Micro Structures Signs-Power supply

[piemandan64]

Do I need to buy Micro Structures Converter Module to supply power to my signs or can I use a wall wart as long as it has a 4.5V output?

TIA,

Dan Day

[MisterBeasley]

Wall warts are fine.  With an appropriate resistor, you can use higher voltage wall warts, too.

I run my structure lighting with a 4-amp, 12 volt supply.  I have a bus under the layout for this, and I've wired my Shamrock Hotel sign to it as well.  First I took a meter and measured the current (I) through the circuit using the battery pack, allowing me to calculate the resistance (Rsign) of the unit with Ohm's Law.

          Rsign = 4.5 volts / I

To maintain that same current through a 12-volt circuit, I will add another resistor Rx in series, so the new equation becomes

          Rsign + Rx = 12 volts / I

or

          Rx = ( 12 volts / I ) - Rsign

As I recall, I ended up using a resistor in the 200-300 ohm range.  Get a 1-watt resistor, because it will dissipate power, and if you get a smaller one you may burn it out.

[Mark R.]

I took the easy way out .... I bought a 4.5 volt 700ma walwart from Radio Shack. It's running nine signs with no problem.

Mark.

[rrinker]

 Yes, that is the best way. Resistors are fine for dropping voltage for a single device with a fixed current draw (like an LED), but since the voltage drop is proportional to the current, using a single resistor and then adding multiple loads, which cna be switched on and off, or even a single load that varies in current consumption (say something that turns multiple lights on and off in various patterns) will result in fluctuating voltage levels.

Resistors are also horribly inefficient, in fact nearly 100% INefficient - at low current levels like LEDs it doesn't matter too much. At high current levels (liek dynamic brakes on a loco) they make so much heat then need to be fan cooled. In the case of dynamic brakes it's probbaly not a bad thing, you have to convert the energy to something, usually heat, one way or another, be that with the resistor grids or the friction of the brake shoes on the wheels. But using a resistor to drop the voltage on say a 5 amp circut is going to waste a lot of power just heating the resistor, best to use a power supply of the proper voltage than try to drop a higher voltage one.

                       --Randy