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Discussion Boards => General Discussion => Topic started by: #94 on April 12, 2008, 09:14:24 AM



Title: DC Momentum
Post by: #94 on April 12, 2008, 09:14:24 AM
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.


Title: Re: DC Momentum
Post by: Jim Banner on April 12, 2008, 10:48:45 AM
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?

Momentum, per se, does not cause motors to run warm.  Running the motors on dc, DCC, pulsed dc, rectified ac or any other wave form will cause them to create heat and get warm.  The amount of heat produced depends on the speed, the efficiency and the drag of the motor and on the amount of load imposed.  Efficiency in turn does depend somewhat on the wave shape fed to the motor, but this is not usually the dominant factor in heating.  The temperature of the motor will depend on the amount of heat generated and the amount of cooling that takes place.  In large scale, I have from time to time installed forced air cooling fans in locomotives where the motor produces lots of heat and cooling is otherwise poor.

Whether any particular set of operating conditions will cause your motor in your locomotive to heat up excessively is best determined by you yourself.  Does the locomotive feel warm on the outside after running it for a while under the questionable conditions?  Is the motor too hot to touch?  I have had motors get hot enough to sear the skin off my finger tips. which is definitely too hot.  These motors did not survive.  I have also had motors that started melting the surrounding plastic.  That is too hot for the locomotive, but the motors generally survived.  So don't panic if your motor gets a little warm.  It is normal.

Decoders too heat up.  So a locomotive that includes a decoder will run warmer than one without, even if the motor is the same temperature in both of them.  Whether or not a particular locomotive likes momentum has more to do with whether the decoder you install in it has the capabilities of momentum control on dc.  Not all do.  I suspect that what the person was saying was that Bachmann locomotives with DCC on board (i.e. sold with a decoder already installed) are not capable of momentum effects when run on dc.  I will have to try one out to confirm this.


Title: Re: DC Momentum
Post by: Hunt on April 12, 2008, 03:12:59 PM
# 94,
Hot motor is an issue when using DCC to run a locomotive without a decoder installed.

When it can be done, I suggest people using DCC not run a locomotive without a decoder installed as the motor will be running hot and even hotter at the standstill. Over time you will damage the motor.

By the way, not all DCC command stations will run a locomotive without a decoder installed.


Title: Re: DC Momentum
Post by: Yampa Bob on April 12, 2008, 04:06:56 PM
#94
I have 12 Bachmann locos, all DCC equipped, but I currently run them on DC. I have not experienced any abnormal heating, even with a GP35 pulling 30 cars at low speeds. I would classify the heat as "lukewarm" at the most.

There does not appear to be any "momentum" effect when running on DC. If I close the throttle quickly, the locos come to an abrupt stop.  In fact I have to be careful with my Connies, one sudden stop caused the drivers to get out of quarter.

Hope this helps

Bob


Title: Re: DC Momentum
Post by: CHUG on April 12, 2008, 07:45:25 PM
Will dcc make bachman thomas train motors run hot and so forth. Thanks


Title: Re: DC Momentum
Post by: #94 on April 12, 2008, 08:16:17 PM
Thank you all.


Title: Re: DC Momentum
Post by: Yampa Bob on April 12, 2008, 08:17:00 PM
I doubt if there will be any motor heat problem unless overloaded with too many cars. The newer motors are pretty efficient and don't waste much energy on heat.


Title: Re: DC Momentum
Post by: Jim Banner on April 12, 2008, 08:34:34 PM
Will dcc make bachman thomas train motors run hot and so forth. Thanks
Hunt's advice applies to Thomas as well.

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.  Why take a chance on poor old Thomas when a low cost decoder and prevent the problem?

#94
There does not appear to be any "momentum" effect when running on DC. If I close the throttle quickly, the locos come to an abrupt stop.  In fact I have to be careful with my Connies, one sudden stop caused the drivers to get out of quarter.

Bob
 

Thanks, Bob.  I was wondering about Bachmann decoders and momentum with dc.   I was working on a LifeLike E-8 with a Digitrax DH163 decoder earlier today.  Just for fun, I programmed in some momentum on a DCC test track then ran it on a dc track.  The momentum worked on the dc track as well.  I suspect that was the basis of the statement about Bachmann DCC locomotives not liking dc momentum, but that would apply to DCC On Board ones, not DCC Ready ones.


Title: Re: DC Momentum
Post by: Hunt on April 12, 2008, 09:58:35 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.


Title: Re: DC Momentum
Post by: CHUG on April 12, 2008, 10:03:05 PM
hunt spit it out. do bachman thomas trains running and siiting stopped on dcc suffer and so forth. thamks


Title: Re: DC Momentum
Post by: Yampa Bob on April 12, 2008, 10:38:43 PM
I don't plan on running any DC locos on DCC power, even on #10 EZC, the instructions have a clear warning about it. I hope people don't get the idea that DC locos are DCC compatible. 

I only hooked up the EZC one time, to test all my locos, then put the DC pack on again.  Until I get the layout complete I haven't felt the need for DCC. I have some isolated switched sidings at the moment that work well.

For now I just want to keep studying all the aspects of DCC to keep up with the times.

Bob


Title: Re: DC Momentum
Post by: Hunt on April 12, 2008, 10:42:54 PM
hunt spit it out. do bachman thomas trains running and siiting stopped on dcc suffer and so forth. thamks
Jim answered your question so forth and so on.  ;D


Title: Re: DC Momentum
Post by: Hunt on April 12, 2008, 10:46:44 PM
...
For now I just want to keep studying all the aspects of DCC to keep up with the times.

Bob
Just keep in mind with some aspects of DCC what you learn today may be out of date when you get around to using DCC.  ;)


Title: Re: DC Momentum
Post by: Yampa Bob on April 12, 2008, 11:09:28 PM
Very true, that is why I plan to keep up to date as possible. It's interesting to find a web site that supposedly has all the latest information, but at the bottom it says "Last updated 2006". 

It seems that no matter how long you wait to buy something, you usually end up with yesterday's technology. 

Bob


Title: Re: DC Momentum
Post by: Redtail67 on April 14, 2008, 03:11:41 PM
Momentum? I do not understand what you are referring to. Can you explain for a new guy like me? It does not have to a complete deal just a brief that I might understand.

I have been thinking...this model railroading is in many ways the same as real railroding. For instance track problems and freight car problems. I have used the same system tio identify problems and solve them that I used in actual railroad world.

In the real world of engines that used DC traction motors we had "STALL BURNS" caused by putting high current to start a train to the traction motors and still the train would not start. This sitting still with current to the traction motors resulted in stall burns to the armature and burned or melted the insulation of the wiring in the motor itself.

Even it the train started moving engineers had to take into accou8nt the so called "SHORT TIME RATING" of the different types of locomotives. This was just how long under high current conditions a units traction motors would withstand the high temperatures produced without melting the windings in the DC motor. These time were accumulative meaning that if the cooling off time had not been observerd for a unit  the engineer would add that time to the next high current use of the engine so as not to exceed the total time alloewed in a short period of time.

It was excessive time in high current situations that resulted in the vast majority of traction motor failures. The other was excessive speed based on gear ratios that made the traction motors literaly sling the windings off the DC Motors causeing short armature windings. Even thoug I do not think that is a problem with the model engine. "HEAT KILLS" traction motors in the real world and I see the same situation in the little DC motors powering the model train. If you had enough weight in the unit or the train was too heavy or someone held the little engines down to a stall while current was flowing to the motor it would burn the insulation and the armaturte just like the real world engine. Just as a note: in heavy mountain grade situations many an engineer including myself would reverse the locomotives and apply power to hold the train and then release the air to charge the system especialy in cold weather. This of course was a violation of the air brake and train handling rules but was the only realistic way to hold the trains while you charged up. This frequently led to failure of the motors on these engines prematurely.

I have been involved in many hundreds of investigations into derailments mostly track and equippment damage and several involveing death to the engineers or trainman. The same investigative proceedures I used then I have applied to my model train and each time have found the problem.

Anyhow, thi8s reference to momentum in DC motors has me stumped as to what you are talking about.

Redtail67


Title: Re: DC Momentum
Post by: Redtail67 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


Title: Re: DC Momentum
Post by: Jim Banner 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.

   


Title: Re: DC Momentum
Post by: Redtail67 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



Title: Re: DC Momentum
Post by: Redtail67 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


Title: Re: DC Momentum
Post by: Redtail67 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


Title: Re: DC Momentum
Post by: richG 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


Title: Re: DC Momentum
Post by: Yampa Bob 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


Title: Re: DC Momentum
Post by: richG 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


Title: Re: DC Momentum
Post by: Hunt 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."  ;)



Title: Re: DC Momentum
Post by: richG 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