Moderator: pebe
pebe wrote:There was a similar application some time ago that used 555 timers. You may be able to modify the circuit. Search this forum for 'chicken coup'.
pebe wrote:Does the actuator have two limit switches? When do they open and close?
pebe wrote:I meant, do they close at the end of the actuator travel in each direction, or do they open?
pebe wrote:OK. You can start the operation by switching the power supply on (that means you have to turn it off after every op), or you can start it with a push button (leaving the power on all the time).
Which would you prefer?
pebe wrote:Sorry, I got the wrong impression from your first posting. I assumed you wanted a timer that would operate the actuator for between 1 and 90 secs, and when the time period had ended the actuator would retract.
Am I correct in thinking now that you already have an external timer which applies power to the actuator for that period, and you just want a circuit to retract the actuator?
pebe wrote:I have looked at the wiring-up drawing given on the Firgelli website, but it is just a wiring diagram that treats the actuator as a black box. So it is difficult to see what is going on inside it.
The limit switches have no control over operation of the relays because the remote unit turns on one or other of the two relays to effect forward and reverse of the motor. The switched poles of the relay (pins 4 & 5) are paralleled, so there can be no selective control over them by the limit switches. The motor must therefore be limited by disconnecting one or other of the feeds to the movable contacts (pin 1).
So it looks as though the information you were given that the switches closed at stop was wrong, and your original idea that limiting was by opening series switches with parallel diodes was correct. The diagram will not work with switches that close at stop. That also seems to be confirmed by the positioning of the optional (series) limit switch.
On that basis, the attached circuit will do what you want. The V+ rail is permanently energised. When the timer turns on the DPCO relay the motor runs one way for the timed period. At the end of the period when the timer switches off, the relay de-energises and reverses the polarity to the motor to make the motor run the other way until it is stopped by the limit switch.
If, when you take delivery of the actuator, you find that the limit switches actually do close at the end of the travel, then it will be necessary to insert N channel power FET drivers at positions ‘A’ and ‘B’, with their gates forward biased. Both would normally be switched on, but limit switches connected between gate and source of each will turn them (and the motor) off when closed. More of that if the situation arises.
I hope you find that helpful.
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