# Rechargeable Li-Po cell phone battery with 2 terminal wires

Let's say I buy a rechargeable Li-Po cell phone battery with 2 terminal wires. How would I charge this battery without having the cell phone or docking station? How do I know what size battery to use for my project? :)

The battery size would depend on the voltage and current required by the project. A single cell LiPo is about 4.2 volts fully charged with manny different current capacity batteries available. LiPO batteries can be dangerous if mishandled. Here is a link that will provide you with a ton of info about LiPo batteries. If you are new to the LiPo technology I highly recommend that you read it. https://sites.google.com/site/tjinguytech/charging-how-tos

And here is a link to a vendor that has all the different types of batteries that you will ever need. http://www.hobbyking.com/hobbyking/store/__86__85__LiPo_LiFe_NiMH_Battery-Li_Poly_All_brands_.html

The higher cell count, higher capacity batteries can get expensive so be prepared for some sticker shock.

RWW

RWW

1. You could include a charging circuit in your design. www.maxim-ic.com makes a nice chip called MAX1811 that works nice & needs few components.
2. Do some math - how much current do you want to supply for how long? A 1000mAH LiPo will run a 8MHz Promini for quite a while if you power it using the Vcc pin ( bypassing the regulator which is fed from the RAW pin). If you're controlling a bunch of LEDs all drawing 20mA and the uC drawing about 15mA itself, you can do some math, divide 1000/(total current consumed) and that's about how many hours you can expect.

I have a Vin pin next to the 2 GND pins. I read that Vin is routed to the voltage regulator and converted down to 5V. What your saying is just the opposite, as it bypasses the voltage regulator. I'm terrible confused on your math. How would I connect a cell phone battery to the arduino and breadboard physically?

Battery has two little wires coming out, yes? Solder those 2 wire to two pins that you can plug into your breadboard. I have lots of male breakaway headers around, I personally would use two pins from those.

I can’t tell from this thread which Arduino you have. If you have a 3.3V 8MHz Promini for instance, which will run nicely on a cell phone battery, you connect the battery to the Vcc/GND pin.

The math - it was just an example.
Say you had a 1000mAH LiPo battery.
And say you were powering 4 LEDs full on, at 20mA each. They will be consuming 100mA while on. The Promini will be consuming lets say 20mA. So while running, you are drawing 100mA.
So your battery with 1000mAH capacity could theoretically support a 100mA load for 10 hours. 1000mAH/100mA = 10 Hours.

Ok, I'm using the Arduino Uno which has the Vin pin and that goes thru the voltage regulator. I have no Vcc pin. I do understand the math. thanks.

Uno is set to run from >=3.8V for 16 MHz operation. You'd have to connect LiPo battery to the USB input connector so you're not losing voltage across the regulator. If you had 2 cells in series to make >7.4V then you could connect to the barrel jack connector, or to Vin on the power header.

Battery has two little wires coming out, yes? Solder those 2 wire to two pins that you can plug into your breadboard. I have lots of male breakaway headers around, I personally would use two pins from those.
40-pin 1-row 0.1” PCB Male Gold Square Header - dipmicro electronics

I can’t tell from this thread which Arduino you have. If you have a 3.3V 8MHz Promini for instance, which will run nicely on a cell phone battery, you connect the battery to the Vcc/GND pin.

The math - it was just an example.
Say you had a 1000mAH LiPo battery.
And say you were powering 4 LEDs full on, at 20mA each. They will be consuming 100mA while on. The Promini will be consuming lets say 20mA. So while running, you are drawing 100mA.
So your battery with 1000mAH capacity could theoretically support a 100mA load for 10 hours. 1000mAH/100mA = 10 Hours.

How do you come up with 100mA? I see 20mA x 4 = 80mA. I understand the 20mA as the max to draw from any output pin continuously.

"The Promini will be consuming lets say 20mA. "

Don't forget the Arduino itself draws some current. How much depends on the sketch, how busy it is.

CrossRoads: Uno is set to run from >=3.8V for 16 MHz operation. You'd have to connect LiPo battery to the USB input connector so you're not losing voltage across the regulator. If you had 2 cells in series to make >7.4V then you could connect to the barrel jack connector, or to Vin on the power header.

So if using the USB input connector I need a power supply of >=3.8V. For a voltage that low would I be able to draw 5V from the 5V pin? I'm under the impression the answer is no. How would I be losing voltage across the regulator? How do you connect a 2 wire LiPo battery to the USB input connector?

https://www.sparkfun.com/products/10711

Simple shield you connect a LiPo to. It deals with the charging, and the converting of the voltage to 5V.

I would BE VERY VERY careful about connecting either +5V or > +7.5V to the “Raw” pin as there is NO REVERSE protection on EITHER of those two pins.

Bob

CrossRoads: "The Promini will be consuming lets say 20mA. "

Don't forget the Arduino itself draws some current. How much depends on the sketch, how busy it is.

What? That can't be correct? The arduino board's draw should be pretty constant no matter what sketch is running as the AVR is running flat out at 16 mhz no matter what instructions it's running, only the pin 13 led might be considered a 'variable load if being controlled on and off by the sketch. I think only the load on output pins would change the boards Vcc draw plus any current being drawn from the 5V pin.

Lefty

Sure, current varies with how much is being switched, that's the beauty of CMOS. Put it into the various phases of sleep mode, turn off ADC, etc, save some current.

For this discussion of current load & driving LEDs, & battery life, just pick a number & go with it.

CrossRoads: Sure, current varies with how much is being switched, that's the beauty of CMOS. Put it into the various phases of sleep mode, turn off ADC, etc, save some current.

Well yea, but the arduino platform doesn't directly support sleep modes and turning off ADC, etc, that would require user written or 3rd party library functions to be included into a sketch, not a typical arduino users requirement. The AVR is simply clocking away at 16mhz at all times, so the board's steady current consumption (independent of external loads wired to the board and use of pin 13 led) is going to be pretty constant in my opinion, regardless of the sketches contents or 'how busy it is', because it's always busy at 16 Mhz. Perhaps active serial communications might add a ma or 2 but I would think the steady on-board consumption of around 70-80 millis (or whatever it is) could be considered a constant value. Again I'm just responding to your specific statement:

Don't forget the Arduino itself draws some current. How much depends on the sketch, how busy it is.

Where I don't feel the sketch contents or 'how busy' the board is has an effect on board overhead current consumption, but rather that it can be considered a fixed constant value. Lefty

For this discussion of current load & driving LEDs, & battery life, just pick a number & go with it.

ok good discussion! XD

retrolefty:

Don't forget the Arduino itself draws some current. How much depends on the sketch, how busy it is.

Where I don't feel the sketch contents or 'how busy' the board is has an effect on board overhead current consumption, but rather that it can be considered a fixed constant value. Lefty

For this discussion of current load & driving LEDs, & battery life, just pick a number & go with it.

[/quote] I beg to differ.

Doing different things will require the execution of different instructions. Different instructions will activate different combinations of gates. Different combinations of gates consume different amounts of power.

For example, on the Arduino UNO, measuring the Vin current while running different sketches:

BareMinimum (from Examples) consumes 52.8mA

Performing a repeated floating point multiplication (b = b * 1.34897289346) consumes 55.0mA

Toggling an IO pin at full speed (with nothing drawing current from that pin) consumes 54.5mA

So while it's not massive differences, there are differences. I am sure there are other things you can do with a sketch that will increase the power consumption more, such as writing to EEPROM, etc. Not to mention using external peripherals like the USB interface.

majenko:

retrolefty:

Don't forget the Arduino itself draws some current. How much depends on the sketch, how busy it is.

Where I don't feel the sketch contents or 'how busy' the board is has an effect on board overhead current consumption, but rather that it can be considered a fixed constant value. Lefty

For this discussion of current load & driving LEDs, & battery life, just pick a number & go with it.

I beg to differ.

Doing different things will require the execution of different instructions. Different instructions will activate different combinations of gates. Different combinations of gates consume different amounts of power.

For example, on the Arduino UNO, measuring the Vin current while running different sketches:

BareMinimum (from Examples) consumes 52.8mA

Performing a repeated floating point multiplication (b = b * 1.34897289346) consumes 55.0mA

Toggling an IO pin at full speed (with nothing drawing current from that pin) consumes 54.5mA

So while it's not massive differences, there are differences. I am sure there are other things you can do with a sketch that will increase the power consumption more, such as writing to EEPROM, etc. Not to mention using external peripherals like the USB interface.

So for the purpose of planning a 'power budget' and selecting a properly sized power supply for a Uno based project I will standby the concept that the board's 'overhead' current consumption can be considered a constant value (whatever it is) regardless of the sketch code content and this fixed constant should be added to the worst case external circuit current requirements plus a little more for 'headroom' as good engineering practice would include. Your test results just help support my opinion that sketch content is inconsequential in such an analysis. Lefty

retrolefty: So for the purpose of planning a 'power budget' and selecting a properly sized power supply for a Uno based project I will standby the concept that the board's 'overhead' current consumption can be considered a constant value (whatever it is) regardless of the sketch code content and this fixed constant should be added to the worst case external circuit current requirements plus a little more for 'headroom' as good engineering practice would include. Your test results just help support my opinion. Lefty

For selecting a generic power supply that is meaty enough, yes, it can be a ballpark figure.

However, when you're calorie counting for a battery powered system, every milliamp counts - especially when the variation could be as much as 10% or so. It soon becomes significant.

majenko:

retrolefty: So for the purpose of planning a 'power budget' and selecting a properly sized power supply for a Uno based project I will standby the concept that the board's 'overhead' current consumption can be considered a constant value (whatever it is) regardless of the sketch code content and this fixed constant should be added to the worst case external circuit current requirements plus a little more for 'headroom' as good engineering practice would include. Your test results just help support my opinion. Lefty

For selecting a generic power supply that is meaty enough, yes, it can be a ballpark figure.

However, when you're calorie counting for a battery powered system, every milliamp counts - especially when the variation could be as much as 10% or so. It soon becomes significant.

I have no issue with that statement. I would ask however in your above case would you be extra careful on trying to avoiding certain sketch code functions so as to try and minimize current consumption? That sounds like quite a extra effort to take on.

Lefty