I want to use the motor of an electric vehicle as a brake. It is a 36V ~27A motor.
I looked up 500W+ resistors and they are quite pricey, I figured the cheapest alternative would be 100W resistors in parallel.
This is my slightly complicated schematic, I couldn't find a motor symbol, excuse the ignorance.
I don't need to reverse the motor so for the drive I'm just going to use a bunch of MOSFETs (yes I will use MOSFET driver ICs). PWM1 controls the amount of drive current while PWM2 controls the amound of braking, it will only be one or the other never both. I would probably need to add a few more P channel MOSFETS in parallel but I'll think about it later.
So anyway getting back to the problem, in order to achieve 27A of braking current I need a
36V/27A = 1.3 Ohm load. I will order ten 12 Ohm 100W resistors and wire them in parallel this should give me a resistance of about that and still leave some headroom for the resistors because we all know they probably can't live up to what's said on ebay (or at least for long).
What will happen if the resistance is lower than that? The vehicle is moving and is generating plenty of mechanical rotation on the motor shaft, we apply PWM2 100%. I suspect the motor is going to generate more than the rated 27A? If my assumption is correct then why is that? I mean it is clear that the torque on the motor shaft from the vehicle's inertia will be greater than what is required to generate 27A but why does that not just limit the amount of braking torque that the motor can apply?