liveforphysics
100 TW
Persanity said:
No, you've completely misunderstood the reason why that fairly silly pdf says series hybrids are more efficient.
If you've all ready got mechanical power somewhere, a twisting shaft from an engine for example, you're not going to put it to the ground any more efficiently than directly coupling it with a drive-shaft or chain or gear or sprocket etc. Every energy conversion suffers efficiency losses, let's say that you're going for super efficiency at high power with PMBLDC gen/motor to go from the engine to a generator (~93%) to controller (~98%) to traction motor (~93%) and cabling loss (99.5%), you're looking at an optimistic 84% combined system efficiency, and this assumes the traction motor has no further drivetrain losses to the wheel (like a hubmotor).
In the event you're looking to get decent performance, AKA, not running the generator at it's maximum output to maintain your maximum economy cruise speed, you're going to be suffering substantial core losses just to turn that generator and traction motor. This is why AC induction motors or series-wound DC motors start to make sense for high performance EV's, because a PM motor that can output 200hp may have 10hp purely of core loss to make it spin at your cruising speed where you might only require 20hp at the wheels to be moving down the road, but you're stuck sending the motor 30hp because you've gotta eat that 10hp of core-loss overhead. So, you need to generate 50% more power than you require to cruise. Now on the generator side, you have the same penalty, making the engine need to generate 40hp of mechanical power to deliver your cruising power needs of 20hp. This makes your system efficiency during cruising sub 50%...
So, you go to induction generator/motor or a series DC so your core loss is small while cruising, but you're still able to have decent performance when you want it. Now your under high power efficiency is about the same as under high loads as light loads, about 85% for some well designed stuff. So, 85% gen 98% controller 85% traction motor 99.5% cabling, and your combined system efficiency is ~70%.
I know from dyno'ing plenty of racecar engine builds in and out of the car, that a Honda FWD engine/transmission/axles/wheels/tire to dyno roller interface, that 88% system loss from engine to the rubber of the tire on the roller.
Persanity said:
I pay 20k for race engines for my racecars (though I try to keep them under 10k these days). I would happily pay 10k for something that would give my vehicle an advantage. However, this would only give my vehicle an advantage in drive train wear and service intervals (which I don't really care about). This is why you see locomotives using series diesel systems, no clutch to slip or torque converter to heat fluids and/or tranny bands to slip while taking off from a stop, starting from a stop on a mountain pass, etc, situations where mechanical drivetrains would rapidly wear out.
) out of your posts. Maybe you'll come back after learning more. Maybe a bit of school might come in handy?
