li-ion batteries

[mark krawczuk]

i have a about 12 , li-ion 18650 , 3.7 volt batteries , 6 " sure fire "
types and 6 " gtl " brand.

is it possible to connect them all up in series ,in lots of two ( 7.4
volts) , then paralell them all together for more current ? charging
doesnt have to be at max , even min charging current will be fine.

i`ve had a decent look around on the net , but all i could find was
charging in 2 cell lots.

mark k

 

[who where]

On Fri, 29 Jan 2010 15:55:39 +0930, "mark krawczuk"
<krawczuk@adam.com.au> wrote:

i have a about 12 , li-ion 18650 , 3.7 volt batteries , 6 " sure fire "
types and 6 " gtl " brand.

is it possible to connect them all up in series ,in lots of two ( 7.4
volts) , then paralell them all together for more current ? charging
doesnt have to be at max , even min charging current will be fine.

i`ve had a decent look around on the net , but all i could find was
charging in 2 cell lots.

Not entirely sure what your question really is.

Subject to the usual caveat regarding safety and suitability of
charging system, you can charge them in series strings of whatever
length/number you desire. However the difficulty is in achieving
matching SOC in series configurations. While protection modules guard
against unequal SOC, they don't actually remedy it.

If you configure them in parallel, the SOC *will* equalise, as LiXX
charging is voltage driven, unlike NiXX.

 

[Clint Sharp]

In message <MLednbhNNayE7f7WnZ2dnUVZ_qydnZ2d@adnap.net.au>, mark
krawczuk <krawczuk@adam.com.au> writes

hi, i should have been a bit clearer. see attached pic , thats how i want
to connect them up.
I had it the first time but I think you might be better making two

paralleled packs of six cells for 3.7v and then put those in series to
get your 7.4 volt pack. AFAIK, you probably should do some matching of
capacity between the cells but I'm not sure how much having non matched
cells will impact on overall performance and longevity.

i`m trying to find a charger that will charge them in this configuration.
the only ones i could find charged 2 cells at a time.
Perhaps you could include a switch of some kind that enabled you to

'separate' the parallel packs and charge them as two individual packs?
That might solve your charger problem too if you can find a charger that
can provide the power needed.

mark k

--
Clint Sharp

 

[APR]

"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:4qKdncK9q_p57f_WnZ2dnUVZ_o2dnZ2d@adnap.net.au...

i have a about 12 , li-ion 18650 , 3.7 volt batteries , 6 " sure fire "
types and 6 " gtl " brand.

is it possible to connect them all up in series ,in lots of two ( 7.4
volts) , then paralell them all together for more current ? charging
doesnt have to be at max , even min charging current will be fine.

mark k

Hi Mark,

Charging in series is to be avoided unless you have voltage limiting
circutry across the terminals of each battery. Further, minimum charging
currents are also not recommended. If a trickle charge is fed to these
batteries you risk irrepairable damage to the batteries that could result in
fire or worse.

18650 "Protected" batteries can be purchased that do have overvoltage
safeguard however, they are still not safe to trickle charge.

See this page..
http://www.lighthound.com/Rechargeable-Lithium-Battery-Information--Protected-vs-Unprotected-Li-Ion-Batteries--Lithium-Ion-Battery_ep_36-1.html

and this...

http://www.batteryuniversity.com/partone-12.htm