Partlist Wednesday: Lithium-polymer battery charger chips

in partlist by DP | 5 comments

Lithium-polymer batteries are an excellent choice for portable projects. They are relatively cheap, hold a significant charge, and last for a long time. The drawback with these batteries is that they require rather complicated charging protocols. You have to watch out for overcharging, undercharging, overheating, etc…

We are looking for a standard part to use in our projects, so we decided to do a roundup of open source lithium polymer chargers from SparkFun, Seeed Studio, and Adafruit. With the exception of Seeed, all the chargers are based on Microchip’s MCP738xx family of battery management ICs that come in SSOP and DFN packages. They handle all the charging algorithms and usually only require a single external capacitor.

Lithium Polymer USB Charger and Battery from SparkFun is a basic charger designed around the MCP73831 IC. A solder jumper changes the charge current from 100mA to 500mA. LiPoly Fast Charger, also from SparkFun, supports currents up to 1A. This design uses the MCP73843 IC driving an external mosfet that handles higher current. 

Seeed is up next with their Li-Po rider and Li-Po rider pro charger/power supplies. They are based on the CN3065 battery management IC. The charge current is 400mA when a powerful enough source is available. One thing to note is that Li-Po riders are not chargers but compact portable power supplies that deliver 5V at 350mA. Battery voltage is converted to 5V through a switching step up converter. The pro version delivers up to 1A of current. 

Adafruit’s USB/DC Lithium Polymer battery charger uses the MCP73861 IC. A charging current of up to 1.2A can be selected through a resistor. This IC has thermal protection. A standard 10K thermistor can be added to the battery to shut down charging in case of overheating. Their USB LiIon/LiPoly charger uses the MCP73833 IC, and is similar to the previus product. This one doesn’t have the DC IN jack populated, and the maximum current is 1A.

After looking at what everyone is using we are going to add the MCP73833 to our part box. It is cheap, has programmable current, and thermal protection through a thermistor. We also liked Seeed’s use of a dc/dc converter for portable projects.

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Comments

  1. Techmonkey says:

    What about multiple cells? I have a couple projects that need higher voltages and finding an open source LiPo charger with cell balancing is pretty much non-existent.

  2. Sjaak says:

    how about using a larger capacity lipo cell and a stepup convertor?

  3. Techmonkey says:

    Won’t work, I need to be able to dump 20-40 Amps. Step up convertors sacrifice current for voltage. I could use commercial hobby chargers, but I would like to incorporate the charger into my unit and the hobby ones need too much set-up since they work with a large range of batteries. I just want to plug in and forget.

  4. ScottD says:

    Elektor magazine had an article in the June 2010 issue which covered a LiPo autobalancing circuit (http://www.elektor.com/magazines/2010/june/lipo-auto-balancer.1352168.lynkx). That might provide a starting point for a multiple cell charger project.

  5. Warren Harding says:

    I have a G6 chemistry Li-Po (3S 7.7 Amp-Hr) that can allegedly charge at over 50 amps! I’ve charged it at 40 amps a few times now and the battery doesn’t even get detectably warm. My setup uses a relay connected to a 40 amp, 13.8 Volt bench supply that sags to whatever voltage the battery is at during the charge through current limiting built into the supply I imagine. But it gets to the 12.60 volt limit at 40 amps before it’s fully charged so it’s maybe 80% charged when the relay opens. So I’m building a linear voltage regulator to take over from that point and finish it off.
    The charging industry doesn’t seem to be keeping up with the battery advances.
    Happy to help anyone to make their own. It’s not rocket science.

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