but this doesn’t become a *edit: significant factor till the kv or voltage is much higher than is being discussed
but these losses are insignificant when the higher voltage motor is geared to the same top speed as the lower voltage motor
No depends on the motor and how many poles and how used ( what current and speed driven)
I’m sorry, I can’t follow both of you.
If someone could like me a motor which can provide more than 20km of range with 20km/h on 12x 50E cells I would be very thankful.
you’ll have a practical limit in terms of gearing reduction so use the highest kv, lowest electrical resistance, largest size motor and highest battery voltage that allows the lowest adequate no load speed and practical gearing ratio for your tire diameter if you care mostly about efficiency.
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@Chricious-- i ran a simulation for you comparing a 50kv (0.32ohm) direct drive vs a 200kv (0.02ohm) motor with 4:1 gear reduction (same battery voltage, same motor current), both sustaining 25mph on a 10% slope…
^notice:
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the same size same copper fill 200kv motor has 1/16th the electrical resistance of the 50kv direct drive motor (200kv has 1/4x fewer turns and 4x greater cross section wire than the 50kv)
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in the bottom left chart, purple line – vehicle thrust is the same for both vehicles
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in the bottom middle chart, green line – ohmic motor heating drops from about 250w total with the 50kv DD to around 16w with the 200kv 4:1 reduction
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in the top left chart, green line – electrical to mechanical efficiency is far higher with the 200kv
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top left chart, blue line – motor current is the same – 20a with both motors
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top middle chart, yellow line – electrical wattage is far lower with the 200kv motor than the 50kv direct drive motor for the same mechanical wattage output (red line, same chart)
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top right chart, yellow line – the 200kv motor torque at the same motor current is 1/4th the torque of the 50kv motor, but the 200kv motor is spinning 4 times faster with 4 times the gear reduction, so you get the same mechanical power to the wheels either way
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bottom right chart, purple line – battery current is less with the 200kv 4:1 reduction than the 50kv direct drive
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graphs
I’m just going to drop this conversation here… discuss
So the faster you spin with higher reduction, the better. But what about ESC efficiency?
For identical setups one running 50k erpm and the other 100k erpm with twice the reduction, will the 100k erpm produce more waste heat in the ESC?
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since the motor current is the same in both cases, the ohmic heating of the controller is also the same, or slightly cooler with the 200kv since the battery current is less
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So the switching frequency has no effect on mosfet efficiency? I was sure I read somewhere that higher switching frequency will produce more heat at the same current. 
Just throwing another point
A motor is most efficient when the copper loses are equal to the core losses
If this is something you will pursue seriously, a inertia dynamometer is something to look for
Grab a bunch of motors and test them, while the copper losses and Kv tell part of the story, we don’t have data on core loses, and at the low load and low currents you will run at 20 km/h, the core loses can play a significantly part in the the overall loses
My current board, with dual 6355 can do 7.8 Wh/km it I limit the top speed to 25 km/h
So your 12S1P if 50E (~222 Wh) could already do the 20 km your require at even faster than 20 km/h
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the switching frequency is not the same as the commutation frequency… the switching frequency is the frequency that the battery is disconnected and reconnected to the motor during a single commutation, and is unaffected by the motor spinning faster
the controller is doing this hundreds of times (or at least dozens) during a single commutation:
the switching frequency is responsible for the tiny spikes that are visible in this current plot of the relatively constant motor current in between commutations in BLDC:
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Up to a point, core losses are proportional to speed square or sometimes cubed, there is a point that it makes no sense to spin the motors fast since you just loose efficiency
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@professor_shartsis @Pedrodemio
So would something like 270kv motors make sense on a 12s setup provided sufficient reduction can be achieved for a reasonable top speed?
Seems like that setup will have very little cogging on sensorless starts.
Very bad freeroll on the other hand. 
i’d say it makes sense
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Be nice to see how much current used w that gearing at full speed no load. With belt on and off
Id say we don’t now due to the possible way higher core loses, if you have given motor at hand, plug it in, go in VESC tool, use the rpm control and increase in 1000 rpm increments while taking note at the power consumption, if at some point it starts raising way faster, it would not be more efficient to use this setup
There is so much variables that it’s hard to say what is more efficient, even more considering that riding style matters
This case you proposed, if the riders usually just play around at lower speeds, it would probably have an advantage since the bigger gearing means less current in the esc, but if he keeps at full speed all the time, there a chance a lower Kv motor that spins slower is more efficient
In my experience unless your setup is really inefficient with undersized components, it won’t matter too much
When I tried a 1:1 reduction in my board instead of the usual 14/34, the difference in consumption was just 10% more
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but that 10% increase all went into heating up your motor (and controller)… 10% of 2000w is 200w… which is a lot of heat
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Yeah, it is, but in my mind it would be a whole lot more
The sweep spot is actually not a spot
the wattage that goes to heat production is always a small percentage of the overall wattage drawn from the battery (the rest goes to mechanical wattage)… but when larger and larger percentages of the total wattage start going to heat production rather than mechanical… suddenly things start getting quite hot quite quickly indeed
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Waiting for somebody to come up with a pint sized CVT / IVT system for any of these motors… then we talk proper efficiency - I could be wrong though.
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