Battery buffers (again)

[Martin Jackson <mjackson@vcn.bc.ca>]

  "Eric Chang" <ericchang@my-deja.com> wrote:

"Obviously, there is a long way to go.  The most range improvement
possible is 120%.  The EV1 does not attain this because it is very
inefficient when the motor is turning at slow speeds.  

  The only important losses that relate to speed are the ones that are 
  produced at no load. The fan, windage and bearing losses are basically 
  the power required to rotate the motor with a 6, 8 12 or 24 V battery 
  at a measured speed and Amperage. When you load down the shaft, 
  resistive, inductive and eddy current-magnetic losses come into play.

  At zero rpm, any Amps put into the motor do no work and produce only 
  heat. Of course, you don't stay there long. As the rpm increases, 
  efficiency improves because more work / kW is being done (even though 
  mechanical loss is increasing).

  Repeatedly, I hear that bigger motors are more efficient, but they are 
  run at lower than the load required for their best efficiency.

"The silicon transmission just does not match an ordinary mechanical one."

  Here, you're alluding that the inverter is the transmission analog. I
  rather believe that it is the carburator analog while the motor is the
  transmission analog. Not worth fighting about here. In any case, the 
  inverter - controller isn't the point of losses, the motor is.

"One EV club member claimed that the starting efficiency was no more 
than a few percent.  Anywhere efficiency is added along the way, the 
gain will improve."

  Below the design point of a DC motor (rpm & torque or power) and in 
  the low range of operation of any motor, the efficiency decreases to
  zero at no load (even spinning like mad). The only thing being 
  produced at no load is heat. The smallest motor that achieves your
  cruising speed is far better stuck in traffic than the bigger, faster 
  accelerating motor since it operates at efficient rated power more 
  often. 

  As to electric heat, while the resistor is 100% efficient at producing 
  heat, it consumes more energy than moving heat with a heat pump. So,
  the cycle efficiency of the heat pump can be poor and still save 
  operating cost. Entropy loss here only means that you aren't producing 
  heat to lose, you're moving heat you're going to lose. :) 
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