I am setting up signalling on my model railway.
I am using a 'mega' for the work and I have now bought a 'leonardo' as a test rig.
My question is this...
I have recently obtained a PC ATX power supply in very good condition. Can I use the supply lines from this PSU for my arduino's. If yes should I use the 5V or 12V?
Many thanks for any replies.
Really depends. If the Arduino is next to the supply it's fine to use the 5V. If the Arduino is somewhere under the layout, use 12V to supply the Arduino. But then the Arduino can't supply any 5V for other devices.
I've done multiple model railroad stuff and I always find that a modular approach with multiple Nano/Pro Mini's is easier then 1 big and bulky Mega...
Some of those PC power supplies will not turn on without the correct loads on them - I don't remember all the details other than just plugging them in will not work - they require some load of some sort. As for the train, it is not clear if you are familiar with it, but check out DCC for the model railroad - there is a whole lot of stuff out there for controlling the trains using specialized signaling.
mikey
Yeay, some need some load to guarantee they are stable. As far as I know modern supplies don't really bother with that. Simply connect PS_ON to GND and you're off to go.
septillion:
Yeay, some need some load to guarantee they are stable. As far as I know modern supplies don't really bother with that. Simply connect PS_ON to GND and you're off to go.
+1
I use one for a bench supply. It needs no load. The multiple voltages could be handy for a model railroad.
From my experience, if you locate the supply in the middle of the work area and run the lines out like spokes of a wheel, the 5V will work fine for an area of 10 ft x 10 ft. If the railroad area is more like 20 feet x 20 feet, you could try it with one arduino and see first what kind of voltage you get. I think it would be ok even for that. I would only use the 12V for lights and motors. Using it to supply the arduinos Vin will cause the 5V regulators to run hot and th 12V may not be rated enough (allowing 1A/per arduino)
If you only power the Arduino the power loss in the regulator is not that bad @ 12V. And 1A is already wayyy to much for an Arduino even if you power it from 7V. If you use 5V under the layout you don't only have the possible voltage drops but also all the crap on the lines. And if you don't want to stress the regulator at all, DC-DC converters are dirt cheap nowadays. Making a PCB with a Nano, a DC-DC and the stuff your driving/doing what you want is pretty easy and cheap.
Many thanks for all replies.
I have just started to use the PSU for some lighting.
Unfortunately the power for my train controller (DCC by Bachmann) is 16V. so I've ordered an adjustable voltage booster from Ebay.
I have one more question. Are all the 5V lines parallel or is each line separately current limited?
thanks in advance. 
I doubt one of those could handle a model locomotive.
Are all the 5V lines parallel or is each line separately current limited?
WHAT 5V LINES ?
raschemmel:
I doubt one of those could handle a model locomotive.WHAT 5V LINES ?
Sorry raschemmel,I wasn't very clear in my post.
My model layout track is powered/controlled by purpose built DCC model railway controller.
The reason I want to use the ATX power supply is for the 'auxiliary' circuits such as lighting and Arduino powered signals, etc.
The DCC track controller is powered by a DC 16V supply. I will eventually try to power this controller from a 12V line from an ATX PSU line boosted up to 16V.
My question was asking about the several separate 5Volt lines, are they separately current limited?
Hope this makes more sense.
Still don't know what "several separate 5V lines "e means. WHAT is a "5V line" ?
"line" is NOT an electronics term. Be more specific.
I hope to god your not talking about the digital GPIO .c
Also , I doubt the ATX 12V has the power to drive the train but since you haven't looked on the DCC Controller UL label to find out the Wattage we don't know.the dihi
raschemmel:
Still don't know what "several separate 5V lines "e means. WHAT is a "5V line3" ?
"lineq" is NOT an electronics term. Be more specific.Also , I doubt the ATX 12V has the power to drive the train but since you haven't looked on the DCC Controller UL label to find out the Wattage we don't know.
There are dozens of wires exiting the ATX PSU.
Several are red and I understand these are 5 volt lines.
Several are yellow, these are 12 volt lines (called rails on Wikipedia - not to be confused with the rails of the model railway).
Black cables are ground-neutral-earth.
The model railway I'm building is OO scale - so the track wattage is relatively low. The actual AC-DC converter which supplies 16 volts to the controller is current limited at 3 amps. Even with four locomotives running on my layout the current measured to the controller is less than 1 amp, so I'm surprised that you think that power lines from the ATX PSU will not provide enough power.
Can you advise me on the amount of power each separate power line (from the ATX PSU) is able to deliver? please
Measure the voltages and post a photo of the label on the P.S.
raschemmel:
Measure the voltages and post a photo of the label on the P.S.
Thanks for your help Raschemmel, I've carefully read through the entry for ATX power supplies it states that each line is limited to 20 amps. This will provide way more power than I need, so I am happy to utilise this PSU.
For me the beauty is that I only need one mains outlet to supply all the power for my layout. Instead of the several different power supplies I'm using at the moment.
Again thanks for your help and advice.
The downside is that if you make a mistake , instead of a 5V/1A regulator shutting down, your P.S. will deliver enough current instantly set any component on fire (melting the breadboard of course). Have fun with that. I watched an LM555 timer chip burst into flame and go incandescent with only a 10A supply, so 20A would be even more spectacular. Just don't make any mistakes and you should be ok.
The actual AC-DC converter which supplies 16 volts to the controller is current limited at 3 amps
P= I x V
= 3A x 16V
= 48W
Let I = 48W/12V
I = 4A
Is the ATX 12V rated for 4A ?
Is the voltage booster rated for 4A ?
Robert
The (not surprising) answer is that all the red 5V wires on the ATX power supply are connected to the same point on the board. The reason there are so many is to handle all that current and in particular, to permit the relatively small pins in the Molex connector to handle all that current.
The same goes of course, for the black ground wires.
I wonder what would happen if you mistakenly conmect a typical arduino jumper guage wire across the 5V supply ? Would the power supply shut down or would it just deliver 20A through the 24 or 22 guage wire and turn it into a heating coil ? I never tried it but I think the OP should just to find out. Just be ready to turn off the power quickly. It might be a good idea to have a fire extingquisher handy.
raschemmel:
The downside is that if you make a mistake , instead of a 5V/1A regulator shutting down, your P.S. will deliver enough current instantly set any component on fire (melting the breadboard of course). Have fun with that. I watched an LM555 timer chip burst into flame and go incandescent with only a 10A supply, so 20A would be even more spectacular. Just don't make any mistakes and you should be ok.P= I x V
= 3A x 16V
= 48WLet I = 48W/12V
I = 4AIs the ATX 12V rated for 4A ?
Is the voltage booster rated for 4A ?Robert
Thanks rasch...
I’ve certainly considered the possibility of over-powering the more delicate parts of my layout, To the extent that I’ve been viewing ‘afrotechmods’ youtube on current limiters. I will probably install them on the more expensive circuits.
Many thanks for your help. I was hoping to find someone who's played with ATX PSUs and is used to going ‘off piste’ with them.
If you can handle low tech, you can use fuses.
Any computer supply should have a "shut down/ current limit mode in case of a short but when the supply is rated for 20A you have to ask yourself if it is possible that it might not be able to distinguish a short from a 20A load.. If iit only takes 10 A to " vaporize" a small component, would the supply shut down ? I would perform some controlled experiments.
I just installed 6 automatic smoke detector shut-down circuits at work that utilize a consumer home smoke detector to shutdown the contactors that power 240V /100A equipment.
This is essentially an "afrotechmod" . We used to have another term for that before everything became "politically correct". The smoke detector has a Normally Open contact.
(which to me is sort of stupid because the ideal would be a normally Closed that could be used to power a relay so it would shut off in case of fire). So when my boss said " take these smoke detectors with normally open contacts and build a shutdown circuit for our 100A equipment " ( using a relay contact in the detector rated for maybe 100 mA), I had to add a 12V 10A relay to control our 600mA coil 240V ,3-phase contactors, using the N.C. contacts of thd 12V, 10A relay (and a 12V 1A wall wart). The 10A relay coil is connected to the 12V wall wart which powers the smoke detector anx the 12V relay, but the N.O. contacts of the smoke detector prevent the 10A relay from energizing UNLESS it detects smoke , in which case it closes the N.O. contacts, turning ON the 10A relay, opening the N.C. contacts powering the 240V/ 100A/3-phase contactor , thus DE-ENERGIZING the 240V 100A 3-phase contactior , shutting down our 240V equipment automatically in the event of smoke, using a $10 smoke detector.