RailPro > RailPro Specific Help & Discussion
MOTOR FULL LOAD CURRENT
Dean:
With new locomotives, I set the full load current using the automatic mode. Then after running my break-in routine, I measure the full load current again. Usually, there is a drop in the full load current.
Running a four or five engine consist pulling 30 heavy cars, ( 8 oz+ each ) I watch the couplers. The couplers on the locomotives stay tight, going up or downhill.
My break in procedure:
The main thing you are trying to accomplish during a break in of a DC motor is to seat the brushes and polish the commutator.
The armature ( the entire rotating part of the motor including the commutator) moves back and forth in the housing as the speed and load changes.
Getting the brushes to seat is pretty straightforward. Run the engine at varying speeds in both directions for about 20 minutes each direction.
Getting the proper polish takes current passing from the brushes to the commutator and running unloaded doesn't supply enough current. After running light as above, I attach a coal car to the engine that is half full of lead shot. This gets the same 20-minute treatment as the engine running light.
I checked the current draw of some Kato powered engines by placing my finger in front of the engine to prevent it from moving and ran it at full speed for a few seconds. The wheels were allowed to spin on the track. New, out of the box, most engines drew 270ma to 310ma. After break-in, they would draw 220ma to 260ma. Of course, the gearboxes and other running gear also got some break-in time too. But with Delrin plastic in the gearboxes and running gear, I don't think they made much difference.
[ I was an electrician in a rolling mill for 35 years. Over 90% of the motors in the plant were DC. My break in procedure is based on my experience working on these DC motors. ]
G8B4Life:
Going to do a bit of a thread hijack here, but it is relevant to the discussion.
After reading this topic I decided to look at what the Patent had to say about the load sharing function, which is very little with only a little bit of information on one part of the logic. You can easily look it up if you want, I won't put it here as it's not the point of my post.
What I did read which I found strange was the way the modules control the motor. We all know the DCC waveform is square wave right? I've never put an oscilloscope on anything let alone a DCC decoders motor output but I've always assumed that that would also be square wave as well, all the PWM motor control that I've read about is all square wave. Well it appears that Ring has done it differently. From the Patent:
"wherein at least one control module varies a voltage on a motor of a respective motor powered rail vehicle in accordance with a periodic wave shape of a subsonic type between about 2 and 20 Hz with an approximate triangular shape"
What would be the benefit of driving a motor with a triangular waveform (disregard the word approximate for this question)? From what I can gather from reading the above it looks like it's easier to "set" the average voltage that the motor sees without having to drive the output transistors at supersonic speed like modern DCC decoders have to but that's the only thing I can think of.
- Tim
Alan:
--- Quote from: G8B4Life on August 01, 2018, 09:30:35 AM ---... What would be the benefit of driving a motor with a triangular waveform (disregard the word approximate for this question)? From what I can gather from reading the above it looks like it's easier to "set" the average voltage that the motor sees without having to drive the output transistors at supersonic speed like modern DCC decoders have to but that's the only thing I can think of.
- Tim
--- End quote ---
Fewer parts count in the module. The triangular (dual log slope) waveform is the natural output from an oscillator due to timing network charge and decay of C. Wave shaping to a neat square wave requires several more components i.e. triggers. The additional wave shaping provides little benefit to motor control because of the motor's rotating mass relative to the signal frequency. The motor couldn't respond accurately to the sharp rise time of a square wave anyway so a slow rise/fall wave works just as well. There is a power loss using a triangular waveform versus a square wave however that is easily compensated with higher frequency.
Voltage across C over time:
To further hijack the thread, this subject will come into focus when I post my DCC-simulated power supply circuit for Jacob.
KPack:
I'm so confused, lol.
Alan:
--- Quote from: KPack on August 01, 2018, 10:21:14 AM ---I'm so confused, lol.
--- End quote ---
That's why the magic is always kept inside the box out of view! ;D
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