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Conversion to electric vehicle...

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Advanced Member level 2
Jan 29, 2004
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Hello all.
What differs about current consumption in installing a 8KW motor or a 16KW motor for the exact same use of an electric vehicle ?
The 16 KW motor is more capable than the 8KW one, of course; can climb faster, or accelerate in less time, or tow more weight... But if the needs/demand is never over 4 KW by the speed, acceleration, load, a 16KW motor will consume more, less or equal as the 8KW ?
In other words... two $0 same weight motors, install a large or a small if both are well over the needs ? Will one consume batteries faster for the exact same use ?

If you knew for a fact what you needed, sure, size
it to the bone.

But if it's mass marketed to emotional customers
then go big, because your competition will.

There might be minor load-point efficiency differences
as there are construction differences. Single digit
percent range I'd expect. Matters not because you
are selecting the very best free motor, right?

Yes, as you know, the 16kW motor will be heavier in its will mean more battery consumption. Also, their will be more motor iron, as it shoudlnt again, the 16kw will be heavier.

the 16kW will be heavier - but at cruise it's excess copper will make it more efficient - also if it is voltage controlled ( as likely ) it's iron losses may be on a par with the 8kW under cruise conditions.

It will have less losses under the same acceleration conditions, and will again be slightly more efficient under regen braking

Assuming that the electric vehicle is always operating within the same range of speed, acceleration, and load, and that both the 8KW and 16KW motors are equally efficient in converting electrical energy into mechanical energy, then the current consumption of the two motors should be the same when they are used for the exact same purpose.

However, it is important to note that the larger motor may have a higher idle current, which is the current that the motor draws when it is running without maintenance. This means that the larger motor may consume more energy when the vehicle is at rest or traveling at low speeds, which could reduce the overall range of the electric vehicle.
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Such a choice would probably be made based on a full drive cycle
analysis of total energy taken. Of course the character of that test
condition set is highly gamed and maybe not representative of your
particular care-abouts (like, you want to use an urban / suburban
driving profile when you have a 100 mile freeway commute?). Or
conversely fixate on the 1-passenger max range when your real duty
is heavy haulage with stops every 100 ft?

By design one would hope a larger motor might have lower copper losses if enough care is also taken not exceeding the peak demand surge.

But it always depends on your assumptions for design. These curves assume drawing maximum load thus at 0 RPM efficiency is 0.

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