T-Pain Is On A Boat: Re: [Electric Boats] Need help with choosing the right motor!

Thursday, August 4, 2016

Re: [Electric Boats] Need help with choosing the right motor!

My opinion.
I am not trying to sell anything.
Use your favourity nearby industrial supplier.

Use an AC brushless servo motor+driver, at 220V AC (because its cots ie cheap and good).
They are very efficient at all speeds, from 0 to max rpm.

Much better than anything else.
They consume 0 watts unless they need to work.

My experience is that the AC servos "feel" about twice as good as good PM induction motors.

This is proven by the fact that they need much less (half?) the cooling, in 24x7 100% load, vs other tech (PM motors, AC induction).
The less cooling the motor needs, the more efficient it is.
Motor is actually very efficient, but the electronics have fans/heat.
(IGBT I think, don´t know).

I use this stuff on CNC industrial-type equpipment.
Ie heavy load, can run 30 hours 100% non-stop, expected to have 1 error / 5000 hours use.

Example.
Old AC induction motor, 1.5 kw, industrial, vs
new 2.5 kW AC servo.
New motor is half the size (1/4 the volume), for about 160% the power. About the same mass, much more dense. About 20 kg for motor.
So, about 7x better power/size, the new motor has significantly less heat in 1/4 the size for 1.6x more power, or its 660% "better".

The servo motor accelerates to top speed in 20 ms, or 0.02 secs, 3000 rpm, or about 50x faster (no load).
An ac induction motor abut 1 sec.
A 3-phase motor maybe 0.5 secs (depends).
In practice, I use about 0.5-1 sec ramp to not stress mechanical components.

Example:
The 2.5 kW motor, I import and sell these for CNC use, costs about 1400€, with motor, cables, encoder, servo drive, everything.
VAT, EU, here in Spain.

Almost any size is available from manufacturers.

A 2.5 kW AC servo, that I used as the example and use as the spindle motor on my lathe, has 10 Nm continuous, 0-3000 rpm.
It has 30 Nm peak torque, for upto 3 secs (you probably wont care).

I think, based on my understanding and experience and training, it is approx as efficient at all speeds, but don´t really know for a fact.
Based on my understanding of physics, the least efficiency of the servo would be at full speed, where stator/hystereresis/induction or reluctance/magnetic flux losses would be greatest.
The other corner case might be full torque load at zero rpm.