lipoly charger question!!

[mohammad_sa39]

hi friends,
i tried today to charging my lipoly 240mah cell with an adaptor (at 3.5v)and only use from a 3v blob lamp(serial with the cell and adaptor)!!
during the charging the lamp was low light and became about turn off slowly (about 30 minutes)!!!!
and the battery had been charged!!
i did this again and the result was successful!!
my cell even didnt get heat and no warm never!!
does anyone know any thing about this?
does my task was correct?
i guess using from a serial load (lamp) with cell Eventuates the cell put the current that it need for,is this correct?
i never didnt do this for another my lipoliys and dont know if it is correct or no
it was an experiment(perhaps dangerous ;) )(was it a dangerous experiment :o )
anyway thanks for any guide or clue.
best regards.

[jeffs555]

That is a dangerous experiment. Current limiting is only part of the requirement for charging LiPoly. The other part is voltage limiting which you don't have. A normal AC adapter labeled 3.5 volts will put out much more than the 4.2 volts that a single lipoly cell can take. Just because a cell does not get hot, does not mean it is safe.

[Happy Hobit]

Hi Mohammad,

Most important things when charging Lithium (LiPoly) batteries is,

1. Do it somewhere safe. Batteries can explode and burn.
2. Do not charge higher than 4.2 volts
3. Do not charge any faster than 1X. X is the capacity of the battery. A 240-ma battery should not be charged at more than 240-ma

Single cell lithium (LiPoly) batteries are designed to operate between 3 and 4.2 volts. Charging the battery to 3.5 volts won’t fill it very full. This is if the 3.5 volt ‘adapter’ was regulated. If it’s un-regulated the voltage could be much higher and damage the battery.

The 3-volt lamp acts as a resister to limit current. The wattage of the lamp determines the effective resistance of the lamp. Without knowing the wattage I don’t know if you’re charging it with too much current. (Too fast)

If you charge it too high (voltage) or too fast (current) it may not blow-up this time, but it may next time. (See Important Thing #1)

I recommend either buying or building a real charger. Much safer.

See http://www.rcgroups.com/forums/showthread.php?t=130567


Jay

[mohammad_sa39]

thanks alot "jeffs555" and "jay" for your attentions
i didnt have any experiment for exploding any lipoly so i dont know how much it is dangerous(or perhaps i am very brave lol) is this very risky?

"3. Do not charge any faster than 1X. X is the capacity of the battery. A 240-ma battery should not be charged at more than 240-ma"
so is it cool using from slower than 1x or only 1x?
thanks jay i saw this link before and want buid a circuit from it
is this very dangerous blow up from a lipoly cell??
kind regards.

[Happy Hobit]

Hi Mohammad,

Any current less than 1X is fine.

LiPoly cells don’t explode. They swell up, get hot and burn with lots of flames and smoke. A fire in a fireplace or outside in an open area is fine. A fire in your bedroom or basement could be fatal.

There is a thread http://www.rcgroups.com/forums/showthread.php?t=209187 in the ‘Batteries and Chargers’ Forum specifically on LiPoly failures.

Jay

[mohammad_sa39]

thanks alot "Jay"
your answer was nice and the link too
thanks for caution
kind regards, mohammad