So I've been using this unit to run my stuff, and have been very happy with it:

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...but since we're approaching that time of year for memories and nostalgia, I thought I'd break out this old thing and use it:

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Here's my question:

When I run one of my modern-era steamers with the MRC unit, it'll run at a given speed at approx 4-5 volts, and the smoke output is "okay": If I then hook up the AF unit and run the same engine at the same speed, it takes about 8-9 volts so the smoke output is much greater.

It seems to me that the engine would run almost twice as fast on almost twice the volts, but that's not the case. The only noticeable difference is in the smoke output. Is this because the old American Flyer unit is just inherently less efficient? 

I know in the over-all scheme of things, this doesn't matter; I'm just curious... 

Mark in Oregon

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I expect this is due to the different waveform of 'modern' transformers versus the traditional/post-war style.  Inside the engine the electronics 'see' the full output voltage even when the throttle is turned down.  I can get deep into the nuts and bolts of how it works if you want, but basically modern transformers work by turning on and off their full voltage, so the electronics inside a modern engine store more energy.  

Here's a little video I did a while back.  the grey meter shows the AC voltage on the track and the red meter shows the DC voltage that is present inside a modern engine from that track voltage. 

$ This is John Galt speaking.  $

“I swear by my life and my love of it that I will never live for the sake of another man, nor ask another man to live for mine.” 

 

 

JohnGaltLine posted:

I expect this is due to the different waveform of 'modern' transformers versus the traditional/post-war style.  Inside the engine the electronics 'see' the full output voltage even when the throttle is turned down.  I can get deep into the nuts and bolts of how it works if you want, but basically modern transformers work by turning on and off their full voltage, so the electronics inside a modern engine store more energy.  

Thank you John.

So if I'm understanding this correctly (and I'm probably not!) the circuitry for the motor (in this case it is a Dallee unit) reads the incoming current differently than from the (more or less) "direct" line from the track to the smoke unit...? 

Mark in Oregon

Sort of.  The RMS is the "average" voltage measured (Root Mean Squared, so not actually an average, but it gets the point across without getting in to the math.) So, taking a bunch of measurements over the duration of the sine waveform.  The peak is just the highest point of that wave form.  In a pure sine wave the peak is about 1.41 times higher than the RMS voltage.  

The newer transformer produces what is typically referred to on the forums here as a "chopped sine wave". though pulse width modulation is the common term used elsewhere.  here, rather than actually lowering the voltage the proper sine wave output is chopped off on one end for some duration.  Rather than measuring RMS or peak, the amount of the wave that is cut or not cut is called the Duty Cycle.  Changing the duty cycle  can mean that the peak voltage is much higher while the RMS voltage is lower than compared to a pure sine wave.  

The concept is a little easier to think about when used on DC power.  say you have a battery that provides 12 volts of DC.  if you take an RMS reading of the voltage it will be 12 volts (really 13.6 on say a car battery) which is easy to understand, as the battery constantly supplies 12 volts.  If we instead apply a 50% duty cycle, the battery is on for half the readings and off for the other half so our RMS meter ends up reading only 6 volts, even though the peak voltage is still 12 volts.  

How this effects the modern engines is that they all run on DC power internally, and in the electronics that convert AC from the track to DC for the electronics and can motors energy is stored at the peak voltage rather than the RMS voltage.  Because of this there is more stored voltage when using a modern transformer with a higher peak voltage then when using an older one.  This is also why early protosound(1) MTH engines don't work with modern transformers, they read the peak voltage from the track when determining track voltage, so only ever see full power and no power, rather than the low voltage needed to initialize the engine. Most modern engines have electronics that can recognize the desired throttle position from either power source, but there is more total power available for them to use when running on a modern transformer so the smoke will work better and the motors will run better at lower RMS voltages. 

$ This is John Galt speaking.  $

“I swear by my life and my love of it that I will never live for the sake of another man, nor ask another man to live for mine.” 

 

 

Strummer posted:

Thank you John.

So if I'm understanding this correctly (and I'm probably not!) the circuitry for the motor (in this case it is a Dallee unit) reads the incoming current differently than from the (more or less) "direct" line from the track to the smoke unit...? 

Mark in Oregon

More or less.  The modern transformer supplies a higher voltage at all times which gives the Dallee unit more power to draw from.  You can think of the difference in modern and old transformers something like driving a car.  the old transformers work by adjusting how far you press the gas pedal and holding it at your desired speed.  the new ones work by pushing the gas pedal all the way to the floor or taking your foot completely off, really fast.  

$ This is John Galt speaking.  $

“I swear by my life and my love of it that I will never live for the sake of another man, nor ask another man to live for mine.” 

 

 

Thanks again John. 

I tried another (Lionel) engine of similar vintage;  this one has its factory-installed "guts" (not a Dallee), and I got the same results...

So this newer MRC unit is capable of running an engine at say, 30 mph at only 4-5 volts, where it takes the old Flyer unit 8-9 volts to reach the same speed. The output of the smoke unit is dependent on "pure" voltage only, which would explain why the same engine will put out more smoke from the old Flyer transformer...have I got that right?

Is there any potential harm in running these "modern" engines with this older transformer? Do I run the risk of frying the smoke resistor(s)?

Mark in Oregon

Strummer posted:

Thanks again John. 

I tried another (Lionel) engine of similar vintage;  this one has its factory-installed "guts" (not a Dallee), and I got the same results...

So this newer MRC unit is capable of running an engine at say, 30 mph at only 4-5 volts, where it takes the old Flyer unit 8-9 volts to reach the same speed. The output of the smoke unit is dependent on "pure" voltage only, which would explain why the same engine will put out more smoke from the old Flyer transformer...have I got that right?

Is there any potential harm in running these "modern" engines with this older transformer? Do I run the risk of frying the smoke resistor(s)?

Mark in Oregon

With the smoke unit it depends on the design of the engine.  some apply track power directly to the resistor and others use rectified  power.  rectified ones will smoke better on a modern transformer, in theory.  

Before getting too deep down the rabbit hole, however, you might want to put an AC volt meter on the track with both transformers.  It's likely that the dial on the old AF transformer is just misaligned or never pointed to the true voltage in the first place, so while it may be pointing to, say, 10 volts, it might actually be putting 7 or 8 to the track.  

Last, no you won't cause any problems with either one. you may want to search "TVS" here on the forum, though for some added protection for your modern engines. 

$ This is John Galt speaking.  $

“I swear by my life and my love of it that I will never live for the sake of another man, nor ask another man to live for mine.” 

 

 

Strummer, the minimum voltage from a 15B transformer is 7V. The minimum from an MRC O27 is adjustable from 3V to 6V, default is 6V. When the deadman handle on the 15B is pushed down at an indicated zero on the MPH scale there is 7V output and each increase of an indicated 10 mph is about .9V. So for example 40mph is about 10.6V output. If the MRC is just turned on without manual adjustment the minimum track voltage is already 6V. It requires an accurate volt meter to read the voltages to compare the pure sine wave output of the 15B with the pulse width output of the MRC O27. 

Tom

I think that JGL covered it pretty well, but one additional suggestion is better circuit protection.  A modern circuit breaker or fuse for the old AF transformer.

Oh, and your voltmeter won't read the chopped waveform all that accurately, AAMOF, even my Fluke true-RMS meters don't do a decent job.

Okay, I think I got it now.

Just for laughs, I also tried a Lionel model "S" transformer, and got the same results as with the Flyer unit.  I do wish the MRC would help produce more smoke, but at least now I know why. 

I do appreciate all your comments and input... 

Mark in Oregon

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