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ZWL Transformer Output Voltage

BrooksmjBrooksmjOGR Forum Member

I am posting this topic to perhaps save someone out there some stress and worry.

 

I purchased a new ZWL Lionel transformer a few months ago which seemed to be working fine but when I did my track voltage testing the voltage would not go above 16.8 volts using 3 of my standard VOMS and DVOM meters.  After some considerable thought and finally looking at the output voltage on an oscilloscope, I noticed that the ZWL outputs a triangle wave whose amplitude increases as you raise the voltage.  As the voltage approaches maximum the waveform becomes more of a sawtooth or square wave.  I figured this would account for an inaccurate reading since the standard RMS calculation is based on .707 of peak of a sine wave.

   I was worried so I called Lionel and they said they use a TRUE RMS meter, which although having an electronics background I had never heard of.  Anyhow I purchased a TRUE RMS meter for about 30 bucks and what do you know it outputs a little more then 18 volts just like it is supposed to.

 

So, the moral of the story is don't be fooled by your regular voltmeter when measuring the ZWL voltages.  Use a TRUE RMS meter and you can then sleep at night again without worrying that you might have to send your expensive new transformer back.

 

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cjackcjackOGR Forum Member DIGITAL SUBSCRIBER

This won't be helpful but the RMS value is not "based on .707 peak of a sine wave". It is based on the square Root of the Mean of the Squares measured at many points of the waveforms values. It happens that it comes to .707 peak of a true sine wave (I realize that is what you meant), and is different for different waveforms. Inexpensive meters just scale the RMS value to be .707 but as you found out that doesn't work for waveforms different from a sine wave.

 

gunrunnerjohngunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

Chuck's statement is why you see this statement a lot of times describing RMS Value.  As stated, actually measuring the RMS value of a non-sinusoidal waveform is a fairly complicated procedure.  Truthfully, I'm not really sure how accurate the low cost "true-RMS" meters actually do the task.

 

The RMS value of an alternating current is also known as its heating value, as it is a voltage which is equivalent to the direct current value that would be required to get the same heating effect. For example, if we applied 120 V AC RMS to a resistive heating element it would heat up by exactly the same amount as if we had applied 120V DC.

cjackcjackOGR Forum Member DIGITAL SUBSCRIBER

The true RMS meter measures the effective value of the voltage. And 18 Vrms is the answer. the somewhat inexpensive true rms meters use some form of analog method to calculate the rms such as rectifying the wave, finding the average with a capacitor and then calculating the root with an analog log converter. That gets you to an accuracy of maybe a percent or two. The expensive meters can achieve a tenth of a percent using DSP and a digital algorithm.

Either way, the answer is 18 Volts.

cjackcjackOGR Forum Member DIGITAL SUBSCRIBER
Originally Posted by BigBoy4014:
 
Originally Posted by cjack:

interesting...I'm wondering what do the ZWL meters say?

Those meters are so small, its readings may be hard to be accurate to with in a volt or two???

So much for that feature...probably why they didn't use digital meters.

BigBoy4014BigBoy4014OGR Forum Member
Originally Posted by cjack:
Originally Posted by BigBoy4014:
 
Originally Posted by cjack:

interesting...I'm wondering what do the ZWL meters say?

Those meters are so small, its readings may be hard to be accurate to with in a volt or two???

So much for that feature...probably why they didn't use digital meters.

My thoughts exactly...digital meters, done properly, will show the truth

BrooksmjBrooksmjOGR Forum Member

Thanks to everyone who has responded to my ZWL voltage post, particularly Chuck who provided some clarification.  I hope I did not confuse anyone by stating the standard calculation uses .707 of pk.  What I meant by that was that standard voltmeters that are not True RMS meters, do a calculation based on a pure sine wave that produces a result that approximates .707 of pk.  It became apparent to me when I saw the non sinusoidal waveform that some other sort of calculation would be necessary to generate a value that more closely matches the effective value (RMS) of the wave that was produced by the ZWL.

The meters on my ZWL seem to match that of my Radio Shack True RMS meter as well as can be expected due to their small size.

BrooksmjBrooksmjOGR Forum Member

I forgot to mention in my last reply how much I like the ZWL.  I think I like it as much for it's form as well as it's function.  Since I am an old guy I really like the Lionel ergonomics.  The equipment seems more like train gear then computer gear.  That being said I purchased both systems, but I prefer operating the Lionel gear.  The MTH transformer uses digital displays, but I really like the analog meters.  Also, the ZWL has more flexible output voltages. 

MW Mike WyattOGR Forum Member DIGITAL SUBSCRIBER

OK- VERY basic question here.  I am not understanding all this.

I just got a ZW-L and the max voltage I read on my (admittedly) meager multi-meter is about 15.8.  And the old ZW's I have will put out 20 v on the same multi-meter.

LionChief Plus locomotives are supposed to like 18 volts.   Does this mean I am "starving" them running 15.8??  Or am I too high??   Using .707 then my 15.8 is  approx. 22.3 RMS.  

 

TedWTedWOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER
Mike Wyatt posted:

OK- VERY basic question here.  I am not understanding all this.

I just got a ZW-L and the max voltage I read on my (admittedly) meager multi-meter is about 15.8.  And the old ZW's I have will put out 20 v on the same multi-meter.

LionChief Plus locomotives are supposed to like 18 volts.   Does this mean I am "starving" them running 15.8??  Or am I too high??   Using .707 then my 15.8 is  approx. 22.3 RMS.  

 

Here’s another recent thread that discusses the facts about measuring the ZWL voltage accurately.  It may help. 

ZWL output volatage

DG Dave 69 GTELOGR Forum Member DIGITAL SUBSCRIBER
@Brooksmj posted:

I am posting this topic to perhaps save someone out there some stress and worry...

So, the moral of the story is don't be fooled by your regular voltmeter when measuring the ZWL voltages.  Use a TRUE RMS meter and you can then sleep at night again without worrying that you might have to send your expensive new transformer back.

Thank you Mike. This is an old post over 8 years old and I certainly hope you are doing well. This post just saved me a major inconvenience as I have an RMA into Lionel to return my ZWL because it only appears to put out 16 volts at the posts. I have only basic electrical knowledge and only assumed that the reading I was getting on my $20 multimeter was accurate. Now after all this time Lionel technical support knows or should know of this discrepancy and could have informed on the front end the reading was due to my multimeter not being the right type. Thanks again Mike. Yanking this thing out, packing it up, shipping it out, putting it all through that for nothing and then waiting 2 months for it to be returned with a cursory note that Lionel repair could not find anything wrong was avoided. Thanks. I think I have a friend that would have an RMS meter and I'll barrow it.

Last edited by Rich Melvin
DG Dave 69 GTELOGR Forum Member DIGITAL SUBSCRIBER
@gunrunnerjohn posted:

No need to borrow anything, True-RMS meters can be had for reasonable bucks nowadays.

Well that's true but I'd rather borrow something, then spend money on something I will probably only use once. I'm a good barrower and always return what I borrow in a short period of time.

I also want to say how much I love this forum. You can always find your answers here no matter how obscure the question.

Last edited by Dave 69 GTEL
MH Mellow Hudson MikeOGR Forum Member DIGITAL SUBSCRIBER
@Dave 69 GTEL posted:

Well that's true but I'd rather borrow something, then spend money on something I will probably only use once..

Dave,

Many, many, many of us now use 'modern' transformers, which as a group have been with us for 50 years now.  Almost all of them put out out a non-standard waveform unless they're cranked up to 100%.

Given this most of us should be measuring the AC on our layouts with a True RMS meter every time.

Will you really only use a True RMS meter once, especially since they're now quite a bit cheaper than they once were, and they help you to make better decisions?

Mike

Last edited by Mellow Hudson Mike
DG Dave 69 GTELOGR Forum Member DIGITAL SUBSCRIBER
@Mellow Hudson Mike posted:

Dave,

Many, many, many of us now use 'modern' transformers, which as a group have been with us for 50 years now.  Almost all of them put out out a non-standard waveform unless they're cranked up to 100%.

Given this most of us should be measuring the AC on our layouts with a True RMS meter every time.

Will you really only use a True RMS meter once, especially since they're now quite a bit cheaper than they once were, and they help you to make better decisions?

Mike

You're probably right. I just don't know anything about them. I'll check a hardware store next time I'm there or if I'm in the whereabouts of an electrical supply and see how much they cost.

DG Dave 69 GTELOGR Forum Member DIGITAL SUBSCRIBER

I got the TRMS multimeter today. Made in China with instructions written in China which made no sense. I finally figured it out after disassembling the thing just to put batteries in when I actually only needed to remove one screw to remove the recalcitrant battery cover. I checked the ZW-L transformer outputs and by golly it was actually putting out 18.7 volts AC. The voltmeters on it were correct! I'm not sending it back to Lionel thanks to this. What a bunch of @# %&!@.

DG Dave 69 GTELOGR Forum Member DIGITAL SUBSCRIBER
@cjack posted:

Hi Rich,

You obviously don’t have OCD like some of us.

Precisely, however you also wonder if you're not getting the full power advertised could your trains be a little more responsive, could smoke units chuff out smoke a little better if it were and are you getting your moneys worth? Now its led to me learning about TRMS multimeters and having one of these should help me build on my layout.

Last edited by Dave 69 GTEL

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