Have a simple question that anyone can answer. My DCC layout has separate track voltage for the trains and I just added a 12 volt 1.5A plug in transformer from Radio Shack using an 18 Gauge Bus wire. Question: How many lights or LED's or turnouts can be run using that bus for power. Currently, I will be hooking up 6 Tortoise Switch Machines, and adding 2 or 3 more in the future. I want to tap into that bus for ALL lighting on the layout, including crossing gates, building lights and more. Is 12 volts with 1.5 Amp enough? I can always add another one if needed.
No, 12 Volts at 1.5 Amps will not be enough when you start adding lights, unless all those lights are going to be LEDs.
It can handle all of your proposed Tortoise switch motors okay, but incandescent lights would drain the available amperage pretty quickly.
You'd be better off using an old computer power supply with both 12 Volt and 5 Volt output.
Tortoise pull about 15ma per unit, with a safety factor of 20% you could hook up 80 machines. That would use up 1.2 amps( one amp equals 1000ma), if you are only going to have 10 or so then that will use up about .15 amp The lighting question requires more information. What type of lighting? As far as voltage, 12 is plenty. In fact 9 would make the tortoise run a bit slower and a bit quieter, it would also extend the life and dim the brightness of 12v lights. 12v lights can pull between 30-50ma and that can eat up your excess amps( after hooking up the tortoises). LEDS use up less amps, but I'm no expert in that area so I'll leave that to other more knowledgable folks
There are lots of variables, but the basic answer is that 1.5 amps will not be enough, in the long run.
I run my Tortoise machines on 9 volts. They run slower, and I really prefer that.
A single LED will use only a few milliamps. I use incandescents for most of my structure lighting. I like the warm, yellow glow more than the harsh LED color, but I model the Transition Era, so LEDs are not appropriate anyway. I use Miniatronic bulbs for this, and they draw about 30 milliamps each, according to the package. I buy 16-volt bulbs and run them at 12 volts, which reduces the current a bit, once again gives a more pleasing, warmer glow and greatly improves bulb life.
You can add more power supplies, but after a while you'll have a bunch of them, and each will need a separate bus. (No, you can't wire them together.) So, having done that myself, the right solution is to get a more substantial power supply and just use one. It's a good idea to get a fuse holder and a supply of fuses, rated just below the capacity of the power supply. Most supplies like this do NOT have a circuit breaker. They are typically protected by an internal fuse to keep them from burning your house down, but once you blow that fuse you can't replace it.
It takes an iron man to play with a toy iron horse.
On average, 10 ma with a 1k resistor and 12 VDC for most LED's.
I have done the measurments.
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.
With a safety factor of 75%, you can load that 1.5 amp power supply (1500ma) to 1.125 amps (1125ma). 6 Tortoises at 15ma each is 90ma. If you put LEDs in series witht he Tortoise for position indicators, that will reduce the 12V to about 9V which will make them much quieter - and not add tot he current draw. No resistor needed.
So now you have 1035ma left. White LEDs with 1K resistor are indeed 10ma at 12V, so you could hook up over 100 of them. Incadescent bulbs though can be anything from 30ma each to 80 or 90ma each. Pretty obvious why people are going to LEDs for everything - low power, no heat, PLUS they don't burn out.
I would also put a 1.25 amp fuse between the power supply and the bus line. Wall Warts usually have a fusible link inside, so if you short out the power, you can trash the wall wart, it's not repairable. Using the 1.25 amo fuse lets you still pull the 1.125 amps, but an accidental short will blow the fuse and save the power supply.
If you end up needing more power, cut the bus somewhere in the middle, and add another power supply + fuse. Now each half of the bus can supply the above load. That's 12 Tortoises and 200 LEDs - should be enough to light a LOT of buildings and streetlights.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
My take on this is a bit different. I do separate buses for the Tortoises and the lighting. I run 9 volt for the switch machines (although 12 volts dropped to 9 with the LEDs in the circuit as Randy advises works well if you want indicators). I have 3 volt circuits to handle structure lighting to run LEDs.
Given the numbers of Tortoises (~120) and LEDs (~500) and the fact they're spread across the layout, I run multiple, "regional" buses from multiple power supplies. I don't bother calculating with the Tortoises. I simply keep adding them to the existing circuit until the last one installed doesn't get enough juice to throw -- you can hear this NOT happening. Then it's time for another trip to Radio Shack if I don't have a salvaged wall wart on hand to start the next group's bus.
Mike Lehman
Urbana, IL