High Powered Luxeon LEDs: where to buy? how do i learn how to wire them up?

[big bustle]

hey folks,

i want to get my hands on some of these:

http://cgi.ebay.com/5x-Blue-High-Power-Luxeon-LED-Lamp-Light-3-Watt-NEW_W0QQitemZ310085321521QQcmdZViewItem?hash=item310085321521&_trkparms=72%3A1205|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14

when can i get them cheaper and possibly in bulk?

i read about them from multiple instrucables on how to build your own high powered bike lights.

i'd like to use them in pedals, as bike lights and to light my studio.

for pedals: the concept is to basically give your self your own light show whilst playing. home

it says they need 3.2v-4.0v to run (depending on color) and have a forward current of 700ma.

i still dont fully understand ohms law. i was hoping some one could explain how to wire them up and what the 700ma means in terms of wall wart/battery drainage.

i know a lot of fuzz circuits use very little current i.e. less than 50ma. how much ma can a 9v battery provide?

when wiring these up to use a wall wart what does that mean in terms of power needed? for example. i have a few 3v power supplies but they only go up 200ma. does that mean the led will over heat them as its going to draw way more current than it needs? what if i used let's say a 12v 1.2A power supply. how do i step it down to not blow them up but make sure it has enough head room to power let's say 10 of these.

and do i wire in series or parallel?

my original goal for bike light usage is to run 2 or three off of 3 AA rechargeable batteries. the batts themselves say 2300mAh typical 1.2v.

sorry if this posting is a lil all over the place.

thanks!

[earthtonesaudio]

Don't use them for pedals or pretty much anything battery-powered.  You might as well try to light up a toaster with your pedals.

Instead go for high-brightness, 20mA forward current.
http://www.rapidonline.com/Electronic-Components/Optoelectronics/5mm-LEDs/5mm-white-LEDs/64846/kw/

[big bustle]

Don't use them for pedals or pretty much anything battery-powered.  You might as well try to light up a toaster with your pedals.

how come?

[earthtonesaudio]

They require lots of power to even light up, let alone stay lit up.  700mA will drain a 9V battery in, like, 0.6 seconds.

20mA is much more do-able.

[calpolyengineer]

A 9V battery should only really supply up to about 25mA continuously. It can do more, but as you up the current, the power stored in the battery is used less efficiently and the battery does not last as long as it should. That being said, a 9V only has about 675mAh of power. At 700mA the best you could possibly get out of it is just under an hour. But due to the high current, I wouldn't expect more than 20 minutes.

-Joe

[Roobin]

Which bit of ohm's law don't you understand? In general, or in relation to this application? The 700ma indicates maximum forward current (it does for normal LEDs, so I'm assuming the same here).

With normal LEDs, they have a voltage drop across them - the same way a silicon diode has a 0.6 - 0.7v drop across it. This voltage drop stays (relatively) constant for that LED. Call it V(led). Now, let us put a resistor resistance R ohms in series with the LED and the battery (say 9v). If there is a voltage of V(led) across the Led, there must be a voltage of 9 - V(led) across the resistor. Now, here comes Ohm's law - that the Voltage across a resistor is proportional to the product of the current in the resistor and the resistance (ie V = IR). In our case, 9- V(led) = I * R, where I is the current in the circuit. Remember, current is always the same in this circuit. Thus the current flowing through the resistor is the same current flowing through the battery and the LED. Rearranging, I = (9-V(led))/R. We can see that we can increase the current in the circuit by a) lowering the series resistance or b) increasing the battery's voltage. Now, increasing the current increases the brightness of the LED. BUT - there is a caveat. Remember that current rating? That tells you how much current can flow through the LED before it blows. So our job is to choose a resistor to limit the current in the circuit. For this, you need the V(led) which normally comes from the manufacturer. Then you can calculate R.

The reason it's not advisable to use with a 9V is that 9v have a mAh (milliamp hour - basically how many milliamps the battery can supply for an hour before dying) that is pretty low - a quick search on google/amazon showed that rechargeables have a mAh of 175 - 200. Thus, if you were running your led at 600 mA, your battery would run out in 20 minutes. Not good. (For reference, pedals can draw anywhere forma few mA for fuzzes, to 10s of mA to hundreds for multifx)

Again, if using a power supply, you would need to check the specs of the PS. If it says max 12v 200mA, it means that if you exceed a 200mA current draw, things are likely to start smoking.

As earthtonesaudio says, try out ultra bright ones - they won't deplete your batteries (that quickly) and you can afford to break a few experimenting.

Quick google search - http://led.linear1.org/1led.wiz

[big bustle]

i decided to forgo the luxeon

i found some 140k white leds on ebay that supposedly only draw 20ma

we'll see how those work out