On Nov 2, 4:44 pm, "William Sommerwerck"
wrote:
To the best of my knowledge, it's the impedance of the motor that (for a
given voltage) determines how much current flows. The battery is not
generally the limiting factor.

You can use a lower-voltage batttery pack, but the device's performance will
suffer.

As to a car battery damaging a drill rated at 13.8 V or higher -- absurd.

William:

Read my post below. If the motor does not turn at the correct speed, a
car battery that is capable of nearly-infinite amperage will fry the
windings in short order. Due to my secondary hobby (R/C boats &
submarines) I run LOTS of motors at LOTS of voltages, from 3.6 to 24V,
and from everything from true Gates Cells through 2 @ 12V VW batteries
for the big tugboat. It is low voltage at high amperage that fries
motors. Not too-high voltage. An unloaded 12V motor with a properly
epoxied armature and good bearings will take 24V nearly all day. Load
it and water-cool it, for considerable time. A 24V motor unloaded will
not do well at 12V/high amperage. Try it. A loaded 24V motor will burn
up in short order on 12V. That is why resistance speed-controls have
gone out of favor in the hobby except at the very lowest end. Too many
motors were dying. Even in trains, the trend is to pulsed full-voltage
vs. resistance speed controls. Furthermore, those motors are very
specially designed for the use with massive magnets, rather heavy
magnet wire and heavy bearings if they are expected to last.

Of course, train transformers are current-limited - but batteries in
drills, R/C boats and submarines and such as well as vehicular
batteries are not unless outside devices are installed (as most of us
do anyway), relative to the use.

Peter Wieck
Wyncote, PA