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Author Topic: DC Momentum  (Read 5975 times)
#94

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« 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.
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Jim Banner

Enjoying electric model railroading since 1950.


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« Reply #1 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.
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« Reply #2 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.
« Last Edit: April 12, 2008, 03:29:54 PM by Hunt » Logged
Yampa Bob

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« Reply #3 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
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CHUG

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« Reply #4 on: April 12, 2008, 07:45:25 PM »

Will dcc make bachman thomas train motors run hot and so forth. Thanks
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#94

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« Reply #5 on: April 12, 2008, 08:16:17 PM »

Thank you all.
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Yampa Bob

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« Reply #6 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.
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Jim Banner

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« Reply #7 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.
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« Reply #8 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.
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CHUG

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« Reply #9 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
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Yampa Bob

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« Reply #10 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
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« Reply #11 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.  Grin
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Hunt
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« Reply #12 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.  Wink
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Yampa Bob

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« Reply #13 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
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Redtail67

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« Reply #14 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
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