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'[EE]: Largeish? Li-pol system'
2006\08\23@113131 by Ewhost


Does anyone have experience with Larger Li-pol battery systems? By
larger I mean something like c5 48v/40ah. It's going to be used rather
large rc car. (think go kart size).

We are trying to figure out an effective way of designing a charging
system and a source for large cells.


2006\08\23@131329 by Steve Smith

Sounds like a bomb on wheels

Av u seen wot appens to them when they aren't charged proper !!!!

Big fire !!!         need big fireproof box !!


{Original Message removed}

2006\08\23@174317 by Gus S Calabrese

face picon face
jettision burning carnage and pedal away

On 2006-Aug 23, at 11:11hrs AM, Steve Smith wrote:

Sounds like a bomb on wheels

Av u seen wot appens to them when they aren't charged proper !!!!

Big fire !!!         need big fireproof box !!


{Original Message removed}

2006\08\24@062737 by Tamas Rudnai

face picon face

In LiPo terms cells are signed as 's' and 'p', where 's' stands for series
and 'p' for paralell. So 3s2p means you have 6 cells, 3 in series in 2
paralell. If you need 48V, then you need 14 in series (1 cell is
around 3.4V in avarage,
4.2 in full charge, unloaded), and depending on the cell it is around
600-1800mAh, so for 40Ah you would need around 40 in paralell. It's 14s40p =
560 cells. I doubt if there is that large pack you can buy. You can make it,
but in LiIon and LiPo the cells not just put together, there is an
electricity that looks after the cells not to discharge too fast, overheat
protection. Also for charging you would probably need a cell equalizer (for
the sreies only, the paralell is no problem, so a 14 cell equalizer). Also
you have to make a good charger for it that knows how to charge 14s LiPo.
Erm, not impossible, though :-) but if you just put the cells together then
probably it is best to use it somewhere on the Moon -- no oxygen, no fire


On 23/08/06, Ewhost <> wrote:
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> -

2006\08\24@115512 by Marc Nicholas

picon face
You can do it. People have done it. The fact you're asking about it on this
list however, likely means that you wouldn't have the skills to do it safely
and effectively

But, if you're interested in pursuing this, I'd suggest you get involved
with NEDRA ( -- the electric dragster group.

I would recommende Kokam's EV cells. The 40AH unit is ~US$400 per unit and
can do constant 5C and bursts up to 10C. Like virtually all Li cells, it's
nominal voltage is 3.7vdc and it weighs ~2.5kg. You do well to invest in one
of their battery management systems -- they're not trivial to design at that
scale. Ditto a charging system.


On 8/23/06, Ewhost <> wrote:
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> -

2006\08\24@140124 by Ewhost

Hi Tamas,

Yeah we're very aware of the charger concerns, something we are looking
at is packaging the cells into modules each as 4s4p to ease the design
of the chargers we are using 2000mAh cells. Each module will have a
charger built for it with current, voltage and temp
regulation/monitoring and secured in a steel shell. We are unsure if
there will be unforeseen issues in combining the modules for output. The
modules will be arranged 4s5p which should bring the whole pack up to
about 55v @ 40Ah. That will be current and voltage regulated to what we
require. In total it should be 320 cells.

I was just wondering if anyone else has had experience with something
like this. Seems not many people do, but everyone is aware of lithium fires.


Tamas Rudnai wrote:
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>> --

2006\08\24@141342 by Ewhost

Very interesting, Thanks.

Marc Nicholas wrote:
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>> --

2006\08\24@145720 by M. Adam Davis

face picon face
Contact the closest university that does Solar Car.  I know the
University of Michigan used Li-Ion last time I looked.  the battery
cells were standard laptop size, tab welded in parallel into huge
(relatively) packs.  Definitely something to be careful around, but
there's no need to worry about it any more than you need to worry
about welding tanks, etc.  The only difference is that people don't
have the experience with high capacity battery packs that people have
with gasoline, welding gases and tanks, etc.


On 8/24/06, Ewhost <> wrote:
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