Quote:
Originally Posted by TT-Man
Hi e*clipse, thanks for the info posted on the Toyota MGR.
I also several years ago bought an MGR unit, thinking all the same thoughts.
I wanted to convert a small car to a local runabout.
Then started discovering the limitations.
EV's need continuous power ratings.
I thought Toyota MGs would be conservatively rated ..... seemingly not.
The 50kW rating on the MGR seems to be 18 seconds.
Logical for acceleration 0 to 60 mph so to speak.
A continuous or RMS value may not even be half at 25 kW. That might have been OK, until you find that the power available .... apparently .... is not a linear relationship to voltage. Seemingly, the motor is a combination permanent magnet and reluctance motor, all designed about the 650v applied.
I have wondered about rewinding or cutting the windings mid-point to parallel, messy.
And splitting the star point to make a delta conversion will not work.
However, I have an alternative, split the star point. bring out the 3 connections, then run a second switching inverter to effectively parallel the 2 active windings. This inveror at the star point would be slave to the main inverter.
The perceived benefit would then allow the battery voltage to be a more accepable 325 volts maintaining the original performance of the MGR.
So 18 seconds acceleration with High low end torque, and for me 25 kW continuous running power.
I may draw up my proposition and post.
The hard bit making a master and slave invertor!!
Cheers,
TT-Man
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I'm curious - what do you think I'm thinking? All my statements about this motor have been based in solid engineering principles.
Just for starters: No, EV's don't need continuous power ratings. Their operating environment is extremely variable, allowing significantly different peak and continuous power ratings. Industrial motors tend to be built for continuous power ratings and are considerably larger (and heavier) than similarly rated power plants found on vehicles. Thus it's wise to select a motor based on it's ability to provide continuous power for a continuous requirement, like cruising on the highway at 65mph. This number is considerably smaller than the power required to accellerate up to 65mph in 10 seconds. This is true of all vehicles, whether powered by a diesel engine or an electric motor. The 25kW continuous power rating of the MGR is more than adequate for a small runabout like freebeard wants to build. My interest in a multi-motor system is based on dynamic requirements, not keeping up with traffic in a commute.
Also, changing from wye to delta will not change the power output capability of a motor, just the bus voltage. But you don't get something for nothing, and the current will have to be increased if the voltage is decreased. This extra current will result in more I^2R heating, demanding more heat rejection just to keep the same continuous power output.
The continuous power output ability of any motor eventually goes back to the motor's ability to reject waste heat. An example of this are the motors used in EV drag racers. If the motors are cold at the start of the 10 seconds they are used, then the thermal mass of the motor keeps temperatures within a reasonable range even though they pushed to well over 10X their continuous power rating. Again, the ability to remove waste heat is one of the most important factors affecting a motor's power output. This is true for both electric motors and internal combustion motors. This is why people bother with water cooled motors and the military is experimenting with oil spray cooling.
- E*clipse