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I like to mess around with building animated items for my garden railway. To date I have shied away from electronics, mostly because I don't know much about them as opposed to simple electrical circuits.  So in order to get something to reverse itself in a DC circuit, I usually have two power sources (battery) and simply switch off one and turn on the other.  I use mini transmitters and receivers to accomplish this.  

Is there a simple relay that I can use to eliminate some of the bulk of two power sources ?   

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This is how I reverse my Diamond Scale TT.  A simple DC circuit with a  momentary double pole, double throw, center off, cross over switch.  Same could be applied to a double pole double throw relay. 

The center two terminals of this switch are hooked to the turntable DC drive motor.  Red left, Black Right.

Power feed is to the bottom two terminal, (white left, red right) note how the wiring continues with the cross over to the top two terminal.   Red left, white right.

Switch one direction counter clockwise, other direction clockwise.  Momentary switch  returns to the center position.

Last edited by Mike CT

Thanks Rob, but what I was referring to was a relay that can be used in a radio controlled circuit.  The relay would be housed in the animated item along with the radio receiver & power supply.  I have seen the solid state type, but when purchased they never seem to come with a wiring diagram.  

Dan,

Regardless of what type of relay you use, it must have DPDT (Double Pole Double Throw) contact arrangement, also called 2C, where C is SPDT (Single Pole Double Throw). The relay will operate the same as the switch Rob illustrated, above.

Here is an example of a relay contained in a DIP (Dual Inline Package), suitable for PCB (Printed Circuit Board). When the relay is not energized (OFF), power flows from the Power Supply through C (Common) to the NC (Normally Closed) contacts. When the relay is energized (ON), power flows from the Power Supply through C to the NO (Normally Open) contacts. (Excuse my interpretation of all the acronyms, but some readers may not be familiar with them, and I hate to read something when the meaning of an acronym is not provided, and I am left in the dark.)

Relay for Polarity Reversal

Good luck!

Alex

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Last edited by Ingeniero No1
Ingeniero No1 posted:

Dan,

Regardless of what type of relay you use, it must have DPDT (Double Pole Double Throw) contact arrangement, also called 2C, where C is SPDT (Single Pole Double Throw). The relay will operate the same as the switch Rob illustrated, above.

Here is an example of a relay contained in a DIP (Dual Inline Package), suitable for PCB (Printed Circuit Board). When the relay is not energized (OFF), power flows from the Power Supply through C (Common) to the NC (Normally Closed) contacts. When the relay is energized (ON), power flows from the Power Supply through C to the NO (Normally Open) contacts. (Excuse my interpretation of all the acronyms, but some readers may not be familiar with them, and I hate to read something when the meaning of an acronym is not provided, and I am left in the dark.)

Relay for Polarity Reversal

Good luck!

Alex

So it looks like power is always on either way.  What would the diagram look like if there was a center off, so to speak, position on the relay ?

Dan,

For ON/OFF plus Forward and Reverse operations, you would indeed need the third position. There are relays that would step through three (or more) positions, but those are a totally different devices. For the ones we are considering, two-position relays are the ones commonly available. You could use two relays (with two remotes) -  one for ON/OFF, and one to reverse direction.

Also, judging by the relay picture in your link, it appears that it has SPDT contacts, and the fact that it has only five connections would substantiate this observation - two connections for the relay power, and three connections for the contacts; common, normally open, and normally closed.

One possible approach -

Buy a separate DPDT relay (plain relay), connect it and operate it with your remote relay for direction control, and buy another remote relay for ON/OFF.

Alex

 

Last edited by Ingeniero No1

Here's my 2 cents:

The "simplest" solution will be to use a 2 channel transmitter instead of the 1 channel you have linked.  The same seller that was linked for the 1 channel has the 2 channel units for $7.50.  This gives you an A and B button on the remote, and two relays on the receiver board.  From there you can connect the "B" relay to a third DPDT relay following the diagrams posted above for reversing the flow of electricity.  Then connect the feed Positive side of the DPDT relay through the "A" button's relay.  This will give you A button for on/off, and B button for direction change.  

As a note I couldn't find a DPDT relay symbol on the program I used, so I stacked two relays to represent this.  In effect it the same as two SPDT relays that turn on and off at the same time, so you could go that way as well.  

 

Moving on to more complex solutions, for about the same price you could continue to use the single button remote, and add a $2 Arduino and a 2 channel relay board.  With the right programing you would have operation of button pushes of "Push- On(forward), Push-off, Push-On(Reverse), Push-Off."  (As a note, this could also be done with discrete circuitry or some latching relays, but the Arduino is just way simpler.)  

Costs are about the same either way, just depends which you like better, two buttons or one.  

JGL

(Edited error in relay naming from DPST to SPDT)

Last edited by JohnGaltLine

I'm with JGL's first method.  Use the 2-button remote version and 2 of your existing receiver relay modules (or get a 2-channel receiver relay).   One button activates the accessory, the other button selects the direction.  Note the receiver modules you link to have the ability to set the mode of operation to "momentary" or "latching" (they call it "inching" or "self-locking").  For activation you set the corresponding receiver to "momentary" mode so the accessory motor runs as long as you hold down the button.  For direction you set the corresponding receiver to "self-locking" mode where the relay toggles between on and off on each button press. 

s-l500

There are DPDT relays on eBay for under $4 (free shipping) and includes a socket which can cut down on soldering hassles.  The wiring diagram would be as JGL shows.

relay and screw terminal socket

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JohnGaltLine posted:

Here's my 2 cents:

The "simplest" solution will be to use a 2 channel transmitter instead of the 1 channel you have linked.  The same seller that was linked for the 1 channel has the 2 channel units for $7.50.  This gives you an A and B button on the remote, and two relays on the receiver board.  From there you can connect the "B" relay to a third DPDT relay following the diagrams posted above for reversing the flow of electricity.  Then connect the feed Positive side of the DPDT relay through the "A" button's relay.  This will give you A button for on/off, and B button for direction change.  

As a note I couldn't find a DPDT relay symbol on the program I used, so I stacked two relays to represent this.  In effect it the same as two DPST relays that turn on and off at the same time, so you could go that way as well.  

 

Moving on to more complex solutions, for about the same price you could continue to use the single button remote, and add a $2 Arduino and a 2 channel relay board.  With the right programing you would have operation of button pushes of "Push- On(forward), Push-off, Push-On(Reverse), Push-Off."  (As a note, this could also be done with discrete circuitry or some latching relays, but the Arduino is just way simpler.)  

Costs are about the same either way, just depends which you like better, two buttons or one.  

JGL

John, are there some wires missing in your diagram ?   It's late and I'm tired, so I am struggling to follow the path of the electrons from the power source to the motor.  I presume "Motor connection 1 and Motor connection 2 are the two solder lugs on the DC motor.  The 12V symbol is the positive and the negative is the lower right symbol.  

GRJ has it down.  As I said right under the picture: "As a note I couldn't find a DPDT relay symbol on the program I used, so I stacked two relays to represent this. "  Ignore the unused coil on the relays on the right side.  OR, use two SPDT relays if you want and connect the coils together.  

As a side note, my MacBook that I typically use to get on the forum has died at the moment, (Cracked screen), so I won't be able to keep up on things here as often for a little while.  I'll still see replies in email, and if you need some more help I can be reached by email.  

JGL

(Edited error in relay naming from DPST to SPDT)

Last edited by JohnGaltLine

motor reverserActually, if the receivers have SPDT contacts, you don't need any relays, just two receivers.

Normally both sides of the motor are tied to +, so the motor doesn't run. Pressing either button ties one or the other side of the motor to - , making it run in either direction. Pressing both buttons ties both sides to -, so the motor stops.

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Last edited by PLCProf
JohnGaltLine posted:
 

OR, use two DPST relays if you want and connect the coils together.  

Do you mean two SPDT relays?  You can get 12V DC SPDT relay modules on eBay for about $1 each (free shipping).   That might save a couple more bucks though additional wiring/assembly effort is involved.  With some cut-and-paste, that would be:
Untitled a
Or using the original DPDT relay method, some cut-and-paste to eliminate the 2nd coil and make the relay appear as one component (with 2 coil connections on the left, plus 6 contact connections on the right):
 
Untitled
In either case, note that relay coil current is drawn when in one direction (or the other) even if the accessory is not activated.  So given a choice, hook the motor up in the polarity that minimizes relay current relative to how you operate the accessory...seeing as to how you're running on battery power.
 

 

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PLCProf posted:

...Pressing both buttons ties both sides to -, so the motor stops.

And somewhat violently!  I like your idea but depending on the motor/accessory, when you short the windings on a rapidly spinning motor it brakes suddenly often throwing the load or whatever is being driven off the rails so to speak.  So it would be a your-mileage-may-vary situation.

The original method simply removes the voltage from the motor (without shorting the windings) so the motor and load spin down to a stop rather than slam the brakes.

stan2004 posted:
PLCProf posted:

...Pressing both buttons ties both sides to -, so the motor stops.

And somewhat violently!  I like your idea but depending on the motor/accessory, when you short the windings on a rapidly spinning motor it brakes suddenly often throwing the load or whatever is being driven off the rails so to speak.  So it would be a your-mileage-may-vary situation.

The original method simply removes the voltage from the motor (without shorting the windings) so the motor and load spin down to a stop rather than slam the brakes.

That is a point. 

Oh, well.....

Yes, I did mean SPDT, not DPST.  I had a case of the dumb and apologize.  Previous posts have been edited. 

I also thought about simply using the two relays as PLCPROF shows, but figured that operation would be more complex that way.  For the cost of an extra relay it seems worth it to have an on off and direction, as opposed to having to sort through which way the buttons are pressed. 

JGL

JohnGaltLine posted:

...

I also thought about simply using the two relays as PLCPROF shows, but figured that operation would be more complex that way.  For the cost of an extra relay it seems worth it to have an on off and direction, as opposed to having to sort through which way the buttons are pressed

Not sure I understand your comment.  PLCPROF method seems simpler to me.  You press button A to make motor run FWD, you press button B to make motor run REV.  

OTOH with the external DPDT relay acting as a direction switch, the relay toggles on each press and now the operator must "remember" which direction it was last set when activating the motor.  Some of these receiver modules have a little LED showing its relay is closed...but in a remote control application where the accessory is some distance away (and apparently the OP has an outdoor layout) it may be difficult to see this direction indicator.  Of course with our engines, the diesel's directional headlights or steamer's tender backup light indicates which way the motor will turn when you crank up the throttle!

I'm sure there are some accessory applications where the sudden motor braking might be acceptable...or even desirable.  For example with steam engine smoke fan motors the windings are shorted to instantly stop the rapidly spinning DC motor to generate distinct "puffs" of smoke.

 

Well, (to partially redeem myself) you could wire two DPST relays so one was forward and one was reverse. The NC contact on one of the receivers could be used to lock out the other relay to prevent shorting the battery when both buttons were pressed. Then you would have a forward and a reverse button without the braking effect.

Last edited by PLCProf

Here's a quick sketch I made for operating a switch drive in my garden railway.  The Switch drive is either an LGB or Piko product.  They both work on DC.  Well, not exactly.  The LGB drive uses half wave AC if you wire it using their EPL system, but it will work on short bursts of DC.  The 14.8 volt Li-on battery will be used to power the switch drives.  The 12 volt power supply will power the receiver.

Please let me know if you see something that shouldn't be.

 

IMG_3303 

 

 

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