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Motor RPM: 12V vs. 24V — Parallax Forums

Motor RPM: 12V vs. 24V

FalconFalcon Posts: 191
edited 2012-11-08 11:24 in Robotics
I've sourced a set of motors from a Pride Jazzy 610 power chair for an upcoming project. The chair uses two 12V deep-cycle batteries in series so the system, as a whole, runs on ~24V.

I only have one useable 12V battery right now but I would like to determine the RPM at 24V. I have determined that the motor, with no load, spins at 118 RPM @ 12.5V. I assume it will double to 236 @ 24V.

Are there any other factors that will influence the RPM @ 24V? Should I assume 2x Voltage will = 2x RPM?

falcon

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2012-11-08 06:50
    It's not quite a linear relationship.... see this thread...

    http://forums.parallax.com/showthread.php?64476-Motor-speed-vs-voltage

    This might also be helpful...

    http://www.gizmology.net/motors.htm
  • ercoerco Posts: 20,256
    edited 2012-11-08 09:56
    Per Beau and those useful links, many factors come into play. But very roughly, RPM doubles when you double the voltage. Torque & current also roughly double, so power in and power out (Watts) each increase by roughly 4.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2012-11-08 11:24
    It would be hard to predict a 24 volt RPM from a no load 12 volt RPM, doubling is the ideal. Good motor manufacturers do provide actual data, but not all do. A doubling would be the absolute best you might expect.

    The real advantage with going from 12V to 24V for the same motor is not so much an increase in RPMs as it is a near doubling of torque. Also, there is the advantage that the additional power is made available without a need to increase wire size. And a third item is that many silicon devices are rated in the 60 volt range, so it is rather wasteful to use an h-bridge at 12 volts when the same device can accomodate 24 volts.
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