Reviving an old NiMh pack

[TrickyNekro]

Hello guys, I recently got a very old (i386) laptop and I want to explore it for a little fun....
First of all... I want to revive it's battery pack.... and use it for my own...
It's a 12V (somewhere near....) NiMh pack...
It's seems that it's around 0.2V and the smart charger does no good....
I'm currently zapping the pack with a 12V source to lower the cell resistance....
Is that any good???
Have you something else to offer???
It's not that I'm in need of the pack.... but.... why not... I want to play.... not just go out and buy a new....
It seems that it's currently letting 10mA through which means the resistance is somewhere to 1K to 1K5...
That's bad...
Anyway... have to offer any other methods???
I read about freezing methods.... but.... hey.... don't really agree with that stuff..... (ok it might work... but too ghetto....)


Thanks in advance,
Lefteris,
Greece

[SmAsH]

get a 12v 500mA adapter and charge the battery for no more than 3 seconds and see if its voltage has increased..
if it hasn't it is most likely a dead cell.

[TrickyNekro]

I'm using an ATX 12V supply to zap her...
After some time it was held at ~7V....
But with no charge at all....
I think I need a greater voltage to do that... around 24V let's say... for about an hour and measure self resistance...
ATX can give you 24V so I might try it soon enough...

[SmAsH]

just don't let her explode on you
that would be bad...

[TrickyNekro]

Ok..... I started zapping with 24V.... and wait for what it may happen...
And so far.... I almost get a current of 120mA.... Wow.....
Temperature is still good...

And by the end of the post it should reach 200mA meaning a 120Ω internal resistance...
I'll continue to 300mA to get a >100Ω resistance... then rey a normal charge...

And hey... I'll video the fireworks if there are any...


Regards,
Lefteris...

PS: James... don't worry...... I'll try to survive even if I turn my room to vietnam....

[Soeren]

Hi,

You might try slow charging for a couple of days (a week?) and then discharge by 2C to 3C (where C = original nominal capacity) until 0.9V/cell is reached and then repeat. It may build capacity over some cycles.

The freezing method, I'm not too sure about either (only tried a few times with no luck), but don't discard it solely for being Ghetto

Personally, I'd open the pack, as there is nearly allways 1 or a few cell that is dead. Either exchange them with better ones or try to zap them alone - zapping rarely gives anything substantial on a battery with that many cells.


Good luck - and if it fails, you might at least get some good cells out of the bundle.

[TrickyNekro]

Thing is that the pack was working.... But haven't been used for years....
That's why I did prefer the zapping method...
I'll try building a 13V8 steady supply tomorrow with a LM317 and the ATX I have...
Then select with a resistor the C/10 charge rate and see what happens after one day or so...
Good thing is that the pack has build in thermal protector...
Just a two metal wire thermostat but will do the hard work for me...

I charged at 24V.... until the battery was hot (didn't wait for the thermostat of course...)
I gave around 100mA, and assuming most of it was heat.... It did indeed moved a moter for some seconds (30 - 40 seconds)
with a huge voltage drop, but still this is positive... Gotta think that it WILL wake up.... but still I can only hope....


So thanks guys for the ideas so far.... I'll try updating as soon as possible!!!

Regards, Lefteris

[SmAsH]

PS: James... don't worry...... I'll try to survive even if I turn my room to vietnam....

don't you go trying anything...

just out of curiosity, what voltage does the motor run off?

[TrickyNekro]

It starts running from 7 to react 1 point something volts.... when finally stops...
I zapped her for some time... it should be ok....
Just need a charger now....
Bad thing I have exams.... So I'll delay testing that's for sure....
Plus I have may things to do.... So I'll just keep being busy until the end of the next month....
I have other projects I must finish too....

So... thanks so far....
I'll update as soon as possible.... (may write a tutorial.... why not???)

Regards, Lefteris