Building a battery pack

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zarquon Posted: Thu, Jun 30 2005 2:55 PM
Hi everybody,

I want to make a battery pack for a laptop (not really a laptop, more a suitcase-pc I am assembling).
I know some basic electronics, but I am a complete noob at battery technology.
Here is a brief description of the project:

I have:
4 Toshiba PA2487U Laptop Li-Ion batteries, 10,8V, 4Ah each
1 Toshiba PA2488U Charger, seems to be broken (connected to mains, the status LED is green, if put a battery in, it starts blinking red after a few seconds, stops only if I disconnect & reconnect main power)

I want:
A battery pack with a included charging circuit. I can provide 12 V (either car outlet or AC-DC PSU) for charging.
It must be possible to run the pc from the pack (it runs with the 10,8V, but 12V output would be better, because I also want to connect some other stuff) or charge the battery while running the PC or running the pc with the external power when the batterys are full. This should be done automatically, without any manual switching (just like the internal battery of a laptop)

I started researching and thinking about the project and ran into the following questions:
-The PA2487 has 10 connectors on the front an 2 on the top. The 2 on the top seem to be security connectors. I have to brige them to get current on two front connectors. What for are the remaining 8 connectors? I think the might be for temperature sensors or so.
-I found out that Li-Ion cells output 3.7V, so my guess is that there are 3 Cells in each battery. The charger has an output of 12.6V, that would be 4.2V charging voltage per cell. Is that right? I read that the charging voltage has to be very exact for Li-Ions, but you don't have to disconnect power when they are full. Is that correct?

So my naive approach would be connecting all the batteries in parallel, also parallel to a removable stabilized supply of 12.6V and the output to the PC. This would be without any temperature sensors or any other security. Is that an option or just way to kill some good batteries? Besides, how can I generate exactly 12.6V out of "more-or-less" 12V i get from my car or the psu?

I am thankfull for any tips, links, circuits, ideas, etc.

Thank you for your help and greetings from Munich,
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I have no idea but this sounds like a school project.
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Ne0rC replied on Thu, Jul 21 2005 4:38 AM

I think it was said very unrealistic.

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Possible to do...not likely to happen. You are correct that Li-Ion batteries don't have to be charged fully, and they will not get "memory". Now a much, much better and simpiler idea would be to go down to your local radio shack, get an AC/DC converter. Then get a bunch of 12V battery packs for like remote controlled cars and what not. Then get a bread board. Then line the bottom of your breifcase or whatever with these batteries, then cut a hole in the side for the AC/DC input. Then connect the output of the AC/DC converter to the breadboard. Have to rows of batteries, connect each to the bread board. Now this part gets tricky...I can't give you the exact numbers, but I can tell you what to research. Get some transistors/resistors, etc. Also create a fuse failsafe inscase of a power surge. Basically you would have a switch which would allow you to charge one row of batteries while the other one discharges to the laptop. On the bread board you will basically make an inverter. Which will take 12 volts in and give out 12.6V which is what you want. This is where u put the fuse to prevent over voltages. So now, the possable results are, charge both "cells" of batteries without powering anything. Power one row of cells, while discharging the other. If you wanted to get tricky you could build a voltage meter to the bread board so automatically switch from one cell to the other when the voltage drops by X ammount. Maybe 10 battery packs per cell would give you enough amperage for a laptop...maybe, probably 12. So a total of 24 battery packs. At 4 hours to charge, 2 hour's discharge would probably get an addtional 4 1/2 hours of battery life, but all depends on how effecient your inverter is and what kind of battery packs you use. ...that was a big waste of my life....
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violet replied on Mon, Apr 7 2008 7:26 PM

It is a trouble, if you need a TOSHIBA PA2487U battery, why do not buy a replacement  PA2487U battery with cheap price and hi-quality? See this battery, 11.1V,4800mAh,6-cell, also replacement for PA2487U.

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Electronics Lab may have some similar projcts that folks have done which could help you out. great site.. 

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