DC: Multiple units vs amp draw

Discussion in 'DC' started by trainchaser007, Aug 11, 2012.

  1. trainchaser007

    trainchaser007 Passed away September 22, 2017

    It's always been my experience that each time I add a locomotive to a mutiple unit train on a DC system, each locomotive loses power. I think it's because of the amps each additional locomotive draws. If I'm correct, is there anything I can do to increase amps besides buy a stronger/better power pack? I have 4 power packs. Could I increase amps by connecting multiple power packs to the same track? I definitely don't know enough about electricity to know if that's a possible/safe solution.
     
  2. renapper

    renapper Passed away March 8, 2013

    Since power packs have variable voltage output, there is no way to connect them to the same track. Your only real alternative is to purchase or built power packs with more current output.
    Retired electrical engineer
     
  3. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    Brandon, if the locos are old Athearns or some of the older stuff from the 70's or older, they probably draw a decent amount of current. There are two different ways to express the current capacity of a power supply; watts or VA(which is the same as watts, since Watts = Volts * Amps). Let's assume two older locomotives will possibly draw 1.5 amps each. At 12 volts, for just those two locos, the power minimum power requirement would be 12V*3amps or 36VA or 36 watts. Some manufacturers will rate the power supply in amps, others will rate them in watts or VA. If you see either, divide the VA or watt value by the maximum voltage the supply will deliver and you will know the maximum current that it can deliver.
     
  4. renapper

    renapper Passed away March 8, 2013

    Keith is correct to a point. The VA rating is the total output rating of model railroad power supplies. Most commerical model railroad power supplies have a 16 VAC accessory output as well as the track power output. The VA rating is the total output of both outputs combined. It is given as VA instead of wattage because the voltage on the two outputs is different, 16 VAC on one and 0-12 VDC on the other. And most all of the commerical model railroad power supplies are unfiltered DC track power, they usually call it Pulse power or something simular. That is because they have to be able to run the old cheap motors which you had to pulse or kick to get them to start moving. Such pulse power has not been needed for over thirty years in the hobby. On some power supplies you can turn it off. Your better power supplies are electronic and/or transistorized now a days. Get the highest rated VA output you can afford. a voltmeter and ampmeter are also very nice to have on your power supply.
     
  5. trainchaser007

    trainchaser007 Passed away September 22, 2017

    Getting back to an old topic that's been on my back burner...

    1. Is there any way to add an amp booster to an existing DC power pack that has a total output of 6VA? Probably not but I had to ask.
    2. If not (assuming not), what is the most amps a DC power pack can supply to track?
    3. Will each additional locomotive slow down all units because of amp draw... no matter what? (Again... DC) I believe the anwser is yes but I'm not 100% certain.

    I will eventually make the "leap" to DCC but I would still like to weigh the "cost vs benefit" factor of suppling more amps to my current DC layout until I take the DCC plunge... which will be after we move. I'm not sure when or where we'll be moving but sooner or later we will be moving. That's all I'm waiting on... a reason to start a new layout... only with DCC the next time.
     
  6. gjslsffan

    gjslsffan Staff Member Staff Member

    I sent you a PM
     
  7. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    My responses in Red.

     
  8. gstout

    gstout Member Frisco.org Supporter

    I would just go ahead and "make the leap." Installing the DCC power supply to the layout is simple--just hook up two wires and you are done. It can be a bit of a pain installing decoders in your motive power fleet depending upon how many locomotives you are operating and what brand/how old they are. Newer units are often plug-and-play, so you can have them set to go in about the time it takes to remove and replace the shell (on a diesel). Older units will require a bit of soldering, but even the toughest ones I encountered (mostly prehistoric Proto E8s) only took about an hour. That said, I did not install sound decoders, mostly because of cost, but that's a matter of choice. In either event, it took me about a month, converting one or two units per night and setting the CVs (you will learn about those when you buy the starter set. There is nothing to those). When it's done you will be much happier with your layout, and if you want to add power boosters you can do it.

    GS
     
  9. Jim James

    Jim James Staff Member Staff Member

    Come to the dark side. (Spoken in Darth Vader's voice)
     
  10. gstout

    gstout Member Frisco.org Supporter

  11. gjslsffan

    gjslsffan Staff Member Staff Member

    All you need is a more powerful power supply, thats it. You plug it into a wall socket, and yep still two wires to the entire MRR, and all your locos will do what they have always done, by themselves or together. You dont have to spend 150.00 per loco either, and you can bring all your old stuff too. I like it when the street lights around here dim when we run trains. You want DCC one day, fine, if it works for you. Believe it or not, despite what every MRR publication is bent on telling you, it is still OK and not a social faux pas, to run your trains DC.

    If I were just starting or had a small MRR, DCC would be considered, and will likely be used, if I live long enough to build another :)
     
  12. mktjames

    mktjames Member

    I went for DCC for just the opposite reason. I wanted sound and then found out the benefit of multiple unit lashups and running longer trains. I then added a room onto the den to run longer trains a longer distance. I base all of this on the change over to DCC. so beware mktjames. The $ for the radio throttle and Zephyr and sound decoders was just the beginning but I would not go back to DC it is way to limiting on any kind of operations.
     
  13. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    Brandon, if I remember correctly, both the RS-1 and the 44 tonner I sold to you have DCC decoders in them, so they can be run on DC or DCC. The main issue you face is this, do you want to spend more money on a more powerful transformer or make the switch to DCC with that money.

    I looked at the MRC web site and their transformers that you might need begin at $229.95. You can pick up an NCE PowerCab for under $175. You can later expand the power of that system by adding the Smartbooster 5 for under $170.

    Just some thought starters...
     
  14. Jim James

    Jim James Staff Member Staff Member

    Buying an NCE Powercab was probably the one purchase that boosted my model railroading enjoyment more than any other purchase. Ever.
     
  15. gstout

    gstout Member Frisco.org Supporter

    I went with NCE as well, and Jim is right. It's the best thing I ever did. My railroad requires 6-8 operators and with DC it was just a nightmare.

    GS
     
  16. trainchaser007

    trainchaser007 Passed away September 22, 2017

    So can anyone tell me how the output of a simple HO scale NCE Powercab system?
    Volts?
    Amps?
    Thanks. - Brandon
     
  17. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    The NCS Powercab is a 14V 2 amp system. It should be able to run 3 typical HO locomotives at once.
     
  18. trainchaser007

    trainchaser007 Passed away September 22, 2017

    I have a MRC Railpower 1300 power pack with an output of 7VA. How much more power would a MRC Railpower 1370 power pack with an output of 18VA produce? What I really want to know is, would I notice a considerable difference in power output? If so, about how much?

    Another question about power packs...
    I have 2 life-like power packs (they're blue). They are about 24 years old. Once in a while, I'll here a "click" or a "boing" (like a spring or something) and they stop working. After a rest period, they start working again. Are they just overheating and shutting off or what?

    Thanks in advance for the replies.
    - Brandon
     
  19. klrwhizkid

    klrwhizkid Administrator Staff Member Administrator Frisco.org Supporter

    First, the Lifelike power packs are overloaded. What you are hearing is a circuit breaker that consists of a bi-metal strip that the output current travels through to a switch contact. When too much current passes through the strip, it heats up, bends and opens the circuit. When the strip cools it bends back in the other direction and closes the circuit.


    Regarding the VA ratings, refer back to my post #3 in this thread. Look at the maximum output voltage for the track power and divide that voltage into the VA rating of the power pack to get its amp capacity. Compare those two amperage values for comparison. Assuming the track voltage is the same, the 18VA pack can supply about 2 1/2 times the power output.
     
  20. trainchaser007

    trainchaser007 Passed away September 22, 2017

    Thanks for the explanation on the Lifelike power packs, Keith. That was my guess (overheating protection) but I wasn't sure. I get that V x A = VA = watts or that VA/V = A and that 18 VA = 2.57 x 7 VA. Wouldn't an 18VA power pack with an output of 12V and 1.5A provide 2.57 times as much locomotive performance as a 7VA power pack with an output of 12V and 0.583A?

    -Brandon
     

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