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how to reverse the polarity of a DC motor using a DPDT relay, limit switch, and timer? Answered

Ok, i am not an electrician and understand very little, but here's what i want to do.  I have a reversable 18V cordless drill I have taken apart to get at just the motor.  What I want it to do is turn on automaticallly with a timer in one direction and shut off (with a limit switch?) after about 2 seconds.  About 14 hours later I need the opposite action. Both actions automatic using a timer with AC power.  The application is a door opening and closing veritcally (chicken coop door).


I designed this for another 'ibler a few months ago, for his chicken shed too.

You need to find a suitable timer.

The first circuti is made up of parts from Radio Shack, the second kind of shows the circuit your making. Check the pin out of the relays carefully.

Hen door relays.jpgmotorrelay.jpg

PS Consider TWO down switches on the down action, one on the actual door mech, the other on the door edge, so you don't dice your livestock.

PPS The last one we also put a photosensor on, rather than a timer.


Hey Steve, thanks for the info. few more questions, as stupid as they may be... can i use a 12V timer if the motor is an 18V motor with a 25V charger? also the timer can only do 1 minute intervals like an irrigation timer. is this still ok with this circuit? i was thinking something like this:

thanks again, steve

I know this is very old and I hope you found your answers by now. But if you didn't here they are.

Yes you can use a 12v timer with a 18v motor. You have to use two different power sources or step down the voltage with a dc regulator. Tiny thing you can get at any electronics supply store. The same goes for the charger. Step that down to 19 volts first.

However you can NOT do that with the configuration in the diagram up tgere.

Use mine. Just wire the 12v power to the timer and the coil side of the relay and the 18v power to the contacts side of the relay.

Chicken Door 1 DOWN.jpgChicken Door 1 UP.jpg

I know this is very old but just so others can make use of this.

All you need is one timer, one 8 pin relay and 2 diodes.

Wire as shown in the diagrams. The first is the down or closed position. And the other is the up or open position.. I have diagrams for photocell and door down blinking LESs that look like predator eyes at night. Just ask.

Chicken Door 1 DOWN.jpgChicken Door 1 UP.jpg

Your looking for a H bridge configuration as Steve has drawn for you - Lots here from a search.


Hi Rick, can i use a 12V timer if i have an 18V motor? i can't find a timer that will turn on/off in seconds. best i can find is 1 minute intervals. will that still work?