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Author Topic: Cheap Lithium ion/LiPo charge & protect ciruits?  (Read 1150 times)
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I am looking for a simple and cheap way of adding a single 3.7volt Lipo battery to my project. I am running my own custom board @3.3v 

Currently I just buy cheap solar batteries for about $5 which come with solar cell, LiPo battery, USB charging and battery protection circuit. 

I am now wanting to design and integrate something directly onto my PCB. I am thinking about using a MCP73831 to handle the charging side but not sure about the protection side for the battery. Currently I have my board check the voltage via software then if the voltage is below 3.3volts it just keep going to sleep (stills consumes 0.1mAh).   
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Perhaps this will help!

http://www.eevblog.com/2011/06/09/eevblog-176-lithium-ionpolymer-battery-charging-tutorial/
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I like the MAX1811.  Only needs a couple of Rs & Cs to set up for LiPo battery charging.
http://www.maxim-ic.com/datasheet/index.mvp/id/2536
I use it to charge a 1000mAH LiPo in a remote control, charges the battery from a 5V source, such as USB port.
Goes a month+ between having to plug it in.

What are you thinking to have happenfor protection?
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Can you have the main controller have its own vcc? A simple logic level mosfet with a low rds and low gate threshold would work fine to cut off power to everything else, and be energy effecient since its voltage triggered, all you would need is the controller chip to have its own vcc so it doesn't turn itself off
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CrossRoads, The protection is the part I am having issues with, I was thinking about just buying cheap phones batteries maybe as they already have the protection circuit.

winner10920, not a bad idea but as the MCU is what is using the power and is what I need to protect the battery from I might make it cut power to every thing until reconnected to a charger.

For a little background you can find a little info of my PCBs here http://gr0b.blogspot.com.au/
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Well I guess you can just find a low voltage comparator to trigger the mosfet off when its below the threshold, you'll just need a 3.3v reference that's also low power
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Or something like this
http://www.sii-ic.com/en/product1.jsp?subcatID=5&productID=50585
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I'm a huge fan of the max1551 or the max1555.  Virtually the same thing except for when one pin gets pulled low.
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Prebuilt boards: http://www.all-battery.com/protectivepcbsforli-ionandli-polymerbatterypacks.aspx
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Damn! Hard to improve on that.
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You should try on of these:

http://www.sparkfun.com/products/11231

If you  want to integrate it to your board you can use the schematic and eagle files at the bottom of the page.

The TPS61200 (~$3 at digikey) can replace your regulator, provide battery protection and provide a consistent voltage (3.3 or 5v) to your board right through the voltage range of the LiPo (e.g. 2.6 - 4.2 volts).


P.S. If you are running out of I/O have you though of the ATmega32u4 chip? (Arduino Leonardo) or a quantum leap to the Atmega2560?
The AtMega32u4 also has built in USB so you would not have to use V-USB.  The Atmega2560 would use less power than using two Atmega328s yet provide you with many more pins.  The extra memory would allow you to use better networking (e.g. the excellent open source RFM22b meshing library at http://www.open.com.au/mikem/arduino/RF22/) if you were prepared to switch transceiver to the RFM22 ($4.50 from Hope).
It is a bit powerful but is highly configurable to save power.
« Last Edit: July 06, 2012, 07:09:44 pm by lemming » Logged

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Wow those $1 boards are great!
if you want to build your own, you could look at the suggested chips although you can't really beat those prices for the same thing.
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Thanks Chagrin, The $0.99 board are some of the ones I tested but I was getting then for about $3 each (includes shipping) I was also told that they handle charging to but I have to supply 4.2volts.
I wanted to copy it to my PCB but most of the parts are unlabeled and for about the same price I could get a cheap phone battery that includes the LiPo and the circuit. (not too trusting if they really supported charging like the sell said as it did not say anything about in in the spec sheet)

Thanks lemming, I might look into the TPS61200 to replace the AMS1117 but with a price jump to $3 from $0.30 I will need to look into the cost benefit (wanting to keep the boards as cheap as possible while not sacrificing quality)
I also might look into the ATmega16/32U4 chips as I am having a few issues with v-usb under windows, But this is because I don't want to use USB-LIB or unsigned drivers just vanilla HID and default drivers. Not sure if changing chip will help me.
I did also look ate the Atmega2560 but is a lot bigger in PCB side/pin count/cost and with me being newish to SMD soldering I was trying to avoid parts that are complex to work with or too expensive (expected soldering f##kups but have made about 20+ boards so far without a single issue)
As for changing the radios I get the nRF24L01 for less then $2 and have found then easy to work with, I also found they suck less power then the RFM22b. I was thinking about adding both radios (nRF24L01+RFM22b) to some boards in later versions to allow me to communicate other off the shelf hardware.   
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