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Curious if a series wound 12 volt DC motor with 3 terminals can have DC current applied to act as a light holding brake like is done with AC motors?
Curious if a series wound 12 volt DC motor with 3 terminals can have DC current applied to act as a light holding brake like is done with AC motors?
The problem with your simplistic approach is that you need a way to monitor motor commutation. In other words, a feedback device.
AC motors controlled with a VFD in vector mode accomplish this quite well but the feedback comes from the magnetic flux in the motor windings.
You have the choice of using an electro-mechanical brake or else going to need to use a more complex motor controller.
I've seen several AC motors that use a simple dumb rectifier circuit to put DC into one winding which stops the motor from spinning right away and stops it in exactly the same spot every time. This setup is used on toolchangers a lot. No VFD. No feedback.
I want to do the same thing, but I don't care about position accuracy and I don't need a rectifier because we already have DC here. I'd imagine I need a way to limit current (I can figure that out). The motors are essentially reversible starter motors. The windings are .100" thick copper.
There is a difference in motor design between AC and DC.
You can use the DC motor as you intend to slow rotation down but the braking force is a function of the motor current going through the braking resistor. As the rotation rate decreases, the braking force will decrease to zero at zero rpm.
AC braking using DC injection operates by the armature position in essence locking into a winding position. You will have a braking force at zero rpm to max motor speed. With AC injection, you also have to be careful to not cause winding overheating so you either need to turn ovff the DC injection after Stop is achieved or else use some additional controls to reduce the DC current to a tolerable level resulting in a descrease in the braking force.
The problem with your approach is, unless you are going to use tach feedback, the motor controller has no way of knowing if the motor armature is rotating forward, reverse, or stationary.
You could achieve what you are trying to do with an AC motor using vector mode control. This would accomplish everything you are trying to do with the DC motor that you can't.
If you still do not understand why I am telling you that you can;t do it the way you are trying to do it, then you need to study up on AC/DC motor design and theory. Then you will understand why.
Forgot to mention, it also has to work under water. That kind of rules out electronics.
I guess I need to figure out exactly what these motors are. They just say series wound 12V 2.5KW. They have 4 terminals on them and are reversible hence why I thought I might be able to stop one with some current applied to one field coil.
There is a motor type that will do that nicely, called a "hydraulic motor".
Bill
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