Modify laptop/desktop power supply for a simple n scale layout?

[Espee Oregon Branches]

Greetings fellow modelers, 

I've been obsessing over this simple idea and need some help either putting into action or letting it R.I.P. 

I'm re-entering the hobby as a married man living in an apartment with a cuatiously permissive wife. I won over the tidy housekeeper to the hobby with the idea that I would build my simple n-scale layout in an attractive coffee table (oval layout going through a four-sided diarama). Everything is going great except for the power delimma.

I've been watching the bluetooth control technology with keen interest and definately will jump on that bandwagon when and if they make an n-scale board. Since using this technology only requires that the layout have a constant 12v power (the board controls voltage to the loco) I resent purchasing even a cheap DC power supply since I wont even need variable voltage once I switch to the bluetooth technology.

So here's my question: In the mean time, to play around on the oval and test track work, am I crazy to try and modify an old desktop or laptop power supply to power the oval? I have searched this forum and seen where this has been done to power larger scale layouts like O and G but they naturally require higher amperage. Is it too risky for small scales?

I have the advantage of having several desktop and laptop powersupplies handy and being an experienced DIY comfortable with simple breadboard circuitry (my dad is an electrical engineer). I'm thinking I just need to get a pot controller and start sodering.

[Espee Oregon Branches]

i should clarify that this following youtube DIY video is serving as my inspiration

https://www.youtube.com/watch?v=M4TFVhCg6sk

[jrbernier]

If you have an old computer, it is a low cost solution. Way more power than you need for what you propose.
Another solution is to get a 12 volt 'wall wart' power supply. You still need to build a throttle if you do not have one.
You can pick up used MRC power packs on the cheap via eBay. The can always be used as you future power supply, or to power layout lighting.
As much as you are enamored with Bluetooth control, be aware that there is NO standard, and existing control schemes may not be compatible with each other. Bachmann, Blue Rail, and others are out there - Each marching to the beat of their own drum...

Jim

[ricktrains4824]

They have a lot of amps.... Be very careful if you use them. You can fry models quite quickly if done incorrectly.....

[Soo Line fan]

Lap tops typically have a 19v power supply........

[fieryturbo]

Soo Line fan

Lap tops typically have a 19v power supply........

 

No, that's totally incorrect.  For laptops, there's absolutely no standard.

This is because most of the regulation is done inside the laptop, while the power brick houses only a transformer and some filtering for cleaning up the power.

Desktop power supplies have separate lines coming out, and most of the regulation is done in the power supply.

Use a desktop supply if you can.

[Soo Line fan]

I never said it was a standard.  I said typically. At least the four I own and the thousands our company uses.

[cuyama]

Seems like false economy versus a power pack from eBay. Short circuit protection may not kick in with some computer power supplies, could be a problem if that passes a lot of amps through your trains. 

It could be years before an aftermarket Bluetooth-enabled decoder is ready for N scale ... and even then, standards may be an issue for a while longer.

Byron

[Javelina]

Regarding ricktrains4824's concern regarding amperage, correct me if I'm wrong, but the amperage of a power supply is simply the "volumne" of current, using the water hose analogy. The voltage is the "pressure". The power supply will put out it's voltage at a constant level assuming no overload, but the amperage drawn on it will vary with the demand of the device being powered. If a locomotive draws 1/2 amp, that's all it will see. If this were not the case, the old school method of using automotive batteries for power would have melted all the models run with it. 

On the other hand, it would be fun if you have a moronic "friend" who likes to pull the old "put the quarter on the track to stop the train" stunt. That quarter will be nice and hot when he picks it up. 

[richg1998]

Probably more than you want to know.

Modifing PC supplies. Remember, some do not have a bleeder resistor and when powered up without the PC, the caps can hold the charge.

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

http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM

Hope you know what you are doing.

The below link will show you how to build a basic DC throttle.

Twenty five years ago I used a Darlington three terminal low power trainsistor feeding a 2N2055 power thransistor and a 10 k pot.

http://forum.atlasrr.com/forum/topic.asp?TOPIC_ID=69897

The DC from a laptop supply should work just fine.

Rich

[jrbernier]

...or tack soldered to the track! Even though a Loco may only draw 1/5 amp in 'normal' operation, a derailment can introduce a solid short and with a large power supply - it is possible fry the electronics. Fuse your home made unit appropriately.

Jim

[richg1998]

Just remembered that the DC trottles I and the club made had thermal type 1.5 amp circuit breakers in a small metal enclosure. At one time they were picked up surplus.

Probaly more than 25 years ago.

Time'e fun when you are having flies.

Rich

[rrinker]

 You can use a PC power supply IF you fuse the connection between the power supply and the track with a fuse rated for some reasonable amount, for N scale 1.5 amps should be plenty. Otherwise, you risk doing a lt of arc welding and then ultimately destroying the power supply.

 But you can get a proper model train power pack for pretty cheap, even a brand new one. This would also give you proper variable speed control until you go with whatever other control system (is the Bluetooth thing even in N scale yet? The modules are so far too big to fit).

                --Randy

[mobilman44]

Ok, this has come up before and I still have the same thought on the subject.  Unless you are an electronics enthusiast, I would deposit the power supply in the nearest trash can.  The downsides of trying to use it far outweigh the upside (not sure what that would be).  You can fry your locos, give yourself a nice shock, or even start a fire.  

[ricktrains4824]

To clarify the amps concearn:

If you induce a dead short (I.e. "Quarter test", or a derailment) the power supply, without the proper overload protection, (I.e. Circuit breaker) the full power supply, in amps, will be given. This will very quickly melt and/or fry model electronics and motors. 

That doesn't even consider the possible fire and safety issues if there was enough power.......

You will probably be cheaper getting used power packs, made for trains, that include amp limiting features and circuit breakers in most of them, once you consider the cost of breakers, and all the components needed to safely use these other power supplies.

The "Safety starts with You" slogan does not apply only to the 1:1 scale guys and gals. It also applies to all of us here.

[rrinker]

 It's actually not that difficult or really dangerous to modify a PC power supply. You don;t even have to crack them open any more (that's the dangerous part - even unplugged, the big capacitors can retain quite a charge and give you a good wallop). In fact, there are several adapter boards sold by places like Sparkfun that you just plug the standard power supply connector in, and it breaks it out ito seperate fused outputs.

 The key is - fuses on the outputs to limit the current to a reasonable level.

                    --Randy

 

[tbdanny]

Hi,

I've actually adapted a desktop PC power supply, to power the lighting on my layout. Here's a write-up on how I did it: http://bvlcorr.tumblr.com/post/135005793372/a-power-full-lesson-part-2. There are a few other things that need to be done - the 5v rail needs a load, and the wire to the on button needs to be wired to the ground rail.

The key thing if you decide to do this is to make sure you know which wire does what. I would also suggest putting a fuse or circuit breaker in line with the positive output from the power supply, rated for the maximum current you're willing to put through the tracks. How many trains were you planning to run at once?

Having said that, N scale trains don't usually draw that much current. A 2A or 1.5A 'wall wart' type transformer would provide adequate power to drive the trains. Alternately, if you do use a desktop power supply, you may be able to connect the lighting and accessories to the 12v rail through a second circuit breaker/fuse.

[Soo Line fan]

Does blue tooth have a pulse schedule like a good quality MRC pack?

[Espee Oregon Branches]

Thank you to everyone for you input. After searching the web, other forums and this forum for answers to this question I was left with a lot of holes in my argument. Now that I posted this question you guys filled in those holes really quick. What a great resource!

If anyone is curious, what I have decided to do in light of this information is look into a cheap MRC powerpack on eBay since I will need to purchase a throttle control anyway. At the same time I'm going to dig through a couple of orphaned wall bug collections I have to find a 12v, 1.5 amp transformer. This way I can use my cheap DC powerpack for other things when and if I switch to the bluetooth technology.

I will come back to the desktop power supply (I have 6 dinosuar desktops just begging to be repurposed) when I run accross a throttle mechanism...