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Testing for voltage drop

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  • Member since
    February 2002
  • From: Reading, PA
  • 30,002 posts
Posted by rrinker on Monday, December 22, 2014 6:27 PM

 Sure does sound like someting other than voltage drop, especially because a) the layotu is not that large and b) the OP says feeders are installed to all track sections, so there is no power via rail joiners.

 Like Martin says, it doesn't matter if the meter can't accurate read the DCC voltage - if the design of the meter makes it read, say, 1.5 volts low on the DCC signal, it will be 1.5 volts low no matter what, so the relative readings are what you are after. If it shows 12.5 volts right at the booster and 10.2 volts at the farthest part of the layout 0 that's a signficiant enough drop to visibly slow down the locos. Dead stop though, means no power whatsoever, or no DCC signal. On that size layout, not likely it's a DCC signal degradation. Dirty track is the most likely thing.

                          --Randy


Modeling the Reading Railroad in the 1950's

 

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

  • Member since
    July 2008
  • 1,206 posts
Posted by mfm37 on Sunday, December 21, 2014 9:33 PM

A standard meter set to read AC volts will help find voltage drop. Even thoiugh the reading may not be dead accurate, the difference in readings around the layout will show where the drop is occurring. But, you need to have a load on the track to measure voltsge drop. It won't drop without a load. I use a pair of 8 ohm 10 watt resistors in parallel to add a load. This provides a 3 amp load at 12 volts. That's probably too much load for your system. You could use an engine to provide a load or even a couple of lighted passenger cars. A Dc engine would provide a load.

That all being said, it really sounds more like a dirty track or engine or both problem. Voltage drop on a DCC layout will show itself as a engine slowing down before it stops dead from loss of signal.

Martin Myers

  • Member since
    October 2006
  • From: Western, MA
  • 8,571 posts
Posted by richg1998 on Sunday, December 21, 2014 8:36 PM

An AC meter will read about 13.6 VAC with my NCE Power Cab. If the loco strops in a section, with a meter connected to that section, if the meter still reads 13.6 VAC, I have dirty track, wheels or pickups. if the voltage drops a couple volts of more, then I have a defective feeder/connection to that section.

Even if your meter reads say, 19VAC, look for a “trend”, say you see 9 VAC or even zero. You have a defective connection under load. Many are concerned about the actual AC voltage. What you need to look for is a "trend". I learned that from old timers many years ago.

The AC will general be about the same potential as the DC power pack to the DCC controller.

My Power Cab is 13.9 VDC and the DCC signal at the power panel is 13.6 VAC or pretty close. All I look for is “trend” along the layout.

I use the Harbor Freight digital meters.

My old worn out analog meter shows about 11.5 VAC right at the cab output. I use to use that and just looked for a lower voltage. In my mind I figured the AC must really be about 13.9 VAC. My DVM's showed me I was close.

Again, make sure you have a load, loco in each section you are testing. With no load, you usually will see the same voltage unless the connection is broken.

This is not rocket science kids. It is model railroading.

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
    October 2005
  • 1,047 posts
Posted by betamax on Sunday, December 21, 2014 2:59 PM

It is probably dirty track.  That would cause it to stall and then start after a small push.  Cleaning the track and the wheels would be a start, don't neglect the wheels since they spread dirt around.

You could also try the quarter test to see if power is getting to the track and the circuit protection is working correctly, if not, there proabably is a wiring issue.

To measure a voltage drop, you need a load.  Just testing with a meter isn't going to tell you a lot. No current flow, no voltage drop.

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,281 posts
Posted by richhotrain on Sunday, December 21, 2014 2:41 PM

Voltage drop on a 9' x 5' layout?   I doubt it.

More likely dirty track and/or dirty wheels.

Rich

Alton Junction

  • Member since
    December 2008
  • From: Mount Vernon WA
  • 968 posts
Posted by skagitrailbird on Sunday, December 21, 2014 2:26 PM

Since Jim mentioned an NCE PowerCab I think we should asssume he is operating with DCC, not DC. As mentioned a multi meter will not do a real good job of measuring voltage due to the modified AC output from a DCC command station.

But, from Jim's description it sounds like the problem is in the locomotive or perhaps dirty track rather than a voltage drop. If voltage was dropping he would see a gradual slowing of the locomotive.

Jim, I suggest checking these items in the sequence listed:

  1. clean your track--for a small layout such as you describe I would use an abrasive block but whatever the method, get the track clean.
  2. Check and clean all of the locomotive wheels. The simplest and cheapest method is to place a small piece (say 2" x 2") on a section of track, saturate it with isopropyl alcohol, place one of the loco trucks on it and the other on the bare track. While holding it with one hand, turn the throttle all the way up. The spinning wheels on the wet paper towel will get clean. Then pick up the loco, turn it 180 degrees and repeat the process.
  3. If the intermittant stop & go continures, check all wiring connections. If any are using the little plastic clips, discard the clips and solder the connections.
  4. If it still persists, check the motor's brushes and commutator.

I these don't solve your problem you need someone smarter than me. Good luck.

Roger Johnson
  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,330 posts
Posted by selector on Sunday, December 21, 2014 1:36 PM

What?  Nobody has responded yet? Hmm

A multimeter will show voltage, but it won't do a great job if you are using DCC.  Are you using DCC or just DC?

If DC, power your rails and set the dial on your mulitmeter to 20 volts.  The large dial should have several markings.  You must set your meter for DC current, and then rotate the dial to the 20 volt mark (read your manual).  Then, with the meter on, very gently touch the probe tips to the rails, one on each rail, and move along the rails with gentle touches at each point.  Note/keep a record of the voltage when the indication steadies.  Soon, if  there is more than a 2 volt drop, you'll see it plainly and know that you have either a voltage problem or an actual continuity problem/cold solders/corroded contacts...whatever it may be.

If you would like some media tutorials, go to youtube and type "how to measure voltage".  Find at least three videos with more than 10k views and watch all of them.  Look for commonalities.  Soon enough, you'll know what you must do and what to watch for.

  • Member since
    January 2013
  • 42 posts
Testing for voltage drop
Posted by Docjmp on Saturday, December 20, 2014 9:53 PM

Hi everyone,

I've been have issues with my trains running in an inconsistent manner. My switcher will stop soon after I apply power on the NCE Power Cab. If I give it a little push, it will start again, but stop sometime after that. I have a main feeder line of 16 gauge with feeders of 20 gauge to several sections of track, i.e. every 9" piece of track or 36" section. Most of the track has connectors, but I have been able to solder many of the sections. I'm wondering if the problem is a voltage drop. I'm running HO on a 9' X 5' layout. How do I use a multimeter to test for voltage drop and could this be the problem. If it is, will a power booster fix the problem. The problem with the sporadic running seemed to start after I expanded the layout to include a side yard with turn outs. Appreciate any suggestions.

Jim

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