any assistance gratefully received...
does anyone know of a circuit which can recharge a 9v lipoly rechargable battery from a PC's USB port?
I see that sparkfun have such a 9v battery but no real clues provided as to how to recharge it. obviously i could buy a special 9v charger but that adds another bit of kit to lug around. i wondered therefore if anyone knew of any pointers to wiring my own circuit to do it. I should say that i have presumed that this sparkfun gizmo (SparkFun USB LiPoly Charger - Single Cell - PRT-12711 - SparkFun Electronics) won't do the trick.
You may be better off with a 3.7V Li-ion battery and a standard charger IC (e.g. MAX1555). If you then need 9V get a boost converter that does 3.7V to 9V.
To charge a 9V battery you would need some sort of boost converter anyways.
I would put the converter after the more common 3.7V battery.
LiPoly battery at 9V makes no sense, the cells are 3.6V or so, 7.2V and 10.8V I could understand.
A bit of research shows that "9V Li Poly PP3" batteries are actually about 7.5V (8.4V max to 6.5V discharged) - if you genuinely want 9V that's fraud in my book. However it looks pretty well matched for powering the Arduino Vin.
Since its Li Poly you need a Li Poly charger (the alternative is risking fire and explosion). Sparkfun have one that has the right configuration I note.
If I owned one of those I would be worried I'd forget one day and charge it as a NiMH.
Re-reading my reply I realize I should be more definite in my warning:
Li-Poly batteries can catch fire and explode if charged incorrectly. In particular they cannot tolerate over-charge or trickle-charging.
Personally I don't think it's worth the risk to make your own charger unless you take precautions to mitigate the danger (charge the battery in a ceramic container, preferably oudoors?). Lithium fires are very fast, very hot and cannot necessarily be extinquished with water.
Why not to buy a USB rechargeable Li-Polymer 9V Battery?
It's very easy!
620mAh, Very good!
A Mini USB Port for charge at battery bottom side.
U can charge it with PC,Notebook and Mobile adapter.
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