Hi, Everyone
I've been sorting through the various wall-warts, transformers and various power supplies salvaged from computers and bought at surplus houses that have found their way at various locations around my layout.
While searching DC power supply here I came across Mister Beasleys post mentioned in this thread: http://cs.trains.com/mrr/f/744/t/239487.aspx and his situation sounds exactly like mine.
Some places where I installed a signal it got a whole wall-wart all its own. I have two UR91s and two UR 92s each with its own transformer.
So this all needs to be cleaned up and simplified. I have no problem running a feeder around the layout for signals and a few others for building lighting. Some of my structures pre-date the current selection of warm-white LEDs and are higher in the total current draw. My platforms at Union Station alone draw 5.5 amps!
Here's the meat of my question... I have several beefy GE transformers rated at .075 KVA @ 12 v. By my math this should give me about 6.25 amps. So I'll fuse the 115 AC in, feed the 12VAC to a 10 A bridge rectifier and feed this to a group of 2A. circuit breakers and out to the lighting and Tortoise buss.
I see scores of DC power supply circuits shown on a Google search and many of them have capacitors, zener diodes, power transistors and the like before and after the rectifier. I've heard of "filter capacitors" and Voltage regulators as part of these circuits.
I am planning to use a nifty power supply for my signal system. I have several closed circuit TV power supplies that have sixteen 500 mA. protected outputs and a nice terminal strip built in to an enclosure.
DO I need anything besides the fuse > transformer > rectifier > breaker and out for my lighting and LED supply source?
Can anyone point me toward a diagram of a no-frills DC power supply?
Thanks as always, Ed
For a smoother DC waveform, you need to add an electrolytic capacitor to the rectifier output. The general rule on them is, use a Working Voltage at least double, but preferably four times the input voltage (50 Volts) and a high microfarad rating. This will mean a can type electrolytic.
I have built many power supplies over the years. Below are all kinds of circuits. Just do the math. No big deal.
I have used 1000 ufd to 4700 ufd capacitance for model railroading.
Couple times I had 24 vac transformers but made some voltage regulators using the old LM317. Easy to trim with one resistor variation.
Remember, after the main filter capacitor, you need a minimum resistance load or the voltage at the capacitor can get quite high. Again, just do the math. That is why “some” wall warts DC voltage is quite high compared to the specs on the case. There is just a transformer and filter capacitor. With no load, the voltage will be higher.
By the way, you can easily Google this stuff and get more circuits than I provided.
Since you can work will house mains, 120VAC, you can also use a Power supply out of an old desktop PC. Those circuits for model railroading have been posted here before. Circuit breakers or fuses.
http://tinyurl.com/o2qq4sc
Rich
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.
Or for less than $10 you can get a 12V DC 5A power supply and just add the fuses.
Couple of things to keep in mind - the larger the filter capacitor (in capacitance), the smoother and more regulated the output, but there's also a HUGE inrush when the supply turns on if you have a huge cap. And taking a 12V AC transformer, adding a diode bridge and a filter capacitor results in significantly more than 12v DC at the output. Closer to 15V. Voltage will fluctuate greatly from no load to full load.
12 and 15V DC are both common for laptops and computer accessories, so there are tons of 5A or so regulated power supplies at those voltages available very cheaply. Or if you have a spare computer power supply - it's fairly easy to rig up a power switch, power on LED, and a large sandbar resistor for a minimum load so it regulates properly, and you get an insane amount of amps out at 12V. And also 5V. Dividning the output into multiple circuits with reasonable fuses is a MUST with something like that.
I'm considering just building something up with the power sweitch and multiple fused outputs using a Molex connector to plug the power supply in - that way should one ever fail, I just get another computer power supply and plug it in to my circuit board.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
richg1998By the way, you can easily Google this stuff and get more circuits than I provided.
Thanks for the info, Rich. The reason I ask here is because there are SO many circuits on Google... you guys can help sort out what I need and don't need.
That's what I thought about the capacitor, cacole. I even have some 23000 µF but keeping in mind what Randy says, I'm wondering just how much filtering I need for GOW lights, LEDs and Tortoises.
Even though I have all this hardware on hand, Randy got me thinking about the computer PS. I have a bunch of those, too. (Nothing at work gets thrown away without first passing my scruitny!)
Thanks fella's, you gave me lots to chew on! Ed
On our large HO scale club layout, we use a 250 Watt computer power supply for all the lights, switch motors, etc. I ran two power buss lines from it around the layout -- +5 Volt and +12 Volt, connected to power strips periodically so we can tap off what we need where we need.
gmpullman richg1998 By the way, you can easily Google this stuff and get more circuits than I provided. Thanks for the info, Rich. The reason I ask here is because there are SO many circuits on Google... you guys can help sort out what I need and don't need. That's what I thought about the capacitor, cacole. I even have some 23000 µF but keeping in mind what Randy says, I'm wondering just how much filtering I need for GOW lights, LEDs and Tortoises. Even though I have all this hardware on hand, Randy got me thinking about the computer PS. I have a bunch of those, too. (Nothing at work gets thrown away without first passing my scruitny!) Thanks fella's, you gave me lots to chew on! Ed
richg1998 By the way, you can easily Google this stuff and get more circuits than I provided.
Ok. I figured you had experience with power supplies since you had individual components and work with house mains.
My bad. Been working with electronics since 1953.
I have used 1000 ufd to maybe 4700 ufd for low voltage power supplies over the years. Even the two lead caps worked fine. Rare to have to use a can type cap anymore so much is packed into a case.
I keep a bunch of 0.1 ufd ceramics that are useful in power supplies. Usually at the output of a voltage regulator.
I have used can type with 10,000 ufd for a DIY CDU.
Yes, the more capacitance, the bigger the surge current.
Couple links for using a PC supply. I found these a few years ago using Google. Some links to store and play with.
http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/
http://tinyurl.com/ldymujg
richg1998Yes, the more capacitance, the bigger the surge current.
Yeah! That's why the electricians at work use a six foot grounding rod to make sure all the caps are discharged in a power supply for an induction furnace. You should see it when they aren't !!
I don't mind building my own, no worries working with "mains" but like everything in this hobby we weigh time vs. money vs. hassle.
Thanks again! Ed
gmpullman Retired machine mechanic. Know what you mean. lol Rich richg1998 Yes, the more capacitance, the bigger the surge current. Yeah! That's why the electricians at work use a six foot grounding rod to make sure all the caps are discharged in a power supply for an induction furnace. You should see it when they aren't !! I don't mind building my own, no worries working with "mains" but like everything in this hobby we weigh time vs. money vs. hassle. Thanks again! Ed
Retired machine mechanic. Know what you mean. lol
richg1998 Yes, the more capacitance, the bigger the surge current.
This guy has lots of DIY and proven circuits. I have bought a few items from him. I have my own junk box of electronic parts.
http://home.cogeco.ca/~rpaisley4/CircuitIndex.html
Thanks for the link to that site, Rich! Lots of fun stuff to play with there and a good rundown of power supply do's & don'ts. Just what I was looking for... except the raking leaves chapter
Ed
gmpullman Thanks for the link to that site, Rich! Lots of fun stuff to play with there and a good rundown of power supply do's & don'ts. Just what I was looking for... except the raking leaves chapter Ed
Lol.
Just raked leaves for the last time this year.
For the Track Power, LION bought a variable 1-15vdc regulated power supply with an 12 amp output.
LION has several other transformers for other purposes. All of these apply the (-) leg to GROUND, and the other line includes 1) Track (R Rail); 2) Signals and Detectors; and 3) Hotel Power. The Tortises are connected to ground, and the stinger (individual circuits) are + or - according to how the tower levers are lined.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
this is what I use for my lighting
Nice. Kind of low voltage though, isn't it? SHould be 2.4V on the setting you have the knob in the picture, if the NC stands for NiCad and LA stands for lead acid as I suspect.
Also not easy for those os us not working for a railroad to get their hands on. But then I used to have a very nice 12V and 5V rack mount power supply from some networking gear. Hmm, last I knew of the thing I had given it to the L&KV club to use, wonder if they still have it.
---Randy
that xsetting is closer to 3 volts for charging a 2 nicad the settings go from about 1.6 up to 7.1 so for leds its perfect these were being tossed out never used in service when they went to motion sensors different setup I should have got more of them but oh well have 3 and some others that are higher voltage and amps but yes the pc power supplies are cheap and just as easy to use I must have 20 of those some new in boxes I just like the look of these
They still make and use them, under the same brand name, but the new ones or super fancy with LCD readouts and stuff. And I don't want to think about the cost, being built to railroad standards.
That's a beefy looking setup, Mike. Is that a charger from a crossing signal setup? When they are tossing stuff where I work I grab it and figure out what to do with it later. We RR people are necessarily scroungers.
My test bench power supply came out of the trash! That decade box is sure handy for determining what resistor values you need. That old GE ammeter is great for model RR stuff, too. It has taps at 1, 5 and 10 amps. Digital is fine for some things but "old school" can be pretty cool, too! That power supply weighs about 35 lbs.!
Thanks, Ed
they were used to keep the batteries charged for signal or grade crossing relays and like Randy said they still make them just a lot better I guess and should have noted we had to use a different model from a diff company since they supplied the predicters for the grade crossings these were solid state very light weight the small cragg's weighed 10 lbs and the new solid state ones didnt work as well but had to use them I think I hve one of those but its out back and theres too much of that white stuff out there to go look
I am a DIY type of guy, but I also know you can buy 'wall wart' power supplies quite cheap over the Internet(eBay/Amazon/etc...). Even desktop mini-tower computers use laptop power supplied now!
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin