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Power surge on DCC ?

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JRP
  • Member since
    November 2006
  • From: Upland, CA
  • 301 posts
Power surge on DCC ?
Posted by JRP on Monday, November 1, 2010 5:26 PM
I am currently using 1.5 Volt bulbs (with resisters) in the cabs of my HO diesels. When I first put an engine on the track and start up the DCC power, sometimes those bulb lights come on extremely "bright", and I must remember to hit the light button to turn them off for a second.... otherwise they can burn up rather quickly. What causes that surge? Is there a method to keep the start up from turning on those lights at the same time? Note: Once the lights are off, I can go back and turn them on low or hit the #7 button to brighten them if I choose...but even then they are not super bright as that first power on. Thanks. JRP Great Southwest and Pacific RR
  • Member since
    January 2007
  • From: Eastern Shore Virginia
  • 3,290 posts
Posted by gandydancer19 on Monday, November 1, 2010 5:40 PM

Sounds like a good question.

However, I haven't noticed any surge on start-up from my DCC system.  NCE Power Pro.

Elmer.

The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.

(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.

  • Member since
    October 2006
  • From: Western, MA
  • 8,571 posts
Posted by richg1998 on Monday, November 1, 2010 5:43 PM

What is the resistor value you are using? I use a 1.5 volt bulb in a decoder equipped loco and use a 470 ohm resistor. Never noticed any flaring but the bulb is for a beacon. The voltage is around 1.1 volts at the bulb. I use a NCE power Cab at home and NCE Power Pro at the club. Both have a DCC voltage of about 13.8 volts.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

  • Member since
    July 2003
  • From: Sierra Vista, Arizona
  • 13,757 posts
Posted by cacole on Monday, November 1, 2010 5:56 PM

It sounds like you don't have a proper resistor connected to your lights.  I always use a 1,000 Ohm resistor regardless of Ohms law calculations with an LED or 1.5 Volt bulb and have never had any problems with them.

 

  • Member since
    February 2002
  • From: Reading, PA
  • 30,002 posts
Posted by rrinker on Monday, November 1, 2010 7:11 PM

 Light bulbs have different resistance when the filament is cold vs when it is hot, this is probbaly the causeof the 'surge' you see. If it's too high and burns out the bulbs, then you have too small a resistor.

470 ohm is too small for a 15ma 1.5V bulb, just about right for a 30ma 1.5V. For all esle being equal, a closer 'exact' value for a 15ma ulb is 940 ohms - but they don;t make such a resistor in common 10% tolerance types. 1K is the closest without going under - but remember there is a 10% tolerace, so that 1K can be anywhere from 900 to 1100 ohms. Likewise the smaller ones - that 470 ohm can be as low as 420 ohms which is too small and runs the bulbs with too much voltage.

                                          --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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