At right is the basic circuit of how to hook
up 2 cordless drills to charge a 12 volt
battery. Notice that no switch is needed.
This will be true as long as the reverse flow
on the diode chosen is very low. Summary:
A bicycle driven emergency battery charger
can be made rather simply from two
cordless permanent magnet drills and
commonly available parts that will produce
from 10 to 45 watts charging capacity. This
can be used to charge 12 Volt storage
batteries or a modified drill NiCad battery
Take the cover off the battery pack that came with the drill and attaches a wire to each end of each cell without taking the series string apart. These wires are then run to the outside of the case. Then depending on the voltage needed to run the intended device one can tap off that voltage. The series string of cells is charged all at once by hooking the bicycle generator across the battery pack as a whole.
Offered by Mike.