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3.6v 250mAh Ni-MH battery to run 10 5mm LEDs?

I would like to use a rechargeable 3.6v 250mAh Ni-MH battery to directly power 10 5mm LEDs, is that too much mAh?

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No, "mAh" is a matter of how long the LEDs will stay lit.

3.6V isn't really enough to run blue or white LEDs

What colour are these LEDs ?

Don't white LEDs have a drop voltage of around 3.3V? as little as 3V directly across the ELD is enough to (dimly) light my white and blue LEDs.

Yes, but allowing for protection resistors, you won't have the headroom to drive enough current to run them at their rating. If you try it, in a really dark room, you may even find your voltmeter on Ohms will run them.

Well I mean forgetting the protection resistors entirely. At 3V and less, I have not had any need for series resistors. The 3mm white LEDs I have will work with 3V in parallel just fine as an indicator light, even though it is not good practice to power LEDs with a low impedance source. For simple applications, I have not had any issues.

(though a fully charged 3S NiMh battery would be at a maximum of 4.2V, and a protection resistor will absolutely be nessesary.)

True, but the LEDs are barely working - the diode equation in action...

The "working on 3v" trick is used with the "LED throwies" idea.

lifeofB (author)  steveastrouk2 years ago

Sorry, forgot to mention they're white. I have tried a 3v coin battery with 10 yellow, but I would like to run 10 white. It's for a Star Wars Y-Wing. I want a battery that will last a long time between charges and will fit in a 100x25x20mm hole.

I'd use one LED and fibre optics to light the model, if it were me.

You can get white LED's that run on 3.2V but even those won't stay on full brightness for long as the battery goes below that value.
Best option IMHO would be to use special low voltage LED's like this one:

http://www.rapidonline.com/electronic-components/5...

Add a suitable resisotr to each LED and they should run quite long on your tiny battery.

Sorry for the typo, should of course read "suitable resistor to" ...

lifeofB (author) 2 years ago

The model I'm building calls for 13 LED's and fiber optics running from about 6 more LED's. I have managed to get them all running on one arduino and breadboard, I just hope I don't burn the house down, this being my first ever project.

The arduino will run on a mains adapter and has a pot for flashing speed, a pot for brightness, and an on/off switch.

After lots of trial an error and a lot of luck I have the other LED's acting just as I want. But I am having trouble getting 11 and 12 to stop flashing, any ideas?

int sensorValue = 0; //make a variable where you can store incoming
//analog values

void setup(){
pinMode(12, OUTPUT); //tell arduino what you'll be using these pins
pinMode(11, OUTPUT); // for (output).
pinMode(10, OUTPUT);
pinMode(9, OUTPUT);
pinMode(8, OUTPUT);
pinMode(7, OUTPUT);
pinMode(6, OUTPUT);
pinMode(5, OUTPUT);
pinMode(4, OUTPUT);


Serial.begin(9600); //initialize serial
}

void loop(){ //we put the code we want executed in a loop

Serial.print("sensor = " ); //sends what's in quotes via serial
Serial.println(sensorValue); //sends our variable (sensorValue)
//via serial




digitalWrite(12,HIGH); // lights the led
digitalWrite(11,HIGH);
digitalWrite(8,HIGH);


digitalWrite(4, HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(4, LOW);
delay(15);

digitalWrite(6, HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(6, LOW);
delay(15);

digitalWrite(5, HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(5, LOW);
delay(15);

digitalWrite(7, HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(7, LOW);
delay(15);


digitalWrite(5, HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(5, LOW);
delay(15);

digitalWrite(10,HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(10,LOW);
delay(15);

digitalWrite(9,HIGH);
sensorValue = analogRead(0);
delay(sensorValue + 25);
digitalWrite(9,LOW);
delay(15);


}

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-max-2 years ago

To know how long your LED will run, we need to know how much power they will be taking. Are you powering them dimly at a few microamps, or pushing the full 30mA or more into them? You can probably make them light up all day and night if it is draws very little current.

-max-2 years ago

mAH is actually a rating of charge, and it is one of the factors (the other one being nominal voltage) you need to figure out WH. Just multiply 2 to get WH, which is capacity, or how much energy can be stored.

For reference: 1 Watt-Hour can deliver power for 1 Watt for one hour. Likewise, 2WH can deliver 4 watts for half an hour, 2 watts for an hour, or 1 watt for 2 hours, etc. The 2 just multiply together. You can never have too much!!!