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Old 04-01-10, 10:31 AM   #1
newleefixed
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Generator Light to Battery Powered

I was wondering if anyone had converted a generator style light to work off of batteries and if so is it at simple switch. I'm sorry if this has been a topic before I didn't search for it. Thanks for any help.
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Old 04-01-10, 11:29 AM   #2
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I sometimes use a 6v / 4.5AH sealed lead acid battery. They're rechargeable and last for years of regular use. I run the system through a toggle switch and tuck the battery into a small seat bag. Not for weight weenies, but you can't beat the ease and reliability.
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Old 04-01-10, 12:49 PM   #3
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For incandescent/halogen lights it should be pretty simply. You'd need a battery pack that puts out about 6 volts, 3 watts. Wire that to a switch and then to the light. IIRC, Bottle dynamo systems usually use the frame as half the circuit, so you'd either need to add another wire to the light, or wire your a battery terminal to the frame (connected to bare metal, not paint).

LEDs (which I doubt is what you are using) are a little bit more complicated. They care about the direction of the current, and so use a rectifier to convert the AC current from the dynamo to DC. Your battery will put out DC, so I think it would just be a matter of finding out which connection should be which.

Check out dealextreme.com for batteries and parts. Also, the electronics & lighting forum would be a good place to ask any more detailed questions.
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Old 04-01-10, 06:21 PM   #4
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A forum fellow sent me this link;
http://www.pilom.com/BicycleElectron...moCircuits.htm
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Old 04-02-10, 02:43 AM   #5
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^^ The link with the circuit designs is interesting. But I believe reliability is an issue as most don't address the LED's forward voltage limit and current draw. Typical of these high flux emitters, 3.6-4.0VDC is Vf. And 650-1000mA of current draw. No regulation in most of the offered circuits. And the complication level of the latter circuits is undesirable as cost and reliability become serious considerations IMO.
A better and simpler method is to combine both worlds so to speak. Implement a battery powered design with the generator as recharger. The spikes in its output are easily shunted by a rechargeable battery pack, offering flicker free light, plus more importantly, illumination while at a stand still. Just connect a full bridge rectifier to the dynamo to yield DCV and connect parallel to the battery pack. 4.5-6V is enough to drive a typical white LED. A limiting resistor in series with the LED is all that's needed for regulation. Or a switching power supply puck if you desire high efficiency. IMHO, it's not needed here, as the dynamo will extend the runtime of the batteries during a night ride.
It's just a down-sized version of what is every car's headlight system.

As for converting your existing incandescent dynamo light to batteries....
simple substitution of power source. BUT, you can do better just by replacing the set up with LED lighting. More light, less bulk. Unless you're wishing to preserve the look of the headlight, then search for a 3W white LED drop-in conversion bulb for your headlight. There are PR bayonet mount style bulbs for 3, 4.5 and 6V flashlights.
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Old 04-02-10, 02:51 AM   #6
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What do people have against generators?
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Old 04-02-10, 03:31 AM   #7
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What do people have against generators?
They only work when moving,
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Old 04-02-10, 08:16 AM   #8
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get a standlight circuit. Or wear a helmet light

the modern high power LED are well matched to dyno power because you don't need a regulator. The dyno will not put out more current than the LED can handle. The circuits at the link above have more complexity depending on the speed you want to produce light. If low speed light production is an issue, a voltage doubler is used. Since this can cut down on the light at high speed, there are switching circuits to pull the doubler out at a certain speed.

With LED lights at least, adding a battery adds considerable complexity since they can put too much current through the emitter. Similarly with a incandescent dyno to battery conversion, you have to worry about over-driving the bulbs.


I'm moving this to electronics and gadgets

Last edited by unterhausen; 04-02-10 at 08:19 AM.
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Old 04-02-10, 03:41 PM   #9
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Quote:
Originally Posted by Im Fixed View Post
They only work when moving,
Why do people keep repeating this obnoxious and untrue idea?

Nearly every dynamo light available today has a "standlight" option that keeps the light on when you stop for several minutes. It doesn't turn off when you stop.
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Old 08-08-11, 08:11 PM   #10
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Resurrecting this one from the dead. I have a B&M Lumotec IQ Cyo LED headlight leftover from when I had a dynamo generator front hub. Would like to put it back into service using battery power. Is it as simple as connecting a 6 volt battery pack of the required capacity to keep it powered as long I need it to between charges? Would this work? http://www.batteryspace.com/waterbot...bikelight.aspx
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Old 08-18-11, 07:08 AM   #11
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I went out on a limb and bought a 7.4 volt Li ion battery from Magicshine to power my Cyo. Works great so far, I'll post up some more details like run time, etc when I have used it for a while.
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Old 06-06-13, 05:30 AM   #12
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Lightbulb Connect any dynamo light to regulated 6V?

Quoting xb_Nutt:
>>
Quote:
Originally Posted by xB_Nutt View Post
I went out on a limb and bought a 7.4 volt Li ion battery from Magicshine to power my Cyo. Works great so far, I'll post up some more details like run time, etc when I have used it for a while.
>>

How did that work out?
Is it possible to just connect a 6V battery to any dynamo light? provided the battery can supply the current, of course.
If the dynamo output is AC, the headlight will have a rectifier at the input so a 6V DC input should be fine. can anyone confirm / refute this?

Thanks!
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Old 06-06-13, 05:49 AM   #13
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6v with no regulation probably will reduce the lifetime of your light considerably. Dyno lights work without regulation because the dynos put out 500mA and the emitters will withstand 1000mA. If you have a battery that has internal resistance to keep it from overdriving the emitter, it will work fine. You can overdrive modern led emitters, but it reduces their life and efficiency.
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Old 06-07-13, 04:59 AM   #14
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Question

Quoting unterhausen:

Quote:
Originally Posted by unterhausen View Post
6v with no regulation probably will reduce the lifetime of your light considerably.
With a little electronics to achieve regulation, and current limiting, it should be fine then? My assumption is that the circuitry inside a modern LED light will be controlling current anyway.

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Dyno lights work without regulation because the dynos put out 500mA and the emitters will withstand 1000mA.
I was under the impression that the dyno works like a permanent magnet AC machine (voltage determined by the speed of revolution), and current determined by the external circuit and winding resistance, i.e. as a voltage source.

The other point was whether these lights have a DC blocking cap on the input side. To me that seems highly unlikely, since it would have to be an AC cap rated for full current.
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Old 06-07-13, 05:57 AM   #15
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dynos are generally considered to be a current source. Obviously, the amount of current and voltage they put out varies somewhat with speed. But the voltage follows the current and the hubs can only put out about 500mA. Which is why I wouldn't expect to see regulation in a dyno light. It just wastes energy.

The German lights don't seem to have a blocking cap. The ones I'm familiar with do have some kind of boost circuit. It isn't really possible to generalize about dyno headlights since they appear to all be different.

I don't doubt the person above that reported success. You can overdrive a modern power emitter. It just reduces the efficiency and lifetime. Best to limit the power to within the recommended current limits.

Last edited by unterhausen; 06-07-13 at 06:01 AM.
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Old 06-08-13, 12:13 AM   #16
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Quote:
Originally Posted by unterhausen View Post
dynos are generally considered to be a current source. Obviously, the amount of current and voltage they put out varies somewhat with speed. But the voltage follows the current and the hubs can only put out about 500mA.
Interesting. I'm from a power electronics background and seems non-intuitive to me. Can you point me to anything that explains this model of a dynamo?
I was under the assumption that the dynamo was basically a permanent magnet ac generator...
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