Enquiry about Damaged Kato power pack / Tomix pick up wheels

[KenS]

Hi Ken,

 

I've never heard of this form of output called "pulse" power.

 

All true statements: there are specific terms with specific meanings.  However, I think the reality is less than you assume.  I have an MRC pack (c. 1970's) that creates "pulsed power" according to its manufacturer, and yet it's just doing half-wave rectification. Marketing and Technical terminology sometimes diverge, and manufacturers will try to give the impression they're doing something sophisticated even if they aren't.  I applaud Kato for not calling their packs "pulsed", although they could.

 

In a technical sense, "pulsed" just means "not smoothed". It's not actually wrong for a manufacturer to use that term for an unsophisticated form of non-smoothed power.  And the effect on the motor will mostly be the same.  Where more complex systems have an advantage is that they can cut the level of pulsing at higher voltages (my c. 1990 MRC pack with "pulsed power" does just that) where it isn't needed, to provide more power for pulling heavy loads.

 

I don't know if Westcott's observations would still be true today in detail, although they are in the broad sense: that's what "supersonic" DCC is all about.  The main issue is to saturate the motor windings and create a sustained magnetic field when the voltage is too low, or the pulses too brief, to do so. Doing that depends on the impedance of the motor's coils, which is going to vary with the motor design.  For the typical Kato motor, I measured the impedance last year and derived a minimum frequency of around 12 kHz, so the typical 15 kHz "supersonic" decoder will do that just fine while AC-derived frequencies (60 or 120 Hz) will not.  I have not, however, seen a DC power pack that does the same thing, perhaps because they mix their pulses with some amount of constant DC (which a true PWM output like DCC does not).

 

Even my c. 2010 MRC Tech 4 220, while generating synthetic semi-square waves, is actually still doing them at line current frequency.  I have not investigated more complex hobbyist-built supplies like the TAT throttles though. And I need to re-examine my packs with my new oscilloscope at some point, just in case I overlooked anything interesting due to the limitations of the old one.

 

Good point about the potentiometer current issue with modern N-scale.  I'd only used mine with N-scale trains on a test track, where I wasn't trying for sophisticated control and hadn't noticed that (it will produce slow running, but probably not realistically slow speeds). I avoided using the pack for modern trains after I had some problems with it that made me concerned that its half-wave approach might be harmful.  I'll add a note about that to my page on throttles.

 

I like Kato's control as well.  That's where most modern DCC controllers really fall down: they think just because they're digital they can get away with buttons like a TV volume control. Ugh!  Try switching from 10 to 60 quickly on one of those. The use of smartphone touch screens is something of an improvement, and none are as prototypical as something like the Tomix pack with a level throttle, but I like smoothly operating knobs for fine control purposes.

[KenS]

Wow KenS! 

 

You must have some electrical training! That was some serious electrical diagram! 

 

I can't do so well, in fact my electrical diagram-ing sucks and my physics teacher hates me... 

 

Actually, I'm self-taught on the electronics. Which is sometimes a problem. I started out building my first solder-it-together kit around age 16, which was a 5V DC power supply for playing with electronic circuits.  I read a bunch of books I picked up at the local Radio Shack store to get the basics of resistors/capacitors/diodes down, but never really grasped transistors at the time.

 

I had a little exposure in college, but that was mostly at the logic-gate level (in a comp-sci computer architecture course), which is good for understanding what digital circuits do, but doesn't explain anything about how they do it.  That's also when a friend showed me the basics of using an oscilloscope (I think I also used one in a couple of physics-class labs, but the teaching assistant did all the setup work).

 

More recently, as I started getting interested in model railroad controls and accessories a few years ago, I've just been doing a lot of online reading. I still make mistakes (sometimes major ones) due to my lack of formal training, and I've gone off on some real tangents at times.

 

If you're interested in this stuff, I encourage you to build a few store-bought solder-it-together kits and read a basic introduction textbook for hobbyists.  That's a really good way to get a feel for how real circuits work. With that for a foundation, it will be easier to learn on your own (via google, etc). Playing with Arduinos (beyond just driving a few LEDs) has also been a  real learning experience for me.

[brill27mcb]

Yes, when I was younger I was disappointed at the way the old MRC power packs behaved. I would try to start the train smoothly on "pulse" power (half-wave), then throw the switch to "DC" (full-wave) to run after starting up. Of course, the average voltage jumped up and the transition was not acceptable, so you had to choose one mode of the other and then stick with it.

 

Rich K.

 

All true statements: there are specific terms with specific meanings.  However, I think the reality is less than you assume.  I have an MRC pack (c. 1970's) that creates "pulsed power" according to its manufacturer, and yet it's just doing half-wave rectification. Marketing and Technical terminology sometimes diverge, and manufacturers will try to give the impression they're doing something sophisticated even if they aren't.  I applaud Kato for not calling their packs "pulsed", although they could.