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.
All it takes to use these cost-effective ATX power supplies is a bit of rewiring.
First, you need to procure a power supply. 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. Looking over the selection at my local store, that means you’d have to buy the $20 400 watt power supply rather than the $15 450 watt power supply. But the tradeoff is worth it. That 400 watt power supply provides 300 watts on that 12-volt line. At an estimated 2.5 watts per bulb, it can power 120 bulbs. I would hesitate to put that $20 power supply in a computer, but lights and solenoids are a lot less demanding than CPUs.
On to rewiring. 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 a twist a blue wire nut on them and secure the end with a bit of electrical tape if need be.
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.
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. 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.