Just wondering what you are using for monitoring of AC Track Voltage. Also we have sections of track we need to setup to about 16 volts using a Cab-1. Has anyone succesfully used a light bulb or series of LED’s to remotely monitor this voltage, if so what voltage lamp? Thanks, Dave
You can pick up cheap multimeters at Radio Shack that will give you fairly accurate readings of AC Track Voltage… Using light bulbs or LED’s won’t work without comparator circuits. Not worth the bother to design or build.
Harbor Freight sells Digital Volt meters for under $5.00.
The A.C. range will give you a two digit measurement.
It also has a 10 amp range. Place a large bridge rectifier in series and the Amp meter across the D.C. terminals.
That is good information.
Almost all AC meters rectify the waveform and measure the average (the DC component) of the result. This gives a value which is about 90 percent of the RMS voltage of a sine wave; but the meter face is marked to correct for this error. The method suggested by Spike for making an AC ammeter is good, but will show that 10-percent error when used with a sineusoidal current waveform. However, since you would be using an otherwise unmodified DC meter, you would have to make the 11 percent correction for yourself.
If your voltage is not a sine wave, an ordinary AC voltmeter can give you a very inaccurate reading. For example, here is a table I have posted before for the CW80 transformer. It shows the actual RMS voltage corresponding to what you would read with a voltmeter. It applies only to a phase-control “transformer” with an 18-volt maximum output–like the CW80. You can see that the error is nearly 4 volts in the middle of the range.
CW80 RMS
0 0
1 2.7
2 4.4
3 6
4 7.3
5 8.6
6 9.7
7 10.8
8 11.8
9 12.7
10 13.6
I wonder how the new Voltmeter cars from K Line will do? They look cool but are they practical? I just might consider one for the heck of it.
Just got back from Harbor Frieght and all they have is digital multimeters for $3.99.
I am looking for just a volt or amp meter even analog will do at a great price. The reason that I want a regular panel type meter is that a multimeter may short out under constant useage, to the best of my knowledge a multimeter is just for a few minute use not for long term like I want.
Lee F.
I can’t imagine why a multimeter would care whether you measured continuously. In a half-century of using them, I have never heard of one’s failing for that reason.
Lionelsoni an A.C. digital multimeter across an A.C. load will read true A.C. just like a analog A.C. meter.
A D.C. amp meter connected between the D.C. terminals of a bridge rectifier will give you a true amprage reading and you will have A.C. to your load.
But if the gentleman wants an analog meter and not digital. That is his choice. I only made a suggestion.
I use a digital meters for all my requirements execept to observe the movement of my switch machines. Then it is easer to watch the swing of the needle.
The bridge-rectifier ammeter will indeed reduce the track voltage, actually by a little more than a volt, but it won’t rectify the track voltage. Only the current through the meter is rectified, the way Spike proposed it.
The way AC voltage is measured is in RMS volts. (And AC current is measured in RMS amperes.) An AC voltage of 120 volts RMS delivers the same power to a resistive load, like an incandescent lamp, as a DC voltage of 120 volts, for example. But the AC voltage, if it is sinusoidal, as it usually is, actually has a peak voltage of 170 volts 120 times each second, and spends much of its time below 120 volts.
“RMS” stands for “root mean square”. It is the square root of the average over a complete cycle of the square of the instantaneous voltage. RMS voltage is not what virtually all AC voltmeters, analog or digital, actually measure. What they measure is the average of the absolute value of the instantaneous voltage, because that is far simpler to do. For the same waveform, these are proportional to each other. So, if you know the waveform you can calibrate the simpler meter circuit to indicate RMS voltage for that waveform. The measurement is not valid for any other waveform. The waveform universally assumed is a sine wave.
So it is not true that “A D.C. amp meter connected between the D.C. terminals of a bridge rectifier will give you a true amprage reading…” Since it is calibrated for DC current, it will read about 90 percent of the RMS current.
When the voltage or current waveform is far from sinusoidal, readings with any conventional meter designed for a sine wave can be substatially in error, as in the example of the phase-control waveform of the CW80.
Lionelsoni From what I do not understand from your replys.
Why are you fooling around with meters at all?
The precision you require for your Laboratory Lionel is a dual channel Oscillascope.
With an Ampprobe and a voltage probe you can continiously monitor Amperage and Voltage with no lose.
For me the .7 volt drop across each of the bridge diode has very little effect.
Bob,
The other part of the reason I don’t want a multimeter is that it looks too bulky and needs to be front wired, in other words it looks too tacky to me or ugly!. I want something like a panel meter with wiring capabilities on the backside of it.
Lee F.
Did I say I was fooling around with meters? I have no meters attached to my layout. I do own an oscilloscope; but it sits on my workbench.
The errors I was describing in using rectifiers and DC meters have nothing to do with the forward drop of the diodes; they are inherent in that technique of measurement. I described the nature of the limitations of the rectifier method of measuring AC voltage and current as a caution to those who want to do it for themselves.
Lee, I wouldn’t use one either; but I think it would work for someone who didn’t mind how it looked.
You are a rivet counter.
I was just suggesting a easy way to see what his trains were doing.
My suggestion are easy to do and inexpensive and would work over the long term.
I would not, but if I were going to try to insult someone by calling him a rivet counter, I would spell it correctly and do it in a more moderate typeface.
Anyone who has seen my layout knows that I am not one.
Phillyreading
I do not know where you live. Around Chicago area there are many Electronic Swap meets & Model RR Flea markets where you can find a very large varity of meters to fill your desire.
I hope I was helpfull.
Dude, talking about the merits of methods of measuring voltage in a thread devoted to measuring voltage is not “rivet counting.” Bob is giving us some very clear and useful information.
Back to the original question of the thread… I did a quick eBay search and found several analog AC voltmeters for around $15 including shipping. They’re panel-mount, so you’d be able to hook them up without more unsightly wires. I couldn’t find any that were 0-25 volt (which would be ideal), but I did find some 0-50 volt meters. That wouldn’t be so bad–you should be able to tell the difference between 16v and 18v on that. I wouldn’t want to use one of the 0-300v meters I found because I’m not so sure I’d notice a drop of 2 volts on one of those.
Someone I know found a couple of very old analog voltmeters, probably dating to the 1940s or very early 1950s, on eBay once. They had Bakelite cases, much like a lot of the older Lionel transformers, so they looked very good in front of his Lionel layout. I don’t see anything like that on eBay right now, but I sure liked the look of the stuff he found.
spikejones52002,
I live down by West Palm Beach FL or should I say Scalper City as far as prices go for electrical stuff, panel style meters would cost me $78.00 plus tax down here new.
Not many Flea Markets left down here or they sell jewelry or fake flowers.
Lee F.