On 12/6/2014 12:07 PM, KenO wrote:
> mike,
>
> "educational purposes only" have you taken a cellphone battery apart?
Yes, in virtually every used cellphone I've bought.
Protection board is usually held on the end of the cell by the plastic
over-wrap.
>
> "I might start with 100 mA charge current voltage limited at about 3.7V depending on the exact chemistry involved." Agree it is best to start very conservatively.
>
> Do you know of any websites that give reliable info concerning cellphone battery protection circuits?
>
> Thanks
>
> Ken
Problem is that there are many different types of protection circuits/chips.
Individual battery details are usually not available to the public.
Check the numbers on the protection chip.
bq29311 is one such chip. There are others in the BQ series.
Another thing that happens with laptop batteries is the fuse.
The fuse has a heater in it. When the protection chip decides
that you should no longer have use of your battery, for whatever
reason, it activates that heater and smokes the fuse. You're
dead in the water until you replace the fuse.
Never seen one on a cellphone battery, but all mine are OLD.
If the cell is completely discharged, you can't measure the volts
to determine which is the + terminal. It's probably not the one
you'd expect by looking. Make SURE.
I can't overstress the safety aspect.
You cannot assume that the designer of the system followed
reasonable design procedures.
I had a Dell laptop that had nothing but a fet between the
charge port and the battery. Current limit was in the wall wart.
Charging it from a voltage source burned a hole in the motherboard.
I got lucky. If the FET had failed shorted, it would probably have
exploded the battery.
I had a battery start sizzling. Got it out the front door
before it exploded. I never found the guts of the cell that
went boom.
Nothing drives it home like asking yourself, "Hey, what are those
drops of hot electrolyte doing on my glasses?"
What's a battery cost?
What's the value of your eyesight?
Does your kid ever use your phone?
It's just not worth it.