Complete dynamo LED circuit

Hi guys!

Recently I've installed a dynamo hub on my bike, and I'm looking to make a full LED system (front and rear light), powered just by the dynamo itself (no batteries). I want to make a balanced system that will give me enough light in the front, and from back to be seen by any driver, at a safe distance no matter the weather (heavy rain, fog, pitch black)

What parts are most suitable for me (plenty of light, but not to put too much strain on the dynamo).

I was thinking about an underdriven XM-L LED, and 6 pieces of 5mm LED's on the back.

I'm waiting for your ideeas and suggestions guys.
Thanks!

I've built what I think is a fairly optimized dynamo light, but I don't think it is adequate in the dark in the heavy rain. A wet road reflects light like a mirror instead of being illuminated such that you can see the surface well. Plus.. there is the problem of the lights from oncoming traffic being reflected into your eyes too. It's a really difficult scenario, and even cars have trouble with it.

Fog is problematic too. I worry mostly about being seen from the rear. A Cateye LD1100 supplements my dynamo lights, and I've got a white xenon strobe light that I use at times too. Like rain at night, fog is tough enough for cars, and a bike dynamo is never going to be as good as a car's lights.

With that disclaimer in place... my basic strategy has been to run my headlight and taillight in series, with the headlight composed of two white LEDs at slow speeds, with two more switched in at higher speeds. The taillight is composed of ten 5mm red LEDs wired in parallel, although nowadays you might prefer to just use a large Cree or other higher power red LED.

I do run the dynamo power through a full wave rectifier first. Schottky diodes are more efficient than plain silicon diodes, and mosfets can be used for the most efficiency.

I've designed standlights for the headlight and taillight, but they are a bit complicated for most folks. There have been a couple of good standlight threads here that can guide you to a relatively simple but adequate standlight.

For background, you'll probably want to familiarize yourself with some of the circuits by a fellow named Martin (what's his whole name?):
http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm
I don't use the boost capacitor myself, but others have. I've designed a circuit to switch from 2 to 4 LEDs in the headlight automatically as the bike's speed changes, which provides a means of matching the headlight power to the power that the dynamo can deliver.

The development of my headlight is documented here:
http://www.flickr.com/photos/kurtsj00/sets/72157621965148305/
I will say that there is not that much difference between having 2 LEDs lit up and having 4 LEDs lit up. Human vision is logarithmic, and a doubling of lumens is just not much of a change. 4 LEDs is brighter, but it's hard to say if it's worth making the automatic switching circuit.

Well THANK YOU Steve!

That was a lot of help up there.

Yes, your right... a dynamo won't put too much light in the front of the bike, BUT I also have a 2x XM-L which puts about 1800 lumens on high (low+high beam), but i don't usually take that light with me, because in my area, robbery is a big problem...

I want something simple, that can light my way at low speeds. Now i have a Basta Halogen lamp, which is ok, but it's HALOGEN (If you know what i mean) LED is the only option for me, and I want to use a single LED (XM-L, probably), and for the tail light I'm gonna use 6 pcs of 5mm LED, wired series/paralel.
I'm thinking about installing a superCAP (1.5F maybe), inside the headlamp, and maybe wiring some DRL's, so i can use them as standlights/and parking lights.

What should I use to prevent the capacitor from discharging all the power into the dynamo when the bicycle is stopped. A diode maybe?

The standard arrangement is to use a bridge rectifier to convert the dynamo's AC output to DC suitable for LEDs. The bridge rectifier will keep current from flowing back into the dynamo.

Ok, thank's a lot Steve!

I appreciate your help!

Theres not a lot of point using XMLs in a dynamo light as they typically output 500mA. XTE/XPE are fine and you can get a nice tight beam out of them without resorting to huge optics.

Well which one is better? XTE or XPE?

I don't want a tight beam, i want something like xenon cut-off (for legal road use).

I forgot to ask, aren't 200 lumens too few?

I don't think that 200 lumens are enough. How many lumens does a 6V 2.4W halogen put out?

znomit said:

Theres not a lot of point using XMLs in a dynamo light as they typically output 500mA. XTE/XPE are fine and you can get a nice tight beam out of them without resorting to huge optics.

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out of curiosity, what optics can you recommend in order to get a tight beam? I've used the Ledil Rocket smooth spot with the XR-E and been quite happy with the results.

khrystyan27 said:

I forgot to ask, aren't 200 lumens too few?

I don't think that 200 lumens are enough. How many lumens does a 6V 2.4W halogen put out?

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If you run two modern white LEDs in series, the dynamo will be delivering approximately 6v at 0.5A, or 3 watts. With most LEDs producing 100 lumens per watt (or better), you'll be getting 300 lumens. With good optics, this is usually pretty satisfactory, and a lot better than standard incandescent dynamo headlights!

Steve K said:

If you run two modern white LEDs in series, the dynamo will be delivering approximately 6v at 0.5A, or 3 watts. With most LEDs producing 100 lumens per watt (or better), you'll be getting 300 lumens. With good optics, this is usually pretty satisfactory, and a lot better than standard incandescent dynamo headlights!

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Modern white LEDs meaning what type of LED?

XM-L/XP-G/XR-E/XT-E/XP-E/MC-E?

Someone recommended me 1x MC-E, which will have all die's in series along with 1 ohm 5W resistor.

khrystyan27 said:

How many lumens does a 6V 2.4W halogen put out?

Click to expand...

Approx 50 lumens.

JacobJones said:

Approx 50 lumens.

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Thx for your answer.

khrystyan27 said:

Modern white LEDs meaning what type of LED?

XM-L/XP-G/XR-E/XT-E/XP-E/MC-E?

Someone recommended me 1x MC-E, which will have all die's in series along with 1 ohm 5W resistor.

Click to expand...

Answer for that?

Is the MC-E the best sollution for dynamo circuits?

The MC-E is handy if you want multiple LED dies in one package. The datasheet (circa 2008) indicates it puts out just under 100 lumens per watt. By contrast, the Cree XP-E is perhaps slightly better. As Znomit mentions, it is in a smaller package, so it can use a smaller optic to produce a given beam shape.

I'm not sure what would be the reason to add a 1 ohm resistor in series. It's not needed for a dynamo light.

And if I want to add the stand light function?

What should I use? A LM317 perhaps?

I think this has been the most detailed and informative thread on standlights...

http://www.candlepowerforums.com/vb...Will-this-circuit-work-)&highlight=standlight

All it should take is a supercap, a few diodes, and a resistor, if memory serves...

12v (or 6V) easywhite XML is a better option than MCE.

Steve K said:

out of curiosity, what optics can you recommend in order to get a tight beam? I've used the Ledil Rocket smooth spot with the XR-E and been quite happy with the results.

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I recommend carclo spot triple 20mm with xp-e. I've had great success with XR-E and 8° dx.com optics. Both of these give great narrow beams with limited spill.

mrbubbles said:

I recommend carclo spot triple 20mm with xp-e. I've had great success with XR-E and 8° dx.com optics. Both of these give great narrow beams with limited spill.

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Love the DX one, find the 20mm triple is too floody for the road.
Been using the cxp optics from Ledil a bit.
http://www.ledil.com/datasheets/DataSheet_CXP.pdf