Power Question

Discussion in 'FAQs' started by kchronister, Jan 10, 2006.

  1. kchronister

    kchronister Member

    Okay, here's an electronics question from the... let's say I'm more mechanically inclined...

    If I have a power supply setup as shown here - 2, 12V 2A power supplies in series powering a bus around my layout to feed DC needs... Do I have 2amps or 4amps?

    While we're at it, can someone tell me if I've got this right...

    one turnout power consumption on my layout = 1 tortoise @ stall = 16 mA, 4 LEDs (two on control panel, two for signals) = 20mA each = 80 mA, = 96 mA total per turnout.

    In other words, I'll need roughly an amp for each 10 turnouts?

    If that's true, anyone care to recommend a good source for a 10amp+ DC power supply? Preferably that doesn't cost $200 like the ones I've seen...

    Attached Files:

  2. jim currie

    jim currie Active Member

    your drawing will give you 24V you need to put the the power supplies in parallel you have them in series.as far as a cheep high amp power supply look to a battery charger:) other than try ebay i saw a 40 amp 12V surplus one at buy it now for 25$ a while back.
  3. ezdays

    ezdays Out AZ way

    Jim is right on both points. Your series hookup will give you 24 volts at 2 amps. If you want 12 volts at 4 amps you have to parallel them...but...you've got to be really careful because if the voltages don't match exactly, one will attempt to carry the load and the other will just coast adding to the load rather than supplying current to it.

    And you can use a battery charger to supply the current you need, but you might want to filter it a bit because they are fairly nasty and "dirty". Batteries don't care about unfiltered DC for charging, tortise machines and other electronics probably do.
  4. jim currie

    jim currie Active Member

    your right Don i should have mentioned that a large filter cap. is needed on the charger out puts as most of them are only half wave rectifiers.
  5. 60103

    60103 Pooh Bah

    Consider splitting the DC needs so you don't have to wire the transformers together.
    Do you know what voltage the Tortoisies run on? I seem to remember that it's lower than 12, possibly 4. You could wire them to a collection of wall warts.
    (just read somewhere that they're 8 volts.)
  6. ezdays

    ezdays Out AZ way

    That's true, and of course, the higher the current drain, the bigger the filter capacitor you need. I had several lab power supplies to do electronic testing with, but needed a bigger supply for testing light display systems. I got my battery charger out and put a 22,000 mfd cap across the output before it would give me clean DC at around 10 amps. Now that's a physically large cap and you won't find something like that at Radio Shack.

    As suggested, using several smaller supplies might be the best answer.
  7. kchronister

    kchronister Member

    Thanks all. I've since been educated that my calculations are off. When wired in series you don't sum up the amperage as I did. That means my amperage needs are far less than I thought (about 2 amps to run the whole schmear), which decomplicates power notably. I found a nice little adjustable voltage 2-amp power supply for $20, and will probably pick up two and divvy up the layout into two "accessory power" districts.

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