Posted on Feb 5, 2014

AC power is rectified and applied to the motor in the same polarity when the momentary switch is held in one direction and reversed polarity when the motor is held in the reverse direction. The remote car starter package that I used includes a control unit, an extended range receiver, a status LED, a valet switch, and four wiring harnesses. In thi

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s application, much of this is not needed and can be discarded. All that is needed is the control unit and extended range receiver. The receiver plugs into the control unit with a supplied cable. I made only 5 connections to the control unit: power, ground, unlock, lock, and trunk. The latter three connections are outputs, and in their default configuration act just like momentary switches to ground. For the PLC, I`ve chosen an E10-npn model. The npn  designation refers to the PLC outputs, which are NPN transistors switched to ground. A relay output model is also available, but not suitable, as the relay outputs are single pole only. I need at least double pole double throw relays to switch the lift motor polarity, so I used external relays. The radio receiver outputs, which are switches to ground, match exactly the inputs of the E10-npn. I connected these directly. I also wired the panel switches in parallel so that I and the service company personnel can operate the lift without the remote. My up and down position limit switches will also be simple switches to ground (I have these on hand but have not yet installed then). As the PLC inputs are low voltage and low current, safety in the case of a short or exposed wire is not a big concern. (Note that a short on the limit switches will cause operation to stop, which is a good fail safe mode. ) In place of the original momentary DPDT switch, I substituted a pair of relays...

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