Accsessory Voltage

Discussion in 'FAQs' started by Play-Doh, Aug 4, 2007.

  1. Play-Doh

    Play-Doh Member

    Quick question

    I am currently without a voltage meter (I know, I know, I should already have one, im getting one next week) but I have a question one thing you folks may know.

    I have a rail power cheapo transformer. This one.

    Railpower 1300 (mrcaa300) MRC Model Train Power Supply / Transformer

    Now I have a turntable that says to not exceed 12V or I may blow the motor. How much do those accessory hook ups usually pump out? The specs dont say on the unit or on the website.

    Any help is always apprecieated.


  2. 60103

    60103 Pooh Bah

    If you hook it to the controlled DC terminals (the ones for running trains) you shouldn't have any problems. They will even give you a way to slow down the turntable to an appropriate speed.
    The accessory terminals on a power pack should not be used for any accessory that has a DC motor in it. AC does a number of nasty things to a DC motor, but doesn't run it. They are usually rated above 12V - 16 to 18 often, because the power pack loses a couple of volts in the rectifier and sometimes a bit more in the speed control.
    (If the instructions say to use 12V AC, that's another matter, but I suspect they don't.)
  3. ezdays

    ezdays Out AZ way

    That has to be the worse description of an electronic device that I've ever seen. Nowhere does it say what the electrical characteristics are other than "requires 120 vac". They should tell you the max DC output voltage and the AC accessory voltage. It should also be rated for either power or current output, and power or current input. All that is required to be on the unit.

    That having been said, David is right. Check your turntable specs to tell you whether it is run on AC or DC. IF it's DC, the controlled output should be set for a lower setting and don't run it up to full, which can be up to 18 volts. If it's AC, that output can also go up to 18 volts so be careful. I suspect, as David does, that it's DC so you can reverse direction and change speed.

    One other thing, cheaper power packs are not regulated, so that if you measure the voltage under load, it will be different than with nothing connected to it.
  4. Play-Doh

    Play-Doh Member

    Thank you gentlemen. It is in fact DC (I should have known that.) Before I go hooking anything up ill get a voltage meter on my power pack, and test where that 12V limit is and make sure not to go near that mark.


  5. ezdays

    ezdays Out AZ way

    Just remember, measure the voltage with the load connected, it could be significantly higher if there is no load on the output. Especially with an unregulated or poorly regulated unit.
  6. Russ Bellinis

    Russ Bellinis Active Member

    I think the information that he needs to post is on the unit somewhere. MRC is pretty good about posting specs on their products. I'm not surprised that the link that Play Doh posted did not show specs, that was a retailer's web site. I "googled" Model Rectifier Corporation and got to their home page and looked up the Railpower 1300. Surprisingly, MRC does not list any specs on their web site for their products that I could see, just advertising hype. If the 1300 is like my 2400 model, it has three sets of connections on the side. There will be 12 volt variable dc, 12 volt fixed dc, and 15 volt ac. You did not mention if this is your only throttle, or if you have other throttles and this one is to be a dedicated turn table control. If this is to be the turntable control, use the variable dc to control the turntable speed to something close to scale. If it is your only throttle, then you will need to wire through a selector switch to allow you to select the turntable motor power as a separate block. Just remember to isolate the motor from the turntable tracks so that you can control a locomotive on the turntable once you have it aligned.
  7. Play-Doh

    Play-Doh Member

    Thanks again for all your help! I have one more question. How exactly do I test "Under load" I understand what you mean by that, but how exactly do I hook up to do so?


  8. hgk

    hgk New Member

    Play-Doh wrote:
    You can always use a light bulb for a load test. Connect it to your supply and meter across it. The lamps voltage should be close to
    what you think you'll be measuring. If its higher it'll be dim and lower it'll be bright but either way it'll work as a load.
  9. ezdays

    ezdays Out AZ way

    Like hgk says, you can use a light bulb as a load to get an idea. Use your meter to measure the voltage with no load connected, then put a load across it and measure the voltage again. The chances are pretty good that the voltage will drop under load. The higher the load (lower resistance), the lower the voltage will be and again, like hgk points out, the dimmer the lamp will light. If the voltage remains fairly constant, and the lamp lights, then you have a well regulated supply, but I really doubt that.
  10. 60103

    60103 Pooh Bah

    An easily available load is an automobile side light or brake lamp bulb. You can get mounts for them with wires, but usually you have to provide the ground. When you're done, you can use it to protect against shorts.
  11. Russ Bellinis

    Russ Bellinis Active Member

    If you check the trailer section at your local auto parts store, you may find a marker light with a "pigtail" connected to it. The will give you both the hot and the ground to put across the rails to put a load on the unit for testing. Some of the newest trailer lights are electronic circuit boards with a bank of leds instead of a light bulb. I don't know what sort of load they put on a circuit in comparison to an incandescent light, but I suspect they would use much less amperage, so use a unit that takes a conventional light bulb.
  12. Play-Doh

    Play-Doh Member

    Thanks Everyone! You have been a great help!
  13. Play-Doh

    Play-Doh Member

    A word to newbies

    Things to learn before buying a voltage tester.

    Learn the difference between DC & AC
    Learn the difference between volts and amps
    Read the instruction manual before trying to use the meter

    And most important

    Never use a outlet to "Test" your voltage meter.

    Results are painfull. Im still trying to get my heart rate back to normal.
  14. ezdays

    ezdays Out AZ way

    Yeah, you are right, it can be an "electrifying" experience.... pun intended, but it's not funny. The best way to test any voltage is to turn off the power, connect the meter and turn the power back on. And yes, be sure you know if you are measuring AC or DC. If you're not sure, put the meter on AC and set it for the highest scale. Most meters have an internal fuse, but that's not always enough to protect it and the person using it.

    I hope all you got was a scare and not burned in any way.

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