Powering the Arduino With 2 3.7 Li-Ion Batteries?

Hello! I've just begun using the Arduino Uno and I have a question about powering it other than when it's plugged into the computer. Mine came with a 9v Battery socket that plugs into the power insert on the Arduino and I had a few questions. These might be ridiculously easy, but I am a complete beginner when it comes to circuit boards and such .

If I was to wire two 9v batteries in parallel and then connect them to the Arduino, would it cause the Arduino to break? I know that wiring the two batteries in parallel will keep the same voltage, and add the mAh hours of the two batteries, but I don't know if this would some how do something detrimental to the board.

My second question is, what input does the Arduino take exactly? I know that USB ports on the computer only output 5v and that works fine, but a 9v battery will output 9v. I have two of these batteries:

http://www.batteryspace.com/polymerli-ioncell37v5000mah896474-2c185wh10arateullisted.aspx

Along with a protection circuit and charger for them, would these be a feasible power source for my Arduino in a project I am doing? The project consists of using many digitalWrite statements to turn on around 10 individual sets of lights with some having 5 or 6 LEDs to one pin.

Ask me for any additional information I may need to give you! Thank you for your time!

The Arduino board will not get damaged with two 9V batteries parallel, but the batteries will ! The stronger battery will try to charge the weaker battery, causing heat, leak and more.

The Arduino Uno takes 7 to 12V. The best voltage is 7.5V (for less heat by the voltage regulator).

It is safer to use RC battery packs. Li-ion cells have to be handled with care, although the protection circuit should protect the Li-ion cell. I don't know if you are up to the task to use Li-ion cells.

One Arduino pin can not drive 6 leds, a pin can drive just one led.

If 7.5v is the best range to be near, the two batteries Li-Ion should be great considering they'll be 7.4v wired in series right?

Also, with what you said about the LEDs, I'm not trying to separately control 6 LEDs with one pin, I have 6 3.3v LEDs wired parallel to one pin. I'm not sure if that's what you thought I meant, but the Arduino powered the 6 LEDs fine from one pin as far as I could see.

Thank you!

A Li-ion batter is 3.0 to 4.2V, you can use them in series as long as they both have their own protection circuit.

I mean the current by one pin. Normally the Arduino can supply 20mA with an output pin. That is just one normal led.
When you connect 6 leds (with resistors) parallel, the Arduino gives the maxium of 40mA, and each led gets 40mA/6 = 6.7mA.
Sure they will light up with 6.7mA, but it is dim and the Arduino gets damaged.

Oh, I didn't know that. I guess that's why I'm on the forum :astonished:. How would I go about powering the LEDs then? Right now I have 8 sets of 6 White 5mm 3.3v LEDs wired in parallel with one set to one pin. How would I go about changing this setup to where I still have the same functionality? This was the previous code I was using in case it's any help.

const int led1 = 9;
const int led2 = 2;
const int led3 = 3;
const int led4 = 4;
const int led5 = 5;
const int led6 = 6;
const int led7 = 7;
const int led8 = 8;

int count = 0;
int blinkcount = 0;
int barcount = -1;

int interval = 70;
int extrablinking = 180;
int divisor = 2;

void setup() {
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
  pinMode(led4, OUTPUT);
  pinMode(led5, OUTPUT);
  pinMode(led6, OUTPUT);
  pinMode(led7, OUTPUT);
  pinMode(led8, OUTPUT);
  pinMode(led9, OUTPUT);
  pinMode(led10, OUTPUT);
  pinMode(led11, OUTPUT);
  pinMode(led12, OUTPUT);
}

void loop() {
  
  barcount = -barcount;
  count = (count + 1);
  
  if (count == 1) {
   digitalWrite(led1, HIGH);
   delay(interval);
   
 }
    
    if (count == 2) {
   digitalWrite(led2, HIGH);
   delay(interval);
    }
    
    if (count == 3) {
   digitalWrite(led3, HIGH);
   delay(interval);
    }
    
    if (count == 4) {
   digitalWrite(led4, HIGH);
   delay(interval);
    }
    
    if (count == 5) {
   digitalWrite(led1, LOW);
   digitalWrite(led5, HIGH);
   delay(interval);
    }
    
    if (count == 6) {
   digitalWrite(led2, LOW);
   digitalWrite(led6, HIGH);
   delay(interval);
    }
    
    if (count == 7) {
   digitalWrite(led3, LOW);
   digitalWrite(led7, HIGH);
   delay(interval);
    }
    
    if (count == 8) {
   digitalWrite(led4, LOW);
   digitalWrite(led8, HIGH);
   delay(interval);
    }
    
    if (count == 9) {

   digitalWrite(led5, LOW);
   delay(interval);
    }
    
    if (count == 10) {
   digitalWrite(led6, LOW);
   delay(interval);
    }
    
    if (count == 11) {
   digitalWrite(led7, LOW);
   delay(interval);
    }
    
    if (count == 12) {
   digitalWrite(led8, LOW);
   delay(interval + 400);
   count = 0;
   blinkcount = (blinkcount + 1);
    }
  
    if (blinkcount == 4) {
      digitalWrite(led1, HIGH);
      digitalWrite(led2, HIGH);
      digitalWrite(led3, HIGH);
      digitalWrite(led4, HIGH);
      digitalWrite(led5, HIGH);
      digitalWrite(led6, HIGH);
      digitalWrite(led7, HIGH);
      digitalWrite(led8, HIGH);
      delay(interval + extrablinking);
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      digitalWrite(led3, LOW);
      digitalWrite(led4, LOW);
      digitalWrite(led5, LOW);
      digitalWrite(led6, LOW);
      digitalWrite(led7, LOW);
      digitalWrite(led8, LOW);
      delay(interval + extrablinking);
      digitalWrite(led1, HIGH);
      digitalWrite(led2, HIGH);
      digitalWrite(led3, HIGH);
      digitalWrite(led4, HIGH);
      digitalWrite(led5, HIGH);
      digitalWrite(led6, HIGH);
      digitalWrite(led7, HIGH);
      digitalWrite(led8, HIGH);
      delay(interval + extrablinking);
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      digitalWrite(led3, LOW);
      digitalWrite(led4, LOW);
      digitalWrite(led5, LOW);
      digitalWrite(led6, LOW);
      digitalWrite(led7, LOW);
      digitalWrite(led8, LOW);
      delay(interval + extrablinking);
      digitalWrite(led1, HIGH);
      digitalWrite(led2, HIGH);
      digitalWrite(led3, HIGH);
      digitalWrite(led4, HIGH);
      digitalWrite(led5, HIGH);
      digitalWrite(led6, HIGH);
      digitalWrite(led7, HIGH);
      digitalWrite(led8, HIGH);
      delay(interval + extrablinking);
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      digitalWrite(led3, LOW);
      digitalWrite(led4, LOW);
      digitalWrite(led5, LOW);
      digitalWrite(led6, LOW);
      digitalWrite(led7, LOW);
      digitalWrite(led8, LOW);
      delay(interval + extrablinking);
      digitalWrite(led1, HIGH);
      digitalWrite(led2, HIGH);
      digitalWrite(led3, HIGH);
      digitalWrite(led4, HIGH);
      digitalWrite(led5, HIGH);
      digitalWrite(led6, HIGH);
      digitalWrite(led7, HIGH);
      digitalWrite(led8, HIGH);
      delay(interval + extrablinking);
      digitalWrite(led1, LOW);
      digitalWrite(led2, LOW);
      digitalWrite(led3, LOW);
      digitalWrite(led4, LOW);
      digitalWrite(led5, LOW);
      digitalWrite(led6, LOW);
      digitalWrite(led7, LOW);
      digitalWrite(led8, LOW);
      delay(interval + extrablinking + 300);
      blinkcount = 0;
    }
      
      
}

Also in regards to the two 3.7v batteries, I thought you only needed one protection circuit. The reason I had believed this was from this post I had read a few months back. http://forums.benheck.com/viewtopic.php?f=43&t=34576

8 sets of 6 leds with 20mA = 1A. The 5V voltage regulator of the Arduino can only supply 100mA or 200mA.

To drive those leds, you can use transistors, mosfets, high current shift registers, specific led driver chips, and so on.

To use more than one Li-ion cell in series, you have to be very very careful. They could explode or catch fire. You have to be sure that they are equally drained and charged in way that a weaker/slower cell is also fully charged.

Thanks! I'll look into the transistor method. Since powering these batteries I have is dangerous, are there any other suggestions for power that I might want to try that won't explode?

Use ONE battery and something like this: http://www.pololu.com/product/2562

So just to clarify, I can use one of my 3.7v Li-Poly Rechargeable batteries with a protection circuit, and then use this 5v Step-Up and there won't be a chance of it being dangerous? Or do you mean to use a completely different battery than what I have along with the Step-Up.

A single Li-ion cell with a pcb (protection circuit board) and the step-up converter should be safe. If you have a protection circuit like the one I have, it protects against over-voltage, under-voltage and shortcut.

MAXOFLIFE: So just to clarify, I can use one of my 3.7v Li-Poly Rechargeable batteries with a protection circuit, and then use this 5v Step-Up and there won't be a chance of it being dangerous? Or do you mean to use a completely different battery than what I have along with the Step-Up.

There's two jobs: a) Use a battery safely (make it last a long time, prevent it from catching fire) b) Power the Arduino

The step-up solves (b)