RailPro > RailPro Specific Help & Discussion
MOTOR FULL LOAD CURRENT
Alan:
--- Quote from: G8B4Life on August 01, 2018, 10:41:09 PM ---... With the dual log slope waveform, how much harder is it to work out what the average voltage the motor sees is compared to a square waveform (which is easy)? Given the "1000 speed steps" we have the 2 to 20Hz duty cycle mentioned in the Patent doesn't sound like it'd give that.
- Tim
--- End quote ---
Finally, a use for that Integral Calculus class you took at university years ago!
Close enough to a sine wave to use RMS or 0.707.
Why do you think we can't have 1000 steps? Cycles per second don't have to be integers. I would lay odds it is actually 1024 speed steps since it is a digital system.
G8B4Life:
--- Quote from: Alan on August 02, 2018, 07:27:33 AM ---Finally, a use for that Integral Calculus class you took at university years ago!
--- End quote ---
You have the wrong idea of how far I made it through schooling.
--- Quote ---Why do you think we can't have 1000 steps? Cycles per second don't have to be integers. I would lay odds it is actually 1024 speed steps since it is a digital system.
--- End quote ---
I'm not saying that I think we can't have 1000 speed steps. I was saying that with my very limited knowledge of PWM the face value of the information presented to me made it sound like it was not possible given the duty cycle range, not that it wasn't possible. Now that I know that cycles per second doesn't have to be an integer (I've never seen any reference to it being anything but an integer in any PWM related information I've ever looked at before, it's always shown and written as whole numbers) it now makes sense that there can be 1000 speed steps within the given cycles per second range. In my effort to understand this I've probably got a bunch of other things wrong so I'll just stop now.
- Tim
Alan:
Neither frequency nor pulse width are limited to integer values. Either or both can be real numbers.
Think of it this way... FM radio signals are similar to PWM ( I said similar :) ) except sine instead of square. The FM signal is modulated to represent the audio spectrum (or at least some of it). In this case there is a near infinite number of possible frequency divisions. It is just a matter of how many places to the right of the decimal point you can measure.
Clearly this is the case with RP. As you note, with a bandwidth of only 18Hz the "steps" must be real numbers else with integers we would be limited to 18 speed steps. Which BTW sounds eerily similar to the old 14 step DCC.
As this conversation drifts deep into the weeds it is worth mentioning there are two controlling parameters to square wave PWM when also used to convey control signals (DCC track) - pulse frequency and pulse width (percentage). Obviously at 0% and 100% pulse width there is 0 frequency thus no control signal conveyance. But for everything in between the pulse width conveys digital info while the frequency and width combined determine the total power delivered over a given time period. At the motor output of a module we have no need to convey information so frequency and/or pulse width modulation will do just fine.
Tom:
I am happy to learn that manually setting the MFLC to anything will not harm an HO locomotive motor.
I should say I have had only a very few problems when consisting multiple locomotives, mainly uncoupling in certain circumstances due to one pulling or pushing slightly harder than the other.
Having said this, it is still demonstrable that linked but separated locomotives, mine anyway, will not stay the same distance apart by using the automatic MFLC. I got all locomotives to run close to the same speed, that of about a 45-50 MPH scale speed, by trial and error starting with 3 locomotives and manually adjusting the closest two and then getting each additional locomotive in sync with one of those.
Having accomplished the above it is still noticeable that some locomotives move sooner and start faster than the others and travel at slightly different speeds at different throttle selections. Overall I think they run more smoothly together, but would not want to do what I did with too many locomotives.
Most of the complex electrical comments in this thread are beyond my electrical level of competence, which is close to zero. I still do not fully understand the differences between DC, DCC (never used DCC) and PWR-56. Can someone provide a short lucid tutorial in laymen’s terms: from above comments, a PWR-56 is DC current, DCC is AC current, and Ring modules will run on both DC and AC powered track. But do not run ring modules using a DC power pack with the throttle set at full speed. Never mind for now the signals running through the tracks for DCC control.
Alan:
A picture is worth a thousand words, right? Perhaps this illustration from an old thread will help you.
The top row illustration is a conventional power pack. Notice the constantly fluctuating bumpy output. That is bad for modules. Hence the recommendation not to use power packs with LMs.
The middle row illustrations are DCC at various points in the current path. Left = signal on DCC powered track, Center = rectification inside the module, Right = smoothing inside the module.
The bottom row illustration is the output of a PWR.
Yes, the horizontal axis for zero volts is missing on the last DCC graph. My bad.
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