I am doing a school play with some kids. So I got this idea with large hip hop chains, lighting them up with leds as I got access to about 350 LEDs. They all are yellow, and the specs are 2V and 0.02mA.
The idea came after I accidentally discovered how to light up leds, and managed to light up some leds in parallel here with a resistor between the V+ source and the first led in the array. Between the ground(- of battery) and the first led it's no resistor. This is based on a drawing I found on the net, and seem to correlate with info other places.
But, here I find a lot of different and new info. As I understand it, parallels with one single resistor is a NO NO. Also I found a link here, led.linear1.org/led.wiz, that puts the resistors between the ground and the leds, not between V+ and the leds. Does it not matter where one put the resistor in relation to the LEDs and V+?
So I am a bit confused now.. I have read several posts on this site, but still have a couple of questions.
Specs on the Duracell homepage says the battery(mn1500) here will last for more than one hour at 1.08A. 75 LEDs multiplied with 0.02A is 1.5A. 2 AA batteries can then deliver enough current?
Am I right, that IF I want to power up 75 LEDs in parallel with just one resistor, that resistor would have to lower the current fromn 5A to 1.5A?
3V supply - 2 volt / 1.5 A = 0,67 Ohm. This means I would have to use a 1 Ohm resistor, or is it never a point using 1 Ohm resistors with LEDs due to the variation in usage of current and volts from LED to LED? What is then the minmum of resistance one should use with LEDs?
I have tried to light up 18 LEDs in parallel with one 2,7 Ohm resistor(3v-2v/(0,02Ax18LEDs)=1/0,36=2,78 ohm). The resistor is placed next to the V+ source. The multimeter says the current is 90mA when measuring this circiuit near the ground. Near the V+, between the resistor and the + on the battery, it's about 115mA.
From my understadning, the resistor is lowering the volt, from the ground to the resistor, so we get a higher current from the resistor to the +V? It still puzzles me as it looks like the resistor adds more current from nowhere between the resistor and V+. I understand it as current comes from the ground(minus pole of battery).
Measuring current without LEDs, and only the resistor, display 470mA. If we subtract 470mA from the 100mA I got when measuring with LEDs, we got 370mA. This means the LEDs eat about 370 mA. This correlate with 20mA x 18 LEDs is 360mA. Or am I just doing cargo science now?
I am puzzled by the leftover of 100 mA. Is this normal, or does it mean I should add more resistors? I wonder if it's possible to just add resistors until measurements looks good, instead of relying on math alone.
The 2.7 ohm resistor gets hot after one minute or something, is this an indication something is wrong? The Voltage measurements also show 2,2V from ground to the resistor, that is more that the 2V each LED require. Is this normal?
To lower the 100mA current, I put another 47 ohm resistor in serie with the 2.7 resistor. Current is lowered to around 20mA and volt to 1.8V between the resistor and ground. Between the V+ and ground, it's 3V. This somehow makes sense if the resistor lowers the volt, while the volt of the battery still is there. The lights are weaker, but still strong enough for use on a dark stage. I realize that this is the setup for one LED connected to a 3 V source(3V-2V/0,02A=50 Ohm), still I am surprised how well this works with 18 LEDs, still I want them brighter if it's possible in a safe way.
I am trying to understand the concept that LEDs eat current. I have read "Electronics for dummies", but can't find an explaination there. So I hope those questions aren't too huge to answer here, and the leftover of 100mA puzzles me.
I understand the reasoning for one resistor for each led, as forward voltage vary from led to led, but is it a way I can get away with less than one resistor to each led? Will it work for 10 minuttes without harming LEDs and batteries?
A hip hop chain medallion can fit some 75 LEDs. Is it manageable to light them up with with 2 AA batteries? The area is a circle, measuring 30 centimeters in diameter, made up of hard paper, so LEDs will be easy to install through the paper, wiring it on the back, and adding a tree plate to cover the wiring and attach batteries to.
My idea now, is to perhaps use 4 AA batteries, and put 4 LEDs in serie, each of them connected to 17 or 18 LEDs in parallel. Four 2v LEDs in series requires 4 LEDS x 2V, in total 6V, something that four 1,5V AA batteries in series can provide. Then I am planing to use as few as possible resistors, balancing between stability and resources(money and installing 350 resistors is..). I am also thinking about sorting out similar LEDs to be paralleled. I found a good way to measure LEDs in a breadboard circuit, described here: http://www.allaboutcircuits.com/vol_3/chpt_3/2.html, as measuring LEDs with my 10$ meter don't work very well(meter display a number for a short time, before going blank, and the number vary).
Those LEDs won't be used for long on the stage, and will maybe be put into other more stable circuits for other purposes later, if they still work.
Or is there other better solutions?
The show only last for 5 minuttes or so, but it's imortant to not run risks of overheating or exploding anything here.
Sorry for unclear english, as english not is my native language, but hope this still is understandable!
The idea came after I accidentally discovered how to light up leds, and managed to light up some leds in parallel here with a resistor between the V+ source and the first led in the array. Between the ground(- of battery) and the first led it's no resistor. This is based on a drawing I found on the net, and seem to correlate with info other places.
But, here I find a lot of different and new info. As I understand it, parallels with one single resistor is a NO NO. Also I found a link here, led.linear1.org/led.wiz, that puts the resistors between the ground and the leds, not between V+ and the leds. Does it not matter where one put the resistor in relation to the LEDs and V+?
So I am a bit confused now.. I have read several posts on this site, but still have a couple of questions.
Specs on the Duracell homepage says the battery(mn1500) here will last for more than one hour at 1.08A. 75 LEDs multiplied with 0.02A is 1.5A. 2 AA batteries can then deliver enough current?
Am I right, that IF I want to power up 75 LEDs in parallel with just one resistor, that resistor would have to lower the current fromn 5A to 1.5A?
3V supply - 2 volt / 1.5 A = 0,67 Ohm. This means I would have to use a 1 Ohm resistor, or is it never a point using 1 Ohm resistors with LEDs due to the variation in usage of current and volts from LED to LED? What is then the minmum of resistance one should use with LEDs?
I have tried to light up 18 LEDs in parallel with one 2,7 Ohm resistor(3v-2v/(0,02Ax18LEDs)=1/0,36=2,78 ohm). The resistor is placed next to the V+ source. The multimeter says the current is 90mA when measuring this circiuit near the ground. Near the V+, between the resistor and the + on the battery, it's about 115mA.
From my understadning, the resistor is lowering the volt, from the ground to the resistor, so we get a higher current from the resistor to the +V? It still puzzles me as it looks like the resistor adds more current from nowhere between the resistor and V+. I understand it as current comes from the ground(minus pole of battery).
Measuring current without LEDs, and only the resistor, display 470mA. If we subtract 470mA from the 100mA I got when measuring with LEDs, we got 370mA. This means the LEDs eat about 370 mA. This correlate with 20mA x 18 LEDs is 360mA. Or am I just doing cargo science now?
I am puzzled by the leftover of 100 mA. Is this normal, or does it mean I should add more resistors? I wonder if it's possible to just add resistors until measurements looks good, instead of relying on math alone.
The 2.7 ohm resistor gets hot after one minute or something, is this an indication something is wrong? The Voltage measurements also show 2,2V from ground to the resistor, that is more that the 2V each LED require. Is this normal?
To lower the 100mA current, I put another 47 ohm resistor in serie with the 2.7 resistor. Current is lowered to around 20mA and volt to 1.8V between the resistor and ground. Between the V+ and ground, it's 3V. This somehow makes sense if the resistor lowers the volt, while the volt of the battery still is there. The lights are weaker, but still strong enough for use on a dark stage. I realize that this is the setup for one LED connected to a 3 V source(3V-2V/0,02A=50 Ohm), still I am surprised how well this works with 18 LEDs, still I want them brighter if it's possible in a safe way.
I am trying to understand the concept that LEDs eat current. I have read "Electronics for dummies", but can't find an explaination there. So I hope those questions aren't too huge to answer here, and the leftover of 100mA puzzles me.
I understand the reasoning for one resistor for each led, as forward voltage vary from led to led, but is it a way I can get away with less than one resistor to each led? Will it work for 10 minuttes without harming LEDs and batteries?
A hip hop chain medallion can fit some 75 LEDs. Is it manageable to light them up with with 2 AA batteries? The area is a circle, measuring 30 centimeters in diameter, made up of hard paper, so LEDs will be easy to install through the paper, wiring it on the back, and adding a tree plate to cover the wiring and attach batteries to.
My idea now, is to perhaps use 4 AA batteries, and put 4 LEDs in serie, each of them connected to 17 or 18 LEDs in parallel. Four 2v LEDs in series requires 4 LEDS x 2V, in total 6V, something that four 1,5V AA batteries in series can provide. Then I am planing to use as few as possible resistors, balancing between stability and resources(money and installing 350 resistors is..). I am also thinking about sorting out similar LEDs to be paralleled. I found a good way to measure LEDs in a breadboard circuit, described here: http://www.allaboutcircuits.com/vol_3/chpt_3/2.html, as measuring LEDs with my 10$ meter don't work very well(meter display a number for a short time, before going blank, and the number vary).
Those LEDs won't be used for long on the stage, and will maybe be put into other more stable circuits for other purposes later, if they still work.
Or is there other better solutions?
The show only last for 5 minuttes or so, but it's imortant to not run risks of overheating or exploding anything here.
Sorry for unclear english, as english not is my native language, but hope this still is understandable!
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