What do I need to measure DCC track voltage?

[Bart1701]

I have one block of track where it looks like all of my locomotives slow down just a little bit. I do have feeder wires on my layout about every 2-3 feet.  I have cleaned the track, but nothing changed.

I am assuming that the voltage may be a little low here. What kind of tool would I need to accurately measure the voltage in this section so I can compare it to other sections. I'm not an electronics expert, so I may need a little help on the use of the tool, too!

I think the slow down occurs in the entire block, but would like to check each section of rail to make sure it's not a loose rail joiner causing an a issue.

I use a Digitrax Zephyr on my layout. What would you expect the track voltage to be?

Any other thoughts on why this section would result in a slight slow down for the locomotives?

Thanks,
Bart

[RBrodzinsky]

You can get a RRampMeter, which does measure the true DCC voltage, or you can use a digital volt meter, on AC, but it will be a little off.   The Digitrax Zephyr should but out a DCC voltage of 13.5-14V

[GaryHinshaw]

If the locos really slow down in that section only, it's possible that you have a poor connection between the bus and that section of rail.  Another way to test for this is to measure the DC resistance with an ohmmeter (most multimeters have multiple resistance settings).  If you have a good connection through the feeder, the resistance between the bus and feeder should be less than an ohm, and hard to measure with a typical ohmmeter.  You can check this by testing a good section of track. 

To get an idea for what a bad section might look like, consider that a typical N scale loco will draw ~0.1 amps at full voltage (~12 volts), so the motor has an internal resistance of R ~ 12 V/0.1 A ~ 120 ohms.   If you loco slows down by, say, 10% in the bad section due to a poor connection, that implies that there is an extra 10% resistance in the circuit due to the bad connection, so you should measure a resistance of ~10 ohms between the bus and that rail (it could be either rail, of course).  If you measure both rails and they are less than on ohm, your problem lies elsewhere.

This applies to both DC and DCC.

[Maletrain]

Trying to be practical for a guy who says he is "not an electronics expert":

First, for what you want to do, you don't really need a special meter that can give an exact reading for DCC waveform voltage.  A cheap "multimeter" that measures DC and regular household AC voltage will do what you need when set to "AC voltage".

Second, trying to measure the resistance of a few ohms with the "resistance" setting on those meters is not very easy, because the resistance between the probe ends and the wire or rail that you are holding the probes in contact with will not be zero, and can mask small differences in the actual load carrying connections to the tracks.

So, what I suggest is to look for the actual voltage drop when there is a load on the rails.  For a load, I use a 12 volt automobile light bulb that draws something like 1/2 to 1 amp.  I have both a tubular one that just sits on the N or HO gauge rails and has contact at places that hit each rail, and I have another type that is in a bulb holder with the wires attached to alligator clips that can be clipped onto the rails.  Either one allows me to put a known, constant load on the tracks at a fixed point of my choosing.

So, what I do is to put that bulb load on various parts or the track, and then measure the AC voltage across the track (rail-to-rail) with the meter.  Differences in the resistance between the feeder bus and the rails that is sufficient to cause a locomotive to slow down will be easily visible as a lower track voltage in the section(s) with higher feed resistance.  Note that the bulb load is necessary to do this, because the meter itself draws so little current that the voltage drop with only the meter as a load would be too small to measure. 

So, take your "baseline" voltage reading with the meter and the light bulb at the point where your command station most directly feeds a section of track, and then compare the areas where the locomotive does and does not slow down to that reading.  If you get a pattern of low voltage only where the locomotive slows down, then you problem is low voltage due to high resistance in feeding the track is that (those) locations.

But, there are other reasons that locomotives can slow down, so the first step is to determine if it is really a voltage problem.

[Mike C]

But, there are other reasons that locomotives can slow down, so the first step is to determine if it is really a voltage problem.

Could the track gauge be slightly tight ?

[MK]

Like Maletrain said, nothing fancy for your purpose.  You just want to compare voltages in different sections/blocks, not the exact voltage in each.

Multimeter set to AC and off you go.

[MK]

Could the track gauge be slightly tight ?

Mike

Another possibility!

[Bart1701]

Thanks for the ideas. I especially appreciate Maletrain's post - this was very helpful to a guy who is not an "electronics expert"!

My layout has been complete for quite a few years and this section of track just recently started exhibiting this behavior. I do not think that the track gauge would be the issue, as it is the same track that has always been there.

The only thing I remember doing in this section recently was having to add some ballast to an area where the existing balance had become loose (it was around a joint between two sections of the layout).  Maybe some of the rail joiners got some ballast cement in them? I'll take a closer look at the track to see if this might be what happened.

Bart

[robert3985]

I have one block of track where it looks like all of my locomotives slow down just a little bit. I do have feeder wires on my layout about every 2-3 feet.  I have cleaned the track, but nothing changed.

I think the slow down occurs in the entire block, but would like to check each section of rail to make sure it's not a loose rail joiner causing an a issue.

Any other thoughts on why this section would result in a slight slow down for the locomotives?

Thanks,
Bart

I'm not gonna tell you how to check voltage on your rails.  However, I notice that you don't have a feeder on each and every piece of rail, and are depending on rail joiners to conduct electrical current and DCC signals. 

The "Gold Standard" is to put a feeder on each and every piece of rail on your layout, and NEVER depend on rail joiners to conduct electrical current or DCC signals.

But, most people don't do this, as it's a lot more work than just dropping a feeder every 3' or so and (hopefully) soldering rail joiners to rails, leaving an unsoldered joiner every 6' or so for expansion/contraction of the rails or benchwork, or both.

Here's what I'd do:  (1) determine if the section of track where the slow-down starts has feeders attached to it....I mean SOLDERED DIRECTLY to each rail in that section.  If it does, and both of the solder joints for each track is good (wiggle them to see if they're loose) then the problem is most likely down below where the feeders are attached to your main power bus.  Go under and test those solder joints.  I would probably just re-solder 'em if you're using solder to attach feeders to your power buses (I prefer genuine 3M Insulation Displacement Connectors or IDC's).

(2) If the section has no feeders and relies on tiny little metal strips....oh, JOINERS...to conduct electricity/DCC signals, find the two ends of each of the two rails and mark where they're at using a push pin for each one adjacent to the rail.  Run an engine over to where one of the rail ends is where the slow down starts, and run the engine on to the slow-down section to watch exactly where the engine slows.  It should be as it passes over the rail joint held in place with only a rail joiner.  Back the engine off of the offending track section...just past the rail joints, and stop.  Find the rail joints on the OTHER end of the offending section, and place a small screwdriver exactly in the joint, so the the blade is touching both rail ends in the center of the rail joiner and run the engine on to the offending section again.  If it doesn't slow down, you've found the bad rail joint.  If it does slow down, repeat the process on ALL rail joints until you find the offending one. 

(3) If it continues to slow down even if you're bridging the gap on one rail at at time, it could be that there are two bad rail joints.  Repeat step 2, but bridge both rails' gaps at their respective joints at the same time and watch the engine.

This logic train should show you where the offending rail joint(s) is/are.

My assumption is that an adjacent section of track to the section you're testing has good feeders attached to each rail.  If you've got more than one piece of rail between feeders with multiple rail joiners doing the electrical conductivity, then you may have to test each rail joiner joint between where the feeders are attached.

If your rail joiners aren't soldered between your feeders, you really need to solder them, leaving ONE SET of rail joiners every 6' or so unsoldered between feeders. 

If your rail joiners ARE soldered (except for the unsoldered ones every 6' or so) then you should bite the bullet and start dropping feeders on each and every piece of rail.

If your problem is under the layout were the feeders are connected to your power buses...and you've used solder joints...I'd consider using properly sized genuine 3M IDC's instead.

Or, just hope this is the only problem you're gonna have, and repair each one as it appears...which is what I did for years until finally having enough and ripping my rat's nest of DC wiring out, and re-installing my DCC wiring in a "Gold Standard" manner.  It's been 12 years now since I did that, and I have had zero electrical problems anywhere on the layout...ZERO...and my layout gets broken down and transported at least a couple of times a year. 

It was worth it for me to expend the effort to do it right finally.

Cheerio!
Bob Gilmore