Motor efficiency?

The efficiency of any motor can be judged by the amount of heat it generates. Heat is an energy loss and AC motors in trains generate a lot of heat and therefore not very efficient. The DC can motors in trains run cooler and are very efficient.

You can easily see the phenomena by running a postwar engine and a newer engine with DC motors. It can take 14 volts to run the postwar loco at high speed. It may only take 10 volts to run the newer engine.

You can also just run similar style and weight locomotives at most any speed and measure the track current necessary to keep them going at a set speed.

I don't think it is fair to judge efficiency by speed when models are different, gears are different etc...  Also overall power should be used, not just V or just current.  If an engine designed to run on 14V draws less current it could be more efficient then a motor using 12V if the current draw was much higher.

AC versus DC motor have very different characteristics.  The AC motor also needs power to the field windings to create the magnetic field the rotor rotates in.  DC motors use permanent magnets to create the magnetic field for the rotate.  G

The short answer is, everything electrical or otherwise is more efficient than it was 50 years ago.

That's why I suggest measuring the track current so you can calculate the power usage.

Basic power is Voltage X Amperage.   Assume that both Engine #1 and #2 are doing the same work.  Example pulling 10 cars at the same speed.   

Engine #1:

12 volts  @   3 amps     36 watts.

Engine #2

18 volts  @  1.5 amps    27 watts.

It's never quite this simple,  but Engine #2 is using less energy to do the same work.  More efficient.

 P (power) = V(volts) X I (current in amps).  High School Physics class. 

John,

I think we can agree that "can" motors are more efficient than open frame motors.

Why is this so?

Does the can enclosure strengthen the magnetic field? Are there more field poles? Is the air gap smaller? 

What do you electrical engineers think?

My guess is the permanent magnets used in todays small can motors are greatly improved from magnets and electric field generation in simple open frame motors used years ago.   Even the size of the can motors has gotten smaller.  Note the change out on this Weaver E8 set.

Old can motors.

New can motors.

The magnet strength is a good guess.  Supplying the field with power has to sap the efficiency of the motor significantly I would think.

There is a lot more that goes into it than just magnet strength. # of poles, brush/commutator design, number of windings and wire thickness, all resulting in different torque, speed and power curves versus rpm. Etc...

How many AC pulmore motors are still running 60 plus years later.  I have replaced can motors on 1 year old engines.  So I am not sure efficiency is the metric being used for model train motors.  Now that we are into CC and Cruise DC motor are required.  G

Technologically speaking, the motors being utilized today on MTH/Lionel products are vastly superior to the earlier motors. The need for motors to run cool is very important as many of us may run locomotives literally for hours at a time. Yet, it begs the question, why not employ a scaled down cooling fan that actually works. Also, in systems that are advanced, like Legacy, etc. why not have the operating temperature of the motors actually display on the screen. That way if it appears to be running hot, well then we can side rail that locomotive and lash up another that is not hot.

Just a few thoughts.

Pete

Two huge advances in the last 30 years.  Quality of the can motors and Power to weight ratio of battery pkgs.   I have a couple of early battery powered hand drill/drivers from the early 80's.  They are nothing compared to the ones I use today. Surprisingly those early can motors in the battery drills still work.  How long do these permanent magnets work??? 

Permanent magnets are... well... permanent.  They should last for decades unless they're abused by either strong magnetic fields (stronger than the armature generates), subjected to shocks, or subjected to heat.

Do magnets ever lose their magnetism?

In a (an?) universal motor running on AC, the magnetic field has to pass thru positive and negative orientation in the iron dipoles or whatever they are called, and because of the hysteresis, you have to waste energy doing so.

I learned the above from working at Skil and my current job at an alternator manufacturer. I have never taken a motors class, I was took mostly communication theory and RF when getting my EE. So take it with a grain of salt.

From the same seat-of-the-pants learning, the type of permanent magnet can improve efficiency, and if you skew the armature, you can even out the torque, but it costs more to manufacture. There was also this thing called the "flux ring" which is a c-shaped band that went around the motor to help improve magnetic fields going around the motor but for the life of me I never found out why they just didn't make the metal thicker, unless the ring is sort of like laminations. I know in the presence of a changing magnetic field, laminations help reduce eddy currents in the iron.

In an AC induction motor, it has to be run on AC, and I can't explain why they don't have the same problem. This is the type of motor on a fan or the blower on your furnace, any motor expected to last a long time and doesn't have to be picked up often.