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I want to use relays on my layout, and I'm hoping someone is willing to please help to get me started.

I'm building a ~ 1,500 sqft layout with about 1,200 lineal feet of track.  I'll be using DCS and Legacy.

I own electronic copies of Barry B's books on how to build a layout for DCS and I'm following his guidelines.  I have blocks made up of 10-12 pieces of track that will each have one pair of wires running to them via a terminal block fed from TIUs, all located to limit wire runs.

Relays: I have some blocks and sidings that are very far from the toggles that will control them.  Running a pair of wires from the terminal block (located near the siding / block) all the way to the toggle and then back to the siding/block would make my wires runs too long for a good DCS signal.

I understand the concept of relays - separately powered via low voltage (like how you power switch machines) they would allow a toggle switch that is far from the block to power it on/off without having to run the wire from the terminal block to the toggle directly.  Please correct me if I have any of this wrong.

What I need help with is knowing exactly what relay part to get (one that is easy to use) and instructions on how to wire it.  The most info in Barry's book I found was that "in cases where toggles would make excessive runs of wires relays should be considered" but there is no info beyond that.

I've read several threads on the topic here (usually by people that know way more about electrical wiring that I do) but I find them confusing and I don't see the information I'm looking for.

Can anyone help? I'm powering my layout with a Lionel ZW-L if that matters.

Thanks in advance,

Rob in Rochester, NY

Last edited by Robertejr
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If I understand correctly, what you are trying to do is have a central control panel, and use the relays out in the field, to turn block power on or off.

Sounds like you need a simple SPST relay, with contacts rated for about 10 Amps (track power). The other consideration is the coil power, AC or DC. Common relay modules use 5 or 12 VDC. These modules use SPDT relays, but you will only need the one side.

Something like this should do the job. You can view my search here.


Last edited by Big_Boy_4005

Thanks Elliot!  I have been following your layout thread for years, keep up the good work!

One other question - one of my turntables is also far from the control panel, and it will have 20+ whisker tracks that I'd like to be able to power on / power off - is there something besides the single relay that could accommodate this or am I stuck installing 20 of the modules you mentioned?

Thanks. If you are just talking about the whisker tracks, they shouldn't need as highly rated contacts, since you'll only have a single engine on each, under 5A. They make modules with up to 8 relays, so a few of those should cover it. Try this one. I see they make 16 unit modules now. That may get a little more difficult to manage your wires though. I would stick to the 8's. They also make 2's and 4's. I've used all of them for my uncoupler project.

One nice thing about the number 8 is, that's the number of wires in a Cat 5 cable. Funny how that works.


Last edited by Big_Boy_4005

Elliott has you pointed in the right direction.  A few suggestions...

relay ideas

You can find these relay modules in versions that have screw-terminals on the input or control side.  The 1-relay module suggested previously uses so-called square-pin headers which requires a mating connector that most guys don't have lying around in their parts stash.  Everyone has there opinion about ordering from Asia via eBay vs. paying 2-3x more from a U.S. seller.  To each his own, but if you are willing to wait a couple weeks, you should be able to get the relay modules for about $1 per, say, a 4-channel relay would be about $4 (and that's with shipping included).  

The control voltage suggested previously is 5V DC.  These relay modules are available in 5V, 12V, and 24V versions.  You will need to supply this DC voltage.  In general, most guys buy a wall-wart with DC output (of 5V, 12V, or 24V as the case may be).  Suitable wall-warts capable of powering a few dozen relay modules are less than $5 shipped.  Other guys want to use the AC auxiliary/accessory output of their train transformer - typically 14-16V AC.  In this case you buy an AC-to-DC converter module (less than $5) that converts Accessory AC to DC.

I suggest using 12V DC as your control voltage.  That is, 12V DC would be what your control panel toggle switches send to the relay modules to trigger the relays which then apply the track AC voltage to the controlled blocks/sections.  You may already have your control panel toggle switches already in hand, but note that you can get automotive (12V DC) toggle switches that are illuminated for not much money (25 cents each!).  These can make for a slick looking control panel...not that you can't just look at a toggle switch position to see which way it's oriented!  But in all seriousness, if I had to choose only one DC voltage to run around hither and yonder around a layout, I'd pick 12V DC rather than 5V DC.  

And to your point about wanting exact wiring instructions, I think you'll need to make a few decisions on the direction you're willing to go in terms of types of relays, voltages, configurations etc..

4 switches 4 relays hookup

For example, above shows a wiring diagram hijacked from a previous OGR thread.  Note this shows a relay module with screw-terminal control inputs (on the left side of the relay module).  So to side discussion going on about Cat5 cable and such, note that the wiring on the left of the relay module (the control wiring) carries relative small amounts of current and hence can indeed be thinner wires.  The wiring on the right side of the relay module is doing the heavy lifting and should be the 14-16 gauge or whatever.




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  • relay ideas
  • 4 switches 4 relays hookup


I think I found what you mentioned here but I wanted to make sure before I ordered it.  I would select the 12V option and I'm looking for the screw connectors on both sides.  I did not see any at the $4 price range.  A different link showed screw connectors on both sides but when I selected the product I wanted the picture then reverted to show square pins.

I found this for the power supply (it looks like it meets the specs you mentioned) and I easily found the LED toggles.

Thanks again,



Relay basics: think coils, poles and contacts.  There is also applications. Relays contain an electromagnetic coil which opens or closed a set(s) of electrical contacts.  The relay coils are either AC or DC energized but not both.  You need a constant supply voltage to the coil and there is a minimum coil pull-in current  necessary to operate contacts.

Relays are basically automated switches.  As a concept, you can consider each switch as a pole.  Relays are typically available in 1,2,3 or 4 pole varieties.

The contact set for each pole is typically SPST or DPST.  The contact ratings are in volts and amps.  Volts are usually not an issue.  Amps need to be considered.  The rated amps are generally for resistive loads.  Engines are inductive loads.  Derating for inductive loads are generally 30-40% of the resistive load.  Also, if you are running passenger cars with incandescent bulbs you need to consider in-rush current which is generally x10.

Relays are also available with various terminal types:  solder, spade, plug-in, terminal blocks.

Stan's relay modules are an excellent value. The contacts are 10A resistive.  Just make sure they fit your application.

Last edited by shorling
Robertejr posted:

...I think I found what you mentioned here but I wanted to make sure before I ordered it.  I would select the 12V option and I'm looking for the screw connectors on both sides.  I did not see any at the $4 price range.  A different link showed screw connectors on both sides but when I selected the product I wanted the picture then reverted to show square pins.

I found this for the power supply (it looks like it meets the specs you mentioned) and I easily found the LED toggles.

I just looked and found this one in the $4 range (free shipping from Asia).  Note: AFAIK per OGR terms-of-service direct links to eBay listings are not allowed so I just show photos.
12v 4 channel relay module less than 4 bucks shipped Asia
Elliot brings up a good point about the 12V DC adapter power.  I see the diagram I showed earlier has a 12V DC, 1 Amp adapter.  These 12V DC relay modules should be budgeted for 0.05 Amps (50 mA) per triggered/active relay.  There is negligible current per relay for an inactive relay.  So a 1 Amp adapter could power 20 1-channel relay modules, or 10 2-channel relay modules, etc..  OTOH, for your roundtable where only 1 whisker (relay) might be active at a time, you can budget accordingly.
The diagram also shows a useful connector-adapter that converts the barrel-coaxial connector from power supply into screw-terminals.  You can buy these adapters separately, but here's 2 Amp 12V adapter that comes with the adapter.
12v 2a dc with screw-terminal adapter
As for the illuminated 12V automotive switches, these tend to have spade connectors.  I suppose you could solder wires to the 3 terminals.  Upon reflection you need a crimp tool for the spade connectors though I'm sure you could find a youtube video showing how to crimp them using as hammer and screwdriver (or whatever)!  Note these switches have 3 terminals and orientation is important:
12v automotive illuminated switch



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  • 12v 2a dc with screw-terminal adapter
  • 12v automotive illuminated switch
Choo Choo Charlie posted:


Could Rob use one rotary selector switch with 20+ contacts with one relay (if needed) at the control board in place of 20+ relays? 

He will be using only one of the 20+ whisker tracks at a time.

As stated in the original post, one objective is to eliminate the long run of 20 "thick" power cables to the control panel.  Since the layout is 1500 sq. ft. the distance from roundtable to control panel could be dozens of feet...translating into hundreds of feet of thick, heavy cabling.  The wire alone can be $50 or more!

I only spent a couple minutes but was hard pressed (unsuccessful) to find a 1P20T rotary switch.  I did find this one on eBay:


I'm not sure I'd volunteer to be the guy soldering 20 "thick" power wires to those tiny eyelet terminals!  And while I don't think whisker tracks need a 10 Amp switch, I'd wonder what the actual Amp capability of such a rotary switch was; this eBay listing did not give any specs. 

But space-wise, if only 1 whisker is on at a time, I can see such a rotary switch driving 20 x $1 relays thereby requiring "thin" control wiring from control panel to roundtable relay modules.  I think the money saved from hundreds of feet of, say, AWG 22 vs. AWG 14/16 would pay for the relays!

I'm ignorant about how guys use roundtables, but it seems there might be situations where more than 1 whisker is on.  Since it takes hours to "fire up" a steam engine I'd think you might need to simultaneously power up the engine on-deck and the engine in-the-hole to mix trains with our national pastime. 


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  • 2p24t
Last edited by stan2004

Rob, there have been discussions in the past on the forum about controlling the whisker tracks. It was more of a philosophical discussion involving the use of the rotary switch vs multiple SPST switches.

You can get away with just powering one track at a time (rotary switch), but there may be times when you would want more than one track powered at a time, and the rotary can't do that.

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