I wish comments on how to best achieve a design involving two limit switches on a DC motor, but which does not reverse the motor.

I've researched this design already on this forum; here's my work, I could not find an answer hence this post.

Circuit for a DC motor with 2 microswitches reversing direction

(and several related posts)

My design does not involve reversing a motor.

This is my design

Operation of device: a programmable timer controls an AC power supply, AC2. A seperate AC source, AC1, powers a heat lamp controlled by a AC Thermostat. AC2, via a transformer, powers a DC motor. The DC motor has a shaft that always rotates clockwise, and an “arm” that contracts two “limit switches” (SIC: not sure if that’s the right term!) such that: (1) when Limit Switch 1 touches (brushes past) the DC motor Arm at point “A”, the power to the DC motor is cut (but the heat lamp continues to operate on its own circuit). Then, after a certain time, the DC motor is activated (powered on), by the programmable timer (or is there a better way?), and the DC motor shaft continues to rotate until the Arm touches Limit Switch 2, whereupon the power to the DC motor is cut for a certain predetermined time, and the process repeats. How to build this, using off-the-shelf components?

  • \$\begingroup\$ It can be made with old-school relays and timers, with a micro-PLC or with a microcontroller. If it's a factory situation a PLC would probably be indicated. \$\endgroup\$ – Spehro Pefhany Feb 13 '16 at 16:26

Something like this timer (picked at random) would do the job. It's a pulse timer and, when triggered, engergises for a preset delay and then de-energises even if the trigger is still on.

enter image description here


simulate this circuit – Schematic created using CircuitLab

Figure 1. Dual timer interrupt timers.

How it works

  • The transformer is wired through a normally closed contact of TIMER1. The motor will run.
  • When SW1 closes the timer will energise for a preset time. The normally closed contact will open, disconnecting the motor.
  • After the preset time the timer will drop out, the motor will restart, and after a short delay SW1 will open again.
  • SW2 and TIMER2 perform the same function for the second position.
  • If the same stop delay is required in both instances then only one timer is required and SW2 can be wired in parallel with SW1.

Timer should be rated for 230 V AC power and contacts rated at least for the transformer current.

And no, it's not a "limit switch design" as there are no physical limits to the degree of rotation. "Cam switch design" might be more appropriate.

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  • \$\begingroup\$ I thank you. I think however this design is too complicated for me (and I have an engineering background, though I'm in business). For one thing, here in rural southeast Asia I don't think I can even find a breadboard to check this design, and it seems each switch costs USD $45 or so. Further, not clear where to buy this timer, is it similar to this one? (charter-controls.com/product/time-delay-relays/on-pulse/…) FYI, just to ship something from the USA here takes 30-50 days.Thanks! \$\endgroup\$ – ProposedWaterPlan Feb 14 '16 at 2:42
  • \$\begingroup\$ I will switch to an alternate design involving linear actuators, that maybe is simpler, and will link here. I will mark 'transistor' 's answer as correct, and close this thread. Thank you for your time. \$\endgroup\$ – ProposedWaterPlan Feb 14 '16 at 2:44
  • \$\begingroup\$ Just for my future education, what are the L, N lines on the timers and why are they tied? Is this like a sort of X-OR combination? How do you know to tie them together? Is CircuitLab the way to virtually test this design without a breadboard? Many thanks. \$\endgroup\$ – ProposedWaterPlan Feb 14 '16 at 3:01
  • \$\begingroup\$ electronics.stackexchange.com/questions/217117/… - this is, fyi, an 'alternate design' I am exploring at the moment. Quite possibly it's more expensive but easier to make than this design. \$\endgroup\$ – ProposedWaterPlan Feb 14 '16 at 5:53
  • \$\begingroup\$ The devices I proposed are industrial timers. Each requires a Live and Neutral (your question says you're using an AC supply). I've used a normally closed contact of each to switch your motor on and off. Why don't you explain what you are really trying to do? Then we can propose the simplest solution that will do the job. \$\endgroup\$ – Transistor Feb 14 '16 at 9:17

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