Im new but i kinda get that the kw of a motor is the number of kilowatts it can use.
I have a 1000w ebike which is 1 kw right?
Close... it should be the number of kilowatts of power it can produce (turning the output shaft). Yes, a kilowatt is one thousand watts.
The nissian leaf has a 110kw motor which i wouldnt say is a high performance car.
All the ev kits appear to be 15-25kw
Im so confused how a leaf has such a big kw rating?
Just looked at a tesla model x 100d has a 311kw motor.
110 kW is 148 hp... not particularly high-performance (especially for the mass of the car), but most drivers will never use that much power. In addition, the rated power is available over a broad range of the car's speed range, so an engine would require a higher peak power to get the same performance, unless the car has a continuously variable transmission.
That's the current Leaf rating; before last year, it was only 80 kW, and that was adequate for most drivers.
The Leaf, like any modern EV, has liquid cooling of at least the stator (some also directly liquid-cool the rotor), with a computer-controlled coolant pump, a substantial radiator for the coolant, and thermostatically controlled fan on the cooler. A typical brushed DC motor has a cheap stamped steel fan wheel stuck on the end of the shaft, if you're lucky.
Tesla's ratings are... interesting. That rating will be for a short period, perhaps only several seconds, before overheating reduces the power which the controller will allow. Tesla is much less conservative than Nissan, so they allow higher motor current as long as they think they can get away with it.
To help understand the importance of cooling, consider an example of a motor being fed 100 kW of power and running at 90% efficiency: it would produce 90 kW of output power and 10 kW of heat. That's like running seven typical plug-in portable room heaters at full power, and putting all of that heat into the motor case.
So are all these kits rated at 10-20kw going to deliver terrible slow performance?
Yes, unless the motor is pushed much harder (higher torque by pushing more current and/or higher speed enabled with more voltage) than the conditions on which the ratings are based.
