How do I adapt twin coil control to control single coil

Thread Starter

Brucey30

Joined Jul 3, 2017
36
this has to do model railroad switches (turnout). I have a switch on a panel and it has 3 wires for 2 coils. I the turnout has 2 coils. Energizing on coil turn left. Energizing on the other coil turn right. Works fine. BUT the diffident company railroad turnout I want to use has only 1 coil. And changing the rails left or right by changing the coils polarity by the 2 wires and using same company's controls. I do not want to use company's same controls as maker of turnouts.
I'm thinking there should be a way via diodes or relays this can be done. Note: the coils ONLY get momentarily energized in order to move the rails. How do I do this?
Arnold 7220 turnout controls. ( Want to use)
KATO Uni-Track turnouts I'm using

Thank you
 

dl324

Joined Mar 30, 2015
9,146
Welcome to AAC!

For those of us how don't know about model trains. How are the LEFT/RIGHT coils triggered?
 

tcmtech

Joined Nov 4, 2013
2,868
A diode on each coil would do it.

Just wire them up to a common line and put a pair of diodes on the the other line with one facing forward for one coil dn the other facing the opposite for the other.
 

crutschow

Joined Mar 14, 2008
23,523
Is the switch a center-off and you push it left or right to energize the respective coil?
And you want to use that to drive the single coil in opposite directions, depending upon the direction of the switch press?
Is that correct?
 

crutschow

Joined Mar 14, 2008
23,523
A diode on each coil would do it.

Just wire them up to a common line and put a pair of diodes on the the other line with one facing forward for one coil dn the other facing the opposite for the other.
He is going from two coils to one coil.
 

Thread Starter

Brucey30

Joined Jul 3, 2017
36
Atlas brand model railroad turnouts use 2 coils and 3 wires shown bottom picture . Forgive my lack of artistic abilities. First picture is Arnold brand switch controls I want to use. KATO turnouts reverse polarity to single coil to move rail in direction desired. In the top picture "braun" means brown wire I assume positive ?image.jpegimage.jpeg
 

Thread Starter

Brucey30

Joined Jul 3, 2017
36
Is the switch a center-off and you push it left or right to energize the respective coil?
And you want to use that to drive the single coil in opposite directions, depending upon the direction of the switch press?
Is that correct?
Yes. But the single coil must have polarity reversed to change rail direction
 

crutschow

Joined Mar 14, 2008
23,523
Here's my take on using your two momentary switches to reverse the direction through the coil using a DPDT relay.
When the Right switch is pressed, the relay is not energized and the current goes through the coil in one direction.
When the Left switch is pressed, the relay is energized and the current goes through the coil in the opposite direction.
Diode D1 blocks the voltage from the Right switch so that only the left switch energizes the relay.

The other diodes are to suppress the inductive spikes from the turnout switch and relay coil inductance so the contacts aren't burnt (is that suppression normally done in model railroad controls?).
The diodes could be replaced by two 1A bridge rectifiers, if you wanted to save on parts count.

upload_2017-7-4_0-19-32.png
Edited to clean up schematic.
 
Last edited:
yep. Ignore D2, D3, D4 and D5 to see the logic.

In one case, you energize the turn-about in the "standard" direction and in the other, you reverse the polarity as well. D1 isolates the right from the left switch.

Nice!
 

strantor

Joined Oct 3, 2010
5,160
diodes in series with each coil.
diode + coil pairs wired in parallel.
When you apply polarity in 1 direction, coil1 is energized.
When you apply the opposite polarity, coil2 is energized.
 

crutschow

Joined Mar 14, 2008
23,523
diodes in series with each coil.
diode + coil pairs wired in parallel.
When you apply polarity in 1 direction, coil1 is energized.
When you apply the opposite polarity, coil2 is energized.
There's only one track switch coil in the new design.
 
Last edited:

crutschow

Joined Mar 14, 2008
23,523
Here's a solid-state approach using a simple MOSFET bridge.
The MOSFET substrate diodes provide suppression of the load inductive spikes, so separate diodes are not needed..

upload_2017-7-4_0-39-2.png
 

Thread Starter

Brucey30

Joined Jul 3, 2017
36
Here's a solid-state approach using a simple MOSFET bridge.
The MOSFET substrate diodes provide suppression of the load inductive spikes, so separate diodes are not needed..

View attachment 130312
First. Thank You for replying. I've dabbled very little in electronics and know very little. Am I looking at 2 or 4 MOSFETs? I can understand "how" to hook them up once I understand completely
 

Alec_t

Joined Sep 17, 2013
10,458
This might be worth a try. The cap value needed would depend on the turnout coil characteristics. I assumed a 24 Ohm coil for the sim.
Turnout.PNG

Edit:
This relies on the switch not being a momentary type.
 
Last edited:

djsfantasi

Joined Apr 11, 2010
5,704
Ok, you are using a SPDT switch inline with a momentary pushbutton to activate whatever coil is set by the switch position. This is how I understand your 2 coil setup as I have Atlas switches myself.

Now for the 1 coil solution. Replace the SPDT switch with a DPDT switch. Wire the switch as if it was a reversing switch. Now the two wires from the DPDT common terminals go to the coil. The outside contacts are connected to the switch power. You can connect to either end, but remember you want that the primary route should be the same switch position.

No diodes. No MOSFETS. Just wiring
 
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