Date: Tue, 10 May 2005 10:09:10 +1000 From: Raymond <[EMAIL PROTECTED]> Subject: Re: [LIB] Rebuilding a battery pack
At 11:13 AM 9/05/2005 -0700, you wrote:
Date: Mon, 9 May 2005 20:14:14 +0300 From: John Niemi <[EMAIL PROTECTED]> Subject: Rebuilding a battery pack
I need some help here, I just opened my high-capacity battery (that was dead) and now I'm facing two problems;
1) How to get the 6 battery units out of their terminals(?), you know those metal strips that are connected to the batteries + and - ends...? Are they soldered so that I only need to heat the connection points?
2) Where to get replacement batteries, what is the correct term when I start hunting these sort of batteries thru ebay or other stores? I was expecting to find A or AA size batteries in the battery pack but these are somewhat of an unorthodox size I think?
Also any other tips are most welcome. I would be very happy if I could build a battery pack with the original dimensions that would last 3-4 hours (of course even more would be better if possible :)
Whilst not "hard" as such, rebuilding a battery pack is a non-trivial task unless you have a reasonable background in electronics. They can also explode quite violently if mistreated (most batteries talk about a risk of explosion but that risk is quite low. With Lithium Ion, that risk is *VERY* real and I know someone who has blown a pack up). One big danger is that when you overcharge them (eg. the charging circuit malfunctions), metallic lithium gets plated onto one of the electrodes and heat builds up until the battery explodes, ejecting metallic lithium which ignites on contact with oxygen and flares up on contact with water (and is impossible to put out without special extinguishers). The usual warnings - we take no responsibility for anything that happens nor the accuracy of our advice, yaddah yaddah yaddah. Having said that, I *have* done LiIon packs in the past and *touch wood* I've been fine. Here are a few pointers if you're not discouraged!
- The batteries in the pack are a standard Lithium Ion size and come in a variety of capacities. Note that Lithium Ion cells are around 3.7 volts each (as opposed to your standard carbon, alkaline, NiCad or NiMH A or AA size which are around 1.5 to 1.2 volts). They are somewhat more volatile than "normal" batteries so exercise precautions (like don't overheat them or accidentally short them, if they rub against anything in the pack make sure you put some cardboard between it and whatever they rub against so nothing will rub through the coating and short them out)
- LiIon cells should NOT be directly soldered to. Soldering should only be done to tags that have been specially spot welded to the cells for safety reasons.
- LiIon cells require a special charging circuit. That is the circuit board inside the battery pack. Make sure this isn't damaged!
- The *easiest* way of doing the repack is to buy a brand new 6 cell pack on eBay for any laptop that is about the same shape (note though that there is another size of LiIon cell that is slightly fatter and slightly shorter than the ones for the Libretto). I replaced the pack in my 100CT with the cells out of a brand new pack for an early model Portege. These cells will have been sitting on the shelf for some years so their life may not be terrific but I managed 3 hours of runtime on my set. The cells are all spot welded together in the right configuration already and the output tags are in about the right places already so all you need to do is unsolder/cut the tags connecting the old cells to the charging board and solder the new (readily welded together) pack back in its place. Note that each pair of cells is tapped out to the circuit board (to ensure good charging). Some battery places might also spotweld the packs together for you, for a price.
- The pack is a *very* tight fit inside, you may need to do some plastic work to get it all to fit.
- There are 1 (or 2) thermal fuses along the pack (the silver cylindrical things) and a thermal sensor (black thing with two wires coming out of it). Make sure these are in contact with the battery inside the pack. Do NOT short these out, they may be the only thing stopping your pack from going boom!
Good luck!
- Raymond
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