slow running DC and DCC

[mopac]

What I have gathered. If you run your DC locos real slow on DC
you could burn up the motor. If you run your DCC locos real slow
on DCC no problems. Is this correct or what.

[gc53dfgc]

it really depends on the engine and the motor but yes eventually you will burn the motor out running a DC engine on DCC. That is why you buy DCC decoders to run them on a DCC system which offers better running and features over standard DC.

[mopac]

No, I didn't make myself clear. DC locos on DC and DCC locos on DCC. Do DCC
motors handle running really slow on DCC better than DC locos handle running slow on DC? I had heard you would burn a motor running DC motor on DC really slow.

[tankist]

What I have gathered. If you run your DC locos real slow on DC
you could burn up the motor. ...
never heard about that. not with intact DC controller.
you gathered that based on what?

[sstlaure]

I run my engines slowly on DC all the time. No issues at all.

I could maybe see if you had the controller set so low that voltage was flowing into the engines but you weren't providing enough current for the engine to move where it may be a problem.

[xrunner]

Under the control of the DCC board, does the motor receive a DC voltage from it or some type of modulated voltage?

[cabledawg]

Modulated AC voltage to "trick" the motor into thinking it is DC. Hence the reason a DC only loco will buzz if sitting idle on a DCC layout. Long term use of DC only locos on a DCC setup isnt recommended and the motors will burn up if left idle for long periods of time (I had one go in about 10 minutes, but age may have been a factor).

I agree with Scott that DC on DC at slow speeds shouldnt hurt the locos unless the loco is getting voltage but not enough to move.

[xrunner]

Modulated AC voltage to "trick" the motor into thinking it is DC.

Does that type of drive make it run "better" in some manner than a DC voltage?

[Brakeman Jake]

First part of the question...the electric motor (wether DC or AC) has the ability to provide torque while completely stopped.This is why locomotive engineers turned to them for power.No need of ratio selecting transmissions or clutches that would need to slip heavily trying to start movement of heavy loads,making them ideal for trains.

However,this torque means the use of energy (electricity) wich is proportional to the load the motor is linked to wich in turn creates heat.This is why heavy duty motors are usually built with cooling fins and/or a built in fan in many cases.Now for the fan to do its work,the motor has to rotate.In the case of our scale locos,pretty much the same principle with an important difference...many of our small motors are airtight closed and hidden inside a closed shell,so cooling is very poor.

If you run a lightly loaded motor,let's say a lone loco and two cars,heat generation is minimal so that it can run nearly indefinitely even very slow.But if you try to pull high loads,at very low or high speeds,heat will build up faster and this is the killer.What I do is I don't allow any of my locos to pull heavy trains indefinitely without regularly checking heat,I touch them and when they start getting warm,I replace them.It may be overkill,but I have enough locos on hand so why not?

The other part of your question...there's no difference to the motor in either DC or DCC since the decoder rectifies DCC current(actually AC) to send regular DC to the motor.I found out that under even normal loads,some of my decoders (Athearn's MRC equipped articulateds)do get warm after a while,so I check these too every now and then.

In short,check for heat and keep it reasonably low,you shouldn't have any problems.

[xrunner]

...there's no difference to the motor in either DC or DCC since the decoder rectifies DCC current(actually AC) to send regular DC to the motor.

Well I'm still confused as cabledawg said this -

Modulated AC voltage to "trick" the motor into thinking it is DC.

Who's correct?

[tjcruiser]

Jake,

FABULOUS explanation above. Very clear, logical, and well stated.

Thanks,

TJ

[tankist]

in modern DC powerpacks , when set to lower power output pulsing is used to break the condition of "sticksion" that Scott described. still it will not damage DC motor.

Under DCC the decoder will throttle the motor (according to signal it recieves) by applying PWM (http://en.wikipedia.org/wiki/Pulse-width_modulation). it so happens that the H-bridge components will heat up more during low duty cycles, but nowhere near critical temps. if one stays within current limitations of course.

OP didn't ask about that mode:
the quasi-DC compatible mode works by shifting the 0 point of the power wave. meaning when there is more "PLUS" voltage then "MINUS" the train will move. it will stay motionless by being pulsed to go both forwards and backwards simultaneously. not a good thing at all as from Jakes explanation you will understand why such condition can cause excessive heat.


Who's correct?
i think you misunderstand what was said. the statements don't really contradict each others. one deals with plain DC motor and the other with DCC decoder controlled one

Does that type of drive make it run "better" in some manner than a DC voltage?
no, much worse. but it will quasi allow the DCC station to control a motor whout decoder . IMHO that option is just a sale gimmik and never should have been implemented





and yes, Jake, thanks for taking time to write the explanation. should be very helpfull

[cabledawg]

What I said is correct for a DC only loco run directly from the DCC controller (usually address 0). What Jake said is correct after a DCC decoder is installed. Simply put, the motor recieves a modulated AC wave to simulate DC voltage. In the case of the installed decoder, there is additional circuits in the chip to smooth out the signal to an almost true DC waveform. I'm sure there are more technical terms and differences to this, but my last electronics class was over a decade ago, so I might be slightly off.

[tankist]

removed :)

[tjcruiser]

Anton,

Are you sure about that? I thought DC compatibility used "zero stretching", where the lengh (time duration, really) of a plus voltage was stretched out longer, such that it would not be fully cancelled by the shorter-duration negative voltage.

That's a different phenomenom than what you suggest by simply shifting the zero voltage (or true voltage of the top and bottom) up and down.

TJ

[tankist]

hmm really? i guess i need to read up on it.

[tjcruiser]

Good explanation here ...

http://www.loystoys.com/info/how-dcc-works.html

TJ

[NIMT]

All I know is all I know and that aint much!:D
This DCC stuff can be confusing and I've been doing it for over 15 years!:cool:

[xrunner]

Good explanation here ...

http://www.loystoys.com/info/how-dcc-works.html

TJ

I understand it now - thanks for the link.