Large Scale Central

Switching Power Supplies -- Safe for the Trains?

One of the 24V / 5A laptop style power supplies we’ve been using to power the Triple O gave up its ghost. It’s been a multi-year run powering trains in the tropics via a homemade DC controller ( DIY Power – Good, Bad, or Neutral), so we got our money’s worth!

I was thinking about using something called a “Switching Power Supply” as the screw terminals and ability to hardmount this supply makes it an attractive alternative to the laptop power supply that just died. I understand that the magic of transistors does the electrical voodoo to converts and regulats the power and that a switching power supply can generate electromagnetic interference if not properly shielded. Does any of this matter for my locomotives, all of which are rated for 24V DC, all of which will be running feet from the controller, and none of which have electronics more complicated than al lightbulb, anyway?

In the meantime, an old storebought controller has been pressed into service on our smaller inner loop and the other DIY box is moving ka’a ahi (fire coaches) on the other loop.

Thanks in advance!


My trains are battery but I have used those power supplies for other projects. I stick with the Meanwell brand as they are highly regarded as safe and reliable. G Scale Graphic recommend the same. Meanwell Power Supplies

I use three 24 volt, 12.5 amp, Meanwells through Aristocraft Train Engineers without problem.

As above - you should have no issues with a switching supply. Meanwell supplies are cheap and reliable. Some of them use screw terminals for the mains, so you may need to put it in a protective enclosure.

Thanks, Dan, Todd (@Todd_Brody ), and Jon ( @JRad )!

I am assuming that the 12.5A won’t fry the trains, and all I have to do is to make sure it won’t fry the little speed controllers I have for our current kits. Are those good assumptions?

Alos, thanks, Jon, for recommending a case. Our little tool boxes worked but something a bit more rugged is not a bad suggestion, either.

Off to explore Meanwell’s website!


My TEs have 10 amp circuit breakers (to replace the 10 amp fuses) on their outputs.

But MAKE NO MISTAKE! It takes nowhere near 10 amps to fry the traces on the circuit boards and flimsy wiring in the engines and I’ve jumpered/replaced plenty just due to derailment.

When I open them up, I put polyswitches on one set of axles to prevent this from happening again.

In actuallity, if this is of concern you can use a smaller fuse/breaker.


The trains will use whatever they need, current wise. That is, if your loco uses 2.0A under normal running then that’s what it uses no matter the current rating of the supply. The 12.5A is is the upper limit of what the power supply can deliver (think volume of water). So, running 6 trains using 2.0A each is the limit for that power supply.

For the techies, yes I’ve assumed all other conditions are the same, else it gets complicated… :grin:

As Todd says, you don’t want to release the 12.5A all at once - usually happens if something breaks so the fuses / CB’s / polyswitch saves us.


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One more question…I noticed that the motor speed controllers all have a minimum and a maximum voltage. Maximum voltage, presumably, is the upper limit that the controller can handle. Is the lower voltage the voltage required to get “through” the control circuitry to turn the motor? If that is the case, am I correct in assuming that I should look for a motor controller with a lower limit as close to zero as I can find?



No, they all go to stop. The minimum voltage is because the circuitry takes a certain voltage to make it work and pass anything through it. But the controller will only pass up to near the minimum input voltage.

So if it a minimum of 12 volts and a maximum of 24 volts, at 12 volts it will work, but you will not get anywhere near the full speed potential.

Thanks to Everyone.

Another question…I saw the Train Power 4 listed at $100. That gets pretty close to the break point with DIY. I’ve been running with my 5A just fine, rarely running more than two single motor LGB engines at a time. Is this a good solution?

If not, I am going to order the Meanwell 24V / 6.5A power supply later this week. I am assuming that getting AC power into this thing is as simple as finding an older power cord and hooking it into the screw terminals! I’ll look around for a suitable case. I am actually wondering if an old desktop case might be the right solution. Failing that, I’ll order a proper case, find some machine screws, and go from there.


Exactly. I just wired one of those up at work yesterday to power an LED sign. Black to “L” and White to “N”. If it’s a three wire cord, Green to Ground, I think it’s labeled “Gnd”. I needed a weatherproof box that would fit two. A 10x10 steel outdoor box cost us $80! I think that’s more than one supply.

The Meanwell supply has M4-70 threaded mounting holes. Use short machine screws that won’t contact the board.

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You could go this route

Jon & Sean,

Thanks. I feel better about taking this approach and about replacing one battllleworn toolbox with another!


Just open the top for air flow when you use it!


The power supply arrived late last week. Because getting power to the rails has priority over other projects, this went to the top of a weekend’s list of micro-projects shoehorned amidst other activities.

First, I set Kid-zilla loose with a STAINZ and our other power pack to make sure power would flow when we swapped out power supplies.

Next, I cut the plug from the old power supply, and, after crimping on some terminals (only mis-crimped two!)…

…followed Jon’s ( @JRad’s ) instructions, and wired it to the power supply. After that, I used double-sided tape to put everything in place in the old toolbox we’d been using.

With Sean’s (@smcgill ) warning about heat, I also quickly painted “open when in use” on the lid.

In the original, I had a 5A fuse wired into the circuit. This is a 6.5A power supply, so I removed that wire and jumped from the DPDT switch to the outlet wires (You can see the alligator clips in the photo). It all worked, but, of course, I forgot to make sure the power supply was set to 120V. Glad I made the mistake of having it set too high! With that figured out and Kid-zilla-s MOW work, all went very smoothly.

Before closing out this thread, one last question. Should I put that fuse back into the circuit with a 6.5A fuse? I have had shorts across the track in the past that blew the fuse. Or does the power supply protect itself, which the website seemed to imply? In which case, I will simply solder in a wire and be done with this.

Thanks for the help!


A Fuse is cheaper than another power supply … just saying … :wink:

I agree with Sean. Probably not needed, but cheap insurance.

The short circuit protection in these supplies will shut down the output, but then keep checking by powering up every few seconds. That will save the supply from heat damage, but maybe not the tiny wires on a shorted loco. The fuse, once blown, stays blown.

If the old 5A fuse was enough to keep trains running then I would stay with that. The fuse does not need to match the maximum output, but rather what you want the maximum load to be.

The fuse is definitely security, I’d leave it in there too.

Separately, I’ll wager that the power supply will shut down a lot faster than the fuse can react and no train fuses will be harmed in the Mueller household from now on. Bold statement I know… :grin:

Payable whenever I’m next in Hawaii which, unfortunately for Eric, I have no immediate plans.


Mean while at Eric’s house the STAINZ derailed.