Hi - to light my few buildings, I'd like to use an AT or ATX powersupply (I have both sitting on a shelf). These are great in that they put out up to12v and have plenty of amps. I'm using Xmas tree bulbs for the interiors, 3-6 in series, and wonder if I could install a dimmer either on the AC-input side of the powersupply, or the DC output side?
Here's my plan - I'll hook up, say, a 12v line to a small terminal strip and run the interior lights for a house to that. Would a common household dimmer work to manually dim these down? Do dimmers only run on AC?
Any better idea? Thanks!
I would not use the AC dimmer on the AC power to the supply.
Instead I would go one of two ways.
1. Modify the power supply to be a variable voltage supply. Note, depending on the supply you may need to place a load on the 5V portion of the supply to keep it in the on state. Lots of PC supplies will shut down without a load present, requiring you to cycle the power switch to get it back on.
2. Add a variable voltage regulator circuit to the 12V output before your lamps.
Here are a few links. Hope you find them useful.
Adding variable voltage to an ATX power supply
LM317T Voltage regulator info
LM317T Circuit to add variable control to 12V input
TommaHawk Hi - to light my few buildings, I'd like to use an AT or ATX powersupply (I have both sitting on a shelf). These are great in that they put out up to12v and have plenty of amps. I'm using Xmas tree bulbs for the interiors, 3-6 in series, and wonder if I could install a dimmer either on the AC-input side of the powersupply, or the DC output side? Here's my plan - I'll hook up, say, a 12v line to a small terminal strip and run the interior lights for a house to that. Would a common household dimmer work to manually dim these down? Do dimmers only run on AC?
Computer power supplies - designed to deliver a highly regulated, highly filtered, specific DC voltage regardless of input variability.
Says to me a dimmer on the AC side is not going to work.
Since cheap household dimmers work by reducing duration of current flow within the cycle instead of reducing peak voltage - nope, not going to work on the filtered DC side either.
Using a variable resistance on the output to dim the lights is not going to be cheap because of the current. If circuit current is more than 100ma, you need a 50 ohm, 1 watt pot or rheostat. If you are drawing 1 amp through the dimmer, you need a 5 ohm, 5 watt pot or rheostat. Neither is real easy to find.
How about varying the number of bulbs in series to get the desired brightness? Six 2.5 volt bulbs too bright on a 12 volt supply? Try 7 bulbs in series instead. Or 8.
my thoughts, your choices
Fred W
Why not use the 5 Volt output instead of 12 Volt. The Red wire is +5 Volts on a computer power supply. If you're using incandescent bulbs, 5 Volts may be enough to illuminate them. Try it and see.
Or do what I did... Hop on ebay and find a couple cheap used DC "toy train" transformers, and mount them under your bench work. The output is DC, it's variable via the knob, and I got 8 cheap little Bachman's from the 1980's era for $5.00. Just set them up, wire the establishments, and then put in a main power block and use that as the flip switch to turn them on. Might not be as sophisticated as you're trying for, but it sure was cheap, easy, and fun!
What Timmy said,emphatically,why reinvent the wheel and probably spend more on parts than you would if you looked around a bit for an old power pack. BILL
rekleinWhat Timmy said,emphatically,why reinvent the wheel and probably spend more on parts than you would if you looked around a bit for an old power pack. BILL
Ditto!
Marlon
See pictures of the Clinton-Golden Valley RR
Tommahawk,
If you are not absolutely sure what you are doing, and you are not absolutely sure that the final product will not be a fire hazard, PLEASE don't do it!
I learned the hard way several years ago!
Mobilman44
ENJOY !
Living in southeast Texas, formerly modeling the "postwar" Santa Fe and Illinois Central
Common lamp dimmers (the kind that mounts in a wall j-box replacing a toggle switch) only work on AC. The computer power supplies are all designed to keep their DC outputs steady against radical changes in the AC power going into them. If you were to use a lamp dimmer to vary the AC into the computer supply, the computer supply would keep the DC outputs steady until you reduced the AC input so far as to shut the supply off. That's the same as switching the supply off, only you have bought a $9 dimmer to do the same thing as the toggle switch on the supply.
Why do you want variable voltage to your lamps? Real full sized house lighting is either on or off and so having your HO scale house lighting switch on or off seems realistic to me.
If you use 6 volt incandecent lamps powered by the 5 volt output of the computer supply, it will look about right. I think tiny incandescent lamps look better than LED's. The lamps have the warm reddish look of real lamps, LED's are too blue for my taste.
The incandencent lamps run on AC or DC. Was it me, I'd scrounge up a 6.3 volt tranformer to furnish house lamp power, or use an old trainset power pack.
David Starr www.newsnorthwoods.blogspot.com
Also be aware that computer power supplies often have more than one output. All of these outputs must be "loaded" (have some minimum resistance connected across their terminals) for the power supply to be safe. There's a very good explanation of how to use a PC supply for model railroading at www.awrr.com. As I recall, the site author has it listed under "other circuits". Have fun and don't make sparks.
Lou
Not all, modern ATX and above supplies generally only require a minimum load on the +5 output to regulate properly. Most of them will power up with nothign connected but the voltages will be all over the place. The last few old ones I tested, with no load the +5 was actually down to where it wouldn't work properly for logic needing a 5V supply, and the +12 was up over 13V. Putting a load on the +5 raised the 5V and lowered the 12V.
Way back in the day, anyone remember AST computers? The power supplies they used needed a minimum load ont he +12V, to the point that the ocmputers contained a large block resistor that needed to be connected if you didn't have a hard drive. The hard drive was sufficient load, but without a hard drive, the resistor was required to even make the power supply turn on.
You can NOT use an ordinary light dimmer ont he AC side of a computer power supply. Nor will one work on the DC side. Resistors are a very poor way to reduce the voltage anyway. Better bet is to run some diodes in series, each diode will drop about .6 of a volt. You need to use large silcon rectifier diodes to handle the current. Which brings up another point. You do NOT want to feed the entire output of a computer power supply into your layout. Feed it to a terminal strip and branch off multiple circuits with 1/1.5 amp fuses on each individual circuit (or circuit breakers - it's easier to type 'fuse' but a resetable circuit breaker is fine as well as a one shot fuse - just don;t make a mistake wiring and you'll seldom if ever blow a fuse unless somethign bad happens anyway). 30-40 amps at 12 volts is arc welder territory - not to mention computer power supplies do not take well to having the outputs shorted - they often have NO protection against this whatsoever. Think about the potential heat. Can you touch a 100 watt lightbulb when it's on? How about 5 of them together? 40 amps at 12 volts is 480 watts. MULTIPLE SMALL CIRCUITS, please. Be safe. If this makes no sense - then get a bunch of old train set power packs instead of having one monster power supply.
Even then - beware old power packs. Stuff 20 years or less old should GENERALLY be ok. Older stuff can easily have deteriorated line cords. Always inspect for cracks or breaks int he insualtion before plugging one in. Cracked or frayed cords can be a serious shock or fire hazard. Depending on how and where the unit was stored, even a fairly modern pack can be in bad shape. And the REALLY old ones, with selenium plate rectifiers in them - RUN do not walk away. Not worth it at any price. Any selenium rectifier has long reached the end of its useful life and is little more than a ticking time bomb, even if the seller says it works perfectly. When a selenium plate rectifier fails it gives of gases which can cause kidney failure - NOT somethign to be messing around with, especially when there is no reason to.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
cacole Why not use the 5 Volt output instead of 12 Volt. The Red wire is +5 Volts on a computer power supply.
Why not use the 5 Volt output instead of 12 Volt. The Red wire is +5 Volts on a computer power supply.
this is what i do. I google -how to "what ever i want" and there is always some thing for me to go by
i ended up finding a web page that gave me a step by step with pics on how to make a circet bord that would run alot of light useing an old power cord from a cell phone it even has a dimmer on it ,i bought my parts at raido shake they ran maybe $30 and took me about an hour to build
Thanks, all, for your insights. I'll consider these options some more...
rrinkerFeed it to a terminal strip and branch off multiple circuits with 1/1.5 amp fuses on each individual circuit (or circuit breakers - it's easier to type 'fuse' but a resetable circuit breaker is fine as well as a one shot fuse
I don't know what the trip time is on small fuses, but the lower cost circuit breakers I looked at have trip times above 1 second for 800% overload (that would be 8 amps for a 1 amp breaker). Damage can happen in 1 to 3 seconds.
Alan
Co-owner of the proposed CT River Valley RR (HO scale) http://home.comcast.net/~docinct/CTRiverValleyRR/
There's 'fast blow' and 'slow blow' fuses. A fast blow fuse will melt pretty near instantly - nothing will get damaged.
We can't ask for more than to install properly rated protection devices. If that isn't sufficient to protect against damage, nothing will be.
Just to follow up, I went with the cheap-and-easy solution of finding a small Bachmann transformer on eBay for $2. That leaves the aux out on my CW-80 available for a trolley... and I can adjust the light level in my structures to my heart's content.
Thanks again for the feedback.
All the older style AT power supplies I have put out 12 volts and 5 volts. On my previous layout I was using the 5 volt side to light over 25 structures with Christmas light bulbs, 2 to 3 to a structure. This time around I'm using the 12 volt side mostly but I'll be putting in some for the low side too. As far as the Bachmann power pack goes, you'll find that it won't light but a few structures using several lights each. The power output is just too low.
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam
Here is a link to a tutorial that shows how to convert an ATX power supply to a "Lab" Power supply. May be along the lines of what you want to do.
I personally would use cheap power packs, they are a dime a dozen on eBay, and can sometimes be found at local hobby shops for around five dollars. Just make sure they are not too old, or have visible damage, or frayed cords, or have water marks on the case. It's best to be on the safe side.
It's certainly possible to use an unused AT or ATX computer power supply to power lights and accessories -- but I would feel safer with a cheap power pack. Besides, it already has a knob to control voltage, and will output a max of around 12volts.
Howard