Help with a simple DPDT relay circuit please

David Hennessy

May 2, 2015
22
Hi guys, this is my first post here, kinda ashamed that it is a question instead of an answer to help others.

So here is my problem; I need to move a motor one direction when it's hot, move it opposite direction when it gets cold, now that part is OK, It's working that way with a simple thermistor circuit and a DPDT relay, but i need the motor to stop when limit switch is pressed. Currently the two limit switches that i have inserted only turn motor off when it is rotating clockwise and not anti clockwise. Here is how I wired it:

In otherwords it is semi working, when the motor turns clockwise Limit S2 turns it off, but when it turns anti clockwise Limit S1 does nothing, although Limit S1 turns it off when the motor turns clockwise as well, which is pointless.

This is the DPDT relay i'm using http://www.rapidonline.com/design-te...-relay-60-4690 (idk if it helps)

Not sure if i'm explaining myself but hope there is someone here that could help me out.

PS: go easy on me, i'm new to this and mostly can't understand wiring diagrams, something simple would be appreciated.

David Hennessy

May 2, 2015
22
If i could get some help it would be extremely appreciated as this is for a school project i'm working on,

I'm willing to pay up to €5 via paypal (not much, but all i have) if you have a simple solution to my problem :9

Arouse1973

Dec 18, 2013
5,178
Dont you dare think about paying for anything. Its free here. Oh and welcome to EP.

Arouse1973

Dec 18, 2013
5,178
You need to put one of the switches in one of the normally open circuits. You have both on the NC circuit. I assume the motor moves one direction when the relay is off and the the other direction when on?
Thanks

David Hennessy

May 2, 2015
22
Yea the motor moves one direction when relay is energized and opposite when it's de-energized.
Going to try that now.

David Hennessy

May 2, 2015
22
Thank you!

It works! thank you so much for the help

David Hennessy

May 2, 2015
22
Really sorry to bother you again, while testing it out a bit more i realize it is 99% working, What it does now is when it turns anti clockwise, limit switch 1 turns it off when pressed, which is what i wanted, but when the relay is de-energized the motor won't move unless Limit S1 is not pressed.

Limit S2 works perfectly, when it's pressed motor stops and when relay is energized it moves in the opposite direction.

Maybe inserting a diode in series with Limit S1 would work? But not sure what type of diode and how would i do it. Although if there is a way without having to buy a diode it'd be great.

If you could help me out again It would be very much appreciated, again sorry for the trouble, thought it was working but turns out i had a gear loose so it looked like it was.
Thanks.

Arouse1973

Dec 18, 2013
5,178
Hello
What switches are you using?
Thanks

Arouse1973

Dec 18, 2013
5,178
You need a switch with a normally open and a normally closed. This might work. The important part is the direction of the motor when the relay is off must go towards S1 and not S2. The relay direction when the relay is on must go towards S2 and not S1.

Operates as follows, when the relay is off current will go via the top switch and relay contact. When the motor hits S1 the motor will stop and 12 Volts will be supplied to the other side of the motor via S1.

When the relay turns on this will then the contacts change over and put GND on the top contacts and because the bottom contact now has 12 Volts from the bottom switch the relay will go in the other direction. When S1 releases as the motor moves the bottom relay takes over supplying 12 Volts and it carries on moving.

When it hits S2 the circuit breaks and now 12 Volts appears on the other side of the motor, ready for it to move back. When the relay turns off the 12 Volts already on the relay via S2 now moves the motor in the opposite direction.

As S2 releases the 12 Volts from the top relay contact takes over and the motor turns back the way it came.
Thanks

David Hennessy

May 2, 2015
22
Hello
What switches are you using?
Thanks
The switches i'm using are some i got from my school, they have 3 terminals; common, normally open, normally closed. Not sure on the specifications.
They look exactly like this:

David Hennessy

May 2, 2015
22
You need a switch with a normally open and a normally closed. This might work. The important part is the direction of the motor when the relay is off must go towards S1 and not S2. The relay direction when the relay is on must go towards S2 and not S1.
Not quite sure if i understand, in other words i wire S1 instead of Common and NC to Common and NO, and make sure the motor is running towards S1 when relay is off?

David Hennessy

May 2, 2015
22
This should give a better idea of what i'm doing:

that blue 'thing' is the window that opens when it's hot and closes when it's cold. The problem is i have no way of stopping the motor when the vent reaches the maximum points as in the short video above.

Arouse1973

Dec 18, 2013
5,178
Not quite sure if i understand, in other words i wire S1 instead of Common and NC to Common and NO, and make sure the motor is running towards S1 when relay is off?
The common of the limit switches go to the motor. The NC of the switches go to the common of the relay. The NO of the switches go to +Volts I just used 12 V as an example. The NO and NC of the relay connects as in the diagram I drew. When the relay is off the motor drive must go towards S1.

Last edited:

David Hennessy

May 2, 2015
22
ok i'll try that, thanks Adam. I'll post here if it works or if there is any other problem i encounter.

Arouse1973

Dec 18, 2013
5,178
ok i'll try that, thanks Adam. I'll post here if it works or if there is any other problem i encounter.

OK no probs.
Thanks

David Hennessy

May 2, 2015
22
It does work I'm 100% sure now . Thank you very much.

Arouse1973

Dec 18, 2013
5,178
Good David. Hope it all works ok now.

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