If you look in the FIA tech regs for Formula E, this is what they say: 28kW-hr is the most energy that you can take out of the "RESS". In other words, the battery. For example: if the race lasts one hour, the battery can put out 28kW for one hour. If the race lasts two hours, the battery can put out 14kW for two hours, since 14kW x 2hrs = 28kW-hr.
Problem: I can't figure out from the regs if the 28kW-hr is for the full race (1 hour) or for half of the race, until the driver comes in and gets a fresh car. So for now, I will assume that they can consume 28kW-hr in 1/2 hour. As you will see, if it's for the full hour, things only get worse.
If the race lasts 1/2 hour for one car, the battery can put out 56kW for 1/2 hour, since 56kW x 1/2hr = 28kW-hr. But 1kW = 1.34HP. So if the battery is putting 56kW into the motors, it's the same as 75HP. Remember that this is the average over the half hour. Let's say you're accelerating for half the time. So that means you can use 2 x 56kW = 112kW during acceleration, which is equal to 2 x 75HP = 150HP. But the specs also say that the drivers have 270HP available to them when they want to use it. So if the driver has a lead foot, he is going to run out of the 28kW-hr very quickly.
Also, if you put 150HP of electrical power into the motor, you aren't going to get 150HP of mechanical power out, because the motor isn't 100% efficient. But we'll ignore that for now, since I don't know the efficiency.
Let's compare this with the old Formula Ford series. For Formula E, total weight including driver is 800kg. For Formula Ford, the car is 400kg. Figure 70kg for the driver, and you've got 470kg. Formula Ford is (was?) around 125HP at the club level.
Power to weight ratio:
Formula Ford: 125HP/470kg = 0.27HP/kg.
Formula E: 150HP/800kg = 0.19HP/kg average.
Does anybody see a problem with my math? This says that a club Formula Ford is going to blow the doors off a Formula E over the course of a 1/2 hour race, because the E is so heavy, and because of the 28kW-hr energy limit. I believe this also means that a Formula E can't use much wing, because it will cause too much aero drag, which will steal precious energy out of the battery.
It sounds very slow. But I may be misreading the rules. For example, maybe regenerated power is not included in the 28kW-hr energy budget. For the full rulebook: http://www.electrica...Déc.2013_0.pdf
Thoughts/comments?
Edited by Motie, 23 November 2014 - 23:51.