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OK to Park a DC Loco on DCC Powered Track?

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  • Member since
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  • From: Western, MA
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Posted by richg1998 on Thursday, June 07, 2018 11:16 AM

As was said, there is a chance of damaging the motor. The two brushes heat up where they contact the armature. About ten years ago I did temp measurements with an infra red temp scanner on a test stand. I could see the hot spots even in a can motor. With the motor armature stopped and DCC still applied, the temp increased.

The gears are not the issue. The buzz is annoying.

Rich

 

N

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Posted by BigDaddy on Thursday, June 07, 2018 11:43 AM

maxman
BigDaddy

"I don't think so, Tim"

You were supposed to laugh, there goes my new stand up comedy career, down the drain.

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by rrinker on Thursday, June 07, 2018 12:04 PM

 A big heavy Pittman-type motor has a larger mass to help dissipate the heat, a smaller can motor is actually WORSE and more easily overheated. ANd a coreless motor will be destroyed in minutes if not seconds if placed on DCC track. That used to be only high end brass, or remotored locos, but there's at least one new Kato HO loco that had the motors built into the trucks - they are coreless motors and if you set one of those on DCC track without a decoder it won;t take long to damage it. Note sure if they've released any others usign that technology yet.

 ANd a few manufacturers have gone to the trouble of adding a capacitor to their DC light board which causes no issues running on plain DC power, but will short out the DCC system, effectively preventing you from running a non-decoder loco. 

                               --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by maxman on Thursday, June 07, 2018 2:13 PM
BigDaddy
You were supposed to laugh
 
Sorry, I didn't know that.  I guess I need to attend more of the meetings.
 
BigDaddy
there goes my new stand up comedy career, down the drain
 
Hopefully you didn't quit your day job.  And if you did maybe you can ask for it back Stick out tongue
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Posted by bearman on Friday, June 08, 2018 4:05 AM

NOOOOOOOOOOOOOOOOOOOOOOOOOOOO!

Bear "It's all about having fun."

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Posted by ROBERT PETRICK on Friday, June 08, 2018 8:08 AM

Mark R.

On a DCC system, there is no form of DC voltage on the rails of any kind. The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. The decoder is what converts this AC-like voltage to a usable DC for the motor circuit.

When you place a DC engine on a track with DCc voltage, you are in essence applying a low pulse AC voltage to the motor. An AC voltage is an equal pulsing of positive and negative at a very high frequency. So, at speed step 0, the DC motor is receiving small equal pulses of opposing voltages at about 120 time per second. This means the motors armature is occilating back and forth 120 time per second .... this is the buzzing sound you are hearing.

What zero stretching does is either increase the positive or negative amplitude of the AC sine wave. The armature is still occilating back and forth 120 time persecond, but it's occilating ever so slightly more in one direct than the other the higher the amplitude is, creating rotational movement.

This would be the same as you sitting there and throwing the direction switch on your DC power pack 120 times per second .... not that you could actually do that, but that's what's happening to your DC motor when being controlled by a DCC signal .... not good for it by any means.

Mark. 

Right. Thanks Mark. This is the best explanation I've seen describing this situation. Every time I try to explain it, people roll their eyes at me.

One other thing that causes eye roll . . .  When a non-decoder engine is operating on a DCC system at Address 0 and is within a reversing section, and another train crosses the gap, the non-decoder engine will suddenly stop and reverse direction. Slamming on the brakes, full speed reverse, coupler tension bucked, loads shifted . . . not a pretty sight.

Thanks again Mark. Old thread, hope you're still around.

Robert

LINK to SNSR Blog


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Posted by gregc on Friday, June 08, 2018 10:00 AM

ROBERT PETRICK
Mark R.

The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. 

AC sine wave ?

greg - Philadelphia & Reading / Reading

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Posted by ROBERT PETRICK on Friday, June 08, 2018 10:18 AM

gregc
ROBERT PETRICK
Mark R.

The DCC track voltage is very similar to an AC sine wave but at a much higher frequency. 

 

AC sine wave ?

 

I am so sorry to have chimed in.

When a DC loco is at Address 0 in a DCC system and the throttle is at zero, the burbles that go thisaway are equal to the burbles that go thataway and the train remains still. Singing. When the throttle is increased, there are more burbles going thisaway than thataway and the train begins to move. Thisaway. More throttle -- more burbles and faster speed. When the direction button on the throttle is reversed, the burbles go vice versa the other way around and the train runs backwards. 

Clear?

Robert 

 

PS  Edit to clarify. When I said more throttle more burbles faster speed, I should have said more throttle bigger burbles faster speed.

LINK to SNSR Blog


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Posted by gregc on Friday, June 08, 2018 1:18 PM

as others have posted, applying an AC signal to a DC motor results in excessive heat which may damage the motor (melt wire insulation resulting in a short).

i had the impression that this wasn't so bad if the DC locomotive were moving due to pulse stretching which results in a DC component to the DCC signal causing the DC locomotive to move.   

But now i'm not sure.

all motors act like generators when their armatures turn.   The turning armature, even though a current thru its winding creates a force to push, also generates a BEMF which is a voltage opposing the current pushing the armature (i.e. the motor acts like a generator).   The BEMF reduces the voltage across the armature windings which reduces the current due strictly to the resistance of the wire.   In other words, the maximum current thru the armature is when the motor is not turning.

DC on a DCC system is the result of an asymetric AC phase where one phase of AC (+/-) occurs for a longer percentage of the time than the opposite phase (-/+).    The phase with the longer duration determines the direction  and the DC voltage is proportional to the difference in duration.

As with pure DC, the BEMF counters the voltage in the phase with the longer duration.   However, during the opposite phase it adds to it!

For example, if the BEMF is half the peak voltage due to a relatively large DC component, during the in-phase phase, the resulting voltage is the Vpk - BEMF, in this case half the peak.   During the opposite phase, it is Vpk + BEMF. 

if the locomotive weren't moving, it would simply be Vpk all the time,  resulting in Vpk * Vpk / Rmotor in wasted power as heat.

during pure DC operation, the voltage across the motor is Vdc - BEMF.   However, on a DCC system there is wasted power during both phases and in the opposite phase it's even more than when the loco sits idle, although it is for a progressively smaller period of time,

 

it seems me that operating a DC locomotive on a DCC system is never a good idea although i doubt anyone has reported long term damage.

 

greg - Philadelphia & Reading / Reading

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Posted by rrinker on Friday, June 08, 2018 6:09 PM

 It all depends on the motor, if the heat generated by the wated power exceeds the ability of the motor to dissipate that heat, eventually something will melt. As long as you are taking out the same or more heat than is generated, it can run all day.

 Interesting that it was originally conceived for N scale, as in the early days of DCC, not only were all decoders expensive, getting ones to fit in N scale locos was much harder. But consider so many N scale locos are big blocks of metal with the motor clamped between them - not a bad heat sink.

 Coreless motors have no heavy metal to sink the heat. They are quickly damaged by the heat generated trying to run on DCC power. They are also easily damaged by older/cheap decoders that use a low frequency PWM.

                         --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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