Quote:
Originally Posted by Should be biking
50mpg from a 50% efficient engine is disappointing.
I don't know exactly what the conversion losses add up to when going from engine to generator to battery to electric motor, but that's got to be at least 10% more than a manual or automatic transmission connected directly to an engine.
If you always want to have enough power to drive up a long hill, the battery charging threshold would have to be pretty high, so you'd spend most of your time with the engine running and keeping the battery topped up. And at that point your mileage would be worse than a conventional drivetrain because of the conversion losses.
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50 MPG is never disappointing.
Of course it's more efficient to use the engine directly to propel the car, but 50 HP isn't enough for acceleration and ascending hills, which is why for the sake of simplicity and reliability you'd have a series hybrid.
Lets say the generator is contributing 50 HP towards ascending a hill, the battery might only need to supply another 50 HP. You could do that for 20 minutes and only consume about 12 kWh of capacity. If the car had a 60 kWh battery, you could set the lower threshold for 35% when the generator kicks on.
You'd normally get about 165 miles of EV range before the generator kicked on.
It would be simple to allow an override to allow the battery to discharge deeper before running the generator if you knew you'd reach the destination before running out of juice.
Just as simple to allow one to manually start the generator if you know you'll need the extra juice for something.
There's just about no practical situation where 50 HP and a 60 kWh battery wouldn't be more than sufficient, and quite easy to program in limits that reduce speed for the extremely rare times it isn't.
I used WAG figures for the generator and battery, but I bet that is very conservative. One could probably get away with a 40 kWh battery and 40 HP generator and make a fantastic car.