I have what is likely a dumb question about power supplies. I'm trying to figure out how many total amps my modest N Scale layout will draw. Question: Do solid state power supplies draw their marked AC Input amperage regardless of DC current demand on their Output? I'll be using two 120 VAC to 12 VDC power supplies. Both are in sealed plastic cases and are light in weight, so are probably solid state (i.e. without a large wire wound transformer inside). One supply is marked 0.8 Amp AC Input (with output of 12 VDC @ 3.0 Amps) and the other supply is marked 0.7 Amp AC Input (with output of 12 VDC @ 2.1 Amps). Will these draw their marked AC Input amperage regardless of current demand of their output side? I just want to be sure that their AC Input amperage doesn't rise above their input specifications as DC demand rises. Thank you.
That's what I hoped to read -- thank you Dennis! My control panel will have a master power toggle switch and I want to make sure it's up to the task. These two power supplies plus my Kato power pack will equal only 2.3 Amps AC, so I'll have plenty of capacity in a 5 or 6 Amp toggle. Again, thanks.
Power supplies only supply the power needed by demand. The maximums on the label are for sustained power draw, but not for transient power draws. You could see spikes if the output stage of the power supply is not fully filtered properly. Depending on the manufacturer, the output is or is not filtered appropriately. It is best to find this out. Some knock off supplies from China are really bad with the spikes.
Thanks DCE. These are new (surplus) power supplies from Cable TV boxes. Maybe they're made to a better standard to protect the boxes, but I just don't know. I'm guessing that maximum amp draw will come when I switch the layout on and 24 Ea 1,000 MFD Capacitors charge for my turnouts.
The more modern 'switcher' power supplies are a lot more efficient than the older ones and the transformer types. The newest switcher designs have very little power draw when they are idle. You can tell this because they don't get warm unless they are providing an output current. The old switcher and transformer types tend to get warm even if the output isn't plugged into anything.
Mine are definitely the modern "switcher" type I think. They're both lightweight, stay cool in operation and are completely sealed. To be super-safe, I suppose that I could always wire a 6 Amp fast-blow fuse into my AC supply line to assure my toggle switch limit isn't exceeded. The load should be half that, but in respect for DCE's thoughts, it'd provide extra protection.
Switchers power supplies are high frequency switchers, therefore they operate at a higher frequency than the 60 hz power supplies and the transformer is much smaller, plus the filter components after the transformer. I pulled a couple apart some time ago. High frequency oscillator at the input feeds a transformer basically; Rich
Many years ago when I used desktop PC's they had open frame switchers. Those also had transformers but much smaller transformers. Switchers have a high frequency oscillator at the front end instead of depending on sixty hertz or fifty hertz. Also makes them universal for both sides of the Pond. Those supplies are great if properly protected with fuses for model railroad layouts. You have to be careful of the five volt output. It is capable of quite a few amps. Rich
