Using the PDM to use 2way DC motors

[alexmas0n]

I am trying to wrap my head around using my PDM to control electric window motors.

Here is the logic I have:
Output X (window up) goes to motor pole A
Output Y (window down) goes to motor pole B
Both poles on the window motor are also grounded to chassis.

Am I doing this correctly?

[Stephen Dean]

Hi Alex,

If you apply 12V+ to each one of the poles separately with the motor chassis grounded, does the motor drive in two different directions? I have seen these motors in two different configurations, one being where they had two poles, and to drive the motor in each direction that polarity was swapped between the poles, the other where there was a separate ground pole, and the motor was driven in the desired direction by applying power to the relevant pole. If it is the second type of motor, then this is possible to be driven by the PDM in the manner that you described, the first type of motor is more difficult to do with a PDM.

What does the winder system have in the way of limit switching?

[alexmas0n]

Hi Alex,

If you apply 12V+ to each one of the poles separately with the motor chassis grounded, does the motor drive in two different directions? I have seen these motors in two different configurations, one being where they had two poles, and to drive the motor in each direction that polarity was swapped between the poles, the other where there was a separate ground pole, and the motor was driven in the desired direction by applying power to the relevant pole. If it is the second type of motor, then this is possible to be driven by the PDM in the manner that you described, the first type of motor is more difficult to do with a PDM.

What does the winder system have in the way of limit switching?

Thank you for the quick reply.

RE: Motor behavior
Applying 12V to either pole doesn't move it with chassis grounded. Only when I connect the other pole to the chassis ground does it move.

I just realised with what you said that if I ground both poles and apply power to either outputs, power will seek the point of least resistance... so basically the output would circuit right to ground?

RE: Winder system
I'm very much a newbie - I don't know what this is

[Stephen Dean]

Hi Alex,

Driving a motor like this with the PDM is not the easiest thing to do, as the PDM is designed to run a device that works in a single direction, such as fuel pumps and coolant fans. What you need to do is to be able to drive a single motor in both directions using only two wires, as per the diagram below.

Single Motor both directions.PNG (22.83 KiB) Viewed 11673 times

As the PDM only drives the outputs High Side, and doesn't have the ability to sink voltages to ground, you need to find a way to ground the opposing pin when the the motor is driven. A way that this could be done is using the MoTeC DHB (Dual Half Bridge) in a full bridge manner. This will allow for one side of the motor to be driven whilst the other side is sunk, and then change the direction of travelled by swapping the Pin status. If you used a DHB, the PDM can be used to supply power to the DHB, and then the window switches would be wired directly into the DNB to control the direction of the motor.

You will not have any travel limitation with this system, as there is no easy way to integrate the limit switches into the operation of the controller.