PC power supplies are exceptionally cheap and plentiful these days. If you’ve noticed and wondered whether you can use PC ATX power supplies on a train layout, wonder no more. You can.
Thanks to the miracle of mass production, even the cheapest, nastiest PC power supply gives far more power output per dollar than any train transformer. So if the lights and accessories on your electric train layout can run on 12 volts DC, which is a fairly good bet, you can get a lot of wattage for very little money by repurposing an inexpensive ATX power supply, whether new or secondhand. And on a wattage-per-dollar basis, they’re about twice as cost-effective as outdoor lighting transformers, which are another popular option for hobbyists. If you need AC power and more than 12 volts, get a lighting transformer. Otherwise, you can go ATX.
All it takes to use these cost-effective ATX power supplies is a bit of rewiring.
Getting a power supply
First, you need to procure a power supply, whether that means salvaging one from a computer you don’t use anymore, or buying one. A reasonably good power supply will tell you exactly how many watts it provides on the 12-volt rail; for safety’s sake I recommend buying a power supply that has that specification on a sticker on the side.
For example, I salvaged a 350-watt power supply that provides 240 watts on its 12-volt line. That’s enough, at 2.5 watts per bulb, to power 96 bulbs. There’s a reason I’m not using that power supply in a computer anymore but it’s still fine for my train layout. Lights and solenoids are a lot less demanding than CPUs. While I recommend premium brands of power supplies in PCs, on train layouts, cheapies do just fine.
Ideally, look for a power supply with its own dedicated on/off switch on the back so you can easily turn it off without unplugging it. If you can’t source one locally at a good price, used ATX power supplies are plentiful on Ebay. Look for a listing that has a sticker that looks like the one on the right. You should be able to find a 400-ish watt power supply that can give you 200 watts or more of usable 12-volt power for less than $20, shipped. That’s Lionel ZW-like power at a Marx 1669 price.
Rewiring your power supply
An ATX power supply won’t power on outside of a computer, but that’s easy to change. All it takes is splicing two wires.
The power supply will have a large 20- or 24-pin molded plastic connector on it. You’ll want to take the green wire from that connector and cut it off, reasonably close to the connector to give yourself some room to work with. Do the same with one of the black wires. Next, strip back about a quarter-inch of insulation from the green and black wires, then connect those two wires together. I prefer slipping on a piece of heat shrink tubing, then twisting the wires together, soldering them, then covering the wire joint with a bit of heat shrink tubing. But you can just twist them together, then twist a blue wire nut on them and secure the end with a bit of electrical tape if need be.
After this modification, the power supply will power up if you just plug it into the wall and flip the power switch. If it doesn’t have an on/off switch, it will power on any time it’s plugged in.
Powering your accessories with your ATX power supply
To power your accessories, you’ll need a yellow wire and another black wire. You can take the yellow wire off the same connector you got the green wire from, or you can take it off one of the 4-pin Molex connectors if it has one. Snip each wire, strip back about a quarter inch of insulation, and twist the individual strands together.
Now you just need a way to feed that power to the layout. I recommend buying a pair of grounding bus bars, available at home improvement stores and probably most hardware stores. You can expect them to cost about $4 each. Connect the yellow wire to one bar and connect the black wire to the other. Now you have tons of easy-to-connect posts for your lights or accessories.
If you phased your transformers, you can even share your common rail (generally the U post on Lionel transformers like the ZW, or the base post on American Flyer transformers) with your ATX power supply to save wire. The black ground wire connects to the common wire. The yellow 12-volt wire is your hot wire.
Now, the caveat: Most train transformers provide 14 or 15 volts on their accessory line. Your bulbs will run on 12 volts, but they may be a bit dim. If you have 18-volt bulbs in your lights, you may need to replace them with a 14v 1449 bulb, or if you want bright lights, a 12-volt 1446 bulb.
You’ll have lots of unused connectors at this point. The safest thing to do is put a piece of electrical tape on the end of each connector to protect it from stray voltage. Then bundle the wires up with a zip tie to keep them out of the way.
Mounting the ATX power supply to your layout
Mount the transformer to the underside of your train layout with a couple of corner braces. Attach the braces to the mounting holes in the power supply with two of the included 6-32 machine screws. Then use #6 or #8 wood screws to attach it to the layout. Attach the bus bars to the underside of your layout with #6 wood screws.