Modern motor controllers are extremely efficient at almost any speed.
An example is brushless servo motors.
They are about 1/4 the size, and 1/10 the mass, of my old 3-phase 1/2 hp
Bridgeport motor.
The Bp is 18 kg, for 0.5 Hp continuous output.
Its made in maybe 1950 (? 1940), and is near silent.
The 750 W == 1 Hp AC brushless servo motor is 3 kg, at 1/3 the size, and
will output 750 W forever.
Near silent, longevity == 10.000 work hours.
The 2.5 kW servo is ==8 kg, and equally good.
The electronics have fan cooling, unlike the smaller 750 W ones.
VFD-driven 3-phase motors (ie industrial motors) == servo motors, these
days, of different (electronic) designs.
Depending on the design, boat motors may or may not be as efficient.
Mostly, they are not, and thus need cooling.
There is no engineering reason for this, just that the boat market is so
small, most stuff does not come from industry, today (yet).
Usually, where you get lots of amps, heat becomes a factor.
Thus, higher voltage == tends to equate to "better".
Price has no bearing on the matter.
Some servos I use (750) cost 590€ for the motor, controller, everything.
Some others (yaskawa,Siemens) cost about 1500 for the electronics,
alone, and 3000€ for everything.
A 3-phase VFD motor from surplus center, for example, can cost 1500$ for
10 Hp, and 2500$ for 150 hp.
Some controllers for brushed motors need cooling at higher powers.
A well known respected KBIC controller is an example.
Thus, it will be "less efficient" - and this is mostly seen in that more
modern, brushless, designs tend to be better in terms of torque,
efficiency, longevity, maintenance etc.
All above may or may not be relevant -
As for those buying a kit, there are only a relatively few options, and
price + other considerations tend to dictate what you can choose.
For those making their own set from scratch -
Its neither hard not easy - somewhere in between.
The motor and controller is the easy part - and anything modern and
industrial meant for harsh duty/service will work well.
It just needs to be coupled to a suitable driveline.
A boat motor and controller is just about the easiest thing there is,
technically.
Similar to a conveyor belt.
Heavy varying loads for an extended time.
On 10/03/2015 13:06, billhopen@yahoo.com [electricboats] wrote:
> I've a question about your motor efficiency, when you run your motor
> at lower power, does the motor itself get inefficient? I've seen
> power charts for certain motors that seem to indicate that at lower
> speeds, half the electric power is wasted, but at high output they are
> 90% efficient
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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