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AC vs. DC notes from Metric Mind Engineering

I spoke to Victor at Metric Mind Engineering, they offer high end AC systems for EV conversions. Given that most EV hobbyists use DC systems. I am trying to convince myself that an AC system is what I will use. The benefits of DC are:

  1. system costs ~3k less than AC systems
  2. many hobbyists choose DC for its simplicity
  3. does not require sophisticated controller to provide current to the DC motor and therefore, has higher torque for performance “out-of-the-box”.

The benefits of AC are:

  1. more efficient (3-4%) due to higher voltage requirements (312-324V vs. 120-144V typical)
  2. built-in regenerative braking. (10-25% depending on how much braking you do in the driving environment)
  3. Wider rpm ranges so that shifting maybe avoided.
  4. Safer than DC in event of failure. With DC, there is a potential that if the controller fails, the entire voltage from the battery pack is applied to the DC motor, resulting in a run-away! Additional safety “kill switches” and fuseboxes need to be incorporated. With AC, when the controller fails, the AC motor simply comes to a stop because it will not be getting any power from the controller.

I’ve decided on using an AC system given these points. I read somewhere that someone had an issue with his porsche AC conversion not having enough torque and thus lacking performance during acceleration. This issue can be overcome by using a proper controller/inverter (~$6-7k) that will provide a higher current to the motor.


Posted in AC vs DC, MR2EV

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