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Step 3Direct Power!
Why not just connect your battery straight to the LED? It seems so simple! What's the problem? Can I ever do it?
The problem is reliability, consistency & robustness. As mentioned, the current through an LED is very sensitive to small changes in the voltage across the LED, and also to the ambient temperature of the LED, and also to the manufacturing variances of the LED. So when you just connect your LED to a battery you have little idea how much current is going through it. "but so what, it lit up, didn't it?". ok sure. depending on the battery, you might have way too much current (led gets very hot and burns out fast), or too little (led is dim). the other problem is that even if the led is just right when you first connect it, if you take it to a new environment which is hotter or colder, it will either get dim or too bright and burn out, because the led is very temperature sensitive. manufacturing variations can also cause variability.
So maybe you read all that, and you're thinking: "so what!". if so, plow ahead and connect right to the battery. for some applications it can be the way to go.
- Summary: only use this for hacks, don't expect it to be reliable or consistent, and expect to burn out some LED's along the way.
- One famous hack that puts this method to outstandingly good use is the LED Throwie.
Notes:
- if you are using a battery, this method will work best using *small* batteries, because a small battery acts like it has an internal resistor in it. this is one of the reasons the LED Throwie works so well.
- if you actually want to do this with a power-LED rather than a 3-cent LED, choose your battery voltage so that the LED will not be at full power. this is the other reason the LED Throwie works so well.
The problem is reliability, consistency & robustness. As mentioned, the current through an LED is very sensitive to small changes in the voltage across the LED, and also to the ambient temperature of the LED, and also to the manufacturing variances of the LED. So when you just connect your LED to a battery you have little idea how much current is going through it. "but so what, it lit up, didn't it?". ok sure. depending on the battery, you might have way too much current (led gets very hot and burns out fast), or too little (led is dim). the other problem is that even if the led is just right when you first connect it, if you take it to a new environment which is hotter or colder, it will either get dim or too bright and burn out, because the led is very temperature sensitive. manufacturing variations can also cause variability.
So maybe you read all that, and you're thinking: "so what!". if so, plow ahead and connect right to the battery. for some applications it can be the way to go.
- Summary: only use this for hacks, don't expect it to be reliable or consistent, and expect to burn out some LED's along the way.
- One famous hack that puts this method to outstandingly good use is the LED Throwie.
Notes:
- if you are using a battery, this method will work best using *small* batteries, because a small battery acts like it has an internal resistor in it. this is one of the reasons the LED Throwie works so well.
- if you actually want to do this with a power-LED rather than a 3-cent LED, choose your battery voltage so that the LED will not be at full power. this is the other reason the LED Throwie works so well.
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the voltage is 13-14v
my battery runs 12v (car off) and 13.6v (alternator charging)
would this be acceptable to run direct from battery, or should i run a dc-dc converter
the link is what i'm looking at
http://cgi.ebay.com.au/5-PC-BRIGHTEST-25W-WATT-HIGH-POWER-WHITE-LED-1400-Lumen-/390118430163?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item5ad4ded5d3
www.visionxoffroad.com/led/xmitter/
with similar 10w LEDs
cgi.ebay.com/ws/eBayISAPI.dll
i chose 10w ones because they are more cost effective as it seem that the higher power in watts for each unit they get less efficient, also easier to find lenses that i can use.
im also struggling to find out the right way to power them, as i believe the power in a car battery can range from 11-16v (because of cranking, charging...etc) so im not sure how to go about making a power supply i would also like to make one or 2 rather than 20 separate ones for each LED. im actually starting to lean towards using 3w LEDs like the xmitter, as its easier to get the right lenses.
just some things to think about, let me know how you go.