Hi! Just wondering if anybody out there haspreviously used an old Computer power supply (AT) to power lights and other accessories? I am personally thinking of using a 135 Watt one. Thanks in advance!
It would work, though double check with a multi meter how much voltage is being put out. It shouldn’t be more than 20…
–Austin
I use one. I use a 250 watt AT power supply from an old 486 and it pulls everything I need it too. Right now it’s getting a break, only lighting a few structures while I rebuild my layout. On my old layout, it was pulling 52 lights with no problem at all.
As far as the output voltage goes, I use the taps that went to the computers drives. These carry two voltages. There’s 12 volts dc and 5.3 volts dc. These can be cut down further with the use of resistors.
Thanks for the input! It has dual output voltage as do all computer power supplies 12 and 5 on the plug leads … the motherboard power plugs I do not intend to use hehe … I may also experiment with a throttle design I have here to perhaps test out a track to see if I could hopefully make a working throttle … we’ll see if it works !
Thanks again for the input
Glad I could help.
IT’s ironic you should ask this question today as I was walking past my neighbors house I noticed he had thrown away an old PC. I took the power supply out and plan on using it on my layout for structure lighting etc. As mentioned they have 12 v, 5v and they also have a 3.3 volt output. The 3.3 volts will work great for powering most LEDS and you don’t need to mess with resistors. This one is a 14 amp 3.3 supply so you can run a butt load of 18ma LEDS with it. Most computer power supplies require you to load the 5 volt supply with a 10 ohm large watt resistor or it won’t turn on. I downloaded an article on it a while back I guess I need to dig it out. Terry
That sounds like an ATX power supply. If you had an AT power supply, you wouldn’t have to put a resistor on it. Just flip the power switch and away she goes. All the lights come on. I’ve been running mine 24/7 for 6 years now. The only break it’s had was when hurricane Rita knocked out the power for almost a month.
Jeff Actually I never have used one yet. I was going by the article I downloaded from somewhere indicating you needed a resistor to provide a load. If that is not the case then great one less thing to buy. It does have a 3.3 v PP so that will save at least 20 cents in resisitors. Whooo Whooo. Thanks for the info and how do I tell what type PP I have? If it works great if not I may need the load resistor? Terry
Yes, we do at the club. Currently the 12vdc is used to power both lights and some of tortoise turnout motors. The only issue with it for the tortoise is that we prefer the common wire scheme using +12/-12, rather than the DPDT wiring.
I can’t tell if you mean to use the power supply for accessories AND the throttle, or if you mean INSTEAD of using it for accessories. Generally it is a good idea to use separate power supplies for the trains and for other things.
Terry, if it has a separate power switch that’s wired directly into the power supply, it’s a good bet that it’s an AT pp. If it has no power switch wired to it, and instead has a switch on the back, then it’s an ATX pp.
Jeff after reading the tag on the back it says LC-300 ATX. And it has a 115/220 sw and an on/off switch on the back just below the power cord socket. So that means I need the load resisitor correct? If I remember correctly the article called for a 10 ohm 100 watt resisitor? Terry
Yes, you will need a load resistor for that one.
A PC power supply can work well. I used the instructions in the link and have a couple of very effective supplies.
Simon Tks for the link. That was exactly what I was trying to find. Terry
Saved me having to look for it as well. Thanks.
A 10 ohm resistor would give a .5 amp load on the 5 volt circuit, which should be plenty. Means the resistor will be dissapating 2.5 watts under steady-state. Use a 5 watt rating for the resistor to be on the safe side. Be careful where you mount the resistor, it will get pretty warm.
Also, note that incandescent light bulbs are a great starting load for a switching power supply. They draw more current cold than they do hot. So if you can put enough bulbs on the 5 volt circuit to draw at least 0.3 amps hot, they can replace the load resistor.
my thoughts, your choices
Fred W
Sure you can. I’ve used 3 computer power supplies on a large HO scale club layout for building lights and stall motor switch machines, and one on my home layout to power lights and Tortoise switch motors.
Very ironic I was tiding my work van into the bubbish bin at work and found a dumped PC this morning!! I have yet to investigate the inner bits but it’s a nice find.
Ken.
Don’t connect LEDs directly to the 3.3 volt output without resistors! Unless you have a CURRENT REGULATED power supply (yes there are such things) LEDs will ALWAYS need a resistor. Just smaller ones with lower voltage
Many AT power supplies also require a load to regulate properly. I remember back in the day AST computers actually had a resistor heat-sinked to the chassis that had to be connected to the power supply if you had no hard drive. Of course, if you have a bunch of lights and signals attached to the power supply - there’s your load, and it should work fine. I’m considering building my next one with a second switch to toggle the load in and out of the circuit - with hardly anything connected it won’t regulate, but with all the railroad accesories attached it will, and won’t need the load eating up.
I had to experiment with the 250 watt ATX unit I converted. A single 10 ohm resistor did not provide enough load - I ad to use two in parallel for 5 ohms total to make it work. Note this: with the load being insufficient, the 12V output was low (11.5 or less) but the 5V was HIGH. 5.6V in my case. So if you use the computer power supply to drive logic circuits that need 5 volts, BE CAREFUL! If the load becomes disconnected the 5V side runs away high enough to potentially damage logic circuits. With a 10 ohm load I had 11.5V and 5.4V. With a 5 ohm load I have 11.9V and 5.1V. I didn’t extend the 3.3V lead on mine. Power supplies vary - different brands and different capacities will behave differently. You may need to experiment and measure. One final warning - a switchign power supply has large capacitors that store voltage long after the thing is turned off - so if working inside the power supply case BE CAREFUL. It did all my testing at the external leads, then went inside the case for the final design. I pulled the fan and cleaned and lubed it, put a toggle on the power control leads (ATX supply - the toggle does NOT switch 110V AC), put an LED and resistor on the Power
as for the 10-ohm resistor, you shouldn’t need that period. If you momentarily connect the GREEN wire of the 20-pin connector to any of the BLACK wires (in that conector) you will turn on the supply.
I’ve turned on power supplys in this fashion without having any load on them.
the gren wire is the “ATXPWR” wire. This is the one that turns on the computer when you hit the power button.