I have a PC in the train room to run JMRI. It has a 450W power supply that is only running the CPU, motherboard, a small SSD, and a couple of fans. The monitoring software shows total power consumption at about 120W.
I'm thinking of routing one of the spare Molex connectors out of the case to use for layout power. I need power primarily for the boards that will drive about 40 Tortoise switch machines and the detection boards. I might add a few signals and some led's for structures later.
If I'm doing the math correctly, the 200W I have leftover would be just over 16 amps at 12v. This would be way more power than I need and I'd get the side benefit of the layout powering up when I boot the computer. I'd put a switch and maybe a 2.5 amp fuse in the line.
Any reason not to do this?
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Ground loops is one reason not to do it.
Second reason, if something shorts, it' going to take out your computer.
You can buy computer power supplies super cheap. Make a board with a molex connector plus some fuses and a terminal strip to connect to your lighting circuits. You don;t want to distribute full power around the layout, even a 450 watt poower supply can run over 30 amps on the +12V connection, that's more than enough to melt things. Instead break that power supply connection into multiple segments eachw ith its own fuse at some reasonable level based on how many things you want to power off each bus section.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkerYou can buy computer power supplies super cheap.
How do you tell an ATX supply (no big red switch) to turn on without attaching it to a motherboard?
edit:
Nevermind.
http://makezine.com/projects/computer-power-supply-to-bench-power-supply-adapter/
Better have plenty of fuses or circuit breakers. If you know what you are doing, should not be a problem but don't forget Murphy. Others will comment for sure.
http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply
http://web2.murraystate.edu/andy.batts/ps/POWERSUPPLY.HTM
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.
carl425 If I'm doing the math correctly, the 200W I have leftover would be just over 16 amps at 12v.
If I'm doing the math correctly, the 200W I have leftover would be just over 16 amps at 12v.
You'd imagine, but no. PC power supplies are rated at certain amp loads per rail (12, 5, and 3.3V), generally shared amongst ALL connections using that rail (especially in the lower end & middle-ground of "typical home user PC that was purchased complete from a supplier). So the 12v rail that's supplying your motherboard (several times over) might actually be utilizing 3-5 amps* just with the computer running under low/moderate load.
You'd be better off getting an el-cheapo one from an online retailer ($50 or less), and using that. When hooking it up, remember to use a normally-open momentary contact switch (else, it'll shut down after ~10 sec).
Also, be friggin careful when you're working on building the thing (if you're going the "benchtop PSU" route, like in the tutorial you linked) -- the 110/220 V that the caps are holding on the mains side will really ruin your day if you touch them.
*totally made up for discussion.
-Dan
Builder of Bowser steam! Railimages Site
KABOOM!!
Could be interesting. How white is your hair (before and after).
Life insurance is paid up I hope!
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Might depend ont he power supply, but I've done them witht he power on connection wired though an ordinary toggle switch, not momentary, and they work fine. I went the whole nine yards and put binding posts on the case, an LED on the power good line, and wired a sandbar resistor for minimal load on the inside, affixed to the case with thermal glue (like used to glue heat sinks on - yes, some are glued on, not just a conductive paste with a spring holding it tight). The LED even had a bezel and all.
Most of the more recent power supplies I've played around with all turn on fine with no load, however they regulate poorly. The 12V may be as low as 11V, adn the 5V goes up to about 5.5V on some. Put a load on the 12V and 12V comes up to close to 12V, and the 5V drops to 5.05V
My plan is to run power buses around my layout using the higher voltage - in fact I might even use something like 15v AC. Then I can tap off and convert to whatever I need - a rectifier and filter to get DC, a DC-DC converter to reduce the DC voltage when needed. Depends on how much of each voltage I need. If only a few things will need the 15V AC, I'll run two - an AC and a 12V DC bus, and just use the DC-DC convertors on the 12V DC bus.
hon30critter KABOOM!! Could be interesting. How white is your hair (before and after). Life insurance is paid up I hope! Dave
Alton Junction
rrinker Might depend ont he power supply, but I've done them witht he power on connection wired though an ordinary toggle switch, not momentary, and they work fine.
Might depend ont he power supply, but I've done them witht he power on connection wired though an ordinary toggle switch, not momentary, and they work fine.
If they're following the ATX standard properly (don't expect it from the super-cheap ones), keeping green shorted to ground (e.g. a toggle switch) will cause the supply to shut down -- i.e. the "just kill it now" hard shutdown that you can do by holding your PC's power button.
My high-end supplies (from gaming rigs) will hold a solid rail with little variance ... but I wouldn't count on it from those $20 ones ... there's got to be a reason they're $20, and the high-end ones can run you into the hundreds ...