You Must read this before you read this post:
24-10-2011: update, the P-fet burned one more time today, so i search my scrap box now for a more powerfull fet. So, don't use the TPC8107 P-fet. .
I found that IRF 9540 placed on a cooling plate below the battery works, but think a more powerfull mosfet without cooling plate would bee the best solution. But, i don't have any super power p-fet in my scrap box. And go buy a P-fet, no thanks ;), more likely i will devel something else latter, for now, this project is ended.
Fell free to share your experiences if you deside to 'hack your screwdrier mashine' :)
If you make experiment with Li Ion nad LiPo bateries, YOU and ONLY you is the one taking the chance, LI Ion /LiPo cells might explode or turn into flammes !!!
I hereby disclaim all responsibility for your experiments.
If you expect this is 100% safe, then don't make this hack yourself.
Go purchase a new battery !!
If you will make this Li Ion Hack yourself, then YOU are responsible for all Risk i the project.
And YOU must take responsibility if something goes wrong.
I disclaim all responsibility for your experiments with Li Ion and LiPo cells.
Li Ion / LiPo cells might explode, and they might turn into flames and burn your house down.
Mosfet transistor used is from a scrapped Li Ion battery Labtop, a TPC8107
Low Cutoff voltage is 3 volts per cell, that is 12 volts for the 4 cells in this hack.
High Voltage from the newly charged battery is 16.2 volts
Bosch screwdriver mashine can handle 14.4 volts
I use power diodes to bring voltage down to 14.4 volts
Each diode has a voltage drop of 0.6 volts which is used to voltage down to the DC motor inside the bosch psr1440.
Unfortunately there will be some loss of effect which is converted to heat, but compared to that you get a free Li Ion battery in this screwdriver maschine, then I never mind ;).
16.2 to 14.4 = 1.8 volts
1.8 / 0.6 = 3 diodes
The components of this hack comes from defect Li Ion battery from DELL Labtop and the TL431 comes from a dead psu from a desktop computer.