Well Shamus and everyone:
I need to explain why I use the voltages that I do. Lets start off with the easy one, 12 volts. This is common voltage for every light I have seen that a model railroad manufacture makes.
Then there is that goofy 5 volts that I know Shamus is wondering about.
I build my own digital drivers for my signal lights. ALL digital electronics requires 5 volts.
Now you ask me, "Why are the 12 volt digital drivers for signal lights made by manufactures?"
The answer is simple. They have some kind of voltage dropper at the voltage input. It may be a 7805 voltage regulator or resistors. That is why I have 5 volts.
Now the 3 volts. This is an odd one. I could even remove it if I wanted too. However I use this voltage to power a low power 555 timer chip. I could use the 5 volts no problem. I do use 12 volts in series with my LED's.
I have a question for you Shamus. What in the world do you use 24 volts for?
I do have a common uninsallated ground running under the table. This makes wiring alittle easier. I don't worry about shorts because I use power buses on the outside of my table. PLus they are fused.
I have a main power disbution area on my table. Since all of my accorries run under 1 amp. I use 6 conductor telephone wire. I also use it for remote switches and relays. This is powered by an old notebook computers powersupply.
Besides the trains power to the tracks from the transofermer. I do use the 16 volts for the remote switches on the switch track. Drawing power from your trains transformer actually slows the trains down. Because not only are you drawing current for the trains, but also for you lights, etc.
Everyone should now this formula:
VOLTAGE=RISTANCE(IN OHMS) x CURRENT
EXAMPLE:
V=3(4)
V=12volts
Amps:
12v=3ohms(I) I = amps
12v/3ohms=I
I=4amps
Ohms:
12v=Ohms(4)
12v/4amps=Ohms
Ohms=3
This is known as Ohm's Law. It is very easy to learn. Very simple math. I want everyone to know that 1/10th of an amp will kill you! This is why I stay with low voltage. It usually has a low current rating. When you go above 12 volts, you have to be more careful.
I was thrown across the apartment fixing a Ham Radio ampifier that still had 75,000 volts charged in it's filter capasitor. It was even unpluged!
Speaking about filtering. Did you know if you add a .01 microfarad cermic disk capasitor across you accorries power terminals. They will last 10 times longer!
This is what I was trying to say the first time. I hope this clears it up!
Andy