# Computer Power supply



## trains galore (Jul 22, 2013)

Hi guys
I've been having issues with getting sufficient power to all the lights etc on my layout, and I came across this article http://2railoscale.blogspot.com.au/2011/09/how-to-convert-used-pc-power-supplies.html
It shows how you can use an old atx or at pc supply to power your lights. I have played with old computers alot and have quite a few of them around, so decided to have a go at it.
It says on this site that given the high amount of current the supply is capable of, it's a good idea to fuse the outputs, so I've been working on a fuse board for it
here it is, I have 2a fuses and one 3a to put in, and the max current on the biggest circuit is 1.3a The red switch shorts the green wire to black to start the supply


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## D&J Railroad (Oct 4, 2013)

That should work. I would have gone with the self resetting breakers so ya don't have to hunt for a replacement fuse when ya accidently leave a tool on the tracks when ya power up.


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## rkenney (Aug 10, 2013)

Looks good.

Fuses are a good thing. There was a post not long ago where the merits of fused track was discussed.

Not mentioned though was PTC fuses.










These are resettable fuses. They reset themselves after the short is gone and take up far less space than bulky circuit breakers, fuses or their sockets with the same protection.

They can be attached directly to your terminal strips behind the panel face. The ones pictured are 4A at 30V. Google RUEF 400


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## gunrunnerjohn (Nov 10, 2010)

I like visible circuit breakers, and I don't want them resetting before I'm ready to reapply power. A neat indication is to put an LED across the breaker (with a resistor and diode) to indicate when the breaker is tripped.


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## rkenney (Aug 10, 2013)

gunrunnerjohn said:


> I like visible circuit breakers, and I don't want them resetting before I'm ready to reapply power. A neat indication is to put an LED across the breaker (with a resistor and diode) to indicate when the breaker is tripped.


Different problems/situations require different solutions. That's why we have so many of them.

Diagnostics is certainly a consideration when implementing a particular feature or device.

Circuit breakers provide a mechanical means to restore circuit power and may be more convenient for you to isolate a problem. 

On the other hand a small layout conventionally powered with separate blocks already has switches to isolate track sections so finding a problem is as simple as selectively applying power or if the short follows the train isolating the engine/car that causes the problem.

Circuits other than track have their own special needs. Lighting and accessory circuits may be less demanding than track but still need some level of protection.

Then there are guys who just like switches. So if your bent is to have a control panel that looks like the Apollo 13 Command Module . . .


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## gunrunnerjohn (Nov 10, 2010)

I think you miss the point. I don't want the power restored until *I* decide to restore it. The PTC doesn't accomplish that for me.


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## rkenney (Aug 10, 2013)

gunrunnerjohn said:


> I think you miss the point. I don't want the power restored until *I* decide to restore it. The PTC doesn't accomplish that for me.


Not at all. You were very succinct. You did not provide any reasoning, however, and as I pointed out it is not the best or only solution for every situation.


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## gunrunnerjohn (Nov 10, 2010)

No solution is the best or only solution for every situation, including yours.


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## rkenney (Aug 10, 2013)

gunrunnerjohn said:


> No solution is the best or only solution for every situation, including yours.


I don't believe I ever presented it as such. Certainly don't know what your point is here.

If you don't like PTC fuses don't use them. Not presenting the information or shooting it down when it is presented doesn't help anyone.

Have I 'ruffled your feathers' or offended you in some way? If so I apologize, I have been known to be very direct.


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## gunrunnerjohn (Nov 10, 2010)

Go back and read your response, maybe you could lose the condescending tone. My first reply did not indicate my solution was the only solution, only what I liked and why. Somehow that launched me into outer space.


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## trains galore (Jul 22, 2013)

Ok well there are different solutions that are ALL viable no need to fight it out as said it really depends on the application, I have never heard of PTC fuses so thanks I'll go look them up, they are neat in that they reset themselves however I can see gunrunnerjohn's point in that circuit breakers would allow you too also isolate a circuit while working so it would sort of double as a switch, I like the idea of being able to see whether they are tripped with leds:stroke:
What circuit breakers could i use, I've seen the little black ones with the silver washer but what ones would I need make them work on 12v they all seem to be 240v (the ones at the shop anyhow)

Or can you use any breaker for whatever voltage as long as it is the correct current?
I might consider upgrading to them or ptc later, at least for now I have something as I wouldn't want to melt wires with a fault (been there done that with computer lighting mods, melted wire and only realised after a few minutes and someone saying they could smell something:laugh:

Also slight issue my PSU with no load outputs 17 volts, my lights are 12 and I'm a bit worried about burning them out, I know the load will bring it down a bit but is it neccessary to have a power resistor to drop it or should I just not worry too much

Thanks for all the responses, I really appreciate it as there is lots to learn and there are some very knowledgeable people on here!


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## rkenney (Aug 10, 2013)

No condescending tone. that's sarcasm. But you take it far too personally, if I was directing it at you I would have used your name. Your name isn't 'some guys' is it?


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## trains galore (Jul 22, 2013)

Okay well I got everything hooked up/swapped supplies, one problem- the voltage output from the supply is still 17 volts even under load and is making my 12v lights crazy hot and I'm worried they will blow so I've set the disconnect switch for that circuit to off until I can do something.
The article says to use a power resistor to drop the voltage, should I do this?
Maybe if I put a heavy load it would drop back
Any ideas?


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## gunrunnerjohn (Nov 10, 2010)

If the regulated 12V is 17V under load, use a different power supply, that shouldn't happen to a properly working power supply. Note that many of these supplies need a load on the 5V side to properly regulate, try a 2A load on that output and see if sanity returns.


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## rkenney (Aug 10, 2013)

trains galore said:


> The article says to use a power resistor to drop the voltage, should I do this?
> Maybe if I put a heavy load it would drop back
> Any idea



That's exactly right. If you have enough load the power supply will regulate correctly.
Light bulbs probably aren't enough so use a power resistor as a dummy load to force the switching power supply to regulate he voltages. Use one of the disk drive connectors and mount the resistor in the fan air flow to cool it. The article covers all of this, just do what they suggest.

For those who haven't seen this article, one of them (there are several) is here - http://2railoscale.blogspot.com/2011/09/how-to-convert-used-pc-power-supplies.html


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## trains galore (Jul 22, 2013)

Hmm interesting I mean I know it should be 12v but the article seems to say that since it is a switching supply it may not operate correctly without a load. The 12v has a load, but 3.3v and 5v do not. I tried hooking up a hard disk, but it made little difference. I also tried another supply and it still has the same thing so I think my supply is ok. So I'm thinking either it wants a bigger load on 12v or just A load on the other lines (5v)

The thing I don't get is that why would hooking up a power resistor on 5v line affect the 12v line? I'll try it anyway, they said try a 2 ohm resistor so I'll try and get one (already been rumaging through old stereo's etc but no luck yet


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## gunrunnerjohn (Nov 10, 2010)

Those supplies are designed with one regulated supply, and all the other voltages reference from the one regulated voltage. If that voltage isn't properly regulated, the other voltages go haywire.

For a long time, it was the 5V supply that had to be loaded, but I know some newer ones regulate of the 12V supply.


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## trains galore (Jul 22, 2013)

Ok thanks gunrunnerjohn, I will try and get a power resistor, 2 ohm is reccomended.
For now I might put the lm317 voltage regulator back on to get things running until I can get one
I really wish it would just put out 12v, but oh well, I'm hoping the power resistor will work out


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## gunrunnerjohn (Nov 10, 2010)

Those supplies regulate very well if you have them loaded properly. You can use an old automotive headlight bulb as a load. If you use a resistor, remember that 2 ohms across 5V will dissipate 12.5 watts, so you'll really want at least a 20W resistor for the task.


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## trains galore (Jul 22, 2013)

Ok then, I'll do that, 20w sounds fine.
Unfortunately curiousity got the better of me and I tried hooking up a normal resistor just to ''see what would happen'' well POOF! And now I know why, couldn't handle the current and be able to dissipate the heat:laugh:
Fortunately the power supply still seems to work, hope I didn't blow it though, I guess I'll find out I think it is fine since it still works and I'm thinking it was just resistor that went poof.
And I'm going to get that damn resistor before I try anything else and burnt the house down

Anyway I have made a new regulator box out of spare stuff to get things working again, so I can use it if I must but it seems like a waste to regulate an already accurate supply that could easily handle way more that those tiny little regulators I'm using
Any ideas where I might find one in junk? I've been through a stereo etc and also raided a dead computer psu for it's heatsinks


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## gunrunnerjohn (Nov 10, 2010)

You didn't do anything but toast a resistor. I have no idea where you'd find a resistor like that, but you can make one. Just take some fine wire and unwind enough to be 2 ohms. #30 wire wrap wire is 1.03 ohms for 10 feet, so 20 feet of it would be perfect. Wind it on a non-metallic spool of some kind and you have your resistor.


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## trains galore (Jul 22, 2013)

Well I just got hold of two big ones, hooked them up but... no difference
Tried a 12v car globe... no difference
Then tried a different multi meter, reading of 13v and it had a low battery.
Changed the battery in my main meter with a fresh one and I get a reading of 11.59 volts
All this just because stupid me was ignoring the low battery sign, but I honestly thought it wouldn't have mattered :dunno: anyway the street lamps (12v ones) are still getting really hot so maybe I will try and use a different meter just to make sure
I THINK it's ok now, but I'll be careful just in case something is up. Maybe I can hook up my voltage regulator and see how hot the bulbs still get, or better yet make a 9v circuit just for them to make them live a bit longer


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## gunrunnerjohn (Nov 10, 2010)

You can sometimes combine the power supplies to get different voltages, depending on the supply design. The 3.3 bucking the 12V would give you 8.7 volts.  Connect between the 3.3V positive and the 12V positive, the difference should be what you read at those points, 8.7 volts.


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## trains galore (Jul 22, 2013)

Interesting...
Depends on the supply though, as if it is common ground I think it would short out but maybe I'll try it anyway
Plus I could try running the small lights on the 5v supply, I'll see what I can do...
I still can't believe my meter was out just because of low battery, never had that happen before
Maybe I need to get some probes for my good old analogue meter and dig it out

UPDATE: Got it all working
Thanks for the suggestion of using different voltages for the lights gunrunnerjohn, I was worried the bridge lights were so hot so I actually put them on the 5v supply as they will last longer since they are a pain to replace, they are on their own circuit and fuse. The building lights are on the 12v circuit and are not a problem to replace, they are in bulb holders (MES type)
And the third circuit is 12v but connects to voltage regulators (3v and 9v for signals and auto reverse)
Here are some pics of it, the lamps are more yellowish now that the voltage is reduced, but I think it's more realistic since real street lights don't look like minature supernovas:laugh:


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## gunrunnerjohn (Nov 10, 2010)

Looks like you got it sorted out. 

The 3.3V and 12V share a common ground, but they will still regulate to their own levels. So, if you have 3.3V and 12V, the difference is 8.7 volts. The only thing is, you don't have a common ground, so the 8.7 volts would have to be used with a totally isolated lighting circuit.


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## trains galore (Jul 22, 2013)

Ok interesting
But I don't understand the how you can get 8.7 volts because it is the difference of 12 volts and 3.3 volts? I mean you could put them in series I suppose that that would get you 15.3 volts
But what would happen if you put the two different voltages in parralell, I've always wondered about that, do they subtract:stroke:
I have built lots of electronics kits in the past but it's only now I'm starting to understand exactly how they work as it is easy enough to build the kits just by soldering in the correct parts, but I'd like to start making my own circuits one day, I found this link which I thought has some pretty nice train projects
http://www.talkingelectronics.com/projects/75 Model Railway Projects/75 Model Railway Projects.html
You could build them on vero board probably


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## gunrunnerjohn (Nov 10, 2010)

If you connect the negative side of the load to the 3.3 volt supply and the positive side of the load to the 12 volt supply, you end up with 8.7 volts across the load.

If you put two different voltages in parallel from a regulated supply, they'll fight each other until one dies.


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## trains galore (Jul 22, 2013)

Oh ok then, I would have thought it wouldn't have mattered which ground lead as I thought they would all be common ground, thanks for explaining that!
Anyway i now have have a wide range of voltages I can use to power stuff, so I might try some of the projects on the link, I need to come up with automated signalling or something so I can ''operate'' the layout to a schedule rather than aimlessly moving trains back and forward


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## gunrunnerjohn (Nov 10, 2010)

Just remember, if you're not using the ground as one of the sides of the power feed, you must isolate the whole section that you're powering with the floating power. You can also connect between the 5V and 12V to get 7V. From the 3.3V to the 5V will give you 1.7 volts, etc.


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## trains galore (Jul 22, 2013)

Forgive me for asking
I understand that you would connect one side of the circuit to the 3.3v and the other to the 12v (presumably the positive leads of these supplies so orange and yellow)
But I don't quite understand what isolating the section means, do you mean isolating it from other circuits on the power supply

Thanks for all the explaining! It really helps


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## gunrunnerjohn (Nov 10, 2010)

Since neither of the leads, the 3.3V or the 12V lead are at ground, the circuit these are used in should be insulated from any other circuit on your layout.


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## trains galore (Jul 22, 2013)

Oh ok then!
So just ensure it does not connect to any other circuits on the layout. I suppose you could get a short circuit if that happened (3.3v short to ground)
I still can't believe I don't need to have a ground, but is this is because the lower voltage subtracts from the higher voltage as it is negative?


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## gunrunnerjohn (Nov 10, 2010)

Correct, the two voltages, both being independently regulated, will just subtract, the lower from the higher, and you'll be left with the difference.


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## trains galore (Jul 22, 2013)

Ok then!
I always thought you had to have a ground but I sort of get the fact that the lower voltage subtracts from the higher voltage.
I'm very pleased with the power supply so far, seems to have plenty of juice.
What else could you use as a supply, I mean the average power pack can't power a huge amount and with mine it puts out 16vAc I think so I'd need a rectifier etc not worth the bother as it probably couldn't power much


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## gunrunnerjohn (Nov 10, 2010)

You don't need "ground", just a complete circuit with a voltage differential.


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## trains galore (Jul 22, 2013)

Right ok
I guess that's what a circuit really is, so I suppose strictly speaking you don't necessarily have to have 0v just as long as one is higher than the other but of course you get a voltage difference. Thanks for explaining that, I never had a clue
Everything seems fine for now, I might get some better rated fuses (current ones are 3a I think) but probably what I will end up doing at some stage when I get a break is to just rip out all the old panels and make a nice proper one with breakers or PTCS and also a stud and probe diagram rather than the useless peco button switches I have at the momenthwell: I really have to guess when I'm setting points:laugh: as they aren't labeled...


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