R2LC Smoke Unit Output Voltage

John,

Your technical perspective has value. Yes, when you put the smoke output on a scope and measure the waveform you see what is being sent out of the pin out.

Now, take your technical perspective and explain it to the 1000's of operators in the marketplace who have very "loose" understanding of differences between AC and DC current, let alone how volts, amps and wattage works.

Sure, you can present the technical info to the masses, but in the long run, in my experience, it only serves to confuse the heck out of the user. Yes, this industry has a lot of technically savvy participants, but most, if not the vast majority of them simply do not understand the complexities involved in what really happens inside their trains. Furthermore, explaining the technical side in an easy to understand way is what attracts folks to the hobby.

Having spent the better part of 10 years in the aftermarket upgrade business before coming on board at Lionel and interacting with thousands of users I learned that folks first and foremost seem to know what their trains do, out of the box. Some want to know what they "can do" and even some (albeit a very small percentage) want to know exactly how it does it. We can confuse the vast majority with all kinds of technical jargon and scope readings (I typically leave this for engineers! LOL) or we can explain it in relative layman terms that are easy to understand and the customer feels good walking away, having a basic understanding of how something works.

If you go back and view the videos we have produced within Lionel the focus is on educating the user. I do my best to leave the technical jargon out, except when absolutely necessary. Ask the consumer who has watched the video if they learned anything, most will say they have, because the information is presented in an easy to understand presentation of the facts with familiar terms that they understand (or can at least relate to). That is the true goal.

We could take the "how" to a whole new level using scopes, graphical voltmeters, etc. but most of the consumer base does not have access to these types of devices. As such catering to this genre of consumer, while perhaps worthwhile in your mind, is not the target audience or expertise of the larger audience we are trying to reach. If you want the technical side of the "how" I can almost assure you my videos will be of little help to you. However, if you like the hobby and enjoy your products and want a basic (or in some cases, a more thorough) understanding of the "how" (or as I like to call it, the "magic") of what our products do; to increase your overall enjoyment of the hobby, then yes, our videos will provide that to you, in a manner in which the vast majority of folks understand.

OK, back to the topic of the R2LC output. If you measure the voltage with a digital or analog meter (specifically pins 5/6 for AC hot and pins 3/4 for ground) you will read 12VAC. While holding down 9 you will see 14VAC (this is providing you have used auxiliary code 8 in programming and have 18VAC applied to the track). Which is a very simple way of determining whether the output of the R2LC is functional or has a problem. 98% of the folks who attended the training classes we conducted at Lionel do not have access to a scope, hence the reason the training was based solely on the use of a Fluke Model 179 Digital (True RMS) voltmeter. The wave form output serves very little value in the troubleshooting/repair world. A technician needs to know if it works or it doesn't. If it doesn't work at the output then replace it. If it does, then the problem is somewhere downstream and the R2LC can be passed over.

I am sure you will find all kinds of cool stuff on a scope regardless of whose electronics you scope, but almost everyone wants to fix the problem, not try to formulate why a wave form is done this way or that way. Personally I have no interest in the waveform. Does it work as intended or does it not? Can it be improved without rewriting code? These are the topics of my questions when troubleshooting a product or teaching a class, nothing to do with peak voltage, etc. (As I explained to every participant in our training classes; Lionel has people who make way more money than I do who understand what happens inside the PCB, my (our) world begins where all the magic terminates; the outputs of those PCB's.)

One more way to look at it; a new customer walks into a store looking to get started in a hobby (or an existing customer who wants to expand the functionality of their trains). Are they likely to bite if you start pulling out digital scopes and prodding pins all over the inside of the trains showing them what the waveform looks like? Or are they more likely to bite showing them what the product is capable of doing and helping them understand how to get the most out of all the features their products have to offer?

This is the logic I apply to my approach. I try to steer away from the "technical" whenever possible, when creating learning videos for our customers.

Thanks,

Mike Reagan

Lionel

Mike, I get your reply, and I don't have a problem with the approach. I don't always launch into an involved technical discussion for every issue either.

Let me point out that I made a pretty basic statement and was called wrong, which is what started the whole discussion, see below.  Remember, we were discussing swapping parts around in the thread, it wasn't a non-technical thread to begin with.  For an end user, this discussion of specific voltages and the like would clearly not be appropriate, I certainly agree with that.

I was then informed that I was wrong, which is clearly not the case.  I thought that was sufficient to answer the question, but when the information was challenged, I expanded the answer.  This is the original thread: https://ogrforum.ogaugerr.com/t...e-for-mth-smoke-unit

The main point I was actually trying to make is that the smoke unit puts out DC voltage and not AC in normal operation, which is important to know in some situations. 

Thanks for your clarification of how and why your statements don't match up with mine measurements.

John, Why do you call it DC voltage, because the bottom half is cut off?  From my reverse engineering of the original LCRUs and the R2LC, there was only a single diode that rectified AC to supply the VR for the micro controllers and chips.  Everything else was PWM AC moving through Motor TRIACs and Accessory TRIACS  which are the transistors needed for AC.  There is no bridge rectifier and capacitor circuit to produce a filtered DC

All the TMCC accessories return to Chassis AC ground.  G

I call it DC voltage because it is, it's simply pulsating DC, but there is no negative going part of the waveform.  It's not filtered DC, just raw rectified DC.  If you stick a single diode rectifier in series with the AC and your load, you get DC.  It's quite possible to generate DC using a triac and an AC input voltage, the smoke output can generate either positive or negative DC outputs, depending on programming.

The power in to the smoke triac appears to be direct from the track voltage, as the output of the smoke pin during boost is basically the track voltage minus the drop across the triac.  That's also why there is a little glitch at the zero crossing.  The normal half-wave output very close to the amplitude of the positive side of the track voltage input.

I didn't think to have two channels and show the track voltage next to the triac output, it would have been a good illustration.

"The first waveform is without boost, note that the peak voltage is around 22 volts.  Coincidentally, that happens to be the peak voltage that you'd get from a half-wave rectified 16 volts AC, 16 * 1.414 = 22.6 volts peak.  The second waveform is with the boost, and it represents the full transformer voltage of 16 volts RMS, or 45 volts peak-to-peak."

I guess it is DC from a pure definition stand point, because it is constant polarity.  But it really isn't rectification.  So it becomes confusing in my opinion.  In your statement above, regardless of rectification, the peak Voltage of an AC signal is about 1.414 x RMS value. 

Since the R2LC doesn't rectify the negative portion of the sine wave to positive, the average Voltage  is about .637 of the positive half peak voltage and probably reduced some by the period of no voltage.

It is interesting to me, because the Lionel uses a 27 ohm elements in the early TMCC engines with out AC REG.  So it gets about 12VAC, yet the MTH smoke unit would be getting Real DC voltage at a higher level and with a 16 ohm resistor until about 12-13 volts when it kicks up to 32ohms.  I wonder how the Lionel would do with a 16 ohm in the command mode.   G

Actually George, it's is pure rectification.  It's doing exactly what a diode would do in the same place in the circuit.   It's not filtered DC, but by any contemporary definition, it is indeed DC.  Given that it's exactly half of the waveform, the actual RMS value of the half-wave rectified power would be half of the full wave RMS value, in this case that would be about 8 volts RMS.

I think the 16 ohm resistor may be too much for the smoke triac, as it doesn't have any heatsink.  I know it's rated at 4 amps, but that's with a proper heatsink, it'll handle much less with no heatsink.  I've considered trying 16 ohms and bolting a small heatsink onto the triac to help with the power dissipation.  I'll bet that would be a smokin' combination.

John;

I had to jump in with just a quick comment.

I have used 16 ohm MTH heaters in a few Lionel smoke units with good results.

They smoke really well, but use up the fluid rather quickly.

So I now use 18 ohm resistors for most Lionel retrofits, and they seem to be a good compromise.

BTW, interesting discussion thus far.

Rod

Also, no heatsink needed on the triac. It gets fairly warm, but tolerable. None have burned out thus far.

Rod

I dont know about Mike's meter,but the one I have will read half wave pulsed DC as zero if put on the AC setting. It will read the DC RMS voltage if on the DC setting. You can sometimes use this method to see if a diode leaks backwards in a live circuit.  If I were troubleshooting the unit,I would think it was defective somehow as there would be no AC voltage component across a check point.

Pulsed DC is indeed DC current since it does not change polarity. I have to agree with John here.

Dale H

Just to be clear Dale, it is pure sine wave input from the track and the output is the sine wave top half of the input.  Pulsed DC starts to sound like PWM and is not very specific in it's description.  The pulse is on a 60hz sine wave form.  G

Well, it is only .5 amps if Voltage is 8 V RMS.  The MTH version handles about .75 amps before the second resistor kicks in and the DF Bridge Rectifier is only rated at 1 amp and it also supplies the smoke fan.  G

Good to know this has worked for Rod.  Rod where did you get the 18 ohms, from Lionel?  G

G

John's scope picture is very clear (top graph) .It looks like half waved pulsed DC. If measured with a multi meter on the AC setting it will read zero,not 12VAC. Unless I am reading the graph wrong and the bottom line is not on the zero line and somehow the  the zero axis is shifted. This can be done with various circuitry,but it does not look like PWM. A meter reads and distinguishes AC from DC and measures RMS,not the ripple. Some meters measure peak to show the amount of ripple.  DC current measured on the AC setting will read zero. and AC current measured on the DC setting will read zero.

Forget what anyone said here and do this little experiment yourself. Take any AC PW transformer,lets use a PWZW for instance. Take a common diode 1n4001 for example. wrap one diode terminal around one of the poles,the U for example. Set the voltage at 20 on the throttle so that 20 volts potential is between  A-U. Put your meter on the AC setting and measure voltage from  the remaining diode terminal to "A". On mine it reads zero volts AC. When measured with the DC setting it measures around 9 volts DC, about what you would expect. I use a cheap Craftsman $20 multi meter,not a Fluke.

I read the Forum here to learn something,not to be right or argue. But I do like to get correct information. There are only 2 explanations if Johns scope pictures reads 12 VAC with a meter. One,his scope is wrong. 2, The wave form is simply shifted so it intersects the zero axis and it is indeed AC current and does change in polarity. I guess a third possibility is Johns scope was not referenced from the test point outlets Mike described.  If this is the case then Mike is correct and there is not much need to get into it. I would like some clarification, that's all. We are not doing advanced electrical engineering here,this is 7th grade high school material.

Dale H

John's scope is not set incorrectly.   The zero is indeed at the bottom of the half-wave trace and centered on the AC waveform.

Using my old 1033 bench transformer, I connected a diode, a 620 ohm resistor for a load, and took some measurements with each on AC and DC.

I don't have an analog meter, but I did a little experiment with two different digital meters, one a Fluke 8012A True RMS model and one a Fluke 77 handheld that does not have True RMS for contrast.

I never get zero volts, but I know that some older meters have capacitive coupling for the AC ranges, perhaps that's what Dale sees.

These findings are consistent with what I see with the smoke triac doing half-wave rectification.

The first two photos are measuring directly across the 16 volts from the 1033 using the AC and DC settings of the bench meter.

AC Setting

DC Setting

The next two photos are the bench meter with True RMS measuring across the 620 ohm resistor in AC and then DC.

AC Setting

DC Setting

The final two photos are the handheld meter without True RMS measuring across the 620 ohm resistor in AC and then DC.

AC Setting

DC Setting

i have watched many of Mikes videos. I get the impression that he is wording it  for non tech people.  This frequently leads to things that may not be technically correct but describe the situation .  Don

Don, Mike actually said exactly that in his lengthy post above.  I have no argument with how Mike presents material, and he does an excellent job with the videos, and they're a great resource. 

This discussion grew out of an upgrade question and the question of exactly what you get out of the R2LC smoke output for various settings.  While sometimes, maybe even most of the time, you can speak in generalities, sometimes you need to get specific as to what is really happening.  It's always good to truly understand what is going on if you're making modifications to equipment.

So Dale, you didn't do so well in 7th grade? :-)  I clearly stated about 10 post up this is considered a DC output because of the constant polarity, but I was trying to be clearer with what the signal is.  Pulsed DC while a correct 7th grade definition, is not specific enough to describe what is going on.  As John pointed out you must have a meter issue as clearly the AC Voltage would be able to read an RMS average on the sine wave signature.

Having dived into these boards at a deeper level, it is important to recognize how their design difference effect how you can use other accessories.  Lionel's TMCC design is based on an un-rectified AC track input.  Yes some of the AC is rectified to produce a constant Voltage DC to run the processors, but all the accessories are controlled by TRIACs and use an AC input.  The fact that the Triacs may only pass half the sine wave which now makes it a DC signal is purely a design decision.  But the important factor for the users is the returns are tied to chassis AC common.

The fact that it is sine wave DC Pulse is significant, versus a DC input pulsed as an output.

MTH on the other hand takes the Track AC and immediately rectifies it to DC.  Everything from Processors to accessories driven off the board is using DC inputs.  Return one of those accessories to chassis ground and the board is toast.

All this gets back to mixing an matching of smoke units and choices of element resistance.  Obviously the half sine wave means less effective voltage in the command mode to power a smoke unit.  So a lower resistance may be a better smoker.

John, did you run this in conventional, I seem to remember in conventional the whole sine wave may have been passed.  Or is this the same whether in conventional or command.  G

G

I simply disagree. If measuring pulsed DC the meter should read zero on the AC setting since there is no change in polarity. On an 18 volt AC circuit in series with the diode, I get slightly less than 9 VDC and zero volts AC. If it measured an AC component,it would mean the diode was leaking backwards. So if I was troubleshooting a circuit I would think there was a component problem. So I think my El cheapo meter actually measures correctly. I guess it is just the way the different meters work. My Fluke crapped out many moons ago so I can not try it.

I do not understand the results John gets. The current changes polarity or it does not.  It can not be both DC and AC at the same time. So his meter is not reading correctly the way I see it.

If my meter worked like that I could never properly test a bridge rectifier in a circuit.Old selenium type rectifiers would leak badly this way, even new ones. In old amplifiers and other circuits I actually tested them this way.  It would confuse me if a test point said 12VAC on a schematic and the current is actually half waved pulsed DC.

Perhaps this is not made clear in a service manual, but it should be. I do not mess around with these boards a lot like you do. I enjoy reading your posts and have learned a lot.

Dale H

George, all tests were done in command mode.  It probably would be interesting to do a similar test in conventional mode, I may give that a stab.

All the meters I have, from the cheap harbor freight model to the Fluke bench meter read the half-wave DC signal as AC as I indicated.  I seriously doubt they're all broken.  Some inexpensive meters just use a diode to measure AC and feed that into the DC circuit.  If that's the case, flipping the leads on the half-wave rectified signal may give you a different reading.

You said:

I use a cheap Craftsman $20 multi meter,not a Fluke

I hope you're not actually suggesting that your cheap Sears meter is right, but my lab quality bench meter is wrong, that's just not logical.  Since all the other meters I checked (yes, all digital) get the same results, I'm pretty sure that's the accepted correct reading.  Remember, the meter is not seeing the DC bias, it's merely reacting to the apparent AC waveform it sees.

John

Your pictures prove the meter is wrong. How can the same sine wave be both DC and AC at the same time? Your scope graph says it is DC which contradicts your meter. It can be skewed one way or the other but if it changes polarity it is AC current. Please explain.

Dale H

Any way it is discussed here on another forum. I all depends what is meant by alternating current.

http://www.edaboard.com/thread64925.html

Dale H

Dale the meter doesn't know what the wave form or signal is.  There are many different methods for designing a meter, but it is assumed the wave form is AC sinusoid.  If it is a square ac or triangular ac the meter will give erroneous results as a different calibration factor would be needed.  Advanced meters may allow a selection of wave forms, but our cheap DVM assume a sinusoid for AC.

Same goes with pulsed DC.  The meter is actually looking for constant DC and can't necessarily read a PWM DC signal.

You seem to be implying that because the polarity doesn't change the meter disregards the signal.  There may be advanced meters with discrimination circuits that can measure that, but the basic Digital meter we use can see a half sine wave and provide a reading.  The calibration is off but it will provide a reading.  G

My meter is hardly advanced but it does discriminate between the 2. Please try the diode experiment I mentioned with the transformer. I would be interested to see what you get.

Dale H

Yikes, That wasn't very informative other that making my point about being more specific in what the wave form is.  G

George, I'm going to take a look in conventional when I get a chance, just out of curiosity.

OK John

I got out my digital meter. I get the results you get one way with the test leads. When I reverse test lead polarity I get zero. Does it work that way on your meter?

Dale H

Dale, I never thought to reverse the leads, but I'll give that a try.   Like I said, it will depend on the method used in the meter to measure the AC.

Well, I reversed the leads on three different meters, the two Fluke ones in this thread, and the little $10 meter from Harbor Freight that is the clamp-on and VOM.  All of them indicate about the same 8 volts AC for a half-wave DC signal with the leads in either orientation.

Weird

I guess results depend on the meter used. Thanks for your input.

Dale H

I'm guessing the method of developing the AC reading is why you see this.

Many (most?) DMMs use a DC sensor as its core metering mechanism.  In AC mode the input is rectified and DC is measured.  Some "economical" meters use what amounts to a single diode or half-wave rectification (rather than, say, a full-wave bridge) to convert AC to DC.  This assumes the AC input is symmetrical and sampling just one polarity is sufficient. This would explain why reversing the leads changed everything.

That was my take on it Stan.  I know that some AC panel meters just have a diode when you open them up.

Glad we got this one resolved.

John, Did you try the conventional output yet?  G

George, no, not yet.  I had a little issue with my TMCC test set, I'm resolving that first.

anything that does not cross over the 0 crossing line in a waveform is pulsating dc, if it crosses over the 0 line it is ac. 

The rms rating of ac is .707 times the peak and in peak to peak rating you add  .707+.707 or 1.414 times the peak to peak voltage.  Only if you are troubleshooting a circuit would this info be of any value to you and like mike said  99% do not care about this.  they just want it to work.

Don't think that is correct.  Otherwise you would have RMS Voltage higher than peak voltage.  It is .707 times the peak for a pure sine wave signal.  If  it is something else the factor is different for RMS value.  G

George, I tested in conventional, and indeed it just passes the track voltage directly through to the smoke unit.  The output varies in step with the input, only losing about 1/2 a volt or so going through the triac.

As far as RMS vs. peak voltage...  (RMS voltage * 1.414) * 2 = peak-to-peak voltage

While many "may not care", the fact is that the actual output power from the smoke circuit on the R2LC without boost is about half the track power.  You can argue the merits of expressing it in RMS, DC, or whatever, but if you have 18 volts RMS on the track, you get the heating value of 9 volts RMS out of the smoke unit with no boost.  With boost, it outputs the actual track power. Since we're driving a resistor, the actual power output is what is doing the work here, that is effectively 9 volts RMS.

If someone doesn't care, this is probably not the thread they should be reading.

Norm posted that info about six years ago, I wished I knew that is what you wanted.

Where were you when we were discussing all of this!   What book is that from?

That was from Norm Charbonneau.