Electromotors - can you use them as generators in either direction? - Page 1
Forum section: electronics / general

author: rr100
author_rank: Frequent Contributor
timestamp: November 15, 2012, 10:34:22 am
content: I'm sure it's time for me to learn something new today.I have a "scooter" motor (if interested google for: model 1016 24v 250w) which is semi-popular as a generator (which is my purpose as well). It's a DC motor, permanent magnets and at 2750 rpm I guess it has no internal gearing of any kind.It has two wires - red/black and seems to work the same in both/either directions (reversed polarity), both as a generator and as a motor (although I tried only at a small fraction of the rated load/rpm/etc).Question is: should I use it in any particular direction of rotation (as a generator)? One direction would be let's say the direction in which it moves when (+) is connected to red wire (as a motor) and the other direction is ... the other.

author: Rerouter
author_rank: Super Contributor
timestamp: November 15, 2012, 10:41:03 am
content: in short reversing its direction will reverse the polarity that it generates a voltage in, most scooter moters can be used like that, the motor controllers on some decent ones will even feed that through to the battery when not driven to protect itself (no load can lead to a few tens of volts at normal rolling speeds)just be aware the polarity you feed it to go in a certain direction is the opposite of the polarity it will give out when generating,

author: amyk
author_rank: Super Contributor
timestamp: November 15, 2012, 10:48:44 am
content: Theoretically DC motors can be run in either direction but they may have design features like angled brushes/unidirectional fans that may not be suited to being rotated "backwards".

author: rr100
author_rank: Frequent Contributor
timestamp: November 15, 2012, 12:00:07 pm
content: Yea, I'm aware of the polarity (also for generator) - this is how I define the "forward" and "reverse" direction, based on how it moves when I apply voltage with (+) to the red cable.Thanks for answers, the conclusion would be that the safe choice is just to rotate it in the direction it was designed to rotate as a motor (+ to red). That is what I was thinking as well more or less although I had some argument for the other direction as well. The (weak and partial) argument relates to how torque is applied. I mean when engine has some load the torque is applied "one way" so to speak (one way of thinking about this is how the engine shaft or mount would bend if it would be maleable). In order to reproduce this "bend" when using it as a generator is to put some electrical load on the output and rotate the shaft precisely in the oposite direction. It would make a big difference if the mechanical part inside would be more complicated but I presume it's not, just normal rotor connected cu shaft).

author: G7PSK
author_rank: Super Contributor
timestamp: November 15, 2012, 06:30:42 pm
content: Is it a fixed or rotating field motor. If it is a permeation magnet rotating field it will act as an alternator and can be run in either direction with no problem if it is fixed field you need to check the brushes if angled they will arc badly if run in the wrong direction.

author: rr100
author_rank: Frequent Contributor
timestamp: November 15, 2012, 07:51:56 pm
content: So safest = "natural"/design as motor rotation. In this case I'm almost finished :-)