What does the electricity do when a motor cannot turn?

I have an N scale 4-8-4 electric train locomotive.  It and the track are brand new and clean.

It has trouble making left turns. The movement is jerky, the headlight dims, and it sometimes stalls. Right turns are fine.  Left and right turns are fine in reverse.

When it jerks and stalls, the voltage across the rails drops to near zero and the current through the rails increases a lot.

If something mechanical is forcing the motor to stop, is this data consistent with that?

My other guess would be a short of some kind, however the circuit breaker in the controller does not trip.  I don't know how much current that would take, though.

Sounds like it is shorting on the armature so the resistance in the circuit is dropping to near zero. Your motor most certainly has brushes (not really brushes but still called that). Your little motor can flat burn up and melt your train if it hangs like that to long.

I would check the drive wheel gears and such.

So if I understand correctly, a stalled motor would create a voltage drop and a current surge, similar to a short circuit.

I found this, which helps, but I'm still chewing on it.

As for the train, I applied lube per customer service and ran it for a while in a clockwise loop, but it still stalls on left hand turns.  I'm thinking the left turn is causing something to bind up in the gears.  I'm reluctant to open the gearbox since it's under warranty.  Hopefully warranty service can solve it.

Thanks for the replies.

Yes, basically it is a short.

Most of the time HO trains have the motor in just one of the bogey wheel sets and the other is just along for the ride.  I don't know about your scale train.  I always liked model trains, I had one as a kid that would smoke when you put an oil in the stack.  It was VERY cool but could stink like all get out.

Bogey wheels are rarely driven.
Driving wheels drive.

Bogey wheels just spread weight (on real trains also).

The small motors on things like model trains are often brush commutated permanent magnet motors.
The magnets are stationary on each side of the rotor.
The coils are protected from damage by the winding resistance and the low voltage.

All but one of the HO locomotives I've had has the motor in the middle with one or two shafts. The one that didn't was a 2 axle switcher.

This one's a 4-8-4 with one motor that runs the 4 drive axles. Since the gearbox with the drive axles is fairly long, the axles have a lot of play to move left and right.

It does sound like something is jamming causing it to stop and "short out." There could be a defect or dirt in one or more of the gears. I'd just do a warranty replacement if the company will let you.

Here's how it works.



First think of the voltage you apply to a motor.  Voltage is a term for the amount of energy given to raise a certainly number of coulombs ( a specific quantity ) of electrons to a certain point in order that they can deliver a certain amount of energy in joules.  That ratio determines the amount of work you can or cannot do.  When you pass current through a motor at a certain voltage, the energy available to do work is normally used in creating and switching magnetic fields in the rotor, stator or both.  The rotating and constantly switching magnetic fields drive the motor.  This "consumes" the voltage ( or available energy ) and does work for you.  The energy in the electrons GOES someplace.....to the work via magnetic field switching.



It is the repeated building of of the various fields that converts the energy of the electrons to mechanical, rotational work.  If you aren't building, collapsing and rebuilding those magnetic fields then the energy contained in the electrons is not expended in those magnetic fields....so it has to do SOMETHING.  Your motor is designed to convert ( and thusly consume ) energy.  Well, now it can't consume the energy mechanically....sooooo...instead of all of that available energy being converted to work....it starts backing up in the field windings of the motor because the field windings aren't designed for long term transferal of heavy current at high voltage, they are designed to create a vastly multiplied magnetic field.  What is happening is that the motor is now converting energy to heat
instead of work...the problem is that, by nature, the motor is trying to
convert the electron energy to work...so ( depending on the motor ) it
tries to work harder...so it draws more current...but it can't convert THAT
energy to work....so more energy becomes heat....and round and round until the field windings turn from being a component of an electromagnet to
being a very finely wound resistor.....at some point, the wire gets hot
enough to destroy the di-eletric varnish on the windings and the
windings connect and begin to short across each other....this would run
away and burn up the motor is the motor was not ( or is not ) properly fused for such an
event.
 

You're getting good answers here.  But for your problem it could be a wire rubbing or something like that, that causes a short circuit only wnen the bogie is in the left turn position or by something shifting due to centrifugal force.

It's strange but true - an electric motor is just coils of wire.

If the shaft does not spin, the current flows through the wire as it would have normally done.  In your case, this current flow was high enough your power supply output voltage went very low as it tried to feed as much current as it could.

If the shaft spins, the motor generates a "back EMF", effectively reducing the flow of current in the motor's coils.  The faster it spins, the greater the back EMF and the lower the current flow.

Electric motors are sometimes strange, often counter-intuitive beasts.