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Accessory Panel Using a Wall Wart

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  • Member since
    June, 2018
  • 2 posts
Accessory Panel Using a Wall Wart
Posted by Chessie Fan on Saturday, June 30, 2018 5:08 PM


Can a single wall wart power multipe switches?  I connected a wall wart to two terminal blocks, one for positive and one negative.  Then connected the terminals to multiple switches with the intention of independently controlling multiple LEDs in structures.  One LED on, one LED off.  I used SPST switches and a positive and negative wire for each switch from the block.  Problem is, they act together in that turining one switch off turns off all LEDs. 

When I did my turnout panel, I used a similar terminal block set-up but with DPDT switches.  Eech acts corectly for the turnouts and LED indicators.

Did I wire incorrectly, should I have used a different switch type, or would I need multiple wall warts (one for each group of LEDs)?  Thanks!

  • Member since
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  • From: Collinwood, Ohio, USA
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Posted by gmpullman on Monday, July 02, 2018 11:33 PM

Hi, Chessie Fan and Welcome! Welcome

Chessie Fan
Can a single wall wart power multipe switches?

Yes, sort of. If you have the twin-coil type they require a lot of initial current to get them to throw and a wall wart might not have enough "oomph" to get more than one to throw.

I'm trying to follow what you have going on there. You have to look at the label on the wall wart to see what the current rating is. Some are only 20 mA and that is .2 amp. Others are around one amp or more.

You mention LEDs which do require DC in order for them to light properly but if you are using twin-coil switch machines they work better on AC. Sometimes a "capacitive discharge" switch machine power supply helps to give the initial current "blast" to throw multiple switch machines at once.

Then if you want to have panel indicators you can use Atlas Relays to provide switching to control panel lights or signals.

This site has some useful information:


It would help if you can let us know what type of switch machine you are using.

A "slow-motion" switch machine (Tortoise) is a different animal, using low current DC and reversing polarity to move the points. These can have an LED wired in series in order to show position.

Generally it is best to keep turnout power separate from lighting and accessory power to aid in troubleshooting and to keep building lights from dimming when you throw a switch (turnout).

Regards, Ed

  • Member since
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  • From: Sebring FL
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Posted by floridaflyer on Tuesday, July 03, 2018 7:59 AM

Your intention to use switches to "control multiple LED's in structures" leads me to ask, what do you mean when you use the term "switches", are you referring to turnouts or switches to control lighting?

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Posted by peahrens on Tuesday, July 03, 2018 9:16 AM

Chessie Fan
Can a single wall wart power multipe switches? I connected a wall wart to two terminal blocks, one for positive and one negative. Then connected the terminals to multiple switches with the intention of independently controlling multiple LEDs in structures. One LED on, one LED off. I used SPST switches and a positive and negative wire for each switch from the block. Problem is, they act together in that turining one switch off turns off all LEDs.

Welcome to the Fourm.  You can get your answers here but we may need more info or for you to respond to clarify some things.  My understanding is that you want to have multiple LEDs in one or more structures, with each LED independently controlled on/off.

First be sure you understand the SPST switch; e.g., as in the first diagram in this search group:

The SPST is just an on/off switch, closed (on) or open (off), so it completes or interrupts the circuit.

I understand you have split your walwart output to positive and negative terminal blocks.  So from there, each LED you want lit by a given switch must have a positive wire from that terminal block which goes to the correct side of the LED.  The LED, of course, needs a resistor, the ohms dependent on your voltage; e.g., use a 1,000 (1K) ohm for 12 volt power supply.  The resistor can be on either side of the LED, as long as it is in the circuit to thus divide the correct amounts of source voltage (ignoring the minor wire voltage drop) to the resistor & LED.  A negative wire from the other terminal block goes to the other side of the LED.  If you wired like this, with no switch at this point, you would have a circuit thru the LED & resistor that would have the LED lit all the time.  Now, add a switch in this circuit.  A SPST can be added on EITHER the positive or negative wires from the terminal blocks to open or close the circuit.  If you have, let's say, 8 LEDs wired like these from the terminal blocks, you would have 8 totally independent (downstream of the terminal blocks) circuits, each with an LED, resistor and ONE SPST switch.  If you operate any of the 8 SPDTs it will only affect its LED.  If not clear, sketch this out, from the walwart to the 2 terminal blocks and the 8 LED circuits from the terminal blocks (positive wire, LED & resistor, SPST switch, negative wire.  (The SPST can be anywhere in the sequence). 

If that is clear, also realize that multiple (lets say 3) LEDs could be wired to a SPST switch.  To do that, each LED must see the terminal block voltage, so the 3 must not be wired in "series".  Rather, the 3 must be wired in "parallel".  One way to do that would be to put the SPST in the positive wire from the terminal block, then SPLIT the positive wire into 3 wires, one going to each LED/resistor.  Similarly, the 3 negative wires from the LEDs can then be combined into one wire going to the negative terminal block.

Let us know if these comments clarify for you.

BTW, the typical walwart has an internal circuit breaker that, if a short occurs, will self destruct to prevent excess current flow, permanently killing the walwart.  So if you short the wires that can be bad.  A good practice is to add a replaceable glass fuse in a fuse holder (from Radio Shack) that can burn out if you create a short.

In my case, I have 3 structure lighting circuits.  Each has a 1A (1000mA) walwart, so I add a 3/4A fuse to protect it.   Each walwart circuit has only 1 switch as I am happy to turn on a group of buildings all at once.  I keep track of each circuit's amps load by keeping a notes page that cumulatively adds new building loads (you have to know the approximate load for each LED type) so I stay below the fuse load ability.  


Modeling HO with a transition era UP bent

  • Member since
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  • From: Bedford, MA, USA
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Posted by MisterBeasley on Wednesday, July 04, 2018 11:30 AM

Having done it both ways, I would argue against using multiple scattered wall warts in favor of a few well diistributed power supplies.  This standardization will pay off in more reliable systems down the line.

It takes an iron man to play with a toy iron horse. 

  • Member since
    June, 2018
  • 2 posts
Posted by Chessie Fan on Wednesday, July 04, 2018 12:06 PM

Thank you all for the info.  Reading all this and studying my wiring, I realize my bonehead mistake.  Sometimes, it's the simple things one misses.  My switches (toggle not turnout) had my positive wire soldered to one prong, and negative to the other.  Not quite the circuit one would need to run some structure lights.  Fixing that mistake, I'm moving along well now and getting a lot per wall wart.  Not until I kept reading here and looking at wiring diagrams did it hit me how simple the mistake and fix were.  Thanks again.  I'll be back soon when I get stuck again!

  • Member since
    January, 2009
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Posted by RR_Mel on Wednesday, July 04, 2018 12:19 PM


I agree with Mister Beasley, a good switching power supply would be much better than wall warts.  They run cool and are very efficient.  You can get them anywhere from 12 volts at 5 amps to 50 amps.  I have a pair of 12 volt 15 amp and a 12 volt 30 amp.  I use one of the 15 amp power supplies on my workbench for testing and the 30 amp for my layout.  The second 15 amp is a spare.
30 amps is way over kill for my layout.  I also use DC to DC converters operating from the 30 amp power supply for all non 12 volt voltages on my layout.  I have 1.5 volt micro bulbs for headlights in my vehicles, 5 volts to power my Arduino lighting and signal controllers, 8½ volts for all of my 12 volt grain of wheat bulb (12 volt operating at 70%) plus several other voltages.
I have hundreds of lights and all kinds of goodies powered from the 30 amp power supply on my layout and the total current at 12 volts is just under 13 amps.  I started out with a single 15 amp and after several years of adding goodies I went with the 30 amp when the current reached 12 amps.
The single power supply makes it easier than a bunch of wall warts.
My Model Railroad   
Bakersfield, California
I'm beginning to realize that aging is not for wimps.
  • Member since
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  • From: Reading, PA
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Posted by rrinker on Wednesday, July 04, 2018 5:16 PM

Some - maybe even many, DC output wall warts ARE switchmode supplied, not bulk transfomers and linear regulators. Unregulated ones, and AC ones, almost certainly a bulk transformer, but regualted ooones, especially if they put out a large amount of power for th eize, are almost certainly switchmode any more. Those little USB power supplies used for cell phone chargers? 5 volts at 1 or 2 amps? Switching supplies. Just stay away fromt he absolute cheapest ones, I've seen teardowns where they are wired backwards - so the hot side of the AC passes through the negative of the USB cable, and ones with no or poor quality X and Y capacitors that let the magic smoke out. You don't have to get a major name brand expensive one, stick somewhere in the middle. Just because some companies (over)charge by selling them for $30, that doesn't mean their actual cost is equvalent to a $1 Wun Hung Lo brand - but $10 should net a decent quality one. If you need 5V for something - good for LED lighting. Instead of a 1K resistor like you would use with a 12V supply, try a 470 ohm with 5V. Easiest way to get the power out is to get a cheap USB A to USB A cable, and cut it in half - then you can get two power supplies feeding to wires which you cna then attach to terminal strips or what have you.

Other nice thing is with the little 1 amp cube ones, you don't need one of those special power strips with the extra spacing, they don't block adjacent outlets like a lot of wall warts can.



Modeling the Reading Railroad in the 1950's


Visit my web site at for construction updates, DCC Info, and more.

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Posted by Canalligators on Thursday, July 05, 2018 8:45 PM

I welcome you as well!  I'll offer one hint that helps me a lot.  Draw out a schematic of your proposed wiring.  It really helps to keep your thinking straight.  It's also a good check: if you can't draw the schematic, you probably haven't thought it out completely. 

When you're satisfied with the schematic, just implement it with wire and components.

Bonus: if something doesn't work, you can post the schematic in this forum.  Makes it much easier for others to see where the problem is.

Genesee Terminal, freelanced HO in Upstate NY Loon Bay Transit Authority, run through Amtrak and CSX Intermodal

CP/D&H, N scale, somewhere on the Canadian Shield

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