On 03/12/2007, Martin K <martin@nnytech.net> wrote:

> David VanHorn wrote:
> >> The only problem is that the efficiency of such a system would be very
> >> poor. You'll get losses at each conversion (gas -> electricity,
> >> electricity -> motor)
> >>
> >
> >
> > Why do trains use this method then? (Minus the batteries)
> >
> Some guesses: a train requires enormous torque to accelerate. Electric
> motors provide enormous torque. The linkage from engine to trucks is
> done easier with electric cables than shafts. Electric motors can regen
> and pump hundreds of kW through power resistors on the roof of the train
> - diesels can jake-brake but it adds mechanical complexity. And I think
> the winner is really that you don't need a transmission that can handle
> thousands of foot-pounds of torque. The series hybrid is a nice CVT to
> boot.
> -
> Martin
> --





 Yep,
> I remember being taught that it was used as a CVT. The larger diesels work
> most efficiently at constant speed, and using cables allows the power to be
> delivered directly to the motors at the wheels. Also this permits multiple
> motors to drive from a single power source which would get very complicated
> using a mechanical drive. Steam engines were known for their ability to slip
> the wheels on the track but by distributing the drive to a number of wheels
> this slip could be reduced without having to resort to (too much ?) sand
> which causes wheel & track wear.
>
> RP
>
>
>
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