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Electronics => Electronics => Topic started by: Jdog on April 03, 2009, 08:51:16 PM
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I'm powering an infrared led with a forward voltage of 1.2 volts and a forward current of 100mA from a AAA battery. The LED calculator said I should use a resistor of 3.3 ohms. Do I really need a resistor if the resistance I'm supposed to use is so low?
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you should always use a resistor even if it is 1ohm. it just helps protect the led from burning out ;)
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I guess.
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fine then, go. hook your led up directly to your battery and watch as it burns out faster than normal! >:( ;D lol not really but you can have it hooked up to a battery directly it will just burn out a bit faster than normal.
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The soldering will probably have some resistance, so the resistor might not be needed.
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i thought solder had like .1R resistance?
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Hi,
The soldering will probably have some resistance, so the resistor might not be needed.
If your solderings are that high a resistance that it can protect the IRLED, you better practice... A lot! ;D
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wouldnt you have to use a tonne of solder to achieve more resistance?
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I'm powering an infrared led with a forward voltage of 1.2 volts and a forward current of 100mA from a AAA battery. The LED calculator said I should use a resistor of 3.3 ohms. Do I really need a resistor if the resistance I'm supposed to use is so low?
Your math is wrong. Assuming 6V, I calculated 48 ohms.
What voltage are you powering the LED with? Are you sure its 100mA, because that's a lot for an LED!
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I'm powering an infrared led with a forward voltage of 1.2 volts and a forward current of 100mA from a AAA battery. The LED calculator said I should use a resistor of 3.3 ohms. Do I really need a resistor if the resistance I'm supposed to use is so low?
Your math is wrong. Assuming 6V, I calculated 48 ohms.
What voltage are you powering the LED with? Are you sure its 100mA, because that's a lot for an LED!
i do agree on the 100ma being a bit much for an led tho.
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Hi,
I'm powering an infrared led with a forward voltage of 1.2 volts and a forward current of 100mA from a AAA battery. The LED calculator said I should use a resistor of 3.3 ohms. Do I really need a resistor if the resistance I'm supposed to use is so low?
If you don't use a resistor, the LED will die, perhaps not instantly, but it won't take long. A fresh AAA has got an internal resistance of between 100 mOhm and 300 mOhm (that's not MOhm in case you wondered) so with 0.3V to spare (with a new cell it would actually be up to 0.45 for a short time), a rough estimate of the current flowing is 1A to 3A!
While the battery wears down, current will go down too and you will soon have no power to the LED. A cell starts at around 1.65V and is considered empty at 0.9V, but your LED won't do a thing below 1.2V, so you will not be able to use up the cell.
If you instead use two cells and a Constant Current circuit, you will have a controlled current for the entire life time of the battery.
Btw. Why do you want to just have an IRLED light?
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Hi,
I'm powering an infrared led with a forward voltage of 1.2 volts and a forward current of 100mA from a AAA battery. The LED calculator said I should use a resistor of 3.3 ohms. Do I really need a resistor if the resistance I'm supposed to use is so low?
Your math is wrong. Assuming 6V, I calculated 48 ohms.
What voltage are you powering the LED with? Are you sure its 100mA, because that's a lot for an LED!
As he wrote... An AAA cell.
It leaves the math to: ~0.3V/3.3 Ohm = 91mA
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Hi,
i do agree on the 100ma being a bit much for an led tho.
I have some IRLEDs that are good for ~1A and I have seen them loads beefier.
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triple post much? please try to modify your posts instead of double or triple posting ;) just makes scrolling through topics easier if we only have to go through 10 posts instead of 20-30 :) no offense intended (we've all done it once)
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fine then, go. hook your led up directly to your battery and watch as it burns out faster than normal! >:( ;D lol not really but you can have it hooked up to a battery directly it will just burn out a bit faster than normal.
I didn't say I wasn't going to use one.
Your math is wrong. Assuming 6V, I calculated 48 ohms.
What voltage are you powering the LED with? Are you sure its 100mA, because that's a lot for an LED!
I said a AAA battery which is 1.5 volts.
Yes' I'm sure it's 100 mA. Here's the specs if you don't believe me.http://www.radioshack.com/product/index.jsp?productId=2062565&tab=summary (http://www.radioshack.com/product/index.jsp?productId=2062565&tab=summary)
If you instead use two cells and a Constant Current circuit, you will have a controlled current for the entire life time of the battery.
Btw. Why do you want to just have an IRLED light?
I can't use two cells because I need it to fit inside a highlighter. I'm doing Johnny Chung Lee's multi-touch wii whiteboard project, and I need to make an infrared pen.
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Dang that thing is cool... like a tablet for $40.
Just a thought, maybe open up a 9v battery and get one of the AAAA batteries inside? Those would fit a lot better in a pen.