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Locomotives Do Not Move, Help!

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  • Member since
    March 2024
  • 2 posts
Locomotives Do Not Move, Help!
Posted by Boiler Bill on Friday, March 8, 2024 5:49 PM

Confessed noob here, but I bought a MRC Tech 7 ampac 760 single throttle to run my little On30 0-4-0 loco for my upcoming track build. I have a 6' HO test track and so hooked the transformer with two alligator clips to the track. The Porter didn't move. I put on a HO Atlas Classic GP7 on the track...nothing.

 

I then used my voltmeter and I was getting 20 volts. I put yet another loco, a prized Virginian diesel On the track. Still nothing.

 

I could swear I saw the Porter jump earlier when the throttle was at 3/4, but it hasn't repeated that since.

  • Member since
    November 2013
  • 2,774 posts
Posted by snjroy on Monday, March 11, 2024 10:39 AM

Hi there. Are these locos DCC? I believe that powerpack is DC only. If you have DCC engines, they should be DC-enabled (most are in default mode). You have to crank up the power a bit to get them to move.

I assume you are testing the voltage on the track, not just the output screws on the powerpack.

Simon

  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,892 posts
Posted by wjstix on Monday, March 11, 2024 11:13 AM

Are you sure the power is reaching the track? Alligator clips aren't always reliable; track can be dirty. Maybe try putting an engine in a cradle upside down and touching the wires from the power pack directly to the wheels and see if that works. Maybe turn the momentum off. 

Stix
  • Member since
    September 2004
  • From: Dearborn Station
  • 24,281 posts
Posted by richhotrain on Monday, March 11, 2024 4:01 PM

Is that test track DC powered or DCC powered?

 

Alton Junction

  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,892 posts
Posted by wjstix on Monday, March 11, 2024 4:06 PM

The MRC Tech 7 ampac 760 is DC.

Stix
  • Member since
    October 2005
  • From: Detroit, Michigan
  • 2,284 posts
Posted by Soo Line fan on Tuesday, March 12, 2024 9:20 AM

20v is likely open circuit voltage. What are you seeing with a engine on the track?

Jim

  • Member since
    September 2003
  • 21,669 posts
Posted by Overmod on Tuesday, March 12, 2024 10:53 AM

Yeah, you need to test the locomotives more directly.  There is a test 'tool' available on eBay now that is, basically, a set of test leads that have a copper or brass 'brush' applied to the probe tips.  These would be remarkably easy for most any actual model railroader to 'gin up,

You plug the 'meter end' into appropriate + and - on your variable-DC outlet.  Arrange to clamp or hold the locomotive upside-down, firmly but without deranging any detail, and touch the brushes to the appropriate drivers used for pickup (I'm assuming on an 0-4-0 that's all of them).  By the time you get up to 7 or 8 volts across the terminals at zero applied load, you should be getting enough current through the pickups/wiring and motor to at least make it try to turn, or at least produce a little hum or noise.

You can repeat the exercise with the shell off if you want to test various contact points to see if there's something loose or broken in the current path through the motor.

I would recommend that you install the equivalent of feeders to your individual rail sections, and common buses connecting them, as a means of providing both signal and voltage to a test or programming track.  Don't just kludge it by trying to solder on the equivalent of 'track bonding' around joints in the rail.

When you test a DC power output, ALWAYS do so with a substantial power resistance in circuit, on the principle of a 'megger'.  Very frequently, we had treadmill power boards that would scope out fine, but fail to conduct any particular amperage through the PWM controller or the semiconductors implementing the waveform.  We have had multiple threads here about similar behavior from 'powerpacks'.

(And, as a general rule, in life as well as modeling, never use a prized anything for random testing when you don't know the cause!)

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