# Computer transformer



## norgale (Apr 4, 2011)

Is there any practicle use for a computer transformer on a model railroad? Could it be used to power some lights in building or something like that? 
Anybody know the color codes for all the wires on this Tx? Pete


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## gunrunnerjohn (Nov 10, 2010)

Be a bit more specific. Are you talking about an ATX power supply? If so, you can use them for bulk power, they'll punch out a lot of power for a small package. As long as you keep a load on either the +12 or +5 volt supply, the regulation is good.


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## norgale (Apr 4, 2011)

Geeze I don't know what it is. It's the transformer out of an old DEll desk top computer. Just hate to throw it out if it could be useful. There are a lot of wires coming out of it that I understand give different voltages. Maybe some wires could run building lights and some could be used fir signals on the RR. I really don't know what the heck I could do with it. I'll get a picture of it tomorrow and post it. Then you can see what i'm working with. Thanks for the reply.Pete


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## gunrunnerjohn (Nov 10, 2010)

What I'd like to see is a closeup of the output power plug, the one that plugs into the motherboard. Also, the nametag with the voltages and specs would be most useful.


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## norgale (Apr 4, 2011)

No problem John. I'll bring it home with me tomorrow and then I can take all the pics you need and post them right away. I do appreciate the help. Pete


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## norgale (Apr 4, 2011)

Here are the pics of the transformer I have. Pete


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## gunrunnerjohn (Nov 10, 2010)

Here's the ATX 20-pin Connector Pinout Put about a 2A load on the 12V rails and the supply will work. THe 4 pin connectors have 5V on the red wires and 12V on the yellow wires, black is ground. You'll need a connection to ground on pin 14 to turn on the supply, remove it to turn it off.


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## norgale (Apr 4, 2011)

Thanks for that John. Makes sense to me. I may just use this for power to the bus wire and some of the lower voltages for things like structures and maybe the train signals. We'll see how many LEDS I blow messing with this. Ha! Pete


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## gunrunnerjohn (Nov 10, 2010)

Well, the supply is regulated. so 12 volts will really be 12 volts, 5 volts will really be 5 volts, and 3.3 volts will really be 3.3 volts. I couldn't read the current max on the 3.3 volts, but I'm sure it's pretty substantial.

One thing to keep in mind. The supply is rated at 250 watts, so the TOTAL of all the output voltages/currents has to be less than 250 watts, or the supply will shutdown.

16A of 12V power is 192 watts, and 22A of 5V power is 110 watts. Clearly, you can't run both of those outputs at maximums, even not using the 3.3 volts.

The other outputs are pretty low current, so the three I mention will probably be the most useful.


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## New Berlin RR (Feb 11, 2012)

gunrunnerjohn said:


> Here's the ATX 20-pin Connector Pinout Put about a 2A load on the 12V rails and the supply will work. THe 4 pin connectors have 5V on the red wires and 12V on the yellow wires, black is ground. You'll need a connection to ground on pin 14 to turn on the supply, remove it to turn it off.


for this id use a basic on/off switch type deal (push button or something like that) to keep it simple






gunrunnerjohn said:


> Well, the supply is regulated. so 12 volts will really be 12 volts, 5 volts will really be 5 volts, and 3.3 volts will really be 3.3 volts. I couldn't read the current max on the 3.3 volts, but I'm sure it's pretty substantial.
> 
> One thing to keep in mind. The supply is rated at 250 watts, so the TOTAL of all the output voltages/currents has to be less than 250 watts, or the supply will shutdown.
> 
> ...



John, most PSUs are supposed to do this, and it looks like it will be one that does as it looks newer, however some (as with anything technoligy related) may just suddenly burn up and die for good if over loaded, its just a matter of how over loaded it is, and that "250W" rating is how much total power it can put out if under full load.


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## gunrunnerjohn (Nov 10, 2010)

PC supplies usually have shutdown, though I don't choose to test it.  I have shorted them on the bench and forced a shutdown with no apparent damage, other than the weld marks on the screwdriver!


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## Kwikster (Feb 22, 2012)

Looks like it could be adapted for lighting, don't know that I'd run trains on it myself. Another good feature though is the internal cooling fan. IDK how many I've tossed 

Carl


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## New Berlin RR (Feb 11, 2012)

gunrunnerjohn said:


> PC supplies usually have shutdown, though I don't choose to test it.  I have shorted them on the bench and forced a shutdown with no apparent damage, other than the weld marks on the screwdriver!


I hear ya on that LOL  done that a few times my self, even had one burn its self up (more shorted but what ever)


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## norgale (Apr 4, 2011)

I see on the label +12v and -12v. What does that mean? Pete


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## gunrunnerjohn (Nov 10, 2010)

The -12 is a low current output. I'm not sure it's even used on modern motherboards, it used to be to power the RS-232 serial port drivers, when's the last time you saw one of those ports on a PC?


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## New Berlin RR (Feb 11, 2012)

IIRC the +12 is for the mobo, thats more or lss what every thing uses for power (minus USB and a few other things) how do I know? I modded one of my older PCs to have a 12v power set up to power odd ball things and recharge my cell phones and things like that! heck I thought I had a picture of the mod I did but can't find it


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## gunrunnerjohn (Nov 10, 2010)

Yes, the +12 powers the board supplies for the processor, there is a separate switching supply on the MB that converts the +12V to the low voltages the processor requires. The +12 also is used to power the larger video boards with the separate power connection.


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## norgale (Apr 4, 2011)

From what your saying I guess it's nothing for me to worry about. pete


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## gunrunnerjohn (Nov 10, 2010)

Yep, I'd ignore the -12V, it's not worth worrying about.


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## norgale (Apr 4, 2011)

Good to hear. Thanks. Pete


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## george356 (Jul 19, 2012)

This link gives you all the info you need to use an ATX PSU as a bench supply, all the wire colours, connections and possible voltages available.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

I will be building one of these myself, for lighting purposes.


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## gunrunnerjohn (Nov 10, 2010)

I've done a couple of these for people, they're a lot of power for a little money.


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## norgale (Apr 4, 2011)

george356 said:


> This link gives you all the info you need to use an ATX PSU as a bench supply, all the wire colours, connections and possible voltages available.
> 
> http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
> 
> I will be building one of these myself, for lighting purposes.


Now that looks like something even I can handle. Thanks for the link George. I'll be giving this a try. Pete


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