Does DCC make motors overheat?


railfan

railfan

junk collector
I read this in the wikipedia article on how DCC works:

http://en.wikipedia.org/wiki/Digital_Command_Control#How_DCC_works

"However, because the raw power contains a heavy AC component, DC motors heat up much more quickly than they would on DC power, and some motor types (particularly coreless electric motors) can be damaged by a DCC signal."

I have not read reports on this forum about any issues like this. Just wanted to see if anyone ever had a problem with locomotive motors getting hot with their DCC system. I recently aquirred a prodigy DCC system and will eventually set it up. I have N scale gear.


Mike
 
Mike,

N scale or any other scale engines for that matter equipped with a decoder will not run hot on DCC. The problem comes in when a non-decoder equipped engine is left sitting on the track for a long period of time. If you place a non-decoder equipped engine on the track you will hear a hum. You can run a non-decoder equipped engine on some brands of DCC equipment (I know Digitrax does as I have Digitrax) on 00. Running a non-decoder equipped engine doesn't seem to cause the problem.

Glenn
 
First off, DCC is a square-wave signal, NOT AC, which is a sine wave. One of many things Wikipedia has wrong. Secondly, DCC will never overheat a decoder-equipped engine.
 
DC motors on DCC track will heat up in the majority of cases, with some variance. The reason is that they don't have a decoder intermediary interpreting the signal and rectifying the current to a polarity which the motor can use efficiently. Instead, some systems allow 'zero stretching' which renders the DCC power approximate to a given polarity. However, it is only close, so the motor still gets excited in the opposite direction for brief fractions of a second, which causes the high frequency pitch squealing and squawking from the drivetrain.
 
One thing they have said does seem to be true, as I've seen it on other DCC wiring sites.

Some coreless can motors will overheat very fast on DCC. While I have one steamer with a coreless motor in it, it has run for over 10 years without a problem. However, one engine I had with another brand of coreless motor in it, ran about 5' before the motor cooked. I replaced it with another plain can motor and it now runs just fine. The one that is still running is a Cannon coreless motor, and the one that burned, IIRC was a Mitsubishi.
 
railfan said:
I read this in the wikipedia article on how DCC works:
Click to expand...
Remember wikipedia is a public update thing such that nothing found there can really be considered definitive or even necessarily true and correct.

I have not read reports on this forum about any issues like this. Just wanted to see if anyone ever had a problem with locomotive motors getting hot with their DCC system. I recently aquirred a prodigy DCC system and will eventually set it up. I have N scale gear.
Click to expand...
As the others have said, If the locomotive has a DCC decoder in it this is not an issue since the decoder converts the DCC signal to DC for the motor.

If you are wanting to run a DC locomotive on DCC channel zero, yes there is a good chance you will ruin the motor. It doesn't have to be coreless either. Jeff Wimberly did some tests a few years back and fried HO Athearn motors in as few as 10 minutes. My advice to everyone is to NOT do this. If one wants to use DCC then one should put a decoder in all locomotives to be run (period).
 
GenSet said:
First off, DCC is a square-wave signal, NOT AC, which is a sine wave. One of many things Wikipedia has wrong. Secondly, DCC will never overheat a decoder-equipped engine.
Click to expand...

DCC is a square wave, but it is also AC. AC does not have to be a sine wave.
 
Apologies for going slightly off topic here but the Wikipedia article in question does state that the DCC signal is "a form of alternating current", which is technically correct. Nobody can dispute that the current alternates polarity. If anything the problem here is the assumption that "AC" always refers to a sine wave like the power coming from a wall outlet, rather than an abbreviation for "alternating current".


EDIT: Oops, beaten to it!
 
Math and science were always my best subjects in school and I built working motors and radios out of household junk for fun. I was frustrated to visualize how alternating current worked until I realized it is much like a piston in a cylinder going up and down.


Mike
 
Some interesting stuff...

The reason electricity from the wall is a sine wave shape is because of the generators that used to make it regardless of how many poles they are. Granted they don't do it the same any more - they feed huge amounts of DC current to systems that regulate and produce the sine wave you see at home. The power company is supposed to ensure that it remains an average to 60Hz over the course of 24 hours. They used to have to do this manually by adjusting the speeds of the generators but now it's all computer regulated.

Truely awesome animation of how generator rotation relates to the amplitude and shape of a sine wave.
http://www.wisc-online.com/Objects/ViewObject.aspx?ID=IAU14108

Check out the SIN/COS/TAN buttons on your calculator and see how they relates to degrees by the way. This is trigonometry at its finest right there. Applying this stuff to the generation of electricity is the absolute only way I even started to understand what sine, cosine, tangent etc meant.

Some fun stuff related to that:
http://library.thinkquest.org/20991/alg2/trig.html
 
Yeah, that alternator animation page was cool. Another simple analogy of how alternating current works is a grandfather clock. The pendulum swings left and right as time moves forward.



Mike
 
Back to the original question ....

DCC signal is a square wave similar to an AC sine wave but at a much higher frequency. When a DC motor is exposed to this "AC type" voltage, it will buzz. This buzzing is actually the motor armature chattering back and forth ever so slightly at the frequency of the sine wave. In order to make the motor turn to move the engine, either the upper or lower half of the wave is stretched. What this is doing is causing the motor chatter to be a bit longer in one direction than the other, in essence, creating rotational movement.

If the upper half of the sine wave is stretched, it will turn in one direction and if the lower half of the wave is stretched, it will turn in the opposite direction. The problem is the fact for every movement of the armature in one direction, there's a corresponding / alternating pulse jogging the armature in the opposite direction. This is what causes the motor to heat up. It's like throwing the direction switch on your DC pack back and forth about 160 times per second while set at full throttle !

I've personally seen a number of non-decodered motors destroyed from running them on DCC. The manufacturers have realized this as well, and most newer systems won't allow operation of a non-decodered engine on address 00. They didn't remove that feature for no good reason.


Mark.
 
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