Make your own LED lighting

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lauriematt
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Postby lauriematt » 8 Oct 2008, 10:12am

has anybody tried using 5W LEDs instead of the 3W????
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insanityideas
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Postby insanityideas » 8 Oct 2008, 8:39pm

lauriematt wrote:has anybody tried using 5W LEDs instead of the 3W????


The 5W LED's are the older generation of LED, they were always less efficient. You would get more light output from two 3W LED's under powered to 5W that a single 5W LED... significantly more. And if you went for the same light output you would get better battery life. In both cases you can also use a much smaller heatsink.

All of the high power bike lights out there these days are using the same 3W LED technology (either from Cree or Lumileds/Philips). The only difference is the design of the case and the optics, the battery technology, and the sopistication of the control circuitry. Oh and the number of LED's they want to cram in there.

andrew_s
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Postby andrew_s » 8 Oct 2008, 11:40pm

You are just starting to get lights using the 10W Seoul P7 LED.
eg
http://www.on-one-shop.co.uk/?p=1121

This is actually 4 of the 3W P4 LEDs on the same chip, like the luxeon 5W was 2 of the 3W together.

insanityideas
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Postby insanityideas » 9 Oct 2008, 1:04am

andrew_s wrote:You are just starting to get lights using the 10W Seoul P7 LED.
eg
http://www.on-one-shop.co.uk/?p=1121

This is actually 4 of the 3W P4 LEDs on the same chip, like the luxeon 5W was 2 of the 3W together.


The Luxeon wasn't two 3W on one chip, originally they produced 3 models 1W,3W,5W. The only difference between the 3W and 5W was that the chip was rated to be overdriven, hence the poor efficiency (as it was still a 3W chip). All of their LED's have headroom to overdrive them on current at the expense of lifetime and efficiency. Which is why some manufacturers of LED lights quote different specs for lights with the same number and type of LED's, they are choosing to either over or under drive the LED's to suit the requirements of the product in terms of burn time and brightness, compared with size of battery pack.

Not sure how the Seoul P7 works in practice, but as you say its multiple LED dies on the same chip, which presumably makes it about as efficient as a similar number of 3W chips (on a lumens per W basis). This would be an interesting LED to use, as you could save significantly on size, assuming the chip works with currently available lenses.

Certainly LED lighting is still on a fairly steep improvement curve, which makes upgrading the LED's every couple of years a worthwhile undertaking.

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EdinburghFixed
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Postby EdinburghFixed » 13 Oct 2008, 4:38pm

Well, after spending a generous lunch hour over at the electronics section, I have wired up and test-fired my 2x3W Luxeon tail light.

It is *insanely* bright (brighter if possible than my Ay-Up front light).

I'll take some time this evening to do photos and post up a discussion.

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lauriematt
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Postby lauriematt » 13 Oct 2008, 4:48pm

EdinburghFixed wrote:Well, after spending a generous lunch hour over at the electronics section, I have wired up and test-fired my 2x3W Luxeon tail light.

It is *insanely* bright (brighter if possible than my Ay-Up front light).

I'll take some time this evening to do photos and post up a discussion.


cant wait! :D
i too am having a go but still waiting for a few arrivals in the post
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EdinburghFixed
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Postby EdinburghFixed » 13 Oct 2008, 4:58pm

Well, the good news is that I followed the formula from the Cyclechat discussion and it went together like lego (even with my rudimentary skills).

The question is how long it will run for... in theory, 2600mAh and a 700mA driver makes 3.5 hours (my daily commute is ~2.5 hours max so that would be a comfortable margin).

The AAA's on my Smart LEDs are getting ragged again - I can't wait just to have a no-brainer recharge while I'm doing the front light!

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Postby insanityideas » 13 Oct 2008, 9:46pm

EdinburghFixed wrote:The question is how long it will run for... in theory, 2600mAh and a 700mA driver makes 3.5 hours (my daily commute is ~2.5 hours max so that would be a comfortable margin).


The theory usually matches the practice... although some of the higher capacity batteries don't seem to have as much juice in them as quoted. Also the first few charges from new won't give you full capacity. Luckily LED lights fade quite gracefully rather than just going out.

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Postby insanityideas » 13 Oct 2008, 11:53pm

Laurie asked me a few questions by PM, and as I spent so long writing up the reply I thought I would post it here for the benefit of everyone. As I wrote it rather late at night there is problem some pointless waffle and repetition in there:

Laurie,
I would recommend using this LED: http://www.dotlight.de/product_info.php/cat/637/info/p909_Seoul-Z-LED-P4---white---Rank-U.html It is cheaper and generates the same light output at half the power, or nearly double the light at the same power as the 5w luxeon. This is because of advances in technology in LED production since the 5w luxeon's came on the market.

dotlight also do a range of suitable driver circuits, so if your already placing an order with them you may as well get the driver. The Konlux ones look very compact: http://www.dotlight.de/index.php/cat/c640_Seoul-Z-LED-Driver.html Sadly they don't have a variable current (i.e. dimmable) driver that works at battery voltage, although you could buy two driver's and connect them using a switch to pick one driver or the other (i.e only one driver on at any one time), if you wanted dimable lights. Personally I find this feature very useful for extending battery life, as its rare to need full power all the tim.

The driver you have found is also entirely suitable for the task, and has a lower voltage dropout of 1volt (instead of 2.5v), which is better.

To answer your question about connecting the LED's in series or parallel and battery voltage you have to think about what lights you are trying to design. If you connect the LED in parallel they will require twice the current and half the voltage (approximately) as connecting them in series, but if you use the correct driver in each case you will get the same light output.

so for same light output:
350ma driver in series @ 3.2v = 700ma driver in parallel @ 6.4v
700ma driver in series @3.7v = 1400ma driver in parallel @ 7.4v

Now if you already have a battery pack (or plan to use a particular battery pack) that outputs a particular voltage then you need to pick your wiring to match this. If you are making your own battery pack (out of AA batteries) then you need to think about if you want loads of batteries to give you a lower current draw and therefore longer run time, or fewer batteries and a higher current draw.

Finally the necessary battery pack voltage is calculated as follows:
1) use the datasheet for the LED to find out the correct voltage at the required current - as current draw goes up so does voltage. For the P4 LED linked above this is 3.6v at 700ma and 3.2v at 350ma.
2) Find out the dropout voltage of the driver, this is the amount of voltage the driver uses up to operate. the Konlux driver drops 2.5v, the powerline one 1v. As you can see the lower the dropout the fewer batteries you need (the lights are more efficient).
3) Find out the typical battery voltage when it is "on load", this will be lower than measuring it when disconnected as the voltage sags when there is significant current draw. Most NIMH rechargables are flat when they reach 1v on load, although for most of their discharge cycle they are at a steady 1.15-1.2v. To get lights that work effectively until the batteries are fully used up you need to base your calculations on 1.1v per battery... or whatever your battery pack produces.

example:
LED in series @700ma = (3.6x2)+2.5 = 9.7v @700ma minimum battery voltage
LED in parallel @700ma = 3.6+2.5 = 6.1v @1400ma minimum battery voltage

Any extra voltage gets converted to heat in the LED driver. The maximum amount of over voltage is usually specified in the datasheet for the driver. Depending on how succeptable your battery pack is to voltage sag on load, and voltage drop durring discharge will dictate how much over voltage you need to be with a fully charged pack.

As an idea I use 10xNIMH AA batteries to power my lights, and I can tell the battery is getting flat when it cannot supply the full 1000ma to the front light which is wired in series. This is evidenced as a flickering light caused by the on-off flash of the rear light connected to the same battery. At a lower 300ma setting it doesn't flicker because the pack can still provide enough voltage for that. With only 8xNIMH AA batteries the light would flicker all the time. I found this tendancy to drop voltage to be quite a significant problem, so its worth testing out your battery pack with the load current you intend to use, just to see what voltage it is capable of sustaining.

So in summary for maximum burn time wire the LED in series, and choose a battery pack with a sufficient supply voltage to power the LED. If you only have a low voltage pack available then wire in parallel and accept that you will halve the burn time.

lauriematt wrote:hi there

i was just wondering if you could give me some advice as im having a go at building a front light from scratch.

i will be using two 5w LEDS:
http://www.dotlight.de/product_info.php ... -140-.html

this is the driver i will be using:
http://www.led-tech.de/en/LED-Controlli ... 8_119.html


in order to get them as bright as possible - is it best to wire up the LED's in series or paralell???

from what i understand paralell components use all of the voltage available
whereas series components (say 2 LED's) half the voltage available for each component

so technically paralell circuit would be best???? although the battery would run out quicker.
also i was unsure of the effect of series / paralell on the driver. the LED's and the driver are 700ma. if i ran the LED's in series would i need a 1400ma driver???



finally what voltage battery would you recommend???
the LED's are 6.8v...so if they were run in paralell what is the highest voltage battery pack i could use???

cheers, Laurie


I would also add that while Laurie was asking about getting them as bright as possible, if you wanted to get more battery life you could also run them at lower drive currents and still get a satisfying amount of light out of them, just use a lower power regulator with the same LED. Because LED's become less efficient as you use a higher drive current it can be better to use more LED's at a lower individual drive current than fewer ones at a higher individual current. such that 4 LED driven at 350ma each put out more light than 2 LED driven at 700ma each, even though the total current for both setups is 1400ma (assuming parallel connection for ease of comparison in this example).

As regards the "do I connect my LED in series or parallel" question, it all depends on what supply voltage you have available. Most batteries are sold with a fixed capacity (in mAh) but at several different voltages, so given the choice you would select a supply voltage that allows connection in series (for maximum battery life)... however reality doesn't always give such choice so you may have to use parallel connection or a combination of series and parallel. (things get a bit silly for AA battery packs consisting of more than 10 batteries).
Last edited by insanityideas on 15 Oct 2008, 9:16pm, edited 1 time in total.

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EdinburghFixed
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Postby EdinburghFixed » 14 Oct 2008, 8:48am

Too late for me - but this is a really, really useful contribution (bookmarked!)

D.

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lauriematt
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Postby lauriematt » 14 Oct 2008, 10:52am

cheers for that!
cleared up a few of my questions
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insanityideas
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Postby insanityideas » 15 Oct 2008, 8:39pm

Thanks, I spent a lot of time experimenting to get the right setup (I am too fussy for my own good), so I thought I would share the fruits of my labors, and save some people the bother. Plus I can probably re-write it for my website, when I get round to properly documenting how I made my new lights.

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lauriematt
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Postby lauriematt » 18 Oct 2008, 10:14am

just another question....

obviously the powerline current controller restricts the current going to an LED to 700mah

but does it restrict the voltage too?? or do i need to wire in a resistor???

i will be using a 12v battery - but the LEDs only need 6ish v
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insanityideas
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Postby insanityideas » 18 Oct 2008, 10:20pm

lauriematt wrote:just another question....

obviously the powerline current controller restricts the current going to an LED to 700mah

but does it restrict the voltage too?? or do i need to wire in a resistor???

i will be using a 12v battery - but the LEDs only need 6ish v


The way a current controller controls the current is by varying the voltage, an LED consumes a variable amount of current depending on the voltage it is supplied with. All the controller does is measure current flow and then alter the voltage until the current flow is at its desired level.

This is useful for something that uses a battery because the battery voltage changes as the battery discharges. In normal applications where you knew the input voltage you would choose a fixed resistance which would set the voltage at the correct level for the LED to generate the required current flow. But in a battery situation you need a variable resistance to account for the falling battery voltage.

So for all intents and purposes you can regard the constant current controller as a self adjusting variable resistor (if that helps your brain to understand).

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lauriematt
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Postby lauriematt » 19 Oct 2008, 4:55pm

cheers.....understand completely!
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