DC motor polarity reversing switch - wiring diagram


Z-WAVE ® is used in many new home automation systems, and we are announcing our new Z-Wave interface for our roller shade and blind motors, and Z-Wave control of our skylight and window opener systems. (ZWAVE motor control article series is here). We also have interfacing for all other home automation systems via relays (see our compatibility guide).

Raspberry Pi ® Tinkerer Alert: You may be interested in our article series on how to turn a Raspberry Pi into a low cost home automation controller.

DC motor polarity reversing switch - wiring diagram

FAQ: DC shade motors - can the polarity be reversed with a simple switch?

To reverse our radio equipped blind and shade DC motors, you would use our RollerTrol™ multi-channel RF (Radio Frequency) remote controls (and you can add a ZWAVE home automation hub), so this article would not apply. However, if you are using our non-radio DC shade motors or window/skylight openers, the switches described here can be used to reverse polarity and activate the motor in either direction, providing full reversing capability.

Reversing DC motors requires a specific type of switch, namely a DPDT (double pole, double throw) switch wired in what is known as an 'H Bridge' configuration (pictured at right), so called because the current flow looks like the letter H when you look at a schematic diagram. The 4 upper and lower poles are cross-connected and the motor and power supply are attached as shown in the picture.

We also have a proper DC motor reversing wall switch with open/close/stop buttons. It handles the protected motor reversing break-before-make with a proper H bridge, and it has an internal header you can later connect a home automation system to. (ZWAVE blind and window opener motor control example is here)

You can use slider switches or toggle switches, as shown here. A 'center off' position is also desirable so that you can stop the shade motor at any point. Please note that you should always allow the motor to stop before reversing direction. If you go directly from forward to reverse, it will generate a huge EMF pulse that is very harmful to any DC motor, and you will shorten the life of the motor considerably.DC motor reversing switch - DPDT slider typeDC motor reversing switch - DPDT toggle type

A spring loaded 'center return' type is not the best choice because it would require that you stay at the switch until the blind or shade has reached its full excursion.

This is not necessary as our motors will automatically stop when the travel limit in either direction is reached. This is an especially useful feature when the motors are used for really tall windows such as those found in an atrium or foyer (our motors are capable of unlimited turns between travel limits).

PLEASE NOTE: if you use manual switches like this, rapid switching of the motors from forward to reverse can damage the motors due to powerful counter-EMF forces. Please be sure to allow the motor to stop first, before changing direction. This is generally true of any DC motor.
