battery fix

[Christopher]

Hey, I have a Pismo battery that is shot, but since I have a couple spare clamshell batteries around i thought "their connections are the same, so lets try and do a swap.

The first speed bump i found was the clamshell's battery board is longer.

http://farm4.static.flickr.com/3049/2887419745_264cc1515c_o.jpg

So do I un solder the clamshell batteries to fit the pismo battery board or not. I'm afraid to do that because I do not want to screw something up so bad.

 

[tomlee59]

Hacking lithium-ion battery packs is not for the uninitiated. Leave it alone.

 

[Bunsen]

What's on the battery "board"?

 

[bluekatt]

Hacking lithium-ion battery packs is not for the uninitiated. Leave it alone.

and how do you become initiated if you dont try ?

 

[Franklinstein]

and how do you become initiated if you dont try ?

I think he means "uninitiated" as "someone who has likely never messed with complex electronics before." I agree that before one starts attacking battery packs, particularly those prone to bursting into flame, they should get a bit of practice in with some less hazardous work. For example, one should begin with building RC cars, repairing home appliances (toasters, lamps, vacuum cleaners...), fixing old transistor radios, before moving to complete disassembly and correct reassembly of a white iBook, or recapping an SE's logic board, or recelling an old NiMH battery. Ya know, to get the feel for electronics and what happens when a screw-up occurs (which it will). Maybe then, young Grasshopper, the hacking of LiIon batteries will be in your reach.

I've never personally cracked open a clamshell's battery pack, but unless the batteries are physically the same size (or smaller) as those in the Pismo's pack, I wouldn't even bother. Besides, LiIons often don't take kindly to heavy modifications, what with all of their hazards and fancy safety circuits, so I'd personally just buy a new one (so long as they're available).

 

[Charlieman]

What's on the battery "board"?

The "battery board" provides control systems for "intelligent batteries". The charging controls monitor voltage, current and temperature when the cells are charging; the controls will be very sensitive to the characteristics of the cells. A different control will monitor cell discharge, informing the OS when the cells are losing power and performing the optimisation that maximises battery life and endurance.

Since the Blackbird 5xx series, Mac OS has included software that communicates with the battery control systems. External battery chargers also include intelligent systems, hence the occasional firmware update for early rechargers.

Re-celling an intelligent battery is no doubt possible but non-trivial. You need to obtain cells with identical characteristics to the originals and be able to reset the battery board to recognise the new cells. You also need to be able to solder cleanly (dodgy joints will be a safety hazard) and to disassemble a battery pack containing nasty chemicals without breaking the cells.

As a first test of skill, I suggest learning how to re-cell the battery for a Portable or PB 100, which use lead acid cells. If you want to learn about re-celling NiMH batteries, start with an eMate 300 or similar. LiIons are scary and you really need to understand the safety considerations before you even try to take one apart.

 

[tomlee59]

Hacking lithium-ion battery packs is not for the uninitiated. Leave it alone.

and how do you become initiated if you dont try ?

Franklinstein has it exactly right. From heavymetal's other posts, it's evident that he's not very experienced in the ways of hardware. Playing with lithium-ion battery packs is a dangerous way to start. NiCd or NiMH packs are much more forgiving, so that's where one might get initiated. The fact that heavymetal thinks that having seemingly identical connectors implies electrical compatibility is a sign that he is probably out of his depth, and therefore uncomfortably likely to get into serious trouble.

He should leave it alone. A lithium battery pack doesn't give much forewarning before going Ghostbusters bad, and we don't to lose Forum members to uncontrolled exothermics.

As Clint Eastwood's Dirty Harry famously said, "A man's got to know his limitations."

 

[wally]

...So do I un solder the clamshell batteries to fit the pismo battery board or not. I'm afraid to do that because I do not want to screw something up so bad.

I recommend choice B) , the "or not"!

The chemicals inside lithium ion cells have a thermal runaway characteristic that is quite deterministic. Heat it up to a certain trigger temperature in any one small spot and it will blow, 100% of the time. Heat can come from an unfortunate combination of battery deterioration causing internal hot spots from laptop current, excessive environmental temerature, and you messing with the pack. The fact that explosions are really, really rare can be credited mostly to three things: first, the combination of the battery board safety features and the internal PTC current interrupter works well; second, the user community is not trying to solder connections to individual cells and overheating them, third, the cells have a very low rate of sudden internal shorting if not abused. While the worst chemical is formed in quantity only in charged cells, there is another that is always present and also releases heat when triggered by temperature. Both runaway at considerably less temperature than a soldering iron, and the entire cell does not have to be at trigger temperature, only a spot need be too hot to initiate the process.

I repeat: the runaway mechanism itself is not a chance thing, it is certain if triggered. The observed rarity of explosions in the world is due to the rarity of all the safety measures in intact battery assemblies failing thus allowing triggering. Please do not try to solder lithium ion batteries or their severed tabs. Because any triggered fire cannot be put out by any practical means, battery remanufacturers have to be absolutely certain the internal cell temperature stays below the trigger point and they usually use controlled stored energy spot welding to do this. If you guess wrong trying to solder a severed short nickel tab there could be an overheat explosion with a flaming venting solvent jet several feet long followed by the entire battery cooking off in a fireball, possibly blinding you and burning down your residence. Even if soldering was perfect, if the cells did not play right with the smart battery controller it could blow while in your laptop. It would be a bummer and not only would you be upset, we would be too!