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The Preponderance of Power Packs Puzzle!

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Well Joe here it is, you asked for it. A transformer is an electro magnetic device that converts one voltage to another, its capacity to do this is mesured in VA. This is the same as watts including power factor. So if you have a transformer of 100 VA with an input for you Americasns is 115V 60 Hz RMS, you merely divide the VA by the output voltge in this instance say 12 V which means 100VA/12v = 8 odd amps. And that is all you will get is AC out from AC in nothing else. In a perfect world it will draw 100VA / 115 V = 0.87A from the mains however transformers are very efficient devices but nothing is 100 % so this would probably be more like 1 Amp or a bit less. Now a power supply is just that, a device that supplies power as and when required.In general in the old days, this meant a transformer to give you the voltage you want and a rectifier to convert it into DC, if required. But this is very basic and the variations on this theme are just astronomical. You may consider in this modern day of solid state electronics that many things are required and many sources of power are available. I know a guy that runs a Gas Cromatograoph from natural gas using a generator power supply and a Heinkel engine that runs off natural gas to drive the generator. So as I have said the rquirements are endless. Leaving MTS out of it the normal way a model train power supply works is a transformer from AC to DC, a rectifier to get to DC and a device called a Rheostat. This is essentially a variable resitance with a centre point at which the output voltage is zero. If you want to go forward you turn the controller to toward the forward position, which will increase the voltage thereby causing your train to go faster and faster the further forward you turn it. Reverse is just the opposite. Again the VA rating of your power supply will be the limiting factor as to how much equipment you can run off it. The amperage is only a resultant of the VA rating divided by the voltage. Regards Ian etc.
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