Limit Switches

Hi Dan, I learned a lot about limit switches when I was building my lift bridge and yes they will work if you can place them where the door will hit the little activation lever. Here is a diagram of how I wired it, got it from Stan. And here is a video of how it turned out on my bridge.

Thanks Mike.  I'm trying to figure out a way to use an off the shelf limit switch, but my brain is too tired to do it right now.  In the meantime i have come up with a belt and suspenders plan.  In my diagram the brass flywheel is actually mounted on the front of the motor you see just above.  I drew it this way for clarity.  The relay is radio controlled.  On the brass flywheel there is an insulated section that would break contact as the doors were fully opened.  By using the relay, power would be switched to the brass contact on the left, thus allowing the doors to close.  It's not that difficult to build, but if there is a simpler method I'm all in.  I've included some photos of the project thus far.  

If I understand your application, it seems your motor can only spin in one direction because one of the motor terminals is always connected to the "-" side of the DC power source.  The purpose of a DPDT switch (or DPDT relay) in these circuits is to swap/reverse the polarity of the DC to the motor so that it can rotate in both directions.

If you wire your brass flywheel and contacts as shown below, it can function in place of the pair of limit switches Mike used in his impressive bridge design.  Mike had a manual DPDT switch which he flips to start motion toward to other limit.  You would simply replace the switch with your remote wireless DPDT relay.

Hi Dan, sure looks like you have a sweet idea and it works. I would stick with Stan he knows his stuff and sure makes things easy to understand! He sure helped me out, along with Elliott and others!

stan2004 posted:

If I understand your application, it seems your motor can only spin in one direction because one of the motor terminals is always connected to the "-" side of the DC power source.  The purpose of a DPDT switch (or DPDT relay) in these circuits is to swap/reverse the polarity of the DC to the motor so that it can rotate in both directions.

If you wire your brass flywheel and contacts as shown below, it can function in place of the pair of limit switches Mike used in his impressive bridge design.  Mike had a manual DPDT switch which he flips to start motion toward to other limit.  You would simply replace the switch with your remote wireless DPDT relay.

Thank you Stan.  Yes, the motor will spin in one direction only.  You scheme looks simple enough, that even I can get it.....LOL  

Your initial inquiry was about limit switches in a DPDT configuration.  The DPDT configuration is used because it's a simple way to reverse polarity to a DC gearmotor. 

But it appears you designed your mechanism to operate with the motor rotating only one direction with one rotation corresponding to one opening and one closing.  Hence you don't need a DPDT switch or relay but simply a SPDT switch or relay.  The limit switches (or your brass flywheel) performs the same function of interrupting power to the gearmotor upon reaching the destination.

So was this just a matter of curiosity or perhaps something about your remote-control relays that motivated your inquiry?

Hi Dan, not to sound silly here, but have you switched the polarity on the motor? I was under the impression that most DC motors will run in both directions. But then again I have been wrong many times!

mike g. posted:

Hi Dan, sure looks like you have a sweet idea and it works. I would stick with Stan he knows his stuff and sure makes things easy to understand! He sure helped me out, along with Elliott and others!

I'll second that!

hook the limit switch to a multi contact relay coil and do what is needed with the relay contact .that way the limit switch control multiple circuits. a 3pdt can switch 3 circuits for example

Dale H