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Jul 06, 2002, 10:53 AM
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Review of Li-ion charger


Have learned a lot from reading here and want to return some.

I only recently got involved in electrics with the GWS Stick FD and really enjoy it. Also got excited about the possibilities of using Li-ion batteries salvaged from some old notebook computers. Anyway, the only inexpensive charger I could find was the hobby-lobby.com POT010 at $25 for a bare board so decided to try it out.

Basically, it works! I'm using the GWS Tiger Moth now, with 2 li-ion cells taped together with a connector soldered to them. That should deliver a nominal 7.2v at the 1 amp drawn by the IPS motor. They fit with just a little trimming of foam from the battery compartment. The charger has two banks of switches to set - output voltage for cell type (Tadiran Li-metal or Li-ion) and number of cells (1 or 2) and output current. I set it for 2 li-ion cells and max charge current, 200ma. Power supply for the charger was a 15v unregulated generic p/s. My cells were down to the floor at 3 volts each when first put on the charger. Measured charge current and it was smack on 200ma. At that rate it would take many hours but left it on while closely monitoring voltage. I also monitored the voltage on each cell to make sure there wasn't a big differential, they were exactly the same. The 3 legged transistors/regulators/IC's get quite warm to the touch. By the time it crept up to just a hair over 8.2v the red light dimmed and soon went out, took about 4 or 5 hours. Anyway after that it powers the TM for a good half hour flight.

I think the big danger in Li-ion is overcharging at fast charge rates (the old explode and catch fire scenario) but I still wouldn't leave them on this thing long after the red light goes out, altho it's probably designed with a good safety margin, that is, doesn't completely fully charge to the brim, which is just fine with me! At red-light-out stage the cells are still room temperature.
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Jul 06, 2002, 11:38 AM
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i believe the danger is going over 4.2v


per cell;

the chargers for li-ons must have voltage regulation and not charge at a voltage above 4.2 v/cell;

i believe that the chargers "sense" the voltage across each cell and once 4.2v is reached they cut back the current slowly until trickle charge is reached; continuous trickle charging at 4.2v i don't believe will explode the cells but this is my uneducated conjecture;


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