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#1
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LED help
I've got 8 or so white LEDs, but no specs on them. They look average size
with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? |
#2
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LED help
"garlicman" None wrote in message . .. I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? If you have a variable DC supply (0 to 10 volts or so) and a multimeter, just connect them with a series resistor of 150 ohms or so and slowly crank up the DC voltage. Stop when the brightness is adequate or no longer much increasing and measure the current and voltage drop. |
#3
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LED help
"Charles" wrote in message . .. "garlicman" None wrote in message . .. I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? If you have a variable DC supply (0 to 10 volts or so) and a multimeter, just connect them with a series resistor of 150 ohms or so and slowly crank up the DC voltage. Stop when the brightness is adequate or no longer much increasing and measure the current and voltage drop. Thanks, I have a 0 to 15VDC variable power supply. I just have a cheap multimeter that doesn't measure DC amps. Time to upgrade. |
#4
Posted to alt.electronics
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LED help
"garlicman" None wrote in message . .. "Charles" wrote in message . .. "garlicman" None wrote in message . .. I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? If you have a variable DC supply (0 to 10 volts or so) and a multimeter, just connect them with a series resistor of 150 ohms or so and slowly crank up the DC voltage. Stop when the brightness is adequate or no longer much increasing and measure the current and voltage drop. Thanks, I have a 0 to 15VDC variable power supply. I just have a cheap multimeter that doesn't measure DC amps. Time to upgrade. You can measure the voltage drop across the 150 ohm resistor and calculate the current. |
#5
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LED help
On Mon, 27 Aug 2007 11:33:06 -0700, "garlicman" None wrote:
I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? --- Empirically. Download a few data sheets for common white LEDs and make a note of their typical forward voltage drops with nominal current through them. You'll probably find something like a 3.5V drop with 20mA through the LED, but don't trust me... Get the data sheets and find out for yourself. Since you have a variable power supply, you'll need to put a resistor in series with the LED so that you can measure the voltage drop across the resistor and, using Ohm's law, determine the current through the resistor. Then, since the resistor and LED will be in series, the current through the resistor will be the same as the current through the LED, so measuring the voltage drop across the series resistance will allow you to calculate that common current. For example, using a 100 ohm resistor will result in your setup looking like this: (View in Courier) +-------+ +-----+ | +|-----+------|+ | | | | | | | | [100R] | | | | | | | | | +------|- | | | |A +-----+ | | [LED] METER | | | | -|-----+ +-------+ SUPPLY Now, in order to determine when 20mA is in the resistor, invoke Ohm's law: E = IR = 0.02A * 100R = 2V So, crank up your supply until you read 2 volts across the resistor, and then you'll know that there's 20mA in both the resistor and the LED. Next, in order to determine the voltage dropped across the LED, leave the supply where it is and reconnect the voltmeter like this: +-------+ | +|-----+ | | | | | [100R] | | | +-----+ | | +------|+ | | | |A | | | | [LED] | | | | | | | | -|-----+------|- | +-------+ +-----+ SUPPLY METER VOILA! You now have all the information you need to plug into those online calculators. With just a little more effort you can blow off those online calculators and figure it all out for yourself. Interested? -- JF |
#6
Posted to alt.electronics
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LED help
John Fields wrote:
On Mon, 27 Aug 2007 11:33:06 -0700, "garlicman" None wrote: I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? --- Empirically. Download a few data sheets for common white LEDs and make a note of their typical forward voltage drops with nominal current through them. You'll probably find something like a 3.5V drop with 20mA through the LED, but don't trust me... Get the data sheets and find out for yourself. Since you have a variable power supply, you'll need to put a resistor in series with the LED so that you can measure the voltage drop across the resistor and, using Ohm's law, determine the current through the resistor. Then, since the resistor and LED will be in series, the current through the resistor will be the same as the current through the LED, so measuring the voltage drop across the series resistance will allow you to calculate that common current. For example, using a 100 ohm resistor will result in your setup looking like this: (View in Courier) +-------+ +-----+ | +|-----+------|+ | | | | | | | | [100R] | | | | | | | | | +------|- | | | |A +-----+ | | [LED] METER | | | | -|-----+ +-------+ SUPPLY Now, in order to determine when 20mA is in the resistor, invoke Ohm's law: E = IR = 0.02A * 100R = 2V So, crank up your supply until you read 2 volts across the resistor, and then you'll know that there's 20mA in both the resistor and the LED. Next, in order to determine the voltage dropped across the LED, leave the supply where it is and reconnect the voltmeter like this: +-------+ | +|-----+ | | | | | [100R] | | | +-----+ | | +------|+ | | | |A | | | | [LED] | | | | | | | | -|-----+------|- | +-------+ +-----+ SUPPLY METER VOILA! You now have all the information you need to plug into those online calculators. With just a little more effort you can blow off those online calculators and figure it all out for yourself. Interested? Couldnt have said it better myself.. |
#7
Posted to alt.electronics
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LED help
On Thu, 30 Aug 2007 19:12:03 -0500, Skenny
wrote: John Fields wrote: On Mon, 27 Aug 2007 11:33:06 -0700, "garlicman" None wrote: I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? --- Empirically. Download a few data sheets for common white LEDs and make a note of their typical forward voltage drops with nominal current through them. You'll probably find something like a 3.5V drop with 20mA through the LED, but don't trust me... Get the data sheets and find out for yourself. Since you have a variable power supply, you'll need to put a resistor in series with the LED so that you can measure the voltage drop across the resistor and, using Ohm's law, determine the current through the resistor. Then, since the resistor and LED will be in series, the current through the resistor will be the same as the current through the LED, so measuring the voltage drop across the series resistance will allow you to calculate that common current. For example, using a 100 ohm resistor will result in your setup looking like this: (View in Courier) +-------+ +-----+ | +|-----+------|+ | | | | | | | | [100R] | | | | | | | | | +------|- | | | |A +-----+ | | [LED] METER | | | | -|-----+ +-------+ SUPPLY Now, in order to determine when 20mA is in the resistor, invoke Ohm's law: E = IR = 0.02A * 100R = 2V So, crank up your supply until you read 2 volts across the resistor, and then you'll know that there's 20mA in both the resistor and the LED. Next, in order to determine the voltage dropped across the LED, leave the supply where it is and reconnect the voltmeter like this: +-------+ | +|-----+ | | | | | [100R] | | | +-----+ | | +------|+ | | | |A | | | | [LED] | | | | | | | | -|-----+------|- | +-------+ +-----+ SUPPLY METER VOILA! You now have all the information you need to plug into those online calculators. With just a little more effort you can blow off those online calculators and figure it all out for yourself. Interested? Couldnt have said it better myself.. --- Obviously. -- JF |
#8
Posted to alt.electronics
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LED help
John Fields wrote:
On Thu, 30 Aug 2007 19:12:03 -0500, Skenny wrote: John Fields wrote: On Mon, 27 Aug 2007 11:33:06 -0700, "garlicman" None wrote: I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? --- Empirically. Download a few data sheets for common white LEDs and make a note of their typical forward voltage drops with nominal current through them. You'll probably find something like a 3.5V drop with 20mA through the LED, but don't trust me... Get the data sheets and find out for yourself. Since you have a variable power supply, you'll need to put a resistor in series with the LED so that you can measure the voltage drop across the resistor and, using Ohm's law, determine the current through the resistor. Then, since the resistor and LED will be in series, the current through the resistor will be the same as the current through the LED, so measuring the voltage drop across the series resistance will allow you to calculate that common current. For example, using a 100 ohm resistor will result in your setup looking like this: (View in Courier) +-------+ +-----+ | +|-----+------|+ | | | | | | | | [100R] | | | | | | | | | +------|- | | | |A +-----+ | | [LED] METER | | | | -|-----+ +-------+ SUPPLY Now, in order to determine when 20mA is in the resistor, invoke Ohm's law: E = IR = 0.02A * 100R = 2V So, crank up your supply until you read 2 volts across the resistor, and then you'll know that there's 20mA in both the resistor and the LED. Next, in order to determine the voltage dropped across the LED, leave the supply where it is and reconnect the voltmeter like this: +-------+ | +|-----+ | | | | | [100R] | | | +-----+ | | +------|+ | | | |A | | | | [LED] | | | | | | | | -|-----+------|- | +-------+ +-----+ SUPPLY METER VOILA! You now have all the information you need to plug into those online calculators. With just a little more effort you can blow off those online calculators and figure it all out for yourself. Interested? Couldnt have said it better myself.. --- Obviously. But your ascii drawings really suck. |
#9
Posted to alt.electronics
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LED help
On Fri, 31 Aug 2007 07:58:03 -0500, Skenny
wrote: John Fields wrote: On Thu, 30 Aug 2007 19:12:03 -0500, Skenny wrote: John Fields wrote: On Mon, 27 Aug 2007 11:33:06 -0700, "garlicman" None wrote: I've got 8 or so white LEDs, but no specs on them. They look average size with no particular markings. I want to make a small light using a 12V power source. The online calculators I see ask for their voltage and current ratings. How do I determine these numbers? --- Empirically. Download a few data sheets for common white LEDs and make a note of their typical forward voltage drops with nominal current through them. You'll probably find something like a 3.5V drop with 20mA through the LED, but don't trust me... Get the data sheets and find out for yourself. Since you have a variable power supply, you'll need to put a resistor in series with the LED so that you can measure the voltage drop across the resistor and, using Ohm's law, determine the current through the resistor. Then, since the resistor and LED will be in series, the current through the resistor will be the same as the current through the LED, so measuring the voltage drop across the series resistance will allow you to calculate that common current. For example, using a 100 ohm resistor will result in your setup looking like this: (View in Courier) +-------+ +-----+ | +|-----+------|+ | | | | | | | | [100R] | | | | | | | | | +------|- | | | |A +-----+ | | [LED] METER | | | | -|-----+ +-------+ SUPPLY Now, in order to determine when 20mA is in the resistor, invoke Ohm's law: E = IR = 0.02A * 100R = 2V So, crank up your supply until you read 2 volts across the resistor, and then you'll know that there's 20mA in both the resistor and the LED. Next, in order to determine the voltage dropped across the LED, leave the supply where it is and reconnect the voltmeter like this: +-------+ | +|-----+ | | | | | [100R] | | | +-----+ | | +------|+ | | | |A | | | | [LED] | | | | | | | | -|-----+------|- | +-------+ +-----+ SUPPLY METER VOILA! You now have all the information you need to plug into those online calculators. With just a little more effort you can blow off those online calculators and figure it all out for yourself. Interested? Couldnt have said it better myself.. --- Obviously. But your ascii drawings really suck. --- Yup. Here are some particularly bad ones you can View in Courier: +V | IN OUT +------+ | | |K | O-+ O-+ [DIODE] [COIL]- -|-|- - - - - -| | | | O-- | | O-- | | +------+ | K1A | |K1B | +V | +------|-[A]--+ | | ___ +----+ C | | +-O O--+---|S Q|-------+------[1000]--B NPN | | | S1 | +-|R | | E | | | | | +----+ A--|---+ | | | | | +---------Y OR | | GND | | | | B--|-+ | | | | [10K] | | | +V | | | | | | | | | | | GND | | | +------+ | | | | | | |K | O-+ O-+ | | | | [DIODE] [COIL]- -|-|- - - - - -| | | | | | | | O-- | | O-- | | | | | | +------+ | K2A | |K2B | | | | | | +------|-[b]--+ | | ___ +----+ | | | C | | +--O O-+---|S Q|-------|-+-|--[1000]--B NPN | | | S2 | +-|R | | | | E | | | | | +----+ A--+ | | | | | | | +---------Y OR | | | GND | | | | B--|-|-+ | | | [10K] | | | +V | | | | | | | | | | | GND | | | +------+ | | | | | | |K | O-+ | | | | | [DIODE] [COIL]- -| | | | | | | | O-- | | | | | | +------+ | K3A | | | | | | +--------------------+ | ___ +----+ | | | C +--O O-+---|S Q|-------|-|-+--[1000]--B S3 | +-|R | | | E | | +----+ A--+ | | | +---------Y OR | GND | B----+ [10K] | GND VCC------+----+ | | V+ | [RT] | | | [10K] [R7] +----|-\ | | | | --+--180s +----|----|+/ | | V+ | | | [R6] | [10K] | +----|-\ | | | | --+--150s +----|----|+/ | | V+ | | | [R5] | [10K] | +----|-\ | | | | --+--120s +----|----|+/ | | V+ | | | [R4] | [10K] | +----|-\ | | | | --+--90s +----|----|+/ | | V+ | | | [R3] | [10K] | +----|-\ | | | | --+--60s +----|----|+/ | | V+ | | | [R2] | [10K] | +----|-\ | | | | --+--30s +----|----|+/ | | | +----D [R1] | G--+ | [CT] S | | | | | GND------+----+----+ | _ | R/T---------------------+ +12V---------+--------------+-----+-------+--------------+ | | | | | | | | | [510] [10K] [1M] | | |A | | | | [LED] | +--[10M]--+ |R2 | | |R1 | | [10K]---|-\ E [10K]-+-|+\ | | | -+-[10K]--B 2N3906 | | ----+-----|------|+/ | C IN--[100K]---|------|-/U1A | | U1B| |+ | | LM393 |+ | | [22µF] | | [10µF] | | |C2 | | | | | | | GND----------+--------------+-----+-------+---+----------+ Vcc | +-----+---+ U1A | | | +-------+ | | | |_ | +-[500K] +-O|R | | | | Vin-+------|------|T | | | | | | +------|RC | | | | | | [0.01µF] | | | | | | | +------|C | | | |_ _| | GND +-O|T Q|--+ | | +-------+ | | +-------------+-[0.1µF]---+----------------+ | | | | Vcc [10K] | | | | A--+ | +----+---+ GND +--Y U2A | | | | | B--+ | +-[500k]| U1B | | | | | +-------+ +--B | | | | |_ _| U2B Y--+--OUT | | +-O|R Q|----+ Vcc +--A | | |_ | | | | +------|------|T | [0.1µF] [0.1µF] | | | | | | | +------|RC | +---+ +---+ | | | | | | | | | [0.01µf] | | [10K] | | [1MR] | | | | | | | | Y +-----+------|C | GND | | GND U2D | | | | | A B GND +-O|T Q|--+ | +---A | | | +-------+ | | U2C Y-+---+ +-------------+ +------B +2V | Vcc [10.0K] | | [10K] +----|+\ | | | --+----+ x---+--[10K]--------|-/ | | | Vcc | +-------+ | [10.0K] | | 0V---|b | | | [10K] +--B | _ | +--[10k]--------|+\ | and Y-------|a/b y|---y | | | --+-------A | | | +----|-/ +----|a | | | | +-------+ | GND | S1 | | | | | +-------+ +-------+ | 1V--|1 | +----------------+ | | +------+ | 1-x²|--|1-x² sqrt(1-x²)|--+ +--|x x²|--|x² | +----------------+ +------+ +-------+ Vcc-+---------+-----+-------+-------------+----+-------+ | | | | | | | [10K] [10K] [1M] +---+---+ [10K][1M] +---+---+ | | | |_ Vcc | | | |_ Vcc | +-[0.1µF]-+-----|--O|T OUT|-[0.1µF]-+----|--O|T OUT|--+ | | | | | | | | +-----------+ +---|TH 7555| +---|TH 7555| | | | | |_ _| | |_ _| | | O | +--O|D R|O-+V +--O|D R|O-|-+V | O | +| | GND | | | GND | | | | [2µF] +---+---+ [0.1µF]+---+---+ | | | | | | | | GND-+-----------|---+-------+------------------+-------+ | | | | | +--A | | | Y----+ +------------------------------+ | +--B | | [0.1µF] | A B | +-----+ Y +V | | |A | | | [1M] [1N4148] | +-------+ | | | | |K | O--C +-----+-----+ A--+ [DIODE] [COIL]- - - -| | +--Y | | O- | | | B--+ +-------+ | | | | | +------NO | +--A | C | Y--+------[1000]--B NPN +------B E | GND Just makes ya wanna throw up, huh? -- JF |
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