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Electronics Forum / Basics / August 2007Can all DC motors be reversed?
Can all DC motor leads be reversed so the motor runs in the other direction equally well? I have a 36 V DeWalt cordless drill motor that has a casing with a molded plus sign on it. Clearly they very much want the positive motor speed control lead to be attached at that terminal. But maybe that plus sign is just so that the worker will connect the wire to the right terminal so that the motor will turn in the right direction when the drill's switch is turned to "forward"? Thank you. > Can all DC motor leads be reversed so the motor runs in the other > direction equally well? ================================= I think there is a slight 'timing' or a couple of degrees of 'advance' on the brushes in the preferred direction to give the current a little jumpstart on overcoming the L/R time constant in the windings? > Can all DC motor leads be reversed so the motor runs in the other > direction equally well? [quoted text clipped - 5 lines] > that the motor will turn in the right direction when the drill's switch > is turned to "forward"? The smart thing to do would be to get a voltmeter, clip it across the motor, and see what you get, forward and reverse. Any permanent magnet motor should work like this, although as BobG mentioned, it might affect efficiency. And no, "ANY" dc motor can't be reversed just by swapping the leads - for series wound "universal" motors, you have to swap either the field leads or the armature leads, but not both. Hope This Helps! Rich > Can all DC motor leads be reversed so the motor runs in the other > direction equally well? [quoted text clipped - 7 lines] > > Thank you. In theory one could build a DC motor that would jam the brushes or suffer other mechanical damage were it run in reverse. Practically I would be very surprised to find one unless it were above 1HP output -- and even then I'd be surprised.  SignatureTim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html > Can all DC motor leads be reversed so the motor runs in the other > direction equally well? No. 1. Motors which use coils for both rotor and stator (rather than using permanent magnets for one of them) will rotate the same way regardless of polarity. Reversing the polarity will reverse both fields, leaving the rotation unchanged. 2. Motors which aren't designed to be reversible may have the brushes aligned for a specific rotation. Such motors will often run in reverse, but with reduced efficiency and/or longevity. 3. If the motor has an integral cooling fan, it may not work (or not work so well) in the opposite direction. 4. If the "motor" consists of embedded electronics along with the actual motor, all bets are off. >Can all DC motor leads be reversed so the motor runs in the other >direction equally well? --- No. SignatureJF > Can all DC motor leads be reversed so the motor runs in the other > direction equally well? [quoted text clipped - 7 lines] > > Thank you. Well, I guess you answered your own question. Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 ... >> But maybe that plus sign is just so that the worker will connect >> the wire to the right terminal so that the motor will turn in the >> right direction when the drill's switch is turned to "forward"? > Well, I guess you answered your own question. Not nearly as well as the reply authors. I'm schooled. > ... > [quoted text clipped - 6 lines] > Not nearly as well as the reply authors. > I'm schooled. You're schooled? what the hell is that suppose to mean? Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 ... >>>Well, I guess you answered your own question. >> >> Not nearly as well as the reply authors. >> I'm schooled. >> > You're schooled? what the hell is that suppose to mean? That comment was meant for the authors who provided information. Here's the definition. Main Entry: school Function: transitive verb 1 a : to be taught or drilled in a specific knowledge or skill |
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