Now This Is Weird - A Major MRR Supplier Dissin' Another on Their Website

[peteski]

Btw Max...

The testing you did...

Was any of it under load?

See https://www.therailwire.net/forum/index.php?topic=44120.msg652909#msg652909

The oscilloscope photo also mentions a 50mA load.

[mmagliaro]

Btw Max...

The testing you did...

Was any of it under load?

Heh... people have asked this before.   I just put a grain-of-wheat lamp load of about 60 ma on there.
My thinking was that worst-case, a decoder would see the maximum the power pack could put out *before* the motor turned on.
So there would be very little load on the power pack during those first few moments when you turn up the speed knob.

I did test the 1300 at about 400 ma (close to its full capacity), as I recall, and the peaks drop to about 23v, I think.  It's been a while.

[jagged ben]

Interesting.
Although I didn't say so, I had in mind a motor load.  It would be interesting to see if a high motor load had any visible effect on the waveform.  I'm guessing not, but it still would be interesting.   

[Maletrain]

For what it is worth, power delivered by a non-steady voltage and current source (whether typical "AC" of other steady or unsteady wave forms) is really a sum (mathematically, an "integral") over time of the product of the instantaneous current times the instantaneous voltage.  Those two waves may or may not be peaking at the same moment.  Inductive loads like motors tend to make the current peak lag the voltage peak in time.  On the other hand, capacitive loads (like capacitors, of course) tend to make the current peak proceed the voltage peak.  The electric power industry uses a variable "power factor" to  account for the difference between the product of RMS values for volts and amps to get watts.  The power industry will also use large capacitors to try to get the current peak closer to the voltage peak, as do some equipment manufacturers that use large motors, such as heat pump systems.

Remember that the heat produced in something like a wire is a function of the current going through it and the resistance of the wire.  So, getting the current down while getting the same amount of power to the actual device helps reduce losses.

The same concept applies to square waves as well as sine waves.  Inductors tend to make the current lag the voltage and capacitors tend to make it precede the voltage.  That is what is related to back-EMF.

[mmagliaro]

Interesting.
Although I didn't say so, I had in mind a motor load.  It would be interesting to see if a high motor load had any visible effect on the waveform.  I'm guessing not, but it still would be interesting.   

When I loaded down the 1300, I do remember that I just used some big power resistors, not a motor.  But the waveform did not change at all (only the maximum amplitude, with dropped a little to about 23v as I recall).  And even so, if having the load be a motor changed the waveform and somehow prevented the decoder from failing, I wouldn't consider that to be meaningful.  After all, you could put a decoder in a passenger car and have it control nothing but some LEDs

[peteski]

When I loaded down the 1300, I do remember that I just used some big power resistors, not a motor.  But the waveform did not change at all (only the maximum amplitude, with dropped a little to about 23v as I recall).  And even so, if having the load be a motor changed the waveform and somehow prevented the decoder from failing, I wouldn't consider that to be meaningful.  After all, you could put a decoder in a passenger car and have it control nothing but some LEDs

While using a motor for the throttle's load migh prove interesting (to see its effect on the waveform), it is sort of a moot point for what we are discussing here.  IN our case, the inductive-load motor is separated from the track power by at least a bridge rectifier and H-Bridge transistors on the decoder.  So any effects of the inductive motor load will not propagate back to the track power.

Also using a motor as a test load of the throttle might not be optimal. Free-running motor draws very little current. The motor would have to be under load to provide any appreciable current draw from the throttle.

[jagged ben]

While using a motor for the throttle's load migh prove interesting (to see its effect on the waveform), it is sort of a moot point for what we are discussing here.  IN our case, the inductive-load motor is separated from the track power by at least a bridge rectifier and H-Bridge transistors on the decoder.  So any effects of the inductive motor load will not propagate back to the track power.

Also using a motor as a test load of the throttle might not be optimal. Free-running motor draws very little current. The motor would have to be under load to provide any appreciable current draw from the throttle.

Good points.

I think I actually had two ideas in asking about load.

One was whether the Railpower was doing anything unexpected at high load which might damage a sound decoder.  I think that Max's testimony about that, along with your point about the decoder rectifier, pretty much debunks such a notion.

The second idea was mere curiosity at whether we see any meaningful distortion or power factor with a loaded DC motor and no decoder involved.

[peteski]

. . .
The second idea was mere curiosity at whether we see any meaningful distortion or power factor with a loaded DC motor and no decoder involved.

I would also be curious to see what the waveform looks like under those conditions.

[mmagliaro]

I would also be curious to see what the waveform looks like under those conditions.

I would have to drag out my 1300 test subject, unsolder my mods, hook it to the scope, and then
load down a motor hooked onto the 1300 (could just grab the shaft and squeeze and watch an ammeter).
The desire to know...
I hate scientists... 

[jagged ben]

I would have to drag out my 1300 test subject, unsolder my mods, hook it to the scope, and then
load down a motor hooked onto the 1300 (could just grab the shaft and squeeze and watch an ammeter).
The desire to know...
I hate scientists... 

Not asking you to do more, Max! 

[peteski]

Not asking you to do more, Max! 

Hey, speak for yourself!
Just kidding Max - we are not twisting your arm here - just your pinky.  You have lots of other projects on your plate.  No need to dig this one up again.

[wvgca]

Are any other decoders [besides the ESU] susceptible to the slighly higher peak voltages generated by the MRC power supply being discussed ?

[peteski]

Are any other decoders [besides the ESU] susceptible to the slighly higher peak voltages generated by the MRC power supply being discussed ?

Not that I know of. I think this thing sort of blew up becuase Rapido made it a point to officially finger out a specific power pack.  I also think that the percentage of modelers running (any brand) sound decoder using a vintage-design power pack is very, very small.

To be honest, running sound decoders on DC sucks.

[wvgca]

So far it's ONE brand of decoder, with ONE model of a DC supply ....
that's it ??

[peteski]

So far it's ONE brand of decoder, with ONE model of a DC supply ....
that's it ??

That's my understanding.  The whole thing is kind of weird if you ask me.  But I only frequent this forum, so I don't have a very big picture of what is going on in the N scale world.