Remote switches to control dc motor

Thread Starter

Mark Clemmens

Joined Jun 21, 2020
7
I am adding a geared motor to a turntable on a model railroad module. I would like to control the motor direction and planed to use 2p2t switches on each side of the module using a circuit like this: DP DT and motor.jpg
Is there an easy way to be able to route power to one switch or the other to avoid a short that would happen if two people tried to operate the motor at the same time?
 

dendad

Joined Feb 20, 2016
3,569
You could have the 2 switches controlling a couple of SPDT relays that do the motor switching.
That would solve your problem.
 

ronsimpson

Joined Oct 7, 2019
726
If you use the 3 position switch; any switch set to off (center) will stop the project. All switches must be in run.
If you use the 2 position switch; there will not be a off. All switches, don't touch the switch = run this direction. Flip the switch reverses the direction.
 

dendad

Joined Feb 20, 2016
3,569
Could you expand on this? How would this eliminate a short situation if both of the switches are activated at the same time?
If both relays are operated, it is just the same an neither operated.
Both ends of the motor are connected to the same polarity, and the circuit is open.
 
You can build an n-way switch. e.g. https://en.wikipedia.org/wiki/Multiway_switching using SPDT and DPDT switches, but first you would need a single signal to open/close the rotary turnstyle.

Don't know if you need limits or just have to reverse the polarity or what.

Motors such as door lock motors are controlled with two SPDT relays. The advantage is you get dynamic braking. You can add limit switches as long as the switches can handle the coil current.

Here (motor_limits.pdf) https://forum.allaboutcircuits.com/threads/need-some-direction-on-relays-and-limit-switches-for-greenhouse-roof-window-control.134958/post-1131056 is a comprehensive method of control.

You do end up with two relays with.
On On - this also brakes the motor
On OFF - one direction
Off ON - the other direction
OFF OFF - brakes the motor

You can add another relay that could give you (position 1)/(position 2) type of control.

You would have state info, so you can wire that next to the switch. Put the state info to the right or left of the switch. Flipping the switch the other way would reverse the state.

So, you can potentially have n-station control with indication.

You could use 3-lead bi-color LED and say indicate moving with yellow and the state with RED.
 

crutschow

Joined Mar 14, 2008
25,132
Sounds like two SPDT relays with two momentary push-buttons (or a momentary SPDT switch with center off) for each control point is what you want.
That would not have a shorting problem with more than one person trying to control it at the same time.

Note that to minimize relay and switch contact arcing you will need to add diodes for inductive spike suppression, one on each relay coil, and four on the relay outputs (below).

1592838904541.png
 
Last edited:

Thread Starter

Mark Clemmens

Joined Jun 21, 2020
7
Sounds like two SPDT relays with two momentary push-buttons (or a momentary SPDT switch with center off) for each control point is what you want.
That would not have a shorting problem with more than one person trying to control it at the same time.

Note that to minimize relay and switch contact arcing you will need to add diodes for inductive spike suppression, one on each relay coil, and four on the relay outputs (below).

View attachment 210450
So adding another SPDT center off at the bottom of the diagram (one on each side of the module) would not cause a short? what happens if the two switches are set in opposite directions at the same time?
 
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