Three wire bi-directional DC motor 2

[Clyde38]

How is a DC motor operated bi-directional with three wires. I have had an inquiry for a DC permanent magnet motor to have three wires, with the third wire determining the direction of the motor. All the searching that I've done always leads to a three phase motor or an AC motor. I think that I have seen this before, however I can't remember if I did or how it was accomplished if I did see it. The exact inquiry states "Must have three wires - two motor leads and one return lead (When one lead is excited, motor will rotate in one direction. When the other lead is excited, motor will rotate in the opposite direction)".

Clyde Hancock
Design & analysis of electric motors and generators

http://www.motorconsultants.com

 

[BrianE22]

Two field windings perhaps? They share a common and they are wound in opposite directions.

 

[edison123]

Sounds like BLDC servo motors.

Muthu

http://www.edison.co.in

 

[dArsonval]

A type of motor known as or called a "split-series" D.C. Motor has just three leads
and is externally reversible. (Typically found in low voltage automotive applications.)

Connection Diagram from Veinott's 1939 text book attached.

John

 

[Clyde38]

Thanks for all of your answers. I'm positive that this is a DC motor, not a BLDC. I was under the impression that they are expecting a PM DC motor, but maybe it is a field wound motor.

Clyde Hancock
Design & analysis of electric motors and generators

http://www.motorconsultants.com

 

[electricuwe]

You will find these kinds of motors in older model railroad locomotives from Märklin. They operate it with AC, but it runs with DC as well.

Armature and field winding are series connected and there are two windings for the field. Depending on which one you connect to the supply (the other one left open) there the field will be in one direction or the other and the moto will run cw or ccw.

 

[waross]

According to the diagram the field winding is center tapped.
The field will be energized with the supply voltage.
The armature is designed for 50% of the supply voltage.
The direction of the current through the armature and the direction of rotation depends on the side of the supply that the free armature lead is connected to.
That is according to the link posted by dArsonval.

There is a type of AC motor often used for HVAC damper motors that has three leads.
#1 is the common line.
There is a capacitor connected between #2 and #3.
If #2 is connected to the other side of the line, #3 becomes the starting winding and the motor turns one way.
If #3 is connected to the other side of the line, #2 becomes the starting winding and the motor turns the other way.

Bill
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