Power Supply

Discussion in 'Getting Started' started by tetters, Oct 8, 2008.

  1. tetters

    tetters Rail Spiking Fool!

    So I picked up a couple of these at work for free. They are power supply units for CCTV Cameras. Generally pretty low voltage stuff. I figured I could use them as power distribution points for some of my switch machines or split up my track main buss into four different electrical blocks. With the added fuse protection for each section as an added bonus.

    The question I have is about the fuses that came in them. I'm not too sure if they are more then I need. They are labeled 250V 3A. I was wondering if I should use a lower voltage fuse? I am running an NCE Power Cab. (Suppose I could refer to the manual and see what NCE recommends...)

    So its late and I'm tired... suggestions? Ideas? :confused:

  2. Squidbait

    Squidbait Recovering ALCO-holic

    Is there more to these than what you're showing here? Beacuse apart from a diode, resistor, LED, the on/off switch and the terminal strips, I don't see anything resembling a power supply. :confused:

    There should be a transformer, or an IC at the very least, plus some capacitors to smooth out the output voltage. I think you may be missing some bits... :eek:
  3. ezdays

    ezdays Out AZ way

    To me these look like just power distribution points. Main power in, separate, fused power terminals out. As far as fuse ratings, the voltage isn't significant, that's the max voltage it can take. What is significant is the amp, or current rating. If you're running an accessory that normally draws 100 ma (0.100 amps), you don't want to use a 3 amp fuse in the circuit. But, as Squidbait points out, you'll need a separate power source for these to be of any use.
  4. jgottrains

    jgottrains New Member

    I will not answer your question but…

    Volts X amps = watts
    250V x 3A = 750w

    lets just use 12 volts in this
    12V x 62.5A= 750W
  5. tetters

    tetters Rail Spiking Fool!

    Sorry. Power Distribution Boards is what I should have been saying. I warned you guys, that I am no electrician. :oops:

    I have a 12V power pack at home which I was going to hook up to the two terminals on the far left. I was thinking I could hook up toggle switches to the other terminals which will in turn control some Tortoise machines.

    If it's too much of a hassle or not necessary I'll just leave them out. They were free after all and I thought, hey...I might be able to use these...

    Thanks for the calculations, jgotrains. However, what do they it mean? Like I said, I'm not very good at this sort of stuff and I do apologize if my questions are quite rudimentary. :oops:
  6. pgandw

    pgandw Active Member

    The boards will work fine as power distribution for your Torti. Somewhat of an overkill IMHO, but the price is right, and it is easy to fuse your circuits.

    As pointed out, the current rating of the fuse should be slightly above the maximum normal current of your circuit, but not to exceed the capacity of your wiring. For a Tortoise, stall current is less than 20 milliamps. Fuse for 20-25 milliamps per Tortoise on a given circuit. Unless you are putting lots of Torti (more than 50) on a single circuit or are using 30 gauge or smaller wire, the wire current capacity will not be a factor in this case. Fuse voltage rating is unimportant provided it exceeds normal operating voltage of the circuit. Any voltage rating 12 volts or more will work for you.

    hope this helps
  7. tetters

    tetters Rail Spiking Fool!

    Thanks Fred and everyone else of course. I'll try one out and if I feel it is not needed I'll leave it out. I always like trying things out just to do it differently to keep it interesting.
  8. ezdays

    ezdays Out AZ way

    Fuses are rated by max voltage and max current. While it's true that watts = volts x amps, these are maximum ratings and are independent of one another. One can use a 250 volt fuse on a 12 volt circuit, it's the current rating that matters here. One should always use a fuse that's somewhat above the max that the circuit will draw. Using a 3 A fuse in a 100 mA circuit might result in some equipment being damaged before the fuse blows. Using a 100 volt rated fuse in a 200 volt circuit will probably cause it to heat up and fail, or blow....
  9. 60103

    60103 Pooh Bah

    It seems ridiculous*, but a 3 amp fuse will blow at >3 amps whether it's the 12 volts in our trains or cars or 120V in the mains or 600V in a streetcar** system. Could probably blow on a 1.5V battery. You don't need the expense of a 250V fuse, but since you already have them ...

    * I think I wanted to say counter-intuitive but I ran out of t's. :mrgreen:
    ** 3 amps won't get you far in a streetcar.sign1
  10. ezdays

    ezdays Out AZ way

    I don't think that a 250 volt fuse costs any more than a 100 volt, to be sure, they might be a bit cheaper than say a 50 volt one because they're more popular. We used to buy fuses in bulk for our systems and the power supplies we used to build. I'd always buy 250 volt fuses since I could then use them on a 120 volt AC circuit or a 12 volt DC one.

    And here, take these tttttttttttttttttttttttttttttt just in case you need to write "counter-intuitive" again.:mrgreen: :mrgreen:

    And 3 amps might get you a ride on a streetcar in a country where the exchange rate for their currency, which is the ampere, is around one amp = fifty cents...:eek: :eek: Or was that one rupee = fifty cents? :confused: Oh well, I don't think they have streetcars there anyway.:wave: :wave:
  11. Russ Bellinis

    Russ Bellinis Active Member

    If you check for glass fuses at an auto parts store, they all say 250v max even though they are used on a 12 volt automotive system. The voltage rating doesn't matter as Don says. You can still get glass fuses at auto parts stores or at Radio Shack, and I think at hardware/home centers as well. If 3 amps is too much, at my old job we used glass fuses down as low as 3/4 amp and they were the same physical dimension as the 3 amp or even 30 amp fuses.

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