Make your own LED lighting

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random37
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Make your own LED lighting

Postby random37 » 30 Sep 2008, 9:30am

Hello-

I read a post from someone on here (who I can't find now, unfortunately) who made their own LED dynamo light.
I fancy a go at this, but I was wondering if there was anywhere that sold the bits to make such a thing?
Also, any websites that show what people did?
Chris

aj
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Postby aj » 30 Sep 2008, 10:17am

The Candle Power Forums seem to cover making all types of lights including ones for bikes, may give you some leads on suppliers and designs.

Main forums here

Cycle specific forum here

Adrian

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cranky
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Postby cranky » 30 Sep 2008, 5:46pm

Luxeon 3watt leds can be had for about £6 a pop. A 3watt torch can be had for under £30. Makes you think....
Iain

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random37
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Postby random37 » 30 Sep 2008, 6:29pm

Exactly. I want an LED light to replace my dynamo, but I feel a bit stupid paying £50+ when the parts are so cheap.

tad
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Postby tad » 30 Sep 2008, 6:34pm

A few years ago I made a bicycle powered art installation using an old excercise bike out of a skip and scrap hub dynamo to power 150 LEDs it was very silly but great fun. Also a little bit bright.

I also had to build a regulator/rectifier as I seem to remember LEDs need a constant DC voltage. Maplins did a kit for that for under a tenner.

random37
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Postby random37 » 30 Sep 2008, 6:45pm

Cheers Tad. Will look it up.
Still excited about your new toy?

tad
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Postby tad » 30 Sep 2008, 8:35pm

I found this article, it looks pretty good.

http://www.fieldlines.com/story/2007/1/28/215243/977


When I was fooling with these things I had to make a regulator/rectifier. I think a dynamo produces AC current. An LED requires DC current, the rectifier smooths the AC to DC. The next important thing is a stable voltage. As you tear down a hill a dynamo will produce a higher voltage than when bimbling down a hill. LEDs are very sensitive to raised voltage. There's a simple clculation you have to do to work out what resistor to wire into your lighting circuit and that's depandant on what your voltage is. The regulator restricts the voltage to a set level so no matter how fast you go the voltage doesn't go above what you set. I discovered this the hard way whn pedaling like a loon a whole load of my lights went orange and then died never to work again!

This is the regulator/rectifier kit I used from Maplins. Their catalogue was very helpful, it explains all the electronics (which is simple enough any way) in even simpler terms.

http://www.maplin.co.uk/Module.aspx?Mod ... 8&DOY=30m9

I always wanted to take my project further and now may be spurned into action (as long as I don't spend all my free time on the new mountainbike). I wanted to create a home made LED lighting system that used power from the dynamo to charge a battery during the day so that it could be used as a torch at night.

Right, time to get the multimeter and soldering iron out!

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meic
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Postby meic » 30 Sep 2008, 8:52pm

Busch and Muller do the "ride and charge" which is combined with their IXON battery front lamp to charge its internal 4AA batteries.

However it is 95Euros for the pair. (without the batteries or of course dynamo.)

It would be nice to have such a system to charge the batteries for all your electronic gizmos during the day. I think that it can even charge them while you are using the light at night.
Yma o Hyd

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andrew_s
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Postby andrew_s » 30 Sep 2008, 10:50pm

The difficult part of DIY lights isn't the electronics side of things, but getting the optics right, in a neat & weatherproof housing, and with an adequate heat sink.
If the optics aren't right, you either get light going everywhere, with no real distance in the beam, or you get distracting light and dark rings in your beam
Heat sinks are required because all the energy that doesn't come out as visible light goes into heating up the LED, whereas with filament bulbs it almost all radiates away as IR.

Electrically, if you use a dynamo you use something as simple as a bridge rectifier, a switch and two or three high power LEDs. If you want to get a bit brighter, using separate schottky diodes and a capacitor or two is fairly simple. There are quite a few example circuits around on bike fora -eg here (It starts off as a USB power supply, but meanders into lights).

If you want a battery light, it's much easier to get a pre-built driver circuit such as a buckpuck.

Hong Kong sites like DealExtreme or KaiDomain are good sources of bits (LEDs, optics, drivers etc). Look in Lights -> DIY parts.

Uncle Phil
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Postby Uncle Phil » 30 Sep 2008, 11:02pm

Take a look at this thread for some ideas.

As you'll see, I followed Fisha's instructions and built a front light. And it works, really well. And it's waterproof, and rugged.

I also have a B&M IQ Fly on another bike, and the light compares very favourably with that.

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EdinburghFixed
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Postby EdinburghFixed » 1 Oct 2008, 11:51am

Do you have any ideas about putting together a rear light?

I assume it's not quite as demanding because you are trying to get light spilling around rather than a focussed beam ;-)

I have a spare Ay-Up 7.4V 2600mAh battery and have been thinking for a while that it's a pain they don't sell a rear light equivalent. Then I could charge both batteries together at the same time, and if necessary, use my helmet light battery to fuel the rear light etc!

I guess I need a driver which accepts 7.4V and will output adequate current for a pair of red LEDs. It's hard to figure out all the bits!

kwackers
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Postby kwackers » 1 Oct 2008, 12:43pm

EdinburghFixed wrote:Do you have any ideas about putting together a rear light?

I assume it's not quite as demanding because you are trying to get light spilling around rather than a focussed beam ;-)

I have a spare Ay-Up 7.4V 2600mAh battery and have been thinking for a while that it's a pain they don't sell a rear light equivalent. Then I could charge both batteries together at the same time, and if necessary, use my helmet light battery to fuel the rear light etc!

I guess I need a driver which accepts 7.4V and will output adequate current for a pair of red LEDs. It's hard to figure out all the bits!



That's a big battery, since you don't need to worry about efficiency I'd...

Put 3 leds in series and connect to the battery via a 1k resistor, measure the voltage across the 1k resistor.
(You can use 2 leds - but you can power 3 from 7.2v for the same energy)

Then use R = V / I to work out a value for an appropriate resistor to replace the 1k with assuming say 30mA current (no need to worry too much about overdriving them, they'll be brighter and their life will be measured in years rather than decades - if you know the max rating of the leds then go with that).

After that just make up as many strings as you fancy for the number of lights you need.

2600mAh / 30 = 90 hours continuous. I'd try a dozen (or two) :wink:

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EdinburghFixed
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Postby EdinburghFixed » 1 Oct 2008, 2:18pm

I was thinking about using the big headlight style LED's for a Dinotte-esque light.

From what I understand from the links above, I should be able to pick up a 700mA constant current driver and run a pair of 3W Luxeons slightly under capacity, from my Ay-Up battery?

By my calculation it needs (2.95 x 2) + 1 = 6.9V input, and I have 7.4V

However, I don't really understand the way the driver works. What happens if I am drawing down the battery and the voltage dips under 6.9V?

Should have paid more attention in school perhaps! :?

kwackers
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Postby kwackers » 1 Oct 2008, 2:32pm

EdinburghFixed wrote:I was thinking about using the big headlight style LED's for a Dinotte-esque light.

From what I understand from the links above, I should be able to pick up a 700mA constant current driver and run a pair of 3W Luxeons slightly under capacity, from my Ay-Up battery?

By my calculation it needs (2.95 x 2) + 1 = 6.9V input, and I have 7.4V

However, I don't really understand the way the driver works. What happens if I am drawing down the battery and the voltage dips under 6.9V?

Should have paid more attention in school perhaps! :?



Did they do this stuff in school? Mine didn't :(

Simple answer is it stops working.
It's a linear device - if you think of it as a variable resistor whose resistance drops to try and keep the current the same you won't be far off - however it has losses (hence the huge heatsink) and so it drops voltage too.
If the supply voltage minus it's minimum voltage drop exceeds the battery voltage the lights go out.

Ideally you want a PWM rather than linear driver. In theory since you have identical lights you can simply switch one on and off in time with the other whilst only monitoring the current in one. Beauty of this is it'll use less current and the batteries will last longer.
Alternatively (and best) you should be able to find cheapish buck/boost drivers - since you don't need a big heatsink I would think the price isn't much different.

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cranky
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Postby cranky » 1 Oct 2008, 2:55pm

EdinburghFixed wrote:I was thinking about using the big headlight style LED's for a Dinotte-esque light.

From what I understand from the links above, I should be able to pick up a 700mA constant current driver and run a pair of 3W Luxeons slightly under capacity, from my Ay-Up battery?

By my calculation it needs (2.95 x 2) + 1 = 6.9V input, and I have 7.4V

However, I don't really understand the way the driver works. What happens if I am drawing down the battery and the voltage dips under 6.9V?

Should have paid more attention in school perhaps! :?


The Constant Current supply you quote is a PWM 700mA supply. The Luxeons are 3.7V @ 700mA each. There is no option to run them at 2.95V (AFAIK). You would need a battery giving 8.4V (3.7+3.7+1) at the lowest part of the discharge slope in order to use that particular CC regulator.

Edit: I think you were looking at the second example on the driver circuit page. That's for two RED Luxeons @ 2.95V. I suppose you could always use two driver circuits, one per Luxeon. Also, I'm not at all sure those drivers are PWM. It says "PWM capability" so maybe it means they have an inhibit (switching) input allowing you to connect a modulator. There's no data sheet so I'm not sure.
Iain



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