Vasily wrote:I decided to use this brushless motor
Aeolian C6374KV170 Outrunner Brushless Motor
Rotational Speed: 170 (kv) RPM/V
Continuous Current: 100A
Max. Current: 110A
Input Voltage: 14.8 - 37V
Max. Efficiency: 98%
No Load Current: 1.4A
Internal Resistance: 56m(Omega)
Motor Weight (Motor only): 909g
Do not believe the efficiency specification. It is very exaggerated and faulthy.
Motors perform accordingly to the laws of physics and the specs of Aeolian C6374KV170 equals to 91.21% efficiency, not 98% which of course is a lie.
Calculation data: Voltage = 37V: No Load = 1.4A: RI motor = 0.056R: Pmax = 3000W
37V Safe Efficiency = 89.02% at 510W output and 15.49A input at 62.91W losses (safe level)
37V Peak Efficiency = 91.21% at 1020W output and 30.23A input at 98.34W losses (warm motor)
37V Med Efficiency = 90.51% at 1500W output and 44.79A input at 157.24W losses (hot motor)
37V Worst Efficiency = 84.43% at 3000W output and 96.05A input at 553.44W losses (the motor burns)
If you lower the input voltage the efficiency gets even worse, actually really bad.
Calculation data: Voltage = 24V: No Load = 1.4A: RI motor = 0.056R: Pmax = 3000W
24V Peak Efficiency = 89.20% at 510W output and 23.83A input at 61.76W losses (safe level)
24V Med Efficiency = 84.47% at 1200W output and 59.20A input at 220.68W losses (extremely hot motor)
24V Worst Efficiency = 54.17% at 2550W output and 196.13A input at 2157.13W losses (the motor explodes into flames)
Do not belive all these chinese motor manufacturers. Their specifications are mostly very exaggerated.
In order to reach 98% efficency at 37V input the motor must have less than 8mR phase resistance at 0.5A no load current.
Calculating motor efficiency is easy but it's even easier to get fooled if not being careful when selecting a proper motor.
Vasily wrote:Maybe I should use another motor?
That's up to your target design. If you can live with lower efficency this motor is OK to use when properly cooled.
As can be seen in above data it's fine up to 1100W output at 37V input if properly geared down to match the propeller you intend to use.
1100W = 1.5Hp, a nice and good power level for a small sized boat.