Homemade *bright* LED light setup

torrent99

Esteemed Pedelecer
Nov 14, 2008
395
3
Highgate, London
#61
Yeah soak test is a good idea, I'll be running the LEDs from a stable 12v source, 25watt DC-DC converter which is adjustable so if I find the LEDs are burning out I can simply lower the voltage. I stuck to 120ohm resistors which is for 3 3.2v LEDs in a row each drawing 20mA, whereas the LEDs I bought are rated for 3.4-3.6v, undervolting them will extend life & reduce brightness but heck there's going to be 300 of them so it can't be all that dim!

BTW, I just found the ultimate LED bike light: 100 watt LED :D (but it costs £240+)
100 Watt, that's just silly! ;)

The other idea I had for your circuit was to common each of the LEDS at to it's neighbour. So instead of 20 independent strings of 3 in series you have 3x20 LEDS in parrallel arranged in a series string of 3x 20 parrallel LEDS. (language is failing me here!). That way if a single LED fails it won't take out the other 2 in its serial string as well, the extra current will simply be shared amongst the other 19 in the parallel block. Should be pretty easy to mod your PCB to get this extra resilience. (Having had to retrofit failed LEDS I'm paranoid about resilience! :( )
 

rog_london

Esteemed Pedelecer
Jan 3, 2009
764
2
Harrow, Middlesex
#62
100 Watt, that's just silly! ;)

The other idea I had for your circuit was to common each of the LEDS at to it's neighbour. So instead of 20 independent strings of 3 in series you have 3x20 LEDS in parrallel arranged in a series string of 3x 20 parrallel LEDS. (language is failing me here!). That way if a single LED fails it won't take out the other 2 in its serial string as well, the extra current will simply be shared amongst the other 19 in the parallel block. Should be pretty easy to mod your PCB to get this extra resilience. (Having had to retrofit failed LEDS I'm paranoid about resilience! :( )
No, you can't do that. LEDs don't behave sensibly in parallel, in that there are minor differences in operating characteristics, which means that some take a LOT more current than others if you connect them in parallel. If you vary the current through a single LED and monitor the voltage across it, you'll notice that the voltage does not vary much with quite a large change in the current through it. In other words, like any other diode, it tends to behave as a constant-voltage device (though not quite). Therefore you need a series circuit to keep the current constant through each LED. Even then you may have to 'tune' the resistor if you mean to drive the LEDs close to their maximum rating, as you will get variations as in Haku's 60-LED circuit.

Of course there are LEDs which are designed to work in parallel (since this can be a useful characteristic) but they are more than just LEDs, incorporating some sort of regulator circuit to make them 'pseudo' constant-current, and you pay more for those.

Rog.
 
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#63
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Haku

Esteemed Pedelecer
Jun 20, 2007
339
1
Gloucestershire
#64
The circuit boards arrived last Friday, no solder resist so they're cheaper and quicker to have made:



Last Saturday the resistors arrived and today the 1500 LEDs+push switches arrived:



So I went ahead and soldered up a couple of boards which took 2-3 hours:



When soldering them I was testing each new set of 3 LEDs would work ok with a slightly used 8x alkaline D cell pack (11.5v) and that was bright enough during the daytime, now it's dark I rigged the two LED bars up to a regulated 12v 3A supply - holy [expletive]! you can't look at them direct or you'll get camera-flash blindness.

The most annoying thing I discovered is that after a few minutes they get too hot to touch (alkalines can't put out much amps which is why they didn't get warm on the 8x D pack), so I may have to lower the voltage down below 11v and possibly use lower ohm resistors so they don't dissapate so much heat. Two bars are drawing 10 watts from the 12v PSU, I tried 8x rechargable AAs which were 9.5v and the bars together drew less than 4 watts but weren't as bright.

The heat problem also means I can't use the intended polymorph plastic as the shell/backing for the light because above 60 degrees C it becomes soft & pliable (it's how you can re-form its shape again and again). Going to need a toohpaste tube size of thermal paste & piece of aluminium as the backing. I wonder how good Milliput is as conducting heat...



The only thing that worries me about building such a monster LED array is that a year down the line I'm going to be thinking "I could do with a bit more light..."
 

Haku

Esteemed Pedelecer
Jun 20, 2007
339
1
Gloucestershire
#65
Soldered up a 3rd 'bar' today and have been doing some testing with a bench power supply and my multimeter that can measure volts & amps at the same time to also show watts.

After having to swap out 4 LEDs because they burnt out in a bit of soak testing at 12v, I discovered that at 12v the 3 'bars' were using 15.8 watts and were getting burning hot, but dropping the voltage down to 10v didn't significantly reduce the brightness and the 180 LEDs were then using only 5.6 watts.

So the full 300 LED array shouldn't draw more than 10 watts at 10v, instead of the anticipated 24 watts at 12v, and furthermore I can probably get away with using a 10 watt DC-DC converter I already have instead having to order a 25 watt DC-DC converter from DimensionEngineering. Which is nice :)
 

rog_london

Esteemed Pedelecer
Jan 3, 2009
764
2
Harrow, Middlesex
#66
So the full 300 LED array shouldn't draw more than 10 watts at 10v, instead of the anticipated 24 watts at 12v, and furthermore I can probably get away with using a 10 watt DC-DC converter I already have instead having to order a 25 watt DC-DC converter from DimensionEngineering. Which is nice :)
Most LEDs give almost their full output with well under the maximum rated load, so I'm not surprised your array behaves as it does. Also, the large change in power consumption for the fairly small reduction in applied voltage makes me think that probably your resistors are not dividing the load very evenly and you may be over-running some groups of LEDs while under-running others. This will be due to the manufacturing variances among the LEDs rather than discrepancies in the resistors. The problem can be at its worst near to maximum rating, so your decision to reduce the applied voltage may be a wise one for several reasons!

Rog.
 

Haku

Esteemed Pedelecer
Jun 20, 2007
339
1
Gloucestershire
#67
I was worried that running the array at 10v would adversely affect the brightness as I've finished soldering all 300 LEDs for my light today and couldn't properly test it until a couple of hours ago when it got properly dark.

After charging up a couple of RC car battery packs & putting them in series to power the 10 watt DC-DC switching regulator then taking it out for a test, I can honestly say I can't bloody wait to get it permanently fixed to my bike:



It's like a car headlight! Drivers are certainly gonna know when I highbeam them :D


edit: WOOOOW!!!
I temporarily stuck it over my existing light and went for a spin along some dark roads & cycle tracks with all 300 LEDs powered by the two RC car battery packs, it's fricken unreal, it's like you've got your own personal piece of daylight in front of you! even saw a deer at the end of the journey :)
 
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Haku

Esteemed Pedelecer
Jun 20, 2007
339
1
Gloucestershire
#68
Slow progress the past few weeks, a combination of no spare cash for parts & ill for a week.

Anyway, I've now managed to order a bunch of PICAXE chips + parts needed to make them run so I'll be able to start soldering the control circuitboard for the bike light, with a pile of spare PICAXEs for other project ideas.


I went out a few more nights with the 300 LED array blutacked & taped to my bike, it's too much fun! I discovered that one set of traffic lights that never sees me unless there's a car stopped behind me can be triggered by high-beaming the LEDs and you can get cars to easily dip their highbeam by putting all 300 LEDs on when they're still some distance away. But the 'Blue Peter' fixing method got too much hassle to maintain so I took it off and won't put it back on until it's waterproof & finished. I plan to put some 2mm thick acrylic over the front of the LEDs to stop muck sprayed from the front wheel from getting inbetween them, also making it very easy to clean the muck from the light.
 
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z0mb13e

Esteemed Pedelecer
Jul 28, 2009
578
2
Dorset
#69
Hey Haku,

Interesting project, how is it coming along?

I figured you might be interested in something like this given you are familiar with microcontrollers...

SpokePOV: LED Bike Wheel Images

Have you looked at pulsing your LED array rather than running it at a constant current? LEDs can produce more light and last longer if pulsed. Something your PICAXE can do easily. Not sure what frequency would work best but might be something to explore.
 

monster

Pedelecer
May 13, 2009
120
0
#70
why don't you guys just use MR16's or MR11's they are way better than any amount of led's stuck to a reflector. the amount of time and effort you have to put into this, i would be gutted if one broke. with MR16 you can just replace it for 50p. the efficiency is not all that different and we have big batteries so why not used them?

my bike puts out more light than most motorcycles.
 

LazyViking

Finding my (electric) wheels
Mar 4, 2009
18
0
#71
MagicShine

I recently received my "900 lumnen" MagicShine light from DealExtreme. I'm very impressed with the light.

This has made my two older bike lamps redundant:
* 3500 lumen 35W HID car lamp - big, heavy, eats batteries and frightens pedestrians!
* 130 lumen MR11 LED lamp. Not enough light to see where you're going.

Link to dealextreme:
DealExtreme: $82.45 HA-III Cree SSC P7-C (SXO) 3-Mode 900-Lumen LED Headlamp Set (4*18650 included)
Remember to also order plug adapter!
Ordner now and have it by Easter:D

--LazyViking
 

monkoffunk

Finding my (electric) wheels
Oct 28, 2010
20
0
#73
While I'm very impressed with the engineering going on here, I was planning to use the head of a 98LED torch I got from ASDA on offer for £7 which takes 4.5V at about 2A. I'm going to power the head with a 4.8V NimH pack.

Still much kudos to the cool tinkering going on here!
 

morphix

Esteemed Pedelecer
Oct 24, 2010
2,163
7
Worcestershire
www.cyclecharge.org.uk
#74
Haku, very clever, nice idea/work!
 
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halfer

Esteemed Pedelecer
#75
Interesting thread! By coincidence, I just built a custom rear lamp, and am powering it off the battery on my Juicy Bike. The main lamp component is a 52-LED signage cluster from Maplin. This is somewhat similar to Grandad's rear lamp project (on page three on this thread) but with a larger cluster. The brightness is excellent, and apparently has a viewing angle of 40 degrees - although the LEDs are more recessed than I would like.

I would very much like to hear any advice on how it could be best mounted on the bike in a secure and quick-release fashion. It would mount very well on one of the near-vertical posts that joins the carrier to the rear hub axle. I have a rear-light mounting bracket from Halfords, which has a slide fitting, and am wondering whether a bit of plastic cut to the right shape, might do the trick. Or perhaps there is a two-part bracket available somewhere (I've searched plenty online, to no avail).

As you'll see from the blog post, I'm using a resistor at present to step the 36V nominal (nearly 40V at full charge) down to 11V or so, which is around what the cluster can take at maximum power. Would I be better off with a DC-DC converter instead, as per some of the posts here?
 

jtsubota

Just Joined
Oct 4, 2011
1
0
#76
I also wanted to share my homemade bike light. Complete instructions on how to make the light can be found at Cool DIY Bike Light.

I hope you enjoy the pictures!



 

halfer

Esteemed Pedelecer
#77
Nice work, jtsubota! A custom design service might be a good idea, however - Illustrator/SolidWorks are not readily accessible for most peeps, never mind the skills to use 'em ;)
 

HypnoToad

Finding my (electric) wheels
Jun 13, 2012
24
0
#78
I'm not sure if this has already been mentioned, but if you wire enough LED's in series then you won't need to use resistors or step down converters, that way you get more efficiency. Step down converters are never 100% efficient. ;)

EG, say you have a 36v battery setup; Top voltage will be 42v.

Buy a big pack of white LED's, for example let assume a forward voltage of 3v.

42 / 3 = 14 LED's in series.

When your pack drops to 36v, you'll get less than 3v per LED but even so it will work.

Red LED's have a lower voltage, usually around 2v, so you'll need a load, especially those if you with 48v or high voltage batteries.
 

Alan Quay

Esteemed Pedelecer
Dec 4, 2012
2,341
78
Devon
#79
A good, and cheap source of LED's on Ebay:

RED LED CAR STRIP UNDER LIGHT NEON FOOTWELL FLEXIBLE | eBay

These are great, as they can be cut into 3 LED sections, are self adhesive and waterproof. Cheap too.

You can arrange each section in series, and use enough to divide your battery voltage by 12 (e.g., if you have 36 volt, then use 3 in series). Each section has its own resistor.

I have three strips, each with 6 LEDs on the back of my bike. They are probably a little too bright if anything.

Total measured current for my setup is 44mA - this means that they would run for nearly 10 days solid from a 10ah battery (theoretically, but you get the point).
 

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