If stalling a motor is bad for it (about locomotives)

[cgallery]

I was at an office today, waiting for a server restart, when I looked out the window and saw a two locomotive train starting out.

And I was struck with this question:

If stalling an electric motor (for example, on my band saw) is bad for it, and if locomotives use an electric motor on each axle, then how do they ever start a train from a stop without frying motors?

It would seem that they are starting with all their motors nearly stalled due to the weight they're pulling.

On this particular train they backed all the cars up, then went forward (and I understand why they do that), but they still seemed to struggle to get any speed.

[BobSch]

Here's a Wikipedia article on engines: http://en.wikipedia.org/wiki/Diesel_locomotive

About half-way down there's this

...if a long train is being started, the locomotive may stall as soon as some of the slack has been taken up, as the drag imposed by the train will exceed the tractive force being developed. An experienced engineer (driver) will be able to recognize an incipient stall and will gradually advance the throttle as required to maintain the pace of acceleration.

There's another article on torque converters used by railroads: http://en.wikipedia.org/wiki/Voith_Turbo-Transmissions

[cgallery]

There's another article on torque converters used by railroads: http://en.wikipedia.org/wiki/Voith_Turbo-Transmissions

Amazing. I was under the impression that all locomotives use electric drives exclusively.

So back to the "why don't the electric motors go supernova when locked up," it would seem that they are current limited and the conductor increases current just enough to get the train rolling, but not enough to burn the windings up?

So a related question: If I had a 6.5-amp motor on my bandsaw, and put it on a circuit that could supply a maximum of 5-amps all day long but no more, could I lock-up the motor without fear of causing damage to it (the motor)?

[LCHIEN]

they're almost certainly designed to deliver low speed/stalled torque required to start moving the locomotive and train load without damage. There's probably all kinds of specifications about how much load a loco can pull from a dead stop and how many locos in tandem or plural it takes to move a load of a certain dead weight if it exceeds the maximum capacity of one loco.

those superbig induction motors provide maximum torque at stalling... just can't keep it there, you've got to get it moving.

Either that or they'd all be broken by now.

[Hoover]

A hybrid on steroids.

[master53yoda]

The electric motors used in transportation are variable output motors. typically they very the voltage to the motor which varies the current draw and power delivered. the weak link on a locomotive is the friction between the wheels and the tracks. if they dumped full power to the motors the train wheels would spin on the track as the old steam engine wheels did, At start up they limit how much power is delivered to the friction level on the wheel.

I'm not sure but i would think that the new engines have wheel sensors that tell if the wheel is starting to spin and reduces the power delivered to the wheel to match maximum torque delivered to the track. ( the opposite of anti lock brakes)

[pierhogunn2]

wonder if the research being done by Jaguar (small turbines to drive generators), and all of the electric traction motor experience will pay off for small turbine powered hybrids... would be nice to pour anything into the thing and away you go

[cabinetman]

I didn't notice any stalling on my Lionel.

(Sorry...I couldn't resist)
.

[master53yoda]

I didn't notice any stalling on my Lionel.

(Sorry...I couldn't resist)
.

Yea but that I would think ?? that Lionel engine weighs more in perspective to a real locomotive, and the power is delivered equally to all the wheels.

[jackellis]

wonder if the research being done by Jaguar (small turbines to drive generators), and all of the electric traction motor experience will pay off for small turbine powered hybrids... would be nice to pour anything into the thing and away you go

Turbine engines are relatively inefficient compared with piston engines, especially at part load. They have a huge power-to-weight ratio advantage and they can make much more power than a piston engine of similar size but except for the big turbine engines used on airliners, they use more fuel to produce the same power - sometimes a lot more. That's why you see them on M1A1 tanks but not on long-haul trucks or in cars.

I would love to have a turbine engine on the front of my airplane because it would be a lot more reliable than the 1940s technology that's currently under the hood. Rolls Royce makes a 250 hp unit that's comparable to my 235 hp air cooled flat six. Trouble is, besides costing at least two or three times what my airplane is currently worth, I'd have to burn more Jet A, which is not materially cheaper than avgas and is sometimes more expensive.