Laptop Battery Pack

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Neildo_64
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Laptop Battery Pack

Post by Neildo_64 » Fri May 19, 2006 7:40 am

My friend gave me a funky laptop batter pack(he says it doesnt work right. I havent tested it yet but i shuold have before posting :roll: ). I ripped it open and it has 9 cells. first 3 are wired in parallel, as are second 3, and third 3, then the 3 "clumps" are wired in series. Its 11.1V at 5700mAh li-ion Gateway 600YGR, but if i take out 3 batteries, it will only be 7.4V. I want to do this, but it has a pcb attached to it and all 3 "clumps" are wired in different places.

How can I remove 3 cells and keep it working correctly?

Sorry for no pics, but I will post some later. I just wanted to see if anyone could tell me from previous experience.

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marshallh
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Post by marshallh » Fri May 19, 2006 8:37 am

Better just to leave everything intact and use a stepdown DC-DC converter to get the voltage you want (probably 7.5v right?)
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timmeh87
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Post by timmeh87 » Fri May 19, 2006 9:02 am

agreed
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Neildo_64
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Post by Neildo_64 » Sat May 20, 2006 12:22 am

Well see, that was my first though, BUT (...there is always a "but" getting in the way) I puntured one of the cells (EEK) and It looks deep enough to be a problem. :? Sorry for no pics, i still dont have my camera, but What would be your opinion? Test it, see if it works?

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timmeh87
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Post by timmeh87 » Sat May 20, 2006 9:00 am

someone on the team sent me this in an email a while back

<i>
This is what Andrew mason posted on solar raycing group. Doesn't sound too
good to me!!!!


The electrolyte in lithium ion or li-polys contains organic salts
that when exposed to regular air moisture can produce Hydrogen
Fluoride, an acid gas that is very nasty as the following story
describes:

In 2002 when we received our LiPo batteries for the Queen's car, 3
of the cells had vented during shipping and had leaked a bit of
electrolyte. After being exposed to the air near these 3 leaking
cells for a brief time during unpacking (before we realized there
were ruptured cells), I developed sores on the back of my throat
that made swallowing painful for a few days. I believe it was HF
evolved from the electrolyte that had damaged the mucous membranes
in my resipratory system much like a mustard gas.

This after exposure to just 3 cells. So you can imagine what could
happen if multiple cells rupture and vent inside a battery pack.
The lesson here is: keep your battery box well sealed from the
driver compartment, and ensure your box ventilation system is
working well. And wear a proper mask if you must handle ruptured
cells (3M cartridge # 60923 for the 6000-series respirator masks: it
filters HF, and works great for solder flux fumes too!)

Navarre, space between li-poly cells is quite necessary for
cooling. Generally Li-poly cells have higher internal resistance
than cylindrical Li-ions. You can calculate how much power is being
dissipated in each cell's internal resistance in a worst case
operating mode (e.g. sustained hill climb on an overcast day), then
use a FEA tool to do a thermal simulation to see how hot your cells
will run. Keeping cells below 55C is next to impossible if you
don't allow space for air to flow past, considering that ambient
temperatures can be 35C on a worst case day.

Andrew Mason
Lipotech
www.lipotech.ca</i>
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Krepticor
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Post by Krepticor » Sat May 20, 2006 2:01 pm

So in short... DON'T TOUCH IT!

TI should have a sample you can order for the conversion
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