Notebook battery pack failure & USB H/W development

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OK, I know that I should have known better, but mistakes are made. I repeat the story for the education of others.

A month or so ago, my Notebook, which is jsut short of 2 years of age, came up with a power management error of "Your battery is connected but not charging." Suggest you replace battery!"
It seemed that it would not fast charge , but seemed to trickle charge.
So whilst the PC is not quite out of the warranty period, I thought I will just cop it and purchase a replacement, as I generally leave the Notebook connected to its power supply and trickle charge it. ( I know this is not preferred practice!
I ordered another battery via eBay for about $50 (AU). It duly arrived and after replacing the suspect battery, the error disappeared and all is well.

Being the inquisitive type, I hacked open the old battery to see which battery had failed, with the view of possibly replacing it and having a back-up battery.

I was surprised that all the batteries tested perfectly. They were all the same sitting at 4.2V (Lion cells). A bank of four parraleled cells (total=8).

Mmmm, I thought this is odd, I wonder if the control board has failed! So after reversing engineering the board and realizing that it uses a Texas Instruments chip set (BQ29330), which does just about everything imaginable to porotect the charging of cells ( no wonder the cells were in good condition.)

After some reading of the TI data sheets, the penny started to drop, I wonder whether the fuse ruptured, when I had "around about the same time, done some USB AVR development"
and it was about the same time as when I recall the power management warnings.

So, I checked the fuse, which I became had just become aware of, was a chemical fuse, the characteristics of which, I was not aware of.
Sony call this a Self Control Protector and it can be ruptured in two ways.
a) When it ruptures when to much current flows and
b) When it is told to rupture by a controller by cooking the fuse.
It seems that the controller, when it detects a "unusual" condition, it blows the fuse to remove the condition.
I checked the fuse (SF12AH4) and sure enough it had fused!
I don't know whether, if I replace the fuse, whether the pack will work again or whether it has been disabled by having set a flag in the battery pack flash EEPROM.

Moral of the story.
When developing USB hardware, use an external powered USB hub to connected the USB hardware under test.
I knew that, but I chose to ignore it! It has been discussed here before as far as USB port power driver chip failure! :oops: :oops:

Anyone know where I can get SF12AH4's?

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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if you have a datasheet, why not try to mount a poly fuse. then you can check if the controller chip did not set a 'i am destroyed' flag before hunting the world for getting the sf fuse...

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Thanks meslomp, I had not thought about a work around, but a poly fuse should do the job and I have some at hand.
The pack survived pulling apart quite well, so I may be able to restore it as a spare pack.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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That's good it came apart nicely. Most Li-ion packs I've taken apart have had the two halves of the case melted together. I use a bandsaw to get them apart!