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Li polymer Battery Recharger- Please help!

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Hi

I have built a Li Polymer recharger for one cell successfully using the MAX1555 part.

Now I need to build a 2 cell recharger. The easiest for me would be to use 2 MAX1555 parts and recharge the batteries simultaneously--with the circuits being separate. However to build a circuit with a common point (where the two batteries are connected in series) and the same input V source is baffling me.

Can someone please help me?

Thank you in advance
a.
 
You cannot connect batteries in series with this IC its designed for only to one battery at a time. You place both these circuits separate then charge the two batteries from each IC.GND is the common.powering from a USB is not a good idea for two circuits.
But
When its charging from USB the charging current set to closer 100mA.
When its powered from a DC source the charging current set to 280mA.
 
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I don't know much about LiPo charging circuits, but that's because I decided they were too dangerous to mess around with and just bought my own charger. But I'll say a few things.

Unlike, NiCds and NiMH, Lithium-based cells (like Li-Ion and Lipo) are very sensitive. If you have a multi-cell pack, you have to monitor each cell individually to make sure the pack does not become unbalaned and that no cell gets overcharged or undercharged. Explosions and fires and things happen during charging or during operation if you do not. Commercial packs have a special charging connector in addition to the regular connector. This charging connector gives a connection to each individual cell for the purpose of monitoring and balancing out each cell. This means you'd have to use a different circuit designed for a multi-cell pack, or separate the cells and charge them separately with the MAX1555 and reconnect them together for operation.

I do not know how commercial chargers charge a a bunch of connected cells through the charging terminal (I'm not sure of the connections, but I doubt that the charger uses a bunch of floating circuits to individually charge each cell in a series packs).
 
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It’s worthwhile to look into these pictures before building a Li based charger.
These things were made by poorly designed faulty chargers.
Be careful when charging none (label) brand batteries

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oh noes, fear mongering!

don't let someone else's fears from deterring you on your project. I do recommend you do your homework, read and understand the engineering sheets before you go experimenting.

Linear has several multi-cell charging chips, and they seem to be the simplest to use. Check out this chip from Linear:

friendly 8 pin SOIC package:
LTC1731 - Lithium-Ion Linear Battery Charger Controller
 
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