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Author Topic: power supply  (Read 1975 times)
us trains

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« on: May 07, 2011, 06:18:02 AM »

Hi Jim Banner, I have 4 regulated power supply,s,running from 3-12volts at 2.5 amps,0-14volts at 5 amps,i have also many computor power supply,s at + 3.3v+5v and +12volts at 16amps ,its a shame not to use these,can they be used for lights or anything else on the layout,Ihave a medium size layout 7mtr by 5mtrs,HO DCC,although i live in Germany {an exiled Brit} i am running my layout as the US system but with european DCC control system from ROCO,90% of my trains are US steam with some european vintage steam loco,s, +5 mainline Diesels and 3 shuntersAll rolling stock are US.Iam running 4 mainlines plus 2 turntables 12turnoffs and a village with a reversing trolly sys from Bachmann as are most of my trains and rolling stock,Ihave just recieved 20 wagens with coal load from bachmann shop although i have to change the wheels and couplings which is still cheaper than rolling stock here in Germany.Greetings to all,Bryan

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« Reply #1 on: May 07, 2011, 12:31:24 PM »

I'm sure Jim will give you more detailed info, I use all my old  power supplies with lights by adding an appropriate resistor inline with your lamps, I have also added potentiometers so I can dim them.


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« Reply #2 on: May 07, 2011, 04:48:45 PM »

If you use 16 volt bulbs, the 12V and 14V power supplies will work perfectly and give an appropriate yellow light.   Plus the bulbs last longer, the lower the voltage.
LED lights require a resistor, otherwise you will burn them out.
As for other accessories, check the requirements of each to see if they can be used.

Dave Mason

D&G RR (Dunstead & Granford) in On30
 “In matters of style, swim with the current;
 in matters of principle, stand like a rock.”   Thos. Jefferson

The 2nd Amendment, America’s 1st Homeland Security

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« Reply #3 on: May 07, 2011, 07:25:23 PM »


I assume from your description that at least one of your power sources has variable voltage, from 3 to 12 volts, with 2.5 amps. LEDs use 4.5 volts so you can set the rheostat to that voltage and run LOTS of LEDs. They take only a small portion of the current drawn by incandescents, maybe 20 MA, so you could, in theory, run 125 or so from that one 2.5 amp source. That's enough to model Times Square so you can figure that it will run all of your LEDs. Just be sure to keep your polarity straight because LEDs will only "allow" current through one direction. Good luck with your trains.
                                                                                                                            -- D
Jim Banner

Enjoying electric model railroading since 1950.

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« Reply #4 on: May 08, 2011, 05:00:08 PM »

You have been given good advice although I prefer not to run LED's off a regulated power supply without a resistor.  You have more control over brightness and life if you use a bit higher voltage and a fixed resistor to limit the current.  This is particularly true if using coloured LED's as opposed to white ones.  4.5 Volts across a red, yellow or green LED will blow it in a few seconds.  A regulated power supply is different than the batteries in a flashlight.  Three 1.5 volt batteries in series will give you 4.5 volts with no load.  Start drawing current out of the batteries and the voltage drops.  This is caused by the internal resistance of the batteries and will help protect the LED's in a flashlight from excessive current.  A well regulated power supply will have no internal resistance or even negative internal resistance.  If you need help or advice on calculating resistor values for you LED's and bulbs, just ask.

The only other thing I would do differently is to fuse the outputs of the supplies using 5 amp fuses (not circuit breakers). For computer supplies that can put out say 30 amps at 5 volts and 15 amps at 12 volts, you an divide the 5 volt output into six 5 amp circuits and the 12 volt output into three 5 amp circuits.  The alternative would be to use wiring capable of carrying 30 amps which is large and hard to handle under a  layout.  Putting a 5 amp limit on each circuit will make sure that any overload or short circuit down stream from the fuse cannot cause overheating and potentially a fire.


Growing older is mandatory but growing up is optional.
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