DCC on address "0" and coreless motors

[mmagliaro]

I am branching this off from a question that came up in the other thread on a brass loco being remotored...


Is it true that running DCC on address "0" will kill a plain-DC engine with a coreless motor?   Have you actually seen this happen, and was it to the "serious" corelss motors like Maxon or Faulhaber?

I ask because I have wondered about this and asked about it, and never get a definitive answer from anybody
with a DCC system.  I don't have one, and if I ever want to put one of my straight-DC coreless-powered beautires
onto a DCC track on address 0, I don't want to burn up the motor.

Is the issue that the DCC booster is putting high-amplitude square wave pulses onto the rails on address 0,
at high frequency, so that the decoder doesn't see it, to run the plain-jane DC motors?  Is that what it
actually does on address 0?

Thanks.

[Ian MacMillan]

From what I have been told/read is that the high current and square pulse pretty much "hammers" to death the coreless motors. If you put a 3-6 volt lamp inline with the motor it reportedly prevent damage.

[wcfn100]

I don't know if this contributes or not.

Going back a few years, you had to worry about any/every decoder address 0 or otherwise.  The issue was indeed the wave that was being put out.  Slowly decoder manufacturers started making higher frequency decoders under different names like 'super sonic' or 'silent drive' or whatever and those decoders would be safe for coreless motors.

I haven't done much DCC lately, but it looked like most newer decoders were going to high frequency.  I would think that as long as they operate this way on address 0, they should be fine.

But that's just an opinion.

Jason

[C855B]

It's not a factor of decoders - we're talking about running a DC motor on address 0, which modifies the DCC AC waveform to be biased in one direction. In other words, the DC motor is connected directly to the DCC power/signal bus (a/k/a "rails"  ), with the DCC supplying a modified square wave.

I do believe - Pete, our resident EE may have to correct me on this - the problem is that the coreless motor's lack of iron to momentarily store the flux field reduces its characteristic impedance so much that the motor tries to reverse on every negative pulse, rather than resisting the reversal (known as "reluctance") by carrying forward enough of the collapsing flux field from the previous positive square wave. So, Ian has it right, the modified AC will "hammer" the motor because it has almost no ability to conserve flux momentum.

Anyway, that's my understanding of the physics. It will probably run initially, but may heat up very, very quickly.

[davefoxx]

...the modified AC will "hammer" the motor because it has almost no ability to conserve flux momentum.

Have you tried a flux capacitor to conserve the flux momentum?   

[C855B]

Not yet, but good idea. I'll check with Digitrax for a booster good for 1.21 gigawatts. That way if I run a loco at 88 smph, it'll revert back to a vertical can motor with self-destructing brushes.

[mmyers]

My understanding is the "hammering" that Ian described causes the motor to overheat and burn up (because it has no iron to help dissipate the heat). Same was true with older "low Frequency" DCC Decoders. Today's  high frequency decoders will work with coreless motors.

Martin Myers

[wcfn100]

My understanding is the "hammering" that Ian described causes the motor to overheat and burn up (because it has no iron to help dissipate the heat). Same was true with older "low Frequency" DCC Decoders. Today's  high frequency decoders will work with coreless motors.

Martin Myers

That's where I was going with my post, but like Mike pointed out, this has nothing to do with decoders.  This is the DCC voltage/signal going straight to the motor.

Jason

[peteski]

I agree with the first part of mmyers' statement (as we are talking about a coreless motor being directly powered by the DCC signal from the rails).  Coreless motors use much finer wire than iron armature motors. Also since there is no iron armature, there is nothing to dissipate the heat generated when the DCC (AC) signal passes through the windings.  The full amplitude DCC (AC) signal is always present at the motor, so it heats it up.  You could compare that to having a DC throttle cranked wide open while flipping the direction switch many times a second! The direction is switched so fast that the motor armature doesn't have time to rotate. it just sits there, under full power, twitching back and forth.

I personally never experienced failures of any DC motor when left on DCC powered track but I have observed that the standard Kato and Atlas motors (with iron armatures) got quite warm after a short period of time (just sitting on the track, buzzing).  They were warm enough that you could feel the warmth right through the locomotive's shell.  I have never attempted to place a DC loco with a coreless motor on a DCC powered track (and I don't plan to). 

AFAIK, most manufacturers of DCC systems either moved removed the address 0 functionality from their systems or they highly discourage from using it.  That should give you a hint not to consider using it.  After all, there really is no reason to do that (for extended periods of time).  DCC decoders can be had for around $15 and those decoders can be configured so the loco still works on DC too.  Unless you are making a model so small that you can't fit a decoder in it. 

[robert3985]

Although I'm thoroughly DCC-ized, I have not yet installed decoders into every engine I have. It's just a "time" thing. 

My son is planning on installing Tsunami's in his Kato GS-4's, but neither he nor I have had time for what is a pretty complex decoder install.

At the Evanston show a couple of months ago, he would run his Kato GS-4's on address "00" (I have Digitrax) and then park them on the programming track and switch it to "off".  His engines got warm when running, but not to the point of melting plastic or malfunctioning, and he ran 'em often during the show for several hours at a time.  Of course, sitting on a dead track let them cool down without taking them off the layout.

So, even though I did not plan on the programming track being something used to park non-DCC engines, it is certainly handy for that.

Here's my son Ben running Broadway Ltd. E7's in front of a Daylight consist with the GS-4's parked on the programming track.


I have also recently read on various DCC manufacturer's websites that their new decoders will run coreless motors without them getting excessively hot.  I interpret this to mean that, in the past, coreless motors were also overheating when equipped with a decoder, and were not being run at address "00".

That's good news!

Cheers!
Bob Gilmore