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That has not been my experience. Diesel generator-motor sets are much heavier than a diesel engine with mechanical transmission and are less efficient. That doe

That has not been my experience. Diesel generator-motor sets are much heavier than a diesel engine with mechanical transmission and are less efficient. That does not even take into account a buffer battery weight which you pretty much need for power draw spikes and regenerative braking. Just look at say a Cummins ISB with Allison transmission at 300hp, that's around 225 kilowatts. That combo weighs around 1500 lbs, maybe closer to 2000 with running gear if your comparing to hub motors. A bare frame generator putting out 200+ kw its going to be well over 4000lbs plus whatever hub motors and motor controllers and power systems and batteries weigh. You can go smaller on the generator and make it up on the battery which means more weight, but even a 100kw generator is going to be around 3000lbs and you won't be able to utilize full power for long periods (long grades). Perhaps some advanced generator might be lighter, but it essentially the engine with the same size and weight generator attached to it as needed for motors of equivalent power output. Mechanical transmission on the other hand are pretty light comparatively and have much less losses than the mechanical-electrical-mechanical double conversion.

samatman 8y ago
This isn't a fair comparison, because you're considering a generator that's intended for stationary use. Of course this is going to be heavier than one intended for a vehicle, because the weight isn't a consideration, and lighter is more expensive (more precise, higher-quality materials). What you'd want to be looking at is train powertrains, which are uniformly diesel-electric, because this is the most efficient power configuration. Or the Chevy Volt, for a smaller example which happens to run on gasoline.
- dsfyu404ed 8y ago
  >this is the most efficient power configuration. Trains have 4+ driven axles mounted on bogies that swivel under the chassis. All wheels must be driven (steel on steel doesn't give you much traction) Diesel electric is used in trains because any mechanic transmission that can do that job would be a Rube Goldberg contraption. A mechanical gearbox is more efficient way of transmitting power because if you've sized things right cruising RPM will be direct drive (no loss from gear friction).
- SigmundA 8y ago
  Can you point me to a light weight 100kw or 200kw genset that is under 1500 lbs? Bottom line even if a 200kw genset plus motors and controllers was the same weight as a 200kw engine hooked to a transmission, it would have lower efficiency due to conversion losses unless we get practical superconductors. Trains do not use diesel electric drives trains for efficiency or weight, the need precise traction control to prevent the steel wheels from slipping on the tracks to get moving, the electric drive train gives them that. The actual efficiency is lower than a mechanical transmission once up to speed due to double conversion losses. Modern mechanical transmissions are actually very efficient with very low losses. The Chevy volt also bypasses the electric system at highways speeds due to the inefficiency of converting mechanical energy to electrical and back to mechanical as most (all?) production hybrids. The Gen 2 Volt actually more aggressively move to mechanical drive at lower speed as it was found to be more efficient. The Volt is also heavier then the Cruze even though they share the same platform. This is an excellent breakdown of the Volt operating modes, in CS2 and CS3 mode the engine is driving the wheels mechnically: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/ https://gm-volt.com/2015/02/20/gen-2-volt-transmission-opera... Gasoline hybrids like the volt also typically rely on the Atkinson cycle to get better highway efficiency at the expense of torque which is made up for by the electric drivetrain. Diesels are even more efficient and have plenty of torque but also heavier due to a more robust design, this is why they are much less popular in hybrid configurations except in specialized applications like city buses with extreme urban start stop usage.

samatman 8y ago

This isn't a fair comparison, because you're considering a generator that's intended for stationary use. Of course this is going to be heavier than one intended for a vehicle, because the weight isn't a consideration, and lighter is more expensive (more precise, higher-quality materials). What you'd want to be looking at is train powertrains, which are uniformly diesel-electric, because this is the most efficient power configuration. Or the Chevy Volt, for a smaller example which happens to run on gasoline.

dsfyu404ed 8y ago
>this is the most efficient power configuration. Trains have 4+ driven axles mounted on bogies that swivel under the chassis. All wheels must be driven (steel on steel doesn't give you much traction) Diesel electric is used in trains because any mechanic transmission that can do that job would be a Rube Goldberg contraption. A mechanical gearbox is more efficient way of transmitting power because if you've sized things right cruising RPM will be direct drive (no loss from gear friction).
SigmundA 8y ago
Can you point me to a light weight 100kw or 200kw genset that is under 1500 lbs? Bottom line even if a 200kw genset plus motors and controllers was the same weight as a 200kw engine hooked to a transmission, it would have lower efficiency due to conversion losses unless we get practical superconductors. Trains do not use diesel electric drives trains for efficiency or weight, the need precise traction control to prevent the steel wheels from slipping on the tracks to get moving, the electric drive train gives them that. The actual efficiency is lower than a mechanical transmission once up to speed due to double conversion losses. Modern mechanical transmissions are actually very efficient with very low losses. The Chevy volt also bypasses the electric system at highways speeds due to the inefficiency of converting mechanical energy to electrical and back to mechanical as most (all?) production hybrids. The Gen 2 Volt actually more aggressively move to mechanical drive at lower speed as it was found to be more efficient. The Volt is also heavier then the Cruze even though they share the same platform. This is an excellent breakdown of the Volt operating modes, in CS2 and CS3 mode the engine is driving the wheels mechnically: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-operating-modes-explained/ https://gm-volt.com/2015/02/20/gen-2-volt-transmission-opera... Gasoline hybrids like the volt also typically rely on the Atkinson cycle to get better highway efficiency at the expense of torque which is made up for by the electric drivetrain. Diesels are even more efficient and have plenty of torque but also heavier due to a more robust design, this is why they are much less popular in hybrid configurations except in specialized applications like city buses with extreme urban start stop usage.