so can you just buy a bridge rectifyer? where? im pretty clueless so if you can recommed one, that would rock its a 6V 3W dynamo light system made by schwinn, sold for $10 at target. i dont plan on using the lights it came with.

    i actually havent tried the led with the dynamo, but i thought it would be similar to my DC Hand crank light W/seoul p4. (obviously i was wrong). its a simple $5 hand crank 3led light, i removed everything but the DC motor, gears, and crank and wired it directly to the Seoul P4. Wow. the seoul needs a big heatsink. got 700ma when cranking moderately, 850 when cranking fast. the voltage stays in accordance with the current, between 3.5v and 3.9v. when the led is disconnected, it reads more like 15v. i used a teeny tiny plastic reflector super-glued right onto the star and its perfect for about 45degrees of smooth flood. too bad i cant convert this little generator for my bike, so so simple. at least i have a nice 100+ lumens crank light for emergencies!

    my end setup will hopefully be something like: 2-3 cree P4s bare for close up flood light, each running about 600-800ma on a decent heatsink, powered by the dynamo. also, a 3 cree throw light on the handlebars (like Nightrider's awesome creation) , probably powered 18650 by batteries. im currently too cheap/inexperienced to try to regulate either light with a driver. my commute is 20 minutes so runtime barely matters. dont have much acess to dark trails

    My IDEAL setup is much different, however. I want a truly HYBRID bike light system, one that runs on batteries that are recharged by the dynamo. like a good hybrid car, the dynamo should only engage when the brakes are engaged. part of my commute is down a steep hill for like a mile. breaks are engaged the whole way down, wasting energy. on the way home, its uphill, and id rather not have extra drag from a dynamo then (btw, how much drag can they cause?) im thinking if i were to replace my front break-pads with dynamos, that would technically work, but then id only have rear breaks. i kinda doubt anyone makes a dynamo that could really make use of all that kinetic energy tho. there are alot of red lights to stop for where i ride, would be cool if every time i stopped, my kinetic energy were stored in the battery!

    ok just had an idea: if the load is huge it would slow me down right? just connect the load instead of engaging the breaks... i know when i connect the seoul to my hand crank it become way harder to crank. same with dynamo?

    im sorry this post is huge. thank you for getting all the way thru it!

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    Flashaholic* AndyTiedye's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?


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    Default Re: Will a current regulator perform well with a dynamo hub?

    Quote Originally Posted by yellow
    what is Your dynamo model?
    (I come to similar Amps, but with a Lightspin, not with a hub -> and Your hub wont be affected by dust, rain, ..., as my dyno. Did not know these hubs could give more than 600 mA

    2nd thing: are You talking about a "voltage doubler" here?
    Good at very low speeds, less useful at high
    (btw: thats why I like the mosfet and the automatic switching circuit I posted, light even earlier than with doubler)

    find some ideas here. german site, but the pics speak for themselves:
    http://www.led-treiber.de/html/dynamo-treiber.html

    lightspin is a very good product...but I was told they are no longer making it...& could not really get them in Australia...

    the HUB I use is a shimano dynamo hub, & have also done the same tests on a SON...with the same results...

    you are right, normally the hub, wants to give 500ma @ all speed by changing the voltage…

    by holding the voltage low (series cap), the current rises

    using a 100uf Bi-polar cap in series before the bridge ref I get:

    7km/hr=8.47v @ 50ma
    15km/hr=9.44v @ 250ma
    23km/hr=10.24 @ 610mq
    27.5km/hr=10.62 @ 910ma
    37km/hr=10.14 @ 630ma

    using a 200uf bi-polar cap in series before the bridge ref I get: (same speeds as above)

    100ma, 480ma, 18km/hr peak @ 660ma, then 600ma @ 24km/hr, I use this curve for off road racing & the 100uf curve for on road commute…

    I bigger the cap the more boost down low & the less peak power…

    You can mix 2 different curves together, or even mix in a voltage doubler for up to 75ma @ 4km/hr, 100ma @ 5km/hr & 200ma @ 7km/hr…the voltage doubler is just a extra thing, to add later to boost power below 12km/hr, as this is not a auto switching unit...martin & I are working on a more complex circuit @ the moment that is 'auto'...but the above circuit is just a very simple version...to get people started...

    So a lot can be done just by using a series cap before the bridge ref…

    Dom & I have come up with this as a light housing...





    Last edited by ktronik; 04-12-2007 at 04:17 PM.

  17. #17

    Default Re: Will a current regulator perform well with a dynamo hub?

    Great info - thanks people. Yellow, I have a question about your automatic switch circuit for extra LED's. If you wanted to make the switching point adjustable, could you do it by making one of the resistors of the transistor circuit adjustable, and if so, which one. Or do you need to substitute a zener diode of the value needed instead.
    I'm also interested in the Fet rectifier too. I tried it a couple of times a year or two ago, but did not know about the 'no reservior cap' rule. It might be time to start work on that again too.

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    Default Re: Will a current regulator perform well with a dynamo hub?

    Quote Originally Posted by Calina
    Markus, Yellow and ktronic thank you for the great info.

    It is too bad that it is so hard to find good dynos in North America. The choices are very limited; it is either low hand or top quality from a few specialized shop; nothing in between. I'm especially thinking about AXA HR and a few others, just unavailable here.
    Usually, for this type of over-loading, people tend to use hub dynamos. While the Schmidt SON is still top of the heap, the cheap(er) Shimano (Suntour, Sanyo, SRAM) ones (at least over here) tend to roll up the market from below, almost any new bike, even from supermarket chains, seems to be equipped with one - and if you buy them individually, they're not noticeably more expensive than a decent bottle dynamo. The only problem is that you'll have to (re-)build your front wheel.

    One advantage is that these dynamos won't slip - which can be a problem with bottle dynamos, especially when they're higher loaded and/or in non-perfect weather, and that you'll hardly notice whether they're running or not (both from the drag and sound).

    Bye
    Markus

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    Default Re: Will a current regulator perform well with a dynamo hub?

    need to substitute a zener diode of the value needed instead.
    as far as I understand the circuit, as soon as the zehner voltage gets too high and the voltage (?) flows through the diode, the basis of the transistors dont get enough to switch and thus block, current runs over the last led. One would need another zehner value to change the point.

    PS: while hub dynos run at every condition, I dont like something I am not able to switch off if not needed. Thus I have something like this here: http://cgi.ebay.de/UNION-FORMEL-P-FA...QQcmdZViewItem mounted.
    Dunno the name, a dyno that mounts below the bottom bracket, on/off with a brake cable while pedaling possible. Only time it has failed to my by now was heavy snow.

    PPS: my LBS still has 2 of the Lightspins, but they are very expensive. Charging some € 80,-- for one afir. New model with improved spring.

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    Flashaholic* Martin's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    yellow, tspoon, above automatic switch circuit exploits the voltage variation across the upper LED to decide.
    The forward voltage of a white LED is in the area of 3.2 V depending somewhat on LED bin, temperature and drive current.
    The darlington circuit is dropping 1.2 V from base to emitter, so 3.2 + 1.2 = 4.4 V from base to anode of upper LED. Around there would have to be the steep part of the zener's curve and it looks like a ZPY5.2 does it.

    If you use a larger value for the zener, chances are that T1 will not open any more (upper LED limits the voltage) and if you use a lower value T1 might permanently be conductive. One is not free to change the zener voltage much, it is a result of the LED's forward voltage.

    So while a slight variation of the zener voltage will shift the transition point, a little too much will make it not work any more.
    One easy way to increase the zener voltage by just a little bit is adding a schottky in series.

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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

    Quote Originally Posted by yellow
    I have something like this here: http://cgi.ebay.de/UNION-FORMEL-P-FA...QQcmdZViewItem mounted.
    Dunno the name, a dyno that mounts below the bottom bracket, on/off with a brake cable while pedaling possible. Only time it has failed to my by now was heavy snow.
    According to Myra Simon site they are named roller generators or bottom bracket generators.

    Here's what she says :

    " Roller generators are known as bottom-bracket type in Britain, but not by foreigners: who cunningly find other (less dirty) places to mount a roller. Anyway: the generator is itself the roller, driven by contact with the centre tread of the tyre. rollers

    Rollers need a high contact pressure to work in the rain, because water centrifuges out to this part of the tyre and is channelled onto the roller by the rear mudguard. They are nevertheless preferred by those who want to site their generator inconspicuously. There is also a belief that the larger diameter (compared to the common bottle-type pulley) must reduce drag. Noise is certainly reduced, not least by intervening parts of the bike and the riders body. But all is not as it may seem or sound! "

    Source : http://www.myra-simon.com/bike/dynotest.html#bottles
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    Flashaholic* Calina's Avatar
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    Default Re: Will a current regulator perform well with a dynamo hub?

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