# testing voltage



## Da&Co (Jan 27, 2016)

Here's another of my complete-beginner questions. I now have a run of scholarly books and articles on the PRR in at the turn of the century, so I can discuss the complexities of US economic policy in re transportation debates ... but I'm powerfully clueless about wiring.

My total track layout for the moment is about 40'. Let's say that I have a bus wire and a number of feeder wires. How do I check that there is power--and consistent power--in the wires and running through the track? I mean: how do I check both the wire (where it's exposed) and the track? 

I have seen many references to two pieces of equipment: a multimeter and the RRampmeter. The latter looks pretty straightforward: stick it on the track. But I've also read that most people don't use one but use a ... multimeter. Does that also test track voltage? 

I know that there must be a guide for newbies and I would appreciate any links. If someone has the time to explain it, great. I'm interested not only in what tool I need but what I do with it. What am I looking for? How do I know what the right voltage is on the tracks? Or am I looking for amps? Or both? You see where I am....

The bottom line is that I'd like to know if, when I hook up a feeder wire, the connection has worked and the power is flowing correctly. Obviously, I'll know to a large extent if the train runs. And maybe that's all I need. But my sense is that a train might well run even if half of my feeders are faulty--it will just be underpowered.

Thank you all so much!


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## highvoltage (Apr 6, 2014)

A multimeter does what the name implies, multiple measurements. It can be used to measure voltage, current, and resistance. The most common usage is for measuring voltage.

There are two leads, one red and one black. When placed on the center and outside rails of the track you will be measuring voltage. Most trains will be running DC (or direct current) of around 20 volts or less. Find a setting that will measure that voltage, then touch the probes to the track at various places around your layout. Your readings should be consistent around your layout, which would indicate good connections.

Multiple feeds are used to used to insure good voltage around a layout. Even if half your feeds are faulty as you say, you will still be running but it might slow down at the furthest point from the transformer.


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## Da&Co (Jan 27, 2016)

Super. That makes sense. Is there a standard voltage that I should be achieving? In other words, what number do I want to see?

And, out of curiosity, will I see a slight voltage spike immediately after the feeder wire? Does the voltage run down, even if only slightly, from one feeder wire until it gets to the next one?

Finally, I'm curious what people use the RRampmeter for. I can see that it does both volts and amps. Is it primarily for amps? Is it more accurate? I've read that it's a nice tool but not necessary.


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## highvoltage (Apr 6, 2014)

Da&Co said:


> Super. That makes sense. Is there a standard voltage that I should be achieving? In other words, what number do I want to see?


The answer is, it depends. The transformer dictates the voltage by the position of the handle. All the way off, 0 volts. Moved to its maximum position, upwards of 20 volts. In between, well, various voltages depending on position



Da&Co said:


> And, out of curiosity, will I see a slight voltage spike immediately after the feeder wire? Does the voltage run down, even if only slightly, from one feeder wire until it gets to the next one?


If you have multiple feeders on a modest sized layout I wouldn't expect to see much voltage variation at all. Maybe a few tenths of a volt between feeds. Don't know, never measured my layout, I guess it's time to experiment. 



Da&Co said:


> Finally, I'm curious what people use the RRampmeter for. I can see that it does both volts and amps. Is it primarily for amps? Is it more accurate? I've read that it's a nice tool but not necessary.


Based on a quick internet search, it's used for either voltage or current measurements, just not at the same time. 

Accuracy appears to be less than a multimeter. I would say get a decent multimeter and you can use it for any measurement you may need.


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## Da&Co (Jan 27, 2016)

Thank you, highvoltage. Your answers are encouraging and very helpful.


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## AmFlyer (Mar 16, 2012)

Reality might be just a bit more complicated in that the measurements you see are misleading. First, you did not say if you were using AC or DC for track power, it would be helpful to know that. 
If you just apply power to the track and measure the voltage it will be equal everywhere regardless of how many feeders are used. Why? Because without current draw by a load there can be no voltage drop. The meter draws a negligibly small amount of current. Two formula's, E=IR and P=I(squared)R. This is for DC circuits but is ok to use for most model train applications. If you have 15V on the track and apply a 5 ohm load it draws 3 amps (first formula.) The 5 ohm load consumes 45 watts (second formula.) If the track has one ohm resistance between feeders then the voltage drop in the track is 2.5V. Use the first formula to calculate the current with now 6 ohms of resistance (track plus load) and then use that current to calculate the drop across the one ohm track resistance. Real track resistance should be much lower than my example. With trains and light bulbs the actual result will be different because electric motors and incandescent bulbs are non linear loads. But this is a good first approximation.


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## DonR (Oct 18, 2012)

You can get a very usable Multimeter at
a Harbor Freight store for 4.95, and often
they give them away free.

This device is all you need for model railroad
purposes. It can also be useful to check
household or vehicle electrical problems. It comes
with a printed manual that instructq you
in how to use each function.

Don


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## traction fan (Oct 5, 2014)

*Photo*



DonR said:


> You can get a very usable Multimeter at
> a Harbor Freight store for 4.95, and often
> they give them away free.
> 
> ...


 I agree with Don. Here is a photo of a harbor freight meter. They have several types and Don may be referring to a different model, but they would all work. This one has a current clamp feature which allows you to read the current through a wire without disconnecting it. This might put to rest your concerns about the amount of current at each of the drop wire feeders on your layout. They should all be very close. Any multimeter can read current. Normally, you have to disconnect a wire and connect the meter into the path of that wire. The clamp thing just makes this a little easier.

Traction Fan:smilie_daumenpos:


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## Lemonhawk (Sep 24, 2013)

Does the current clamp only work on A/C?


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## MarkVIIIMarc (Oct 19, 2012)

Testing continuity and resistance or lack there of is another good use of a meter.


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## highvoltage (Apr 6, 2014)

Lemonhawk said:


> Does the current clamp only work on A/C?


Yes. As you can see next to the numbers on the dial there is the ~ symbol, which indicates AC.


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