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Relay for 3 way switching with 2 wires

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GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If you want to extend it to a third or additional switches the additional relays will have to implement the cross wired DPDT function of a four-way switch.
Still just the two wires from the SPST switch to actuate it though.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
170327-0915 EDT

K8MHZ:

justin13me has implemented my suggestion 1 in post #36 to divorce the "exclusive or" from the input switches and locate the "xor" somewhere else.

The truth table for XOR is:

A B . Out .... A and B are binary inputs and Out is the resulting binary output
0 0 = 0
0 1 = 1
1 0 = 1
1 1 = 0

It should be noted that this a basic part of binary addition. Binary addition is:

C A B . Out where C is carry from the previous stage
0 0 1 = 1
0 1 0 = 1
0 1 1 = 0 with carry
1 0 0 = 1
1 0 1 = 0 with carry
1 1 0 = 0 with carry
1 1 1 = 1 with carry

For comparison AND is:

A B . Out
0 0 = 0
0 1 = 0
1 0 = 0
1 1 = 1

Have not proofread, have to leave.

.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
gar said:
170327-0915 EDT

K8MHZ:

justin13me has implemented my suggestion 1 in post #36 to divorce the "exclusive or" from the input switches and locate the "xor" somewhere else.

The truth table for XOR is:

A B . Out .... A and B are binary inputs and Out is the resulting binary output
0 0 = 0
0 1 = 1
1 0 = 1
1 1 = 0

It should be noted that this a basic part of binary addition. Binary addition is:

C A B . Out where C is carry from the previous stage
0 0 1 = 1
0 1 0 = 1
0 1 1 = 0 with carry
1 0 0 = 1
1 0 1 = 0 with carry
1 1 0 = 0 with carry
1 1 1 = 1 with carry

For comparison AND is:

A B . Out
0 0 = 0
0 1 = 0
1 0 = 0
1 1 = 1

Have not proofread, have to leave.

.
Click to expand...



And here we go using a sledge hammer to put in a thumbtack.

Let's make the simple complicated. :roll:
 
R

ronaldrc

Senior Member
Location
Tennessee
Switching circuit

Switching circuit

Here is the way I would have did 7 years ago



After I drew the diagram I notice I should have used a threeway switch and used one traveler and the common
so the switch would not have the off and on the handle.



Two_wire_light_switching_circuit_zpstg4cis6b.jpg
 
Last edited:
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I am glad that the OP specifically said that the plan is to simply run new wire but continue the discussion for theory fun; because I am happy to dive in :)

My first thought along the lines of over-complicating things so that 2 wires could be used in a 3-way setup is 'diodes'. Use a 4 way switch with a diode connected across two terminals. Depending on switch position the circuit will conduct electricity in one direction or the other.

With 2 diode/switch assemblies you conduct current only when both diodes are 'pointed the same way'. This gets you 3-way switching with only two conductors between the switches. Problem is that you now have reduced voltage at your load, so you still need something to provide full voltage to the load.

I think that ronaldrc has the most elegant solution other than just running the new conductors. As I understand it, he used a single pole switch to turn a relay on and off, and wired the terminals of the relay to look like a 4-way switch. So you would add in a new 3-way/4-way switching circuit to control the light, with _one_ of these 'switches' actually being a relay, and you would use the existing 2 conductors to control the relay.

-Jon
 
R

ronaldrc

Senior Member
Location
Tennessee
winnie said:
I am glad that the OP specifically said that the plan is to simply run new wire but continue the discussion for theory fun; because I am happy to dive in :)

My first thought along the lines of over-complicating things so that 2 wires could be used in a 3-way setup is 'diodes'. Use a 4 way switch with a diode connected across two terminals. Depending on switch position the circuit will conduct electricity in one direction or the other.

With 2 diode/switch assemblies you conduct current only when both diodes are 'pointed the same way'. This gets you 3-way switching with only two conductors between the switches. Problem is that you now have reduced voltage at your load, so you still need something to provide full voltage to the load.

I think that ronaldrc has the most elegant solution other than just running the new conductors. As I understand it, he used a single pole switch to turn a relay on and off, and wired the terminals of the relay to look like a 4-way switch. So you would add in a new 3-way/4-way switching circuit to control the light, with _one_ of these 'switches' actually being a relay, and you would use the existing 2 conductors to control the relay.

-Jon
Click to expand...

Thanks:

I started to posted something with Diodes and then this happen come to mind. Its just a little simpler

Anyway I got bored and made a GIF of this circuit.


Two%20wire%20control%20of%20a%20relay%20controlled%20fourway_zps1y29wbrp.gif
 
J

justin13me

Member
Location
CANADA
Thanks everyone for the great feedback and input! It turns out I don't have (2) spare 24vac relays so I went to the supplier to get it and they only had the 'ice cube' style w armature. It's a 2 pole: has 2 NO, 2 COM, 2 NC but only 1 A1 and A2. The guy at the counter says 'it's like having 2' and I believe him.. (They're only $16 a piece, stupid me shoulda taken 2). I take to site, happy at saving from the labour intensive work of running new wires across the warehouse but in no time am stumped.. Is it possible still when only 1 input to turn on/off this relay? I think it's not as previously I had to turn each (relay) on and off with the load. However contactors are so versatile maybe it is possible but just above my pay grade lol
 
J

justin13me

Member
Location
CANADA
I don't think it works w the double poles on single relay as every time a switch is pressed the contacts have to change states. Should have been obvious, but maybe (?) still possible...? As its 24V the neutral could be switched but I don't think it would make a difference. I'm going to stop pursuing, I have a second relay for tmrw
 
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