# PC Power Supply Specs



## Grandcheapskate (Jan 5, 2006)

I was in a mega computer store yesterday and checked out an inexpensive ($30) ATX power supply. It was 500w and listed the specs for the output lines. There was a 3v and 5v which said they supplied 18 amps each. There were two 12v lines but I can't remember the amps, although I know it was a pretty high number. Then there were two other outputs which showed negative voltage; I believe it was a -3 and -12 at a low amperage.

This looked like a supply that would have enough power for a home track, especially one that is only used by one person at a time.

However, I am always confused by the lines with negative voltage. What are these outputs?

Thanks...Joe


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## 440 (Feb 23, 2008)

Hey Joe, its been a while. How've you been? 

At any rate, I have a spare PC PWRS too and have been thinking of using it on my home track too. I like you, have been slightly confused as to the power outputs on the supply.


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## AfxToo (Aug 29, 2003)

> However, I am always confused by the lines with negative voltage. What are these outputs?


Negative voltage just means that the polarity of the output voltage is negative relative to the power supply's common reference voltage. Negative voltages are commonly used in concert with their positive mates (say -12V and +12V together) to power differential line drivers used for high speed communication lines and circuits. Basically, these are 2-wire communication lines where the positive voltage reference signal is sent on one wire and its opposite polarity (mirror image) negative reference voltage is simultaneous sent on the other wire. This makes the combined transmission more immune to electromagnetic noise because the same interference source (common mode noise) affects both lines differently electrically, it adds to one line and subtracts from the other line, so it is easily detected and rejected. A computer uses differential drivers in several areas so it needs these positive and negative voltage pairs available from the power supply.


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## clemedc (Feb 2, 2011)

you would have plenty of amps but only 12 volts and therefore not as fast as lets say the 18 to 22 volt power packs


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## Grandcheapskate (Jan 5, 2006)

clemedc said:


> you would have plenty of amps but only 12 volts and therefore not as fast as lets say the 18 to 22 volt power packs


I'm sure (based on my complete lack of electrical experiance) you can combine the 12v with either the 3v or 5v (or both) to get a voltage of 12v, 15v, 17v or 20v. That should be enough of a range and variation to satisfy most applications. I guess you could even combine the two 12v lines to get 24v.

Joe


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## usdra (Jan 23, 2007)

You would be better off with something like this. http://cgi.ebay.com/DC-POWER-SUPPLY...805?pt=LH_DefaultDomain_0&hash=item3c9aaa2d8d More than likely if you try to combine the voltages on the pc supply you will fry it or the higher voltage will over power the lower & it will not contribute & therefore give you no gain. 

Eric
www.mobydiditperformance.com


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## Grandcheapskate (Jan 5, 2006)

usdra said:


> More than likely if you try to combine the voltages on the pc supply you will fry it or the higher voltage will over power the lower & it will not contribute & therefore give you no gain.
> 
> Eric


 So, are you saying that you cannot combine the 12v and 5v lines to create a 17v output? And if you can combine them, how would you do it? I'm guessing you would try to configure it like batteries.

In order to add together the voltage produced by each battery, you connect them positive to negative. But let me take a guess here. Because each positive line uses the same common ground, you can't connect positive 12v to negative to positive 5v to negative because the ground wire goes to the same place.

Joe


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## Rolls (Jan 1, 2010)

Grandcheapskate said:


> ... Because each positive line uses the same common ground, you can't connect positive 12v to negative to positive 5v to negative because the ground wire goes to the same place.
> 
> Joe


That's what I'd be concerned about, Joe. I don't know and I haven't tested a contemporary PC power supply, but I'd guess the outputs are more likely to be tied to a common ground than isolated, given the PC is their intended application. I'd also guess they are fairly well optimized to met the specific needs of powering a PC at the lowest possible cost. 

There are so many other good and affordable options to power a track, I personally wouldn't even take the time to investigate appropriating a PC supply to a track. It seems more like a good electronics hobby project, than a viable alternative to options out there already. Just my opinion, of course. Hope it helps.


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## slotking (May 27, 2008)

you can with batteries, ie add a 6v with 12v for 18 (19 in reality)

or

you can run a low amp 18v PS through 18v of batteries to run the race track and maintain a steady 18v all day long with no dips.


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## usdra (Jan 23, 2007)

Grandcheapskate said:


> So, are you saying that you cannot combine the 12v and 5v lines to create a 17v output? And if you can combine them, how would you do it? I'm guessing you would try to configure it like batteries.
> 
> In order to add together the voltage produced by each battery, you connect them positive to negative. But let me take a guess here. Because each positive line uses the same common ground, you can't connect positive 12v to negative to positive 5v to negative because the ground wire goes to the same place.
> 
> Joe


More than likely no. There are some high end power supplies that can be hooked up in series. Most of the low end stuff will not handle it. When you can buy this http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160461609153&ssPageName=STRK:MEWAX:IT for less than $65 including shipping & it will power whatever you throw at it, why would you use anything else?

Eric
www.mobydiditperformance.com


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## Grandcheapskate (Jan 5, 2006)

I guess there's really no reason to go out of your way to use a PC power supply. It's just that sometimes you may have left over or unused PC power supplies that you want to use. Also, it's so tempting when you see new supplies for as low as $14-$15.

Joe


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## 440 (Feb 23, 2008)

I happen to have an old one laying around so I'm probably not going to give up on the PC power supply idea. If nothing else it'll be fun to mod one up for giggles. Especial since slot car power supplies for now are out of my price range.


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## alpink (Aug 22, 2010)

yep, if you wire any of the negative wires directly to a positive wire coming out of a PC power supply you will get an instant short and very likely a blown AC circuit in your place of use along with a nice electrical fire. I say go for it. but, please, set up a long distance video recorder of the event for future entertainment. I am all about watching others entertain me by destroying their property in a manner that was foreseeable and preventable. go for it!


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## Rauncy (Sep 1, 1999)

*How to :*

Here's the specs for a pc power supply. +12v and + 5v = +7v , +5v and -12v = +17v.
more on page 12 of this

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


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## cwbam (Feb 8, 2010)

Cheap Power - save your old (TOMY TYCO LifeLike powerends)

30volt old HP printer power supply (off White) Drag Race anybody?

18volt laptop power i.e. DELL SONY ect.. 2.25 amps

12 volt Nintedo GAMECUBE 3.25amp GJETS bench power ect... (kids haven't used in years) 

Look what you have laying around the house read the brick details or thrift store.


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## pshoe64 (Jun 10, 2008)

You can't combine the voltage leads from the same rectifier source without issues. Any DC converter creates AC bleed which will shorten your slot motors life and hinder best performance. All AC to DC converters (except real expensive ones) have AC bleed over. The more efficient the converter, the less bleed over, the cleaner DC you get. But you can combine separate rectifiers. A positive to positive, negative to negative gives you the same voltage but combines the amperage, a positive to negative combination adds the voltage and keeps the lowest amperage level of the lowest source. I have combined the AFX tri-power packs at 22 volts and gained 2 amps. But nothing beats a single, clean DC converter with 18-30 amps or batteries are even better. If you go the route of a high power DC converter, make sure your house power has an appropriate circuit breaker (amps) to meet the draw form the power supply. I ran a separate breakers for my tracks, just so I wouldn't interfere with something else in the house. You don't want your TM to get upset if your track blew the same circuit her TV was on Slot tracks don't fit well in the doghouse!

-Paul


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## noddaz (Aug 6, 1999)

*Only need 12 volts?*

The cars run fine on it... Really, they do...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-536

I use one as a bench supply when working on cars...

But I understand that 18 volts is the "standard"...


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## Rolls (Jan 1, 2010)

Rauncy said:


> Here's the specs for a pc power supply. +12v and + 5v = +7v , +5v and -12v = +17v.
> more on page 12 of this
> 
> http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply


+5 and -12 = +17V, but at what current? The -12 is rated at less than an amp... can it take in 10x that current from the +5 side? 

Might end up with a 17V supply with the same current output as a Tomy wall wart.

The strength of PC power supply is good quality 5V power with abundant current at 5V and a rock bottom price. I just don't see it as a viable supply for a track if you want 16-22V at an amp or two per lane. 

Maybe I'm too quick to dismiss it, but that's how it looks to me. 

At the $15 price point, I think what a fella by the name of kimochi over on SCI did this month with two laptop chargers is a much better way to go.


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## Hornet (Dec 1, 2005)

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## AfxToo (Aug 29, 2003)

I have a very good understanding of electrical engineering and DC motor theory and practice and I agree with Hornet on this one. These little 3-pole brushed DC motors are built to ancient design standards and are sloppy little beasts. The relatively small amount of AC ripple on even a low end switching power supply is nothing compared to the self induced electrical noise from commutation and sparking caused by armature reaction (magnetic related timing alteration) and armature winding inductive reactance (current related timing alteration). The fact that these motors have to operate over such a wide range of conditions means that the static motor parameters (like brush timing, winding type, wire type, lamination design, etc.) will never be optimal for all possible operating conditions. 

The main criteria for power supply selection should be to eliminate all surge effects and to supply enough current so the power supply does not lose regulation under peak demands. The low cost wall warts that come with race sets suffer from both of these conditions, surge and loss of regulation. Do wall warts "hurt" your car? No, they just reduce the enjoyment level of your racing experience, unless of course you enjoy the semi-comical effect of seeing your competitors go airborne whenever you wreck.


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## pshoe64 (Jun 10, 2008)

I've noticed a few replies using voltage regulators to step down voltage rates to 20v or 18v. Assuming we're talking about 2-12v car batteries wired in series to produce 24v with abundant amps available, what is recommended to get the voltage down to, say 20v without reducing the amps to negligible amounts. I have found plenty of adjustable voltage regulators but most reduce the amps somewhere between 1-5 Amps. Any better examples I could learn from? I can find 12v batteries cheap and easy, 6v units seem to be considerably more pricey. Would a regulator on 24v be cheaper in the long run and are they out there without restricting the amperage?

Thanks for the feedback.
-Paul


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## Hornet (Dec 1, 2005)

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## dhamby123 (Jan 6, 2007)

ive used these for cheap power supplies but not a supply for a track . they work good for breaking in motors and such . a good place to find them are at goodwills they run about 5 bucks each you rarely find a 500 watt unit but 300 watt units are easy to find . i tie all the yellow wires together 12v and all the black wires together neg. you have to take one black neg wire and the one and only green wire inside and tie them together to turn on the unit or put a switch between the two .


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## Slott V (Feb 3, 2005)

Hornet said:


> I hear alot about dirty power supplies/AC bleed etc. shortening up a slotcars life,anybody got any real data besides "hearsay" that that's actually the case.
> When i switched from batteries to a switching power supply years ago,i took 2 Wizzard cars set them up with new bigfoot brushes/ stock 6.7 ohm Tyco arms, dialed them in on my homemade dyno,then let them scream for 20 hrs on 19.2 volts,at the end,i couldn't measure any differances in brush lengths between either style of power.
> So just what are you guys basing your theories off.
> Remember what a slotcar motors life conditions are,on and off the power constantly,and i personnally don't think AC ripple is as big a factor as most guys think it is,the motor never runs at a stable enough RPM level to ever notice the ripple.
> So i'd like to see some actual test data to back up some of these claims of AC ripple screwing up a car,if you got any


Greg Williams of AHORA offered this a few years ago. It at least showed the AC bleed of the wall pack and how a large capacitor cleaned up the output to the armature:

http://www.planetofspeed.net/phpBB3/viewtopic.php?f=6&t=3757

-Scott


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## Hornet (Dec 1, 2005)

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## Hornet (Dec 1, 2005)

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## Slott V (Feb 3, 2005)

I'll see what I can do Rick. I expected a little feedback from that post.

If one wants to prove that dirty DC output from unregulated power supplies causes heat you need a control to work from as a baseline. IMHO you will never break it down enough in layman's terms for Joe Average to truly understand. You start getting into some trig breaking down sine waves in AC voltage and how cheap DC rectification only chops off the lower part of the sine wave. The power coming out of wall sockets in the US is alternating current at 60hz, which is 60 waves or pulses per second. UK is 50hz. This pulse is the root of the issue when you get into the timing of the DC brushes and comm plates at higher RPM's. If you could break down the revolutions of the armature at full speed and compare that to the half wave pulse coming through the DC at 60hz you would probably see the real issue. Heat is the by product of any engine doing work. In an electric motor the heat is caused by electrical resistance. That AC pulse still coming through the DC voltage generates more resistance between the armature windings and the motor magnets through a disturbance. If you accidentally hook up an Aurora Vibrator AC power output to your DC HO cars you will immediately see what happens. This is an exaggeration of the issue but you will see the pulse of 60hz in this scenario and how the motor struggles to do work, or in that case fails as it cannot jump from comm plate to comm plate in a natural rotation.

What we really need is the Mythbusters!


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## Hornet (Dec 1, 2005)

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## Hornet (Dec 1, 2005)

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## Slott V (Feb 3, 2005)

That's interesting. I'd be curious to see heat comparisons after running on the track for a set period of time when the chassis is bound by the pull of magnets to rails. Do controlled tests with a wall wart and a filtered power supply of equal voltage and current with only the have wave of the dirty wall wart output being the difference.

I wouldn't expect pure AC at that voltage to cause instant heat in the windings but I'm pretty sure letting the motor sit buzzing like that for a while would eventually toast the brushes or comm plates. The fact that AC alternates from pos to neg doesn't allow the DC arm to rotate and the single set of windings getting energized acts like the solenoid type buzzer device in the Vibrator cars.


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## Hornet (Dec 1, 2005)

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## Slott V (Feb 3, 2005)

I have a nice adjustable Lambda filtered supply on my track and also wall warts in a box but need an infra red temp gun. I've been meaning to pick up one of those inline amp meter/recorders as well- one of these days. With Chicago becoming the new Seattle with record rains I might as well keep busy in the man cave. :-(


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## Hornet (Dec 1, 2005)

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## SDMedanic (Apr 21, 2011)

Hornet said:


> Steve (SDMedinic) you always got an opinion,chime in here,do i have rocks in my head,lol


Hornet,

This subject gets debated every few years along with how much power do you need? Despite information to the contrary a lot of folk still believe the folk stories that say (for example) that you need a 5-Amp power supply for T-Jets or that dead strips are the only way to reliably count laps. Operating experience and tests have shown that neither of these are true. There is similar truth here and I don't believe that you have rocks in your head. 

We don't run slot car motors at a constant speed or a constant load or within their design margins. Multiple factors can impact motor heat and motor or motor brush life. These include ride height, magnetic downforce and associated drag, available voltage, motor brush type, motor spring tension, body and tire choice, pickup choice and setup, pickup spring tension and driving style. Since these factors cannot be controlled between racers any heat vs wall wart vs regulated power supply vs battery comparison is useless as it cannot be reliably verified. Therefore, the debate continues.

AC ripple is not desirable. The national organizations moved to batteries years ago. They recently allowed regulated power supplies to be used for several classes. I personally won't use an unregulated wall wart and moved away from batteries many years ago. I would not use regulators downstream of a wall wart as the base problem (the unregulated power supply) still exists. I also don't believe in using adjustable voltage regulators for each lane. All lanes should get the same power from the same source. 

My track has multiple linear and switching power supplies (19V and 12V) that feed a very large capacitor bank via a diode auctioneering circuit. This allows me to change voltages by flipping one switch. The diodes also prevent power supply failures due to a short on a regulated power supply with a large cap attached to its output. 

Non regulated wall warts are fine for the toy slot car sets sold by Matell, AW, Tomy and others because they are dirt cheap for them to obtain and cost is a big factor to them. Anybody that is serious about slot racing should immediately dump these things and go with a good regulated power supply (linear or switching).

My opinions have been slammed by unknowing individuals on both POS and SCI. After that I decided not to get into these arguments. What I do works for me. What others do is up to them.


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## alpink (Aug 22, 2010)

SDMedanic, nicely said. and I tend to agree about one source of power for all lanes to prevent an advantage or disadvantage in one lane.


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## beast1624 (Mar 28, 2009)

About a year ago I got a HY3010EX-3 variable switching supply from Mastech. It has 3 outputs (two variable 0-10A and 0-30V; one fixed 3A and 5V).

I hooked one variable output to lanes 1&2 and the other to 3&4 (I will probably try to use the fixed for accessories or as a test lead for motor break in). This gives up to 5 amps per lane. I was a little concerned with spending $250+ on just the power supply but after a year I can say without a doubt that it has been the best investment on our track. 

The layout is a little over 108' and amazingly there are no power drops anywhere even though we have not wired any jumpers (still plan to add some but so far having too much fun running cars!). All the cars, from T-Jet through Mega-G, run smooth an cool. We keep the power set at 20V for normal and 8-10V when the kids get on. The amp meter reads in tenths and shows approximately how much is being pulled at any given time as cars are running. If anyone is able to budget for a variable like this, whatever the brand, I would say definitely consider it...especially if you're like me and no good at custom building electronics!


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## Hornet (Dec 1, 2005)

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## 440 (Feb 23, 2008)

What about using one of these?

I see the word "linear" thrown around on here when it comes to track power supplies and found this on Grainger while trying to find LPS-3 Lubricant for my coal stove. 

Would this be a decent/ok/good power supply to use on a small "tuckaway" track?


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## SDMedanic (Apr 21, 2011)

Linear supplies tend to be larger and more expensive than a comparable switching supply. The one you linked to is a regulator board and still needs an external power supply. I would keep looking.


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## SDMedanic (Apr 21, 2011)

Linear supplies tend to be larger and more expensive than a comparable switching supply. The one you linked to is a regulator board and still needs an external power supply. I would keep looking.

Here is something that might fit the bill. I have a Tripp-Lite PR4.5 and it will put out 18V. The Tripp-Lite unit goes for about $40. While advertised at 12V the Trip-Lite has a small pot on the board that allows you to tweak the voltage. I am unsure about this one but for $10 its worth a try.

http://www.frys.com/product/1992595?site=sr:SEARCH:MAIN_RSLT_PG


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## Hornet (Dec 1, 2005)

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## Rolls (Jan 1, 2010)

Pretty interesting, Hornet! Not sure what the heck is going on, but it's good to see some data. While it's no easy trick to try to corral all the wild variables, my hat's off to ya for doing the work and sharing the results. Thanks.


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## Hornet (Dec 1, 2005)

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