For the last number of years, I’ve been using a 12 volt / 3 amp transformer to run my auxiliary lighting. It’s time to expand and the old supply is almost maxed out for how much more I can add to it.
I have a number of surplus computer supplies that will provide the same 12 volts, only they are rated at 10 amps. My concern is that if I were to replace my original supply with one. I’m envisioning popping building and signal LEDs in one very short bright display !!!
No, the increased amperage output of the computer power supply is not going to have any effect on your existing lights as long as you arleady have resistors wired in place. It just means that the new power supply can be used for a lot more lights than what you have now.
Think about adding fuses between the power supply and the loads. Two, three or four branch circuits will make trouble shotting faster. Ten amps can melt small wire if you develop a short.
Ditto Ned’s comment. Don’t feed a single line rated at 10 amps around the layout. Also not many computer power supplies need a minimal load ont he 12V line to actually regulate. Older ones often won’t even turn on, more modern ones will turn on but the 12V will usually be low, near 11 volts, and the 5V lines will be high unless there is sufficient load on the power supply. There are several web site that show how to add a resistor to create a workable load and make the computer pwoer supply usable for just about anything.
I’ve been using an old AT computer power supply for years to run the lighting on my layout. I use miniture Christmas bulbs rated at 3 volts, two per structure in series on the five volt feed of the power supply. This is the low voltage feed for the drives. Each bulb in the structure gets 2.5 volts. (checked it and know it to be a fact) The structures are all connected on a parallel circuit with the bulbs in the structures connected to each other in serial. I had forty-seven structures on my old layout, that’s ninety-four bulbs. It pulled that load 24/7 for nine years and only three bulbs buirned out in that time. I’m sill using it today and it still runs 24/7, though it’s only pulling four structures right now. I have to wait until my health is just right so I can contort into weird angles under the layout to install more bulbs. Easy enough to understand. Anybody need a step by step diagram?[:)]
Computer power supplies are built to furnish lots of logic current (tens of amps). Older computers used 5 volt logic, the newer ones use 3.3 volts. They do still supply plus and minus 12 volts but very little of it, fractions of an amp rather than tens of amps.
If you are beefing up your layout lighting system, consider going to 6 volt bulbs, or LED’s with 180 ohm current limiting resistors on your new structures, and using a 5 volt computer supply rather than a 3.3 volt job. You can still use the plus and minus 12 volt outputs, but they are pretty wimpy, a dozen bulbs might be all she wrote.
Another way to go is pull the guts out of a computer supply and put in your own homebrew power, a transformer for AC or transformer and rectifier for DC. The computer casework gives you a nice enclosure, a line cord, a fuse, and an on-off switch. The enclosure keeps fingers away from the 120VAC needed for the transformer. Any computer repair place is an unending source of dead computer supplies.
As others have pointed out, 12 volts is 12 volts. The bulbs take what current they need and don’t care how much juice the supply might furnish to other bulbs.
I already have the computer supply modified and ready to go … many online sources provided some great instructions. As for using the 5 volt rail and lower resistors, thats out of the question as I already have over 150 leds with resistors installed in many buildings and signal towers … I’m not about to go back and redo them now !!!
I spent about 5 years teaching electrical theory to mechanics and this correlation seemed to work well for the mechanically inclined:
An electrical circuit is much like a piping system:
Voltage is the pressure at the discharge of the pump in the piping system.
Resistance of the circuit is the headloss of the piping system.
Current is the flow is the flow resulting from the interaction of the pressure and headloss.
Don’t read too much into it because the correlation falls apart quickly when you move into deeper theory, but it does explain (basicly) why 12V from Power Supply A is the same as 12V from Power Supply B.