DC motor with DCC

[richG]

Since there have been some questions about running DC only locos with a DCC controller capable of running DC only locos,  Yes, it is kind of technical. I had no way to measure the mechanical vibrations which will eventually affect a motor.
I did some temperature measurements as an experiment. The applied DCC signal is 30 volt pulses at a frequency of about 6khz.
Remember, the motor signal is the same as the track signal and at zero throttle, the pulses are still affecting the motor.

I recently used a MRC 2000 DCC controller that can run DC only locos to look at motor temperatures. The first was using a small can motor used in my HO scale 4-4-0 locos.  The motor temp was 68F at the start. With zero throttle, the temp went up to 92 F after ten minutes.
At one third throttle, the temp went to 105F after five minutes.
Back to zero throttle, the temp dropped to about 96 F after five minutes.

I then did the experiment with a open frame motor from a older MDC box cab.
At zero throttle, the temp went to 85F after five minutes.
At one third throttle after five minutes,  the temp went to 104F.
After five minutes at zero throttle, the temp was 95F.

In both cases, the motor is in open air with only a flywheel for a load. You could say these are ideal conditions.
With the motor enclosed and sometimes run near max throttle and pulling a load, a lot more heat can develop.
I had no desire to do life testing or take measurements at higher speeds. The few results speak for themselves.
I used a Raytek Mini Temp infra red thermometer with laser pointer for temp measurements.

http://www.raytek.com/Raytek/en-r0/ProductsAndAccessories/PortableThermometers/PortableThermometersSeries/MiniTemp-AutomotiveHandheld/Default.htm

Rich

[Barney R]

Hi RichG- How do these measurments compare to dcc motors running on dcc and dc motors running on dc?
I don't know what the norm is for normal operations. Is an operation temp of 105 bad?
Barney

[Jim Banner]

Barry, I have seen can motors in large scale locomotives get hot enough to sear the skin of your fingers before they (the motors) failed.  As a rule of thumb, if you can hold your finger on the motor, then it is not too hot (I guess that would make it a 'rule of finger' wouldn't it.) 

As Rich pointed out, motors get far less cooling when they are inside a locomotive shell.  I think the most significant temperature readings in Rich's tests were the ones with the motors stopped.  Collective experience indicates that those are the conditions when can motors over heat and fail - stopped with DCC power applied.  Conventional wisdom and Rich's test results suggest that further testing should be done with the locomotive shells in place.

[Barney R]

Thanks Jim for your thoughts and experience. Your statement supports my question as to what is the normal operating environment. The subject is DC motor with DCC. I am sure that RichG was looking for the safety aspects of running DC on DCC and that leads me to wonder what the norm and expected temps would be. 96 degrees will not sear my finger, nor will 105. Maybe Mr. Bach Man could ask the tech staff for the specs that they have or request from the production factory. Just a thought/question-

Barney

[Hunt]

The following is from Bachmann. I do not except them to say more about the matter.

Note: When operating an older analog locomotive be sure to monitor it closely.  Some analog motors are subject to overheating and damage when they are run for long periods of time on  DCC systems.

Quote from http://www.bachmanntrains.com/home-usa/ezcommand.php?ezpage=1



There is also a school of thought the damage is cumulative up to failure with some motors.

[richG]

Hi RichG- How do these measurments compare to dcc motors running on dcc and dc motors running on dc?
I don't know what the norm is for normal operations. Is an operation temp of 105 bad?
Barney

Hi Baney

One thing to note, there are no DCC motors, only DC motors. Some people ASSUME there are DCC motors. I have seen this in other DCC forums.

Below are waveforms for DCC pulses from a Decoder as applied to the motor.

Zero throttle. Zero volts DC on a meter.


Minimum throttle forward 2 volts DC on a meter.


FWD Half throttle 7 volts DC on meter.


Notice the pulses are about fifteen volts, positive for forward, negative for reverse.

Rev Minimum Throttle minus 2 volts DC on meter.


I put six volts DC, or half throttle,  on a can motor for 20 minutes and the temp went fron 68 to 75 F. No big deal.

Again, only the motor with a flywheel for a load.

I think this is going to confuse some people even more. Oh, well. I never went into teaching.

Rich

[Jim Banner]

Rich, I for one am glad you posted what you have found.  I have seen lots of words posted on the subject but this is the first time I have seen them backed up with any kind of numbers.

[richG]

Hi Jim

Thanks, I was beginning to wonder if I was confusing people. I tried to keep the photos to a minimum.

Here is a photo of the waveform as applied to the track and what the motor sees when the loco has no decoder and the controller is capable of running DC motors. I could not sync the scope to be able to see the "stretched zero bit".
The below waveforms are always on the motor, even at zero throttle when running DC locos on DCC.



At least for small motors, the only important issue is noise. The MRC 2000 instruction manual spells this out and recommends keeping it to a minimum time.

Rich

[richG]

The photos of the decoder waveforms were from a Micro-Tsunami dual mode decoder.

Please note, if running the decoder with a DC power pack, the waveforms are the same. The power pack has to be turned up to at least halfway though and you have a much smaller range for control on the power pack.

Rich

[Barney R]

Thanks  RichG-
Now let me feed back what you have said so far, If I understand.
1- All motors are DC.
2- DCC sends a constant pulse to the motor, even at rest which causes an increase in heat-
If both above statements are correct- then the heat issue is with DCC technology, weither the loco is DC or DCC.
However, this still does not identify the acceptable operating temp. expected for a DC motor, either at rest or half throttle, etc. You originally discussed the temp. reading that you identified. I am still interested in what is considered acceptable, without damage occuring to the motor.

Thanks,
Barney

[Hunt]

Informative pictures Rich for those understanding what they are seeing.



Barney,

Inquiring mind wants to know is recognized and the simple answer is the amount of damage done to a DC motor powered by DCC is – it depends on the design and materials used to produce the motor as well as a few other factors, which I will not be getting into other than to restate what Rich has, damage is not all heat related or to just the motor.

If motor is damaged it can be replaced. If avoiding damage is a major concern, then when the analog locomotive is run, disconnect the DCC system, remove all decoder equipped locomotives from the layout and connect the DC power pack.

Obviously using DCC decoder equipped locomotive makes this a non-issue.

Realize not all DCC systems support running an analog locomotive.

Some DCC systems with their latest upgrade have eliminated the zero stretching feature. Thus they can no longer be used to run an analog locomotive.


I guess next will be the subject of how long can a DC motor be run using AC transformer. Just kidding! 

[Yampa Bob]

One unknown factor is the winding temperature rating of small DC motors used in our models.  For a quality motor, these ratings may range from 105 - 180 degrees C, (356 F) Motors are also rated in duty-cycles.

I have re-wound many of these small motors for radio controlled race cars, sometimes the motor got so hot the body shell melted, but the motor was undamaged. Think about discharging a 12 volt 3 amp-hour nicad battery in a 3 minute race.

Talk about an expensive hobby, I once burned up 3 batteries in one night of racing, using a 10 minute quick charger. ($27.00 each), in order to win a $50 purse.

http://www.motorsanddrives.com/cowern/motorterms4.html
Site is probably related to industrial motors, but certain parameters still apply.

http://www.trainweb.org/girr/tips/tips5/motor_tips.html
A brief section on "Curie" temperature.

[Barney R]

Thanks Yampa Bob-
You answered my question-
Hunt-
What is this about- "Informative pictures Rich for those understanding what they are seeing."
I just installed a DCC decoder in an old Rivarossi Heavy Pacific and it runs very well. The motor is exposed at the back of the cab, however I was still concerned about heat.
My layout is wired with both DC and DCC with a toggle switch between so I can change to either. However, once I started using DCC, that is where the switch stayed. That is why I decided to try converting an older loco and why my interest in the topic of " DC motors with DCC.
Thanks Yampa Bob and RichG

Barney

[Yampa Bob]

Rich,
Thank you, I am delighted that you posted this thread.  The pictures will be enlightening to all modelers from novice to advanced. If I had your test equipment I would be inclined to perform a destructive test on a 6 volt motor drawing 7 amps at 12 volts. (this was the typical operating conditions I formerly used in electric powered aircraft, except the prop provided cooling via air ducts)

I hope you don't mind my adding some additional information regarding DC motors.

The following site has a plethora of information, a bit overwhelming to navigate, but just click every link you can find. 

http://www.mabuchi-motor.co.jp/en_US/technic/index.html

Some specific and elusive pages regarding motor windings, temperature and performance, in case you miss them from the main menu.

http://www.mabuchi-motor.co.jp/en_US/technic/t_020203.html
http://www.mabuchi-motor.co.jp/en_US/technic/t_020204.html
http://www.mabuchi-motor.co.jp/en_US/technic/t_0203.html
http://www.mabuchi-motor.co.jp/en_US/technic/t_0100.html

[richG]

Hi Bob

Thanks for adding info. The subject can get quite complex though.
I just ran a Mantua upgrade can motor I picked up in the 1990s and ran it with the MRC 2000 at half throttle for 30 minutes. The motor is not Sagami motor quality but still a pretty good motor.
Max temp was about 108 F.

I then ran an open frame motor from an old MDC box cab loco motor at half throttle for 30 minutes.
Max temp was 99 F.

The open frame motor current was 400ma.

The can motor current was 195 ma.

Open frame motors appear to dissipate heat more readily than can motors.
The "Can" holds in much of the heat. The hot spot on the can was just outside of where the brushes would be.

Yes, this was done with only two motors.

We have to be careful when saying a loco motor will dissipate heat more readily when the loco is moving.

Rich