# Use a PC Power Supply for a Layout?



## xrunner (Jul 29, 2011)

Seems like a good idea, see site below.

A PC supply has 5V and 12 V at a decent amperage, and they are very cheap.

Anyone ever do this?

http://www.nysry.com/phase4_status.htm


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## Massey (Apr 16, 2011)

The only drawback is you have to keep a load on the PS or it will fry itself in seconds. Those are very delicate with the load things but if you can keep a load on it you can do just fine with one.

Massey


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## gunrunnerjohn (Nov 10, 2010)

I've used PC power supplies for several projects, just not for trains. It's a good idea, and there are tons of old PC's being pitched, so you can probably score the supply for free if you look. I have several sitting in my closet right now.

Note that you have to have a load either on the +5V or +12V line for many (most?) of them to run, a couple of amps does it. It used to always be the 5V line, but modern designs actually use more 12V and switching regulators on the MB for the processor and video, so new ones frequently need a +12V load.

EDIT: I've never seen no load damage a PC supply, they just won't produce any voltage.

Your link is bad, FWIW.


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## xrunner (Jul 29, 2011)

gunrunnerjohn said:


> Your link is bad, FWIW.


Hmm I just checked it and it links OK.

But yea I didn't know a PC supply would fry with no load, that seems odd. Massey why do you say that?


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## gunrunnerjohn (Nov 10, 2010)

I've assembled dozens of PC's the days of the 8088 and onward, I've never had a PC power supply die because it was powered on with no load. What happens is... nothing. The fan will sometimes twitch upon first applying power, then stop.

I just took one out of the closet and powered it on with no load, it started and ran fine. I measured the +5 and +12, they were well within 5%, 5.15V and 12.11V. Apparently, the ATX supplies may not even need a load, the old AT ones usually do.


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## xrunner (Jul 29, 2011)

gunrunnerjohn said:


> I just took one out of the closet and powered it on with no load, it started and ran fine. I measured the +5 and +12, they were well within 5%, 5.15V and 12.11V. Apparently, the ATX supplies may not even need a load, the old AT ones usually do.


Thanks I had a spare one myself and was going to check it tomorrow.


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## 93firebird (Dec 25, 2011)

great post...gets me thinking :thumbsup:


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## gunrunnerjohn (Nov 10, 2010)

FWIW, I took an older AT supply out, sure enough, it required a load on the 5V to get going. It did what I described earlier, the fan twitched and that was it. Connected the 2A load and it ran fine. I used a 2 ohm 75 watt resistor as a load, so I guess that was 2.5A.


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## Massey (Apr 16, 2011)

I do IT for a living and I have had many PCs roll across my bench with a bad PS that was brand new, just not attached to the mother board or drives when powered up. One guy I was working with also "tested" a couple by checking the voltage when it was not attached to a PS tester or a proper load. Once these were installed they didnt work either. We sent them back for warranty and each was denied for improper use. These were early AT power supplies that may not have had a protection circuit included. I simply do not take a chance any more and make sure at least 1 drive it plugged in before powering them up.

Massey


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## NIMT (Jan 6, 2011)

If you look really close at the pics they are using the PC Power supply to power the accessories and equipment but not track power threw the DCC controllers or boosters.
I read an article years ago how well it would work powering the DCC controller..Well In about 15 seconds it went full tilt nucular and went into a compleate melt down compleately fried both the power supply and the controller, lucky for me I one of the first run of the DCS200's so they wanted it back to find out what happened...they told me that it compleatly cooked it like it was hit by lightning! I can only guess that there was some sort of feed back that caused it to keep making more amps or volts????
All I know is never again! I now use a 28 Volt, 24 amp, DC supply limited to 8 amps to each DCC controller, it's a telephone system power supply!


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## tankist (Jun 11, 2009)

PC power supply is what i tried first. then i bought the 5$ cheapo tyco powerpack from set (craiglist) and it was 10 folds better. at 20-30$ for nice preowned MRC TechII throttles i do not see why bother.

i suggest to use the right tool for the job: PC PSU to power a PC, powerpack to power layout


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## xrunner (Jul 29, 2011)

Well, the guy who's using several in that huge layout I linked, for even accessories, I have a good bet that he's not some newbie that doesn't know what he's doing - just look at what he's built and has built in the past - it's pretty impressive. Here's the link again -

http://www.nysry.com/phase4_status.htm

I don't discount either his experience or anyone else who's posted in the thread, but I (we) need more technical facts - if it does work (and certainly we can assume that guy knows what he's doing) _why_ does it work. And if they don't work, we need to know _why_ they wouldn't work, in technical terms. 

Here's another example of a tutorial of how to convert a PC power supply into a lab power supply. So we know they can power things other than PCs.

http://www.instructables.com/id/ATX-->-Lab-Bench-Power-Supply-Conversion/

Power is power, a load is a load. Why couldn't a PC power supply power any load up to it's power rating? Does anyone have a _explanation_ of _why_ it couldn't, in addition to their experience?


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## gunrunnerjohn (Nov 10, 2010)

I don't see any reason that a PC power supply won't do the trick properly installed. If the supply goes nuts in your PC, it'll nuke that in a hurry as well.

The key thing with a PC power supply is always having a small load to make sure the regulation is working properly. Many older AT supplies required a load to properly operate. Some work without a load, but to be safe, I'd always have a fixed load. As I said, the two ATX supplies I tried (all I have in the closet) worked fine with no load and regulated properly. However, the older AT supply wouldn't start at all without a load.


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## tankist (Jun 11, 2009)

xrunner said:


> Well, the guy who's using several in that huge layout I linked, for even accessories...
> http://www.nysry.com/phase4_status.htm
> 
> Here's another example of a tutorial of how to convert a PC power supply into a lab power supply. So we know they can power things other than PCs.
> ...


yes, power is power of course. but you use hammer to drive nails even though a pry-bar is heavy and metal, and technically can be used for that too. simple - proper tool for the job. of course power from PSU will make the train move. but it is not going to give you momentum effects, not going to pulse on low power settings, not mentioning it is of only 3 constant voltages that are not easily changeable. in the first link you provided it seems that PSU is powering a digitrax system, that is fine, not sure if feeding it 12V instead of 14V is a big deal. but for DC control PSU is not comfortable at all without major mods.

now , if you considering hacking a PSU into MRR powerpack then i'm all for.


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## gunrunnerjohn (Nov 10, 2010)

Obviously, you can't use the PC power supply to run a plain DC layout, hopefully nobody took that away from the discussion!  :laugh:


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## Massey (Apr 16, 2011)

If you look at the pics that show his boosters and electronics carefully you will see that the boosters are not powered by the PC power supply. They have a Digitrax PS and in one a home made looking 14V ac PS. I am going to guess that the PS supplies are simply for accessory equipment that only needs DC power. Also note that the guy is not using the filtered power that normally plugs into the mother board but the unfiltered power that goes to the drives. Power to the drives is not as finely filtered as the power to the motherboard, it is also usually on a single bus for all drives which means you share the current between all the plugs. Remember this when setting up accessories and also note that most PC PSs only supply 1 amp or less to the drives but it can supply much more to the mother board.

Oh and those appear to be modern PC power supplies, much newer than the ones my coworker fried. 

Also power is not power... A power supply can be filtered, or non filtered and the quality of that filtering can vary from pulsed DC at 30Hz (horrible half wave rectifying) or pure constant DC with so slight of a ripple most scopes would have a hard time finding it. You pay more for the better filtering and some equipment wont care other stuff will get fried with poor filtering. a PC power supply is going to use switching regulators, and full wave rectifiers but the motherboard power bus will be higher quality filtering than the drive bus will. This is true for most low level PC supplies. Higher end gaming power supplies will filter the drive bus as well since sometimes those lines are used to power video cards and suppliment power to the processor. The 4,6,or 8 pin plugs that have the yellow and black wires that plug into the video cards and mother boards near the processor are fine filtered.

Massey


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## gunrunnerjohn (Nov 10, 2010)

I'm not sure what power supplies you're looking at, but I can assure you that modern ATX power supplies will supply FAR more than 1A to the disk power connectors. Many video boards that require 90-120 watts include an adapter to allow you to power them from the disk power connector, we're talking 7-10 amps from one of those connectors! In addition, if you place a small load on the power outputs of an ATX supply and look at them with a 'scope, you'll find they're pretty well filtered.

On supplies with a single +12V bus (some have a split +12V bus), the disk power comes from the same connection inside the supply as the MB +12V comes from. Remember that any modern motherboard has another set of switching regulators to supply the low voltages required for modern processors.

For instance, the Vcore on this I7 equipped machine is at 0.912 volts! That is supplied by the motherboard switching P/S driven by the +12V connection.

Have you actually taken an ATX supply apart or bench checked it to verify your facts? I think you'll find they do a lot better than you're giving them credit for.


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## xrunner (Jul 29, 2011)

Massey said:


> Also power is not power...


Massey, what are the power supply requirements for the power input of a DCS100? 

AC, DC, filtered, unfiltered?


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## gunrunnerjohn (Nov 10, 2010)

I know the DCS200 takes AC or DC, it's not particular at all about the power.


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## NIMT (Jan 6, 2011)

I'm not massey, but I can answer this one!
Max Input AC 50/60HZ 20V RMS
Max Input DC 28V
MIN AC 12V
MIN DC 12V
Optimal Input Current 5 Amps

Using a 12V DC supply will put you right at the bottom of the performance end of the scale.
I get 12.5 volts to the rails on N scale setting and 14.5 volts on HO scale setting.
So I would guess that using a 12 input will give you a lower output yield. The DCC controller uses some of the power for it own use and in the distribution and regulation.


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## Massey (Apr 16, 2011)

It will take both AC and DC power but the requirements are different for each. The power supply I use is a Digitrax PS that puts out about 16V AC @ 5 amps, and it is not filtered. AC power is typically not filtered just regulated.

John the PC units I was refering to are the cheapo ones that you get in these bargain PCs You can usually get them cheap or free and they are not the best in quality. Yes some of the newer ATX supplies do give more than 1amp to the drives, I have a cheapo one that I use for testing that only has 1amp on the 5V bus for the drives, not sure but I think the 12V bus is 3 amps. This is only a 150W PS, it came out of a $400 Dell 

Massey


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## Massey (Apr 16, 2011)

Thanks Sean I dont have access to my books or the Digitrax website right now.

Massey


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## gunrunnerjohn (Nov 10, 2010)

Gee, I haven't seen a 150 watt PC power supply in years!


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## xrunner (Jul 29, 2011)

What I'm wondering then is, what type of input circuitry the DCS100 is using.

Certainly it needs a good DC voltage internally, as it uses computer logic circuits, yet, the input can be either AC _or_ DC. It doesn't _need_ DC input, since it can convert an AC input to DC. So, would it not then be able to filter an already direct current source, albeit "noisy" to a better DC voltage? Again, since it can accept AC (a far cry from DC) shouldn't it be able to cope with a noisy DC voltage input? I don't know I'm just curious.


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## gunrunnerjohn (Nov 10, 2010)

I suspect you can feed it almost anything. I'm sure there's a switcher in there that has rectification for AC and then generates the power needed. That's doubtless what the large heatsink is for.  

A switching supply just charges a large capacitor on the input side and then runs a high frequency power oscillator to produce the AC for a toroidal transformer internally. Since it's high frequency, the filtering on the other side is much less of an issue than for 60hz, so the capacitors are much smaller. The transformer is much smaller as well.


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## xrunner (Jul 29, 2011)

gunrunnerjohn said:


> I suspect you can feed it almost anything. I'm sure there's a switcher in there that has rectification for AC and then ...


That's what I was implying when I said "power is power", 12 watts is 12 watts, whether it's generated by 60 Hz AC, pristine DC or a noisy sawtooth waveform, they're all providing exactly the same power to the load if 12 watts is measured.

As you said, I suspect the DCS100 doesn't care what is fed into it as long as it's within certain parameters such as a high voltage limit. It just goes into the converter and out comes enough voltage to drive it and the tracks, if it gets enough to work with.


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## NIMT (Jan 6, 2011)

Well I'm no electronic enginer! All I know is there is a whole lot of electronics inside the control box! Hey I didn't know that it's got a battery for the Board just like a PC motherboard!


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## xrunner (Jul 29, 2011)

NIMT said:


> Well I'm electronic enginer!


I have an EET degree (Electronics Engineering Technology). 

I didn't know about the batteries either! Are they to be replaced at some point? 

Are those 8200 uF Caps? Nice.


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## Massey (Apr 16, 2011)

The batteries are for keeping command station settings when there is no power applied. The batteries will last for years, so far I have owned mine for 6 years and have never lost any settings. A friend of mine went over 10 years with no setting loss. The batteries are common and easy to replace.

As for power being power it is not all the same. You may get 18V RMS but that is just the useful voltage not the total voltage. If your dirty voltage spikes too high even for a split second you can release that magic smoke they stuff into those little chips.

Massey


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## gunrunnerjohn (Nov 10, 2010)

Those large 8200uF caps are the filters for the switcher primary input after it goes through the bridge rectifier. 

The two batteries I believe are so you can swap them out one at a time and not lose settings.


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## xrunner (Jul 29, 2011)

Massey said:


> The batteries are for keeping command station settings when there is no power applied. The batteries will last for years, so far I have owned mine for 6 years and have never lost any settings. A friend of mine went over 10 years with no setting loss. The batteries are common and easy to replace.


They look like CR2032's. Like I posted in a thread 'bout Tea Lights, you can get 2 Tea Lights for $1 at the Dollar Store and 2 brand new CR2032's along with them. Don't buy CR2032's from Radio Shack.

Thanks.


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## gunrunnerjohn (Nov 10, 2010)

They are CR2032's, you can see that in Sean's picture.  He only has one installed, so when he removes it, it's total loss of memory time.


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## xrunner (Jul 29, 2011)

gunrunnerjohn said:


> They are CR2032's, you can see that in Sean's picture.  He only has one installed, so when he removes it, it's total loss of memory time.


Bwahahahaha! What's up with that NIMT? :dunno:


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## NIMT (Jan 6, 2011)

Loss of memory...Who me...Who am I...Who are you ...Where am I...Where did I leave my truck?
Wouldn't be the first time I've been at a loss!


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## Massey (Apr 16, 2011)

The reason why there are 2 slots is so you can put the new battery in before removing the old one. No memory loss for anyone other than NIMT

Massey


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