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# How many RPM does it take to reverse the process of a 1.5V DC Motor?

I excavated a toy train and pulled out a 1.5V DC Motor. I have not found a use for its motion, so I was thinking of reversing the process and creating a hand crank flashlight. But should I hand crank? How many RPM would it take to generate its standard voltage? Thank you for your answers.

## Discussions

Best Answer 7 years ago

Depends on the motor, I'm afraid. Generally, faster rotation than that voltage would drive the motor at; motors are not highly efficient generators. There's also the question of "into what load" -- getting 1.5V across a short circuit requires a huge amount of current, getting 1.5V across an open circuit is much, much easier, most real-world loads will be somewhere between the two.

Answer 7 years ago

The load is a 1.5V flashlight bulb I plucked from a broken flashlight. Hope that helps.

Answer 7 years ago

. Do you know how many Watts the lamp is rated for? How many/what size batteries were used?

. As steveastrouk pointed out, it will take a little more speed to produce the rated 1.5 V than what the motor turns when driven with 1.5 V. How much more depends on the motor and the load. If the motor speed is more than about 100 RPM, you're going to have a hard time hand-cranking for very long and will need a gear box.

. If your lamp is just a few Watts, hook it up to the motor and give it a good spin with your fingers - you should get at least a brief, faint glow.

Answer 7 years ago

Actually, I pointed that out, but I don't particularly mind being confused with Steve.

Answer 7 years ago

. Oops.

Answer 7 years ago

I checked everywhere and the wattage is not listed, but it ran off of one AA battery. It was a small handheld flashlight. But thank you for your answers, I know what to do now: nothing, lol, atleast until I figure out a system that will crank it that fast, any ideas (besides drill).

-E