Power,Voltage,Current & Resistance of a motor

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so connected 12v motor on pretty big car battery other day (12 volt,70ah). when motor rotating shaft free (no load) voltage across terminals 12v , current drawn 200ma. when squeezed shaft fingers (a significant amount of load applied) point motor ready stop, voltage 8v , current drawn 1a.

my questions:
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>could please explain me in terms of both power law (power = voltage x current) , ohm's law (voltage = current x resistance)?

>is there such thing lower resistance motors? (if equation v=ixr applied, in first case [no load] resistance 60 ohms drops 8 ohms in second case [full load])

>why did voltage drop 12volts 8 volts? (i using pretty huge source of stable dc energy)

>am right on this? : "the 2 factors determining current drawn voltage supplied , resistance of something. if voltage steady (or drops), resistance has drop in order current drawn increase "

any "light" question appreciated. thank in advance :)

ohms law not apply since motor non-linear device.

firstly if battery voltage fell 8 volts, battery dead.

when motor spins generates emf opposes supply voltage, current drawn determined supply minus emf.

when apply load motor, speed slows emf reduces, therefore supply minus emf increases , hence current increases.

the resistance of motor winding plus brushes plus commutator governs maximum current flows (as determined ohms law) when motor @ complete stop.

after motor starts turn ohms law goes out window


Arduino Forum > Using Arduino > Motors, Mechanics, and Power (Moderator: fabioc84) > Power,Voltage,Current & Resistance of a motor


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