Here’s how the two SPDT relays work to reverse polarity/direction of a DC motor. I’ll be using this circuit to open/close high tunnel sides and gable vents based on the temperature inside the tunnel and will also be closing the sides in high winds. If it’s hot and windy, I’ll have them close 80% of the way using a proximity switch to stop them at that point. I originally found the image as below, with all wires being shown as black. I made my own graphics and added color and in drew it in all scenarios
Pretty ingenuous use of relays. Not my idea. Just something I found on the interwebs. With the motor I’m working with, there are two brushes. One goes to positive terminal and one to negative so there is continuity between them already which is why applying positive voltage going to both does nothing. Naturally there is no continuity between either terminal and the metal case of the motor. When I found this method and a graphic like the top image, they had the positive and negative from a power supply reversed, giving positive voltage to both NC terminals which I thought seemed backwards to me. I’ll be using a logic controller to run the relays and will never be applying positive voltage to both terminals so the last image doesn’t really apply.
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