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Author Topic: DC Momentum  (Read 5755 times)
Redtail67

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« Reply #15 on: April 14, 2008, 03:19:09 PM »

Had to laugh after that post..you know I am an engineer by the spelling and punctuation.

Redtail67
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Jim Banner

Enjoying electric model railroading since 1950.


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« Reply #16 on: April 14, 2008, 04:15:14 PM »

Redtail67, model railroaders keep trying to make their models look like the real thing and even handle like the real thing.  But one thing that we cannot model directly is the inertia/momentum of a real train.  We control the speeds of our models by applying more or less voltage to the motors.  If we crank up the voltage quickly, our models accelerate quickly, far more quickly than real trains.  Same slowing down.  We can stop a train traveling at a scale 60 mph in a few car lengths, using only the locomotive wheels for braking.  So how can we make our model trains feel like they have inertia/momentum?

The easiest way to give the feeling of inertia/momentum is to electronically limit how fast our trains can accelerate and decelerate.  All that is required is a circuit that slowly increases or decreases the voltage to the locomotive motors even if we turn the speed control quickly.  Such circuits predate DCC by decades.  Today, almost all DCC decoders come with these circuits built in.

Where the confusion arises is that the circuits, whether analogue or digital, give our locomotives limited acceleration and deceleration but we talk about these circuits giving our trains momentum.  Technically, I suppose we should say "the feeling of momentum" but you know how we always seem to manage to shorten up whatever we are talking about.  "Surf the net" instead of "search the inter-computer communications network," or "I'll call him on his cell" instead of "I will contact him on his cellular telephone."   I hope this helps clear up the confusion.

   
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Redtail67

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« Reply #17 on: April 14, 2008, 04:47:12 PM »

Jim:

Thanks for the explination I now understand what momentum is about.

What I do not understand is that if my power pack allows the slow increase or decrease in speed ( or voltage) then you must mean a more sophisticated controller that allows a finer increase or decrease in voltage?

Or is it a controller that does the increase or decrease automaticly. Say I was to go to full voltage setting and then some cicuit then slowly and steadily increases the voltage over time all by itself?

Is this something that I would add to mine or is it just one that you buy that is much better than mine?

Redtail67

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Redtail67

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« Reply #18 on: April 14, 2008, 04:51:08 PM »

Jim, I forgot to mention that right now I am using one of several standard  DC controllers I have. I have purchased a Bachmann EZ DCC Command Controller but have not hooked it up yet. Does this have this feature? Can it be programed into one of the settings?

Redtail67
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Redtail67

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« Reply #19 on: April 14, 2008, 05:49:21 PM »

Hunt

Thanks for the information. Mine does not have that switch.

So its the DCC decoder in the Locomotive that you can make a setting change to but only if you have a DCC Controller that can make it. The Bachmann II have can not change it.

Thats good information to know.

Thanks again, I learn a little more every day.

Redtail67
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richG
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« Reply #20 on: April 14, 2008, 06:37:48 PM »


Strictly speaking, the problem is not so much that they run hot but that stop hot.  When the motor is running, it creates some air flow and helps cool itself.  But when it is stopped with DCC type ac applied, it still draws current but does not have any cooling air flow and can over heat. 

Jim,
Without going into all the test details... testing a non-decoder equipped locomotive run using DCC and using DC revealed a can type motor ran hotter using DCC than when using DC.

The slower the speed the hotter the motor; with the motor being the hottest when locomotive not moving. A contact temperature measurement instrument used for temperature readings on the motor.

There is a school of thought for some types of motors used in model railroading that the damaging effect due to heat is cumulative.


The DCC decoders send zero to 12 volts pulse power to the motors when running. The pulses go to zero when the  command station calls for zero throttle.

Rich
« Last Edit: April 14, 2008, 06:43:35 PM by richG » Logged
Yampa Bob

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« Reply #21 on: April 14, 2008, 07:53:41 PM »

Quoting what Red said:  "My power pack allows the slow increase or decrease".  I'm running DC at the present, if I want to start a long train realistically, I just turn the knob very sloooowly, same thing slowing to a stop.  It's called both careful handling of the throttle, and realism.

An Engineer of a real loco wouldn't instantly go full throttle to start up, or chop it to a screeching halt, except in an emergency.  Did anyone watch the Modern Marvels program last week?  The Engineer said: "I must throttle up very sloooowly to keep the wheels from spinning".

I guess I'm old school, I think in terms of "inertia".  The only time I think of momentum is getting up speed to take a 5% grade when pulling 25,000 pounds of beef with my rig.

The space shuttle must attain enough momentum to carry it into orbit. The dictionary defines momentum as "The product of a body's mass and velocity".

To keep it short, how could I call myself an "Engineer" if I have no respect for the throttle?  This old brain somehow can't equate momentum as slowing down.

Bob
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richG
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« Reply #22 on: April 14, 2008, 08:31:27 PM »

When I use to run DC, I used a power pack that had pulse powr and momentum. Never had any motor issues. The club I belong to has run DC power with pulse power and momentum for many years. Never any motor issues.
We both run DCC now which is pulse power also but todays motors are much more efficient.

Rich
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Hunt
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MBB


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« Reply #23 on: April 14, 2008, 09:05:27 PM »


Strictly speaking, the problem is not so much that they run hot but that stop hot.  When the motor is running, it creates some air flow and helps cool itself.  But when it is stopped with DCC type ac applied, it still draws current but does not have any cooling air flow and can over heat. 

Jim,
Without going into all the test details... testing a non-decoder equipped locomotive run using DCC and using DC revealed a can type motor ran hotter using DCC than when using DC.

The slower the speed the hotter the motor; with the motor being the hottest when locomotive not moving. A contact temperature measurement instrument used for temperature readings on the motor.

There is a school of thought for some types of motors used in model railroading that the damaging effect due to heat is cumulative.


The DCC decoders send zero to 12 volts pulse power to the motors when running. The pulses go to zero when the  command station calls for zero throttle.

Rich

Rich,
What is the relevance of your statement with my quote?

Note   am referring to running using DCC a locomotive that does not have a decoder installed .

By the way, I do know how a locomotive without a decoder can be run using a DCC command station capable of "zero stretching."  Wink

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richG
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« Reply #24 on: April 14, 2008, 09:09:18 PM »

I use DC. I know that useing  momentum causes motors to run warm. I believe it was here that someone said that the new DCC ready Bachmann engines do not like DC momentum. Is this true? Will it hurt anything? Also knowing that DCC creates heat what is the difference in heat or heat?
I have an On30 Shay and two porters and a trolley. The Shay would be of most concern.
Just the facts please. I do not want to debate DC vs. DCC, just the issue of heat and or actual damage.
Thank you.

Yes I strayed from the issue. Sorry. Momentum will not cause heating . Momentum is just the characteristic of the DC throttle to increase slowly or decease slowly. I use to use DC throttles with momentum.
I have never read anywhere of momentum causing any issues. But stranger things have happened.

By the way, explain your statement. "Also knowing that DCC creates heat what is the difference in heat or heat?"

Rich
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