DC Generator

Rules of thumb or lessons learned from current experience:

• When generating optimum maximum output power plan on an output voltage of no higher than half the drills rated input voltage. Use 2 drills in series when planning to generate near to the rated input voltage for the given drills.
• I don't recommend running any unit faster than it was designed to run originally. Rated speed for 12 volt unit is 500 RPM, 14.4 volt unit is 550 RPM, and 18 volt unit is 900 RPM. I have noted that one gets about 80 percentage of the input voltage as output open circuit voltage when acting as a generator at rated maximum speed. Use this as a guide to make sure your design doesn't end up going too fast.
• It's hard to say what the maximum sustained current capability of these units is. My best current guess is about 3-4 amps for 12 volt, 3-4 amps for 14.4 volt and 4-5 amps for the 18 volt unit. The short term surge max can be twice the current in the previous sentence. Plan on using no higher sustained output power than 13, 22, and 41 watts for 12, 14.4 and 18 volt tested individual drills.
• Turning the unit at faster than rated speed could ware out the gears and bushings before there time and is not recommended. The electrical components are not designed for voltage much above the rated input voltage. Also, there is a strong possibility of thoroughing a bar on the commentator of the motor due to centrifugal force and heat. This happened on one test run where it was generating into a heavy load at more than twice the rated voltage.
• Output efficiency is about 30 to 40 percent of input power. The rest of the input power goes to gear friction and electrical losses as heat.
• The 14.4 volt cordless drill is the current best unit for hand cranking because of it's higher efficiency and high volts/RPM ratio. This would hold true for water power also. For bicycle pedal powered cranking the 14.4 volt and 18 volt both will work. I favor slightly the 14.4 volt unit however the 18 volt unit might just make up for this by lasting longer.
• On the bicycle generator if you find the power wildly surging with every half turn of the pedals, then chances are the drill drive wheel is too small and the pedaling needs to be made easier. One can also add weight or make a flywheel effect out of the bicycle wheel but this is not recommended due to possibly causing other things to ware out quicker.
• For bike and water wheel applications feel the temperature of the generator from time to time by sticking your finger into the open slot where the trigger switch was to feel the metal case of the motor. Cut down on your output power if it is getting hot. The estimated maximum allowable power output for the 2 drill series combination is twice the above recommendation or 26, 44, and 82 watts.
• Be sure to use a one way rectifier diode in series with the unmodified cordless drill when taping closed the trigger switch to make a DC generator. Use a diode in preference to converting the internal 3 wire component to a diode. I don't have much trust in this component.

Offered by Mike.