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Two DPDT switches with timing for one motor

Hi,

I have a motor (12V DC) that I need to be able to operate both backwards and forwards from two locations. The simple way is to connect it with two DPDT switches with momentary on in each end and off in the middle, i.e. also called (on)-off-(on). The reason for using momentary switches is that there would otherwise be a risk of short circuiting if one of the switches are left in on-position. However, I almost always need the motor to go to preset limits in both directions which takes a couple of minutes (the limits are built-in functions in the motor, so no need to set those). So I was wondering if there was a cheap and easy way of inserting a kind of timer or similar that would only leave the connection on for a couple of minutes only (and yes, there would still be a risk of short circuiting within those two minutes, but it would be unlikely to happen)?

Or perhaps there is an even simpler way of doing it?

Any ideas would be welcome. In (the likely) case the above is not clear, perhaps this will help: I need it to operate a curtain, i.e. moving the curtain up and down, but I need to be able to do that from two different locations. Preferably it would be good if I could also stop the engine somewhere in the middle - as I would be able to do with a switch simply be releasing it. The best/cheapest/easiest way would, I think, be to have two DPDT switches with a spring or something with a couple of minutes delay, i.e. if it is left in the on-position for more than two minutes it would automatically spring back. But such a thing seems not to exist... or?

Would be grateful for any inputs.

Erik


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Here's a relay based circuit I designed for someone on here ages ago, which will do exactly what you want. At the bottom are the "up and down" switches.

Copy of Motor door.png
eriktoft (author) 4 years ago
Dear steveastrouk, bwrusssel and Re-design. Thanks a lot for your replies. I now realise I have not been clear enough in the original questions (have now edited it): The limits can be set on the motor, so there is no need for limit switches.

To steveastrouk: I wonder if that would simplify your design?
And do you have a rough estimate how much the components would cost (to be honest I have no idea what component it is that are shown on the design, but I was thinking I could then find somebody to make it for me).

Erik
So you can just turn the motor one way, or the other, and it will stop ?

In that case you need this circuit, which uses a single relay, with contacts rated for your motor - cost should be less than 15 USD.

Steve
new-1.jpg
eriktoft (author)  steveastrouk4 years ago
Thank you so much for this. Much appreciated.

Erik
bwrussell4 years ago
I'm not very familiar with them but could a few 555's hooked up to transistors or relays work? You wouldn't have to hold the buttons down and I believe they have a reset pin so you could cancel the motion. Add in limiting switches tied to the reset and it would prevent overruns, especially if you stopped and restarted which would reset the timer. It's more components (4x 555's (?), diodes, and transistors/relays and 8x momentary switches) but it should get the job done.
Re-design4 years ago
You need to add a limit switch at each end where you want the motor to stop.