Many thanks to all those that responded to my question... I'm amazed at the amount of technical info that is around... since I'm a retired Computer systems guy.. I really relish the tech info... thanks... I think I was confusing the issue of not running DC and DCC in the same layout vs running a dcc decoder loco on the same track... and understand that it isn't the decoder that will get fried... but the command station in the case of a short where the DC current get onto a dedicated dcc track hooked to a command station... many thanks for the clearification... joeg
joegibHeres my question... if I have a DCC loco on my track... and inadvertely select loco 00,,, the station will send DC current to the track...and hose my DCC loco?
so by DC, do you mean a constant voltage that isn't alternating polaiiry like DCC and varies to drive the motor at the desired speed.
A decoder will see a varying voltage. It probably requires some minimum voltage to start operating (it does have a processor). But without seeing any commands, it shouldn't do anything.
on the other hand, by DC, you could mean and alternating voltage (AC ?) that isn't symetrical. An alternating voltage that is symetrical will have an average voltage of zero. A non-symetrical alternating voltage can have an average voltage that is either positive or negative. Does a motor care?
a spinning motor (coil rotating inside a magnetic field) produces a voltage like a generator (back electro-magnetic field BEMF) that reduces the total voltage across its windings and limiting the current through them. the BEMF voltage is proportional to the speed of the motor.
With a non-symetrical alternating voltage, a slowly turning motor will have a small BEMF voltage that will reduce the alternating voltage during one half the cycle and add to it during the other half.
this doesn't sound like a good way to operate a DC motor. Others can check me on this
joegibI was advised not to have any connection between DC and DCC on the same track... but the DS52 provides this via loco 00...
i think what you were told was not to drive some blocks on your layout with a DC throttle and other blocks with DCC, because if anything with metal wheels cross the gap between the DC and DCC blocks may cause problems.
this isn't the same as driving the entire layout with either DCC or DC.
greg - Philadelphia & Reading / Reading
Joe
I think that what is confusing you here is the difference between the effects of DC on a DCC decoder versus DC on a DCC command station. Most decoders are dual mode and can accept DCC and DC whereas if you accidently connect DC from a DC power pack to the track outputs of a DCC command station you will damage the DCC comand station.
Technical explanation. The motor sees the positive or negative pulses as DC. So will your voltmeter on the DC scale.
The meter on AC scale will see the DCC signal. My NCE Power Cab shows 13.6 VAC for the DCC signal.
Store the links. Some like a visual explanation.
The point where the brushes contact the commutator segments gets quite hot as the armature vibrates at the DCC frequency when the loco is stopped. Not as hot when the armature is rotating.
http://members.shaw.ca/sask.rail/dcc/DCC-waveforms/DCC_waveforms.html
https://sites.google.com/site/markgurries/home/technical-discussions/dc-loco-on-dcc
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
SInce it's not actually putting DC on the rails, the ability of the decoder to handle DC or DCC power doesn;t really matter. The signal on the rails with using address 00 is still a DCC signal,m just modified. It was a bigger deal during the early days of DCC when a motor only decoder cost $60 or more, and N scale ones were few and far between. Digitrax and Lenz have had the feature since the beginning, in their first systems. Original NCE systems actually did support it, but you had to make your own throttle that plugged in to the serial port on the command station, you couldn;t just select address 00 on a throttle. Not surprisngly, few if any people actually used it so they dropped it out of the firmware in newer versions.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Here's what happens when you hit 00 on your command station:
with DCC your rails constantly switch back between positive and negative. The left rail is + and the right is -. then the left rail is - and the right is +. This happens a couple thousand times a second. Based on how long a rail stays positive, or negative turns into a number (0 or 1) which the decoder can read.When you enter 00, what happens is the command station leaves the one rail + longer then it is negative. So it might be positive for 150 ms and then negative for 10ms. For the 10ms it resumes it's normal command protocol where it tries to alternate real quick back and forth. This causes the motor tries to reverse direction as the polarity flips. But the period is so short compared to the forward pulse, it doesn't stop the loco. But this reverse pulse is what causes the motor to buzz. (Especially at lower speeds) Do I recommend it? No. Some motors brushes will burn out if you leave them sitting at speed step 0 for a long time. Athearn motors have done this.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
MisterBeasleyMaybe someone here can suggest a reference for exactly how the the DCC signal works.
IIRC, it's called bit stretching. The DCC signal has a square waveform. To run a DC loco, the command station varies the waveformso that it mimics DC by shifting the peaks and valleys in the wavefrom from being roughly equal to bias them toward the direction set, i.e. higher peaks than valleys. To change direction, it shifts to the opposite bias, lower peaks than valleys.
Digitrax and perhaps others have this option. NCE does not, FYI.
Steve and Mr. B are correct. Nothing to worry about with any at-all-recent decoder equipped loco. The DC loco should not be left on the tracks (or should be parked on a siding or spur that can be turned off), as they advise, when not in use.
Mike Lehman
Urbana, IL
Yeah, you're fine.
When you run a DC locomotive on your DCC track as Engine Zero, you are still putting a DCC signal on the track. You can continue to run DCC engines along with the DC engine. Maybe someone here can suggest a reference for exactly how the the DCC signal works. I have an old copy of a DCC book by Lionel Strang that I found very informative.
The DC engine will run poorly, and will probably make an odd buzzing noise. People generally advise not to do this too much. It's not good for the motor, although stories of burned out motors from this practice seem to have faded into history.
Then, one day, you'll put a decoder in that DC engine and you will like it much better. You have that to look forward to.
It takes an iron man to play with a toy iron horse.
Almost all DCC decoders made in the past few years have been "dual-mode," meaning they recognize direct current and operate fine with it. No worries.
--Steven Otte, Model Railroader senior associate editorsotte@kalmbach.com
I'm a bit confused... being new to DCC.. I'd like some info on this... I've got a DCS52 zepher Digitrax station...and see that entering 00 as loco causes the Run track to be used for "non-dcc" locos... I'm interpreting this to mean that the DCS52 provides DC power to the track. In my other posts I was warned not to have a dcc equiped loco put onto a DC track cause it may burn out the decoder...
Heres my question... if I have a DCC loco on my track... and inadvertely select loco 00,,, the station will send DC current to the track...and hose my DCC loco?
Seems like this is too easy and would occur often.. so I'm wondering if I'm missing something here... in my other post... I was advised not to have any connection between DC and DCC on the same track... but the DS52 provides this via loco 00...
any clearification on this would be appreciated... thanks joeg