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Author Topic: Rechargeable Li-Po cell phone battery with 2 terminal wires  (Read 2160 times)
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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?  smiley
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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

Here is another link to a thread about LiPo batteries on a RC helicopter forum.  Lots of info here as well.  http://www.helifreak.com/showthread.php?t=336421

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

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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.
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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?
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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.
http://www.dipmicro.com/store/HEADS40G

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.


* battery_hand.jpg (125.94 KB, 912x515 - viewed 23 times.)
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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.
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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.
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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.
http://www.dipmicro.com/store/HEADS40G

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.
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"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.
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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?
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The simplest answer to your query:

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.
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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
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"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
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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.
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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:

Quote
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.
« Last Edit: November 12, 2012, 02:41:23 pm by retrolefty » Logged

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