Why not diesel electric trucks?
If a single diesel electric locomotive can pull 27,000,000 pounds, why has it not been scaled down to pull 20-40,000 pounds yet?
Forum Discussion
Quote Yes, I can imagine the drive train...look the last steam engines ever built. They were wildly complicated systems of gears, axles and shafts...and even there not all the wheels were powered. Steam engines do have the advantage that they can put out peak torque from zero RPM similar to electric motors.
I believe hydraulic has been used on some smaller railyard engines but it's not as efficient.
There is no "regen" with diesel locomotives. The available power is what the engine is putting out right now. If the engine puts out more power than the electric motors take up, it's wasted but since trains spend 95%+ of their time running at a steady speed, it's not a big deal. End Quote
Actually, the only steam locomotives that used gears to drive them were low-speed high adhesion locomotives like Shay or Heisler engines that were typically used in logging operations in the early 20th Century. Mainline engines use conventional steam chests, pistons, crossheads, connecting rods and side rods to power the locomotive. As for starting torque, a diesel-electric is much better at starting a train as compared to a steam locomotive. A steam locomotive has to have some movement before it can get a full charge of steam in the pistons. If you're fortunate enough to have an engine with a power reverse, you can charge the pistons to help get things going, but the mechanical reversing bar won't generally let the engineer do this.
As for electrical control in a diesel-electric locomotive, in the older DC powered locomotives the field windings for the traction generator and the traction motors are in series. A locomotive starts with the main power leads to the motors in series. As it picks up speed, the control circuit will momentarily drop load while the relays switch the motors to a series/parallel configuration. As the locomotive picks up more, the control circuit will again momentarily drop load and the relays will shift the motors into full parallel configuration. The load to the motors is controlled by a governor which will automatically reduce power output to the motors and with the traction motors and traction generator fields in series, there's never any excess power generation unless a control malfunction occurs. On locomotives equipped with dynamic braking, the traction motors become the generators and are loaded with a large resistor bank so that EMF is used for braking instead of mechanical brake shoes.
I believe hydraulic has been used on some smaller railyard engines but it's not as efficient.
There is no "regen" with diesel locomotives. The available power is what the engine is putting out right now. If the engine puts out more power than the electric motors take up, it's wasted but since trains spend 95%+ of their time running at a steady speed, it's not a big deal. End Quote
Actually, the only steam locomotives that used gears to drive them were low-speed high adhesion locomotives like Shay or Heisler engines that were typically used in logging operations in the early 20th Century. Mainline engines use conventional steam chests, pistons, crossheads, connecting rods and side rods to power the locomotive. As for starting torque, a diesel-electric is much better at starting a train as compared to a steam locomotive. A steam locomotive has to have some movement before it can get a full charge of steam in the pistons. If you're fortunate enough to have an engine with a power reverse, you can charge the pistons to help get things going, but the mechanical reversing bar won't generally let the engineer do this.
As for electrical control in a diesel-electric locomotive, in the older DC powered locomotives the field windings for the traction generator and the traction motors are in series. A locomotive starts with the main power leads to the motors in series. As it picks up speed, the control circuit will momentarily drop load while the relays switch the motors to a series/parallel configuration. As the locomotive picks up more, the control circuit will again momentarily drop load and the relays will shift the motors into full parallel configuration. The load to the motors is controlled by a governor which will automatically reduce power output to the motors and with the traction motors and traction generator fields in series, there's never any excess power generation unless a control malfunction occurs. On locomotives equipped with dynamic braking, the traction motors become the generators and are loaded with a large resistor bank so that EMF is used for braking instead of mechanical brake shoes.
