Having come through the amateur radio many years ago, Working with voltage isn't my problem. My problem is justifying have twenty to thirty times the necessary available current. I normally worked with something in the 600V range, and about a quarter amp.
However, a computer supply furnishes far more current than I'd ever need, and poses hazards that don't need to be. If I was trying to furnish power to a large club layout, okay, but I'm not. I'm powering a small layout with at most three loco's at any given time. I'm looking at having 4 amps available, which is probably more than twice my need, a reasonable margin.
And unless you're going to run your trains at full speed all the time, there is additional circuitry necessary. Wirewound pots aren't cheap, and cheap pots will soon give up to the currents demanded. A simple one transistor circuit can increase the current that even a cheap pot can control, as long as the pot doesn't have to carry that current. Any semiconductor device has a fixed forward voltage drop, and as an average, I figure one and a quarter volts, or with a fixed twelve volt input, the voltage delivered to the track will be below eleven volts. Twelve volts regulated in, either you'll have to change the voltage, and God knows how they set that in the computer power supply, and He ain't saying, or put up with the lower voltage. This is assuming a straight DC setup, not DCC, although I'd expect the same conditions to exist, a forward voltage drop in the circuitry preventing getting the full voltage to the motor.
There is no perfect answer, only what works for the individual.
Rich
If you want power, look at the below links. It sounds like you understand the potential dangers of working with mains power. You will need fuses or circuit breakers also. These supplies can supply an amazing amount of power. I hesitate to suggest them because some clueless try to mess with them.
http://2railoscale.blogspot.com/2011/09/how-to-convert-used-pc-power-supplies.html
http://www.ppdnmra.com/MRRPWR.pdf
You can Google computer power supply model railroading
For a bench supply, Google computer power supply bench.
There has been some discussion in this forum in the past. Search it.
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
I highly recommend the GML throttles.
For 12 Volts, +/- regulated DC I use computer power supplies. They also provide +/- 5 Volts DC, and some have other voltage outputs.
Even a brand new computer power supply will cost less than the individual transformers, rectifiers, capacitors, etc. needed to construct your own.
Look at these, for example:
http://www.tigerdirect.com/applications/Category/guidedSearch.asp?CatId=106&srkey=power%20supplies
LION built his own power supply back in the 1970s. Components were purchased in Japan while I was still in the Navy. The wire wound potentiomiters that I got for it were great. But that I suppose was just luck. In those days the big wafer rectifyers were something else. Now it is just a little chip.
I still have this stuf around somewhere but it is not in service.
Yes you can do it, but why would you do it? No wait... I *know* why...
HERE is power supply of LION. It is a varriable voltage 12 Amp Regulated power supply.
LION runs 8-16 powered subway cars at any one time, all on this one circuit. That is why it must be regulated. Actually I have never drawn more than 2 amps (with 12 motors running) but I did not know that when I bought it.
But then maybe you are not interested in running annalog automation on your layout. Even so, this one transformer is not enough for my layout. It surely provides enough power, but I run it at 10.2 volts, and I need 12 volts on some of the up grades, so a "sub station" is needed to provide that. Now that I know better, I'll just grab an old PC power supply and use that for the 12 volts. Since the left rail is GROUNDED, it does not matter what source supply I use for the right rail. Gota save on wires, you know.
So there will be two power busses : The "600 Volt" line will carry the 10.2 volts for most of the layout and the "750 volt" line will carry the 12 volt current to locations where that is needed. (600 volts is what the subway uses, 750 volts is what the LIRR uses, still, they can electrically run equipment on each other's lines : DC is very forgiving.)
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
wyatteeSo, I appreciate your effective agreement with me!!!!
Just putting out my reasons for building. Some don't want to, no problem. The last one I built was for a buddy, but if he'd stalled the motor, the wheels would have welded to the track. I don't remember the exact specs, using surplus transformers, but it put out 14 volts and I know more than fifteen amps. Meant he had to put 1 amp fuses on each throttle to keep from burning them up. Allied has an xfmr, 28VCT at 2A, or 14 V at 4 amps, big enough for anything I'll ever need. But I've also got ridiculous supplies of military surplus components, I believe the proper term is "packrat", Transformer is about the only thing I'll have to buy. Maybe terminal strips and barrier strips, haven't looked yet.
Check out my reply to Jim just before your comment. I like electronics and enjoy building stuff. But, that being said, I also found the Tech 7-700 on eBay at Arnies Trains in So. California. They put out almost 2 amps with lots of voltage and at $59.00, it's not worth trying to build your own. Meaning, I too, ordered this model.
So, I appreciate your effective agreement with me!!!!
Texas ZepherIs there any reason you are bound and determine to build your own? I love to build stuff too, but sometimes the pre-made ones aren't only better but cheaper.
Not the one you asked, but here's my two cents on why I build. First, the power supply will be a separate unit, it's sole function being to furnish a regulated 12 volts to everything else, or better yet, 14 volts to compensate for the forward voltage drop in the transistors that control the output to the track. One power supply, I can do almost anything I want and not worry about having places where the return is to a different power supply, which won't work. The loco on a block controlled by one supply, and the tender on a block by a different one won't work. Putting pulse width on the throttles that need it and not on any other is also possible.
Adding 12VAC for the accessories is only a matter of adding one small transformer, after the current requirements are calculated. There's a lot more that can be relatively easy, but that would lead into the book I'm not going to write. A big plus is it's fun.
wyatteeI want to run multiple loco's on my main line which require several amps and I am NOT going the DCC route.
Yea! I agree about off the shelf power supplys. My two level multi block layout design, as best as I can plan, needs about four power supplys. So, I checked out MRC's basic Tech 7-700 and found some on ebay at a discount. I will be using a modified cab control but using properly spaced block wiring because of a couple of reversing loops, a mine operation and some small yards.
Thanks for the info!
Mike Stubbs
wyatteeI have an MRC Tech ll model 2500 that provides 1.6VA (about 1.3 amps) and it works pretty well. Since this model is no longer being made but many are listed on eBay, maybe a couple more of those or similar models will do the job.
I have one 2500 and also the Tech II 2400. I like the 2400 better because it has a pulse switch. l usually leave it in the off position which lets the motors run quieter. Both are very reliable and easy to find on ebay.
Jim
A quick check at Allied Electronics yields something like 113 pages of transformers, assuming you want to build, meaning soldering iron and discrete components. Known brands, like Triad, Stancor, Thordarson. Allied. Pricey in small quantities. (OR I'm still thinking in terms of twenty years ago.) Another place to check would be Digi-Key, if you can navigate their site, Seems they want you to know all the specifics including manufacturer and dimensions before they give you a list. Called Allied to see if they sell retail or just distributor, they will sell to anyone. Might help, Dunno.
Rich.
The last surviving Radio Shack around here sells nothing but cell phones and other geeky devices because that's what sells -- no one builds their own anything electronic any more.
Years ago, we installed the Cooler Crawler High-Performance DC throttle system on our club layout, and used it for over 15 years before switching over to DCC. Cooler Crawler components are still available from TracTronics.
http://home.roadrunner.com/~jimngage/TRACTRONICS/
We powered the Coolor Crawler throttles from a home-made DC power supply that put out 19 Volts pure, filtered DC at 25 Amps capacity. We're still using that power supply, but not for the NCE DCC system.
i think there are more options today. Instead of buying a transformer, rectifier and filter cap, you probably have old wall power supplies that has sufficient voltage and current to provide semi regulated DC to a control circuit.
you could build a traditional DC throttle using a regulator IC, or try building a pulse width modulated control circuit similar to what is used in DCC decoders. You may not be able to buy these components at radio shack, but ebay provide more choices.
greg - Philadelphia & Reading / Reading
Expert, at Radio Shack? The last person the knew anything about electronics quit working there over 25 years ago.
Not so coincidently, that's when I quit working for Radio Shack. LOL.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
wyattee Your data was important to me and kinda made my mind up in a different direction. Thank you!
Your data was important to me and kinda made my mind up in a different direction.
Thank you!
Hi, Wyattee
On my first layout I used 5 amp. GE Variacs to vary the 120v AC into the transformer, then the rectifier and reverse switch. Great voltage control beautiful for smooth DC running!
You might want to keep "Walk Around" capability in mind depending on your layout/room configuration. I went the route of the old MRC Controlmaster 20, it uses ordinary RJ-11 jacks and the throttle has memory so you can "plug in" at a remote location so if you want to do some yard work or watch your train up close instead of having to run back to the "power pack" every time you want to change speed or direction.
If you can find them, the old Aristo-Craft "Train Engineer" was nice too. I had four of those on my layout (still use one outside on the garden railroad) before I did the DCC thing...
Just something to keep in mind before you invest too heavily in fixed powerpacks. You might like walkaround.
Ok. Had no idea on what you were trrying to do.
OK, OK, I'm convinced. I think I'll spend more time researching off-the-shelf commercial M.R. power packs for DC. Radio Shack people are not always helpful with things out of their expertise anyway. I have an MRC Tech ll model 2500 that provides 1.6VA (about 1.3 amps) and it works pretty well. Since this model is no longer being made but many are listed on eBay, maybe a couple more of those or similar models will do the job. I figure I need 4 separate power packs for my pike. I do not want to use power packs that have dual controls. So, separate units are best for my needs.
Most parts I bought were not from RS. I started with the 10k pot, Darlington transistor and 2N3055 power transistor.
Moved up to the link i provided. The suggested mini box was 2" x 2" x 4".
Even when they DID have parts - the potentiometers at Radio Shack were always poor quality - huge dead band at minimum so they made for very non-linear control.
You actually probably can get everything you need for a transistor throttle at Radio Shack, but you migght have to visit more than one store to get it all in stock. The other suppliers are better, and the parts they sell tend to be better as well.
You do not require several amps for HO. I doubt one person will run more that three locos at one time. It was always difficult to match locos using DC in out club.
You don't want a rheostat. That is VERY old school and inefficient. A 10 k pot controlling a power transistor is quite simple. I built a few of these.
http://www.awrr.com/throttle_Thorne.html
You might be disappointed in RS if you have not been there in a while.
All Electronics online is a good store to order from.
Now let us see how many will try to convert you to DCC. lol
Years ago, I built my own power supply from parts that I acquired from a local electronics supply house. That was in the early 60's. I had majored in Electronics in high school and was reasonably adapt at doing this. I purchased a transformer (110v in by 14v out), a fully bridged rectifier, a proper wattage reostat, circuit breaker and DPDT reversing switch. I built three of these setups and they worked great. But, now we have better componets, I'm sure at Radio Shack, and I would like to know if anyone else has done this recently. And, what componets did you use? I want to run multiple loco's on my main line which require several amps and I am NOT going the DCC route.