What kind of time delay switch to choose to reverse motor for just a couple of seconds

12vdelayrelaytime

I would like to know the following:

I have a motor driving a lead screw which transports a part either up or down.
When going down and something comes in the way a switch gets triggered by the obstical which stops the down movement until the obstical is removed (and the switch released). It will continue to go down until it hits an end switch which stops the whole thing.
All this works fine.
However, now I would like to reverse the motor if something gets in the way. So…if going down, something gets in the way I do not want it to just stop. I would like it to go up for 2-3 seconds and then continue to go down until it reaches the end switch which stops everything as usual.

So…I tried to find a time delay relay and noticed that there are quite a few options. A few I do understand and know I can't use them for my application. The other ones….I have to admit….I don't really understand how they work.

Could somebody be so kind telling me what kind of time delay switch/relay I have to choose and how to integrate it in to my current circuit.

BTW a programmable timer will start the down movement if in "on" mode. If timer turns off the motor reverses and the part goes up. Everything is 12V. A DPDT relay reverses the motor.

I hope I gave all necessary info necessary.

Thanks a lot!!!

Best Answer

The simplest way is to use the drive mechanism itself as the timer. Have a DPDT switch which reverses the motor when it hits an obstacle, and arrange the coupling so that the switch doesn't turn off again until the mechanism has backed off a bit. A micro switch with a long lever arm may do it.

If that doesn't provide enough delay or clearance then you will have to use a timer. This would be switched on by the obstacle detect switch, then operate a DPDT reversing relay for 2~3 seconds. Here's a suitable timer:-

Kemo 113A Time switch

Depending on how your existing relay is wired, you may be able to use it for both jobs. The timer outputs would be wired together so that the relay turns on (or off?) to reverse the motor if the obstacle timer is running or if the down timer is finished.

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