Does anyone use old computer power supplies for their layouts? I was wondering how suitable they are for Tortoise machines (and maybe lighting).
How many can I run off a 500 Watt power supply? The hard drive connectors have black, red, and yellow leads for 12V. Are these DC or AC, and which wires do I use?
Thanks.
Hi Terry!
I don’t use the computer power supply, but I know Jeffrey Wimberly does. If He doesn’t chime in here soon, send him a PM.
Sounds like you are getting the layout going. Hope you are well!
Careful with those connections…they’re +12V, -12V, +5V, and -5V. You also have to have a load for the newer power supplies to keep them running. Here’s a great link to building one:
First of all, be careful. I accept no responsibility for sending you this link. The voltages that come out of a PC supply are DC voltages. Since you were not aware of that, it tells me you know very little about electronic/electrical circuits. This is not a case of, If all all else fails, follow instructions. ALL UPPER CASE. READ ALL THE INSTRUCTIONS IN THE ARTICLE FIRST.
The 120vac from the wall outlet is in this power supply when plugged in even if the switch on the power supply switch is off. The line voltage kills more people than higher voltages because people think it is not “that high”.
http://www.instructables.com/id/ATX–>-Lab-Bench-Power-Supply-Conversion/
I use one based on this link http://web2.murraystate.edu/andy.batts/ps/powersupply.htm it has worked well for me. I have 5 and 12v power buses run under the layout so I can tap into them as needed.
The yellow wires are +12V, the red wires are +5V, and the black wires are all ground (negative). All of a certain color of wire start at the same point, so one yellow wire has identicle power to another yellow wire, black with black, etc. Using a PC power supply could be a good way to get a lot of power to your trains, lighting, and whatever else you want in there. And with the red 5V lines, you could light 5V LEDs around your layout without the need of resistors.
“Which wires do I use?” That can take a bit of answering. If the supply powers up, you use a volt meter to read the voltage on each pin. Or you google for it. The plugs to power hard drives and floppy drives are industry standard, the pinout is the same on all machines.
For the voltmeter trick to work, you have to get the supply to power up. Most of the supplies require a steady draw of an amp or so on the logic power (5 volt & 3.3 volt motherboard connector). Without a load on the logic power, the supply won’t start. So the voltmeter trick won’t work.
If you google on the supply part number/model number/maker you ought to be able to find the maker’s web site and a wiring diagram for the various connectors on the supply. It will also tell you how much current each supply output will furnish. To load the logic power enough to get the supply to start try 5 ohm 10 watt resistors across both the 5 volt and the3.3 volt outputs. That’s one resistor to load each output.
The 500 watt refers mostly to the logic power output. The +12 and -12 volt lines won’t furnish nearly as much current as the 5 and 3.3 volt outputs will. I’d guess an amp, max for Plus and Minus 12. Tortoises only need 30 milliamps, so you can drive 30 Tortoises with one amp.
Do be careful not to touch the 120 VAC power line while working on it. Electric shock can kill. Avoid opening the case, there is nothing inside you can service.
Except the fan.[:D] I switched out my PS’s fan about 3 times before I got one in there that I really liked. ([#offtopic] of trains, the “Gentle Typhoon” fans by Scythe are excellent for making a computer much quieter.[:D] Ok, I’m done being [#offtopic][:D])
I have a friend using a 6 amp power supply intended for a laptop to power his MRC Prodigy DCC system, and it works fine.
Having worked on computers for years reading this thread made my heart skip a little beat. I know a lot of you are very familiar with electricity and know better but I just had to say it anyway
PLEASE BE CAREFUL!!!
Hi!
With all due respect to the electricians and electronics gurus reading this, may I say,
“If you don’t know what you are doing, if you are not absolutely positive about it, do NOT mess with using PC power supplies on your layout”.
You could be setting yourself up for ruining your layouts electrical components, or worse you could get an unwelcome shock or burn, or worser still, you could start a fire.
Having been there, done that, I speak from experience.
Mobilman44
I second, third and fourth that motion!!! You would be better off going to Radio Shack and picking up a good 12v and a 5 v power supply. No worries about switches or exposed 120v wiring. They are plug aand play.
I agree. If you don’t knwo a resistor from a light bulb, and don’t knwo which end of the sodlerign iron to hold, do NOT go about attempting to modify a PC power supply. It WILL ‘bite’ you. And a sudden electric shock, even if the shock itself doesn’t harm you, can make you do things lik jerk your arm involuntaroly and plot the sodlering iron in your eye. Not only is AC line voltage applied any tiem the cord is plugged in, but a switching power supply, as all computer power supplies made in this century are, has large value capacitors that can store quite a charge for longer than you might thing, ready to zap the unsuspecting tinkerer.
If you really do understand the hows and whys of pwoer supplies, then use one of the sites linked above for directions. A PC power supply can indeed make a useful source of power, but one thing to be aware of is that they are NOT isolated from the AC input like the typical DCC power supplies. The ground carries through. Do not mix items powered by the PC power supply with ones powered by an isolated supply or another one that may also tie the ground to a different outlet.
As for amount of power - the total pwoer suppyl rating generally cannot be drawn by a single voltage. That 500 watt power supply cannot put out a full 500 watts at 12V. Look on the sticker, there are generally maximums for each different voltage. But since a Tortoise draws about 15ma, a 15 amp 12V output can drive 1000 of them.
Another note - yes all the yellow wires are the same voltage. But do not try to draw the full current from just one wire, it’s not rated for it. Parallel a bunch of them. And run MULTIPLE SMALL FUSES. 12 volts at 15 amps is a good welder. ANd can easily fry electronic things or melt wires. Break it up at the power supply into multiple circuits with 1-1.5 amp fuses or circuit breakers.
&nbs
I use a 500 Watt computer power supply on my HO scale home layout for the lighting, Tortoise switch machines, signals, and everything except the NCE DCC system.
At our HO scale club we use two computer power supplies for the same purpose.
Not running any switch machines with mine as all my switch machines are AC. I am however running scads of miniature Christmas bulbs. On my old layout it was pulling 90+ of the little beggars and not turning a hair. It’s rated at 250 watts.
Thanks to all who answered. My electrical knowledge is average, but after reading the links - forget it. It’s not worth the effort. You cannot simply tap off the wires.
At the very least, a large resistor load needs to be added, a switch to replace the “soft switch”, and fuses. I’ll continue to use multiple “wallwarts” I buy or salvage from old devices. At least they don’t need a fan!
That’s true with an ATX power supply. If you get an AT power supply you can simply tap off the wires, no load required.
Not always true. One fairly well known brand of clone in the AT/386 days came with a load resistor fastened to the chasiss - if you didn’t install a hard drive you had to connect the load resistor, or the computer would not operate. I’m trying to remember the brand…oh yeah, AST.
–Randy
I remember those. AST used a special ATX type power supply in those for some reason I forget. Maybe because if it went out you had to get the replacement from them. With an ATX the power supply is never completely shut down unless you turn off the little switch on the back of it or unplug it. Pressing the power switch on the computer just turns the motherboard off. The transformers and capacitors in the power supply shut down but the AC line is still charged, waiting to get a start command from the mother board when the power button is pressed or in the case of mine when I press the power key on my keyboard. The AT supplies have an on/off switch that’s separate from the supply and is hard wired into the AC line in the supply. The switch is almost always on the front of the computer and locks in the on position when it’s pressed. Turn the switch off it kills the power to the power supply. Turn it on and it will merrily produce power no matter how little is connected to it. All the ones I have will run with absolutely nothing connected to them and put out voltage at the specified levels.
Even on a AT suppy taking a volt check without a load will give odd readings. I put the resistor accross the leads for proper volt reading