Converting a Portable Cordless Drill to a Hand Crank DC Generator
- The unit is light weight (2.5 lb), portable, low cost ($10-$20) and can
be used to recharge single cell batteries at from 1-3.5 amps. It can be
made from a cordless electric drill in a primitive environment. See
A) The simplest way of how to make a hand crank DC generator using a
standard 12, 14.4 or 18 Volt Cordless drill from Harbor Freight Tools
(see below for more info). With no modification hook an alligator clip
jumper to the two charging terminals (on the bottom that the battery
plugs into) see picture http://home1.gte.net/mikelob/CrankGen-7.JPG.
Note that when a 14.4 Volt drill is laid down pointing to the left then
the upper terminal is most likely to be the plus and the lower terminal
the minus for these units.
When one holds down on the variable speed trigger switch, the crank
handle will began to rotate slowly acting like a drill. Grab the handle
with your other hand and crank faster in the same direction it is
turning (trigger switch still held down). If an amp meter is hook in
series with the generator then one can tell when it changes from running
as a motor to becoming a generator and begins to charge the battery.
The current flow will change sign going from “-” to “+” (or vice versa)
on the meter. The forward and reverse switch works as normal and
allows one to crank in the opposite direction to charge the battery
while holding the trigger switch closed.
If you have an unknown drill then hook it up one way and see how many
amps you get when cranking vigorously. Then hook it up the other way
reversing the polarity of the wires and compare the amps using an amp
meter in series with a one celled rechargeable battery (NiMH or NiCad).
One way will charge the battery the other way will bring the charging
current to near zero and it will become hard to crank. Use the
polarity that charges the battery. The procedure outlined above gives
the basic way you can check any cordless drill to see if it is a
permanent magnet motor and wired such that will work as a DC generator.
Determining switch setting for 18 Volt drill: Wire or tape the trigger
variable speed switch wide open or all the way held down. Look at the
top of the battery for the plus and minus. Hook up a dc volt meter
according to the polarity that the battery was hooked up. If one lays
the drill pointing to the left then the upper terminal is positive and
the lower is negative. Now give a twist clockwise to the chuck with
your hands (no crank). Watch the voltage reading and the sign plus or
minus then give a counter clockwise twist and note the sign and voltage.
Also note how hard it is to turn. Pick the direction that gives the
most voltage and is easiest to turn. Note the “L” or “R” switch
setting. I found that for this 18 volt drill when “R” was set that a
counter clockwise turn was best and gave a correct polarity as the
battery hook up. In like manner when “L” was set then a clockwise turn
Warning: With the trigger switch wired or tape closed, one can not leave
it connected to a battery without a diode to keep it from draining the
Incremental improvements can now be made. Use a 6-10 amp external diode
in series with the jumper wires (wired in the direction of the current
flow). If one stops cranking the drill as a generator it will not
continue to turn as a motor. The diode bocks the battery flow. One
can then tape or wire the trigger switch in the full ON position. This
approach produces a hand crank battery charger that in a pinch could
easily be reversed and still used as a drill again. This reversal can
be done by taking the diode out of the circuit and un-taping the trigger
switch and plugging in the battery pack.
Note: Be sure to lock the drill into direct drive mode (locks out the
ratchet screw torque gear arrangement). Chouse a cordless drill that
has a high figure of merit or highest ratio of input voltage to RPM.
The 12 volt/500 RPM and 14.4 volt/550 RPM have a ratio of .024 and .0262
respectively. Note that the 14.4 volt unit is slightly more efficient
than the 12 volt unit. The 18 volt runs at 900 RPM and this gives a
ratio of .02 which is not as high as the other two but not that far off.
The 12 Volt drill item 47156-5VGA currently sells for $9.99 with keyed
chuck and the 14.4 volt drill item 4285-1VGA currently sells for about
$15.99. The 18 volt item 90120-8VGA sells for about $19.99. The 12
Volt units are currently the lowest cost but after testing are the least
desirable (harder to crank). The 14.4 Volt tests as most efficient with
the 18 volt units coming in second due to ease of cranking (lower gear
ratio) with resulting lower output power.
Search for the appropriate item number at http://www.harborfreight.com/
I recommend using the “Keyed chuck” type drill instead of the hand
tighten type. It is a bit cheaper and the hand crank can be tightened a
bit tighter so it doesn’t come loose while cranking. In actual fact
either will work. So use what you have available.
B) Modified Cordless electric drill: If one takes out the variable
speed trigger switch and uses a diode (one way flow device) in series
with the permanent magnet motor then we have a unit that can stay hooked
up to a battery without acting like a motor. When one cranks, it
charges the battery. This becomes a dedicated one direction DC
generator without the added losses of the small amount of resistance of
the variable speed trigger switch. The following items can be removed
from the 14.4 Volt drill see picture
The white wire from the PM motor is positive when cranked counter
clockwise facing the chuck and negative when cranked clockwise for the
14.4 Volt drill. There is also an internal 3 wire component (transistor
or SRC I don’t know which) that has a heat sink that can sometimes be
rewired to act as a diode. Do this in a pinch or emergency, not
recommend using if you have a diode available. A diode will work more
reliably. For the 14.4 volt drill this 3 wire component will flow in one
direction when the black wire is hooked to a positive source (the
motor-generator) and the white is negative. I found this component will
not work for the 12 and 18 volt drills as a diode. Sometimes it blocks
the flow and sometimes is does not block the flow (unreliable).
Use a 4-6 cell battery and check current flow of this 3 wire component
in the blocked direction. This back flow test should be well below one
ma. If it is not, then use a rectifier diode from another source (junk
parts). Otherwise your batteries will slowly discharge, if left hooked
up and not turning.
For this 3 wire component I found for the 14.4 volt drill and clockwise
cranking to hook black to black. For counter clockwise cranking hook
white motor lead to black diode lead. See picture
http://home1.gte.net/mikelob/CrankGen-3.JPG. Note that the blue wire is
not used and is left disconnected but taped up with electrical tape so
it will not short to anything.
A diode must be used with the 12 and 18 volt units. When turning the
chuck clockwise facing the 12 volt drill then the black lead from the
motor is positive and red is negative. Note that one can use say 4
three amp diodes in parallel if that is all one can find. See
For the parts taken out of the 12 volt drill and the end result See
The following is the basic circuit of how to hook up a cordless drill to
charge a single cell. Notice that no switch is needed. This will be
true as long as the reverse flow on the diode chosen is very low. The
amp and volt meter are for testing once satisfied all will work ok they
can be removed from the circuit.
The crank can be made from an 11” long by 3/8” diameter plated treaded
rod. Bend at 1” and to make a 5” cranking radius. The rest of the
length becomes the handle. Make your bends gentle and not too sharp or
it will break. Find a chunk of round wood (closet coat hanger dowel is
about right) and drill a 3/8” hole through the middle of it. Slip over
the shaft and put a nut on it with lock tight or epoxy in the threads
(to make it stay in a permanent location). I also tested a 3/8” ID
rubber hose as a handle but didn’t like it as much as a bigger diameter
wood approach. Optional: Sand or file a flat on three sides of the 3/8”
threaded rod to keep it from coming loose easily in the chuck of the
drill. I experimented with different radiuses and handles. The one that
worked the best for me is the one with the round wood dowel handle at a
5 inch radius. These are the wooden handle ones in the picture
The 12 volt and 14. 4 volt hand crank modified drill generator weighs
about 2 lb 2 Oz with the lead wires and clips. The crank is about 6-7
Oz. Total weight is about 2.5 lbs.
What to do with the battery packs that come with and plugs into the
drill. This now becomes a source of single cell batteries that can be
individual charged. One takes the cover off and attaches a wire to each
end of each cell without taking the series string apart. These wires
are run to the outside of the case where the alligator clips from the
drill generator can be used to charge each cell individually. Then
depending on the voltage needed to run the intended device one can tap
off the voltage needed. Another way is to break them into individual
cells charge them separately and rewire temporally back into a series to
get the voltage necessary to run radios or lights.
Output test results of hand cranking One Cordless Drill.
Comfortable Hand crank speed is about 80-90 RPM (normal cranking). High
speed is about 1.5 to 2 times that speed.
12 volt red drill charging one cell: (.5 to 3 watts)
Fast cranking open circuit 4.1 volts max and 1 to 2 amps at 2 volts or
an average 1.5 amp x 2 volts = 3 watts. Normal Cranking produces .2 to
.5 amps at 1.5 volts or an average of .35 amp x 1.5 volts = .5 watts.
14.4 volt drill charging one cell: (2.2 to 5.7 watts)
Fast cranking open circuit 5.4 volts max and 2.5 to 3.5 amps at 1.9
volts or an average 3 amp x 1.9 volts = 5.7 watts. Normal Cranking
produces 1.1 to 1.6 amps at 1.6 volts or an average of 1.35 amp x 1.6
volts = 2.2 watts.
14.4 volt drill charging two cells in series: (1.2 to 4.2 watts)
Fast cranking open circuit 5.4 volts max and 1.2 to 1.5 amps at 3.1
volts or an average 1.35 amp x 3.1 volts = 4.2 watts. Normal Cranking
produces .3 to .6 amps at 2.75 volts or an average of .45 amp x 2.75
volts = 1.2 watts.
18 volt drill charging one cell: (1.8 to 4.8 watts)
Fast cranking open circuit 3.9 volts max and 2 to 3 amps at 1.9 volts
or an average 2.5 amp x 1.9 volts = 4.8 watts. Normal Cranking produces
.9 to 1.4 amps at 1.6 volts or an average of 1.15 amp x 1.6 volts = 1.8
Summary: Hand cranked cordless drills can be converted to generate a
small amount of electricity in an emergency. Expect to charge a one
cell at about 1 to 3.5 amps or 2 to 5 watts. For each watt of power
generated for one minute (1 watt-minute) will run one white LED for 15
minutes. Thus 5 watts generated for one minute theoretically could
result in 75 min run time for one LED.
In practice one would need to charge 3 separate cells to get the
necessary voltage to run one LED. The cells could be charged all at
once in parallel then rearranged in different battery holders to be
wired in series to run the LED(s) or charge each cell separately while
staying connected in series.
Bottom line: In an emergency one could crank out enough power to keep a
night or task LED light going while it is needed.