Electric Power for Larger Boats

Inverter Control Box for the Honda Motor Drive:
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A hacker’s dream: Plug and Play control of motors.

In response to the 2nd edition of my book Electric Propulsion for Boats, I received a number of questions and requests for ideas to power larger boats in the 30 to 50 foot range with 20 HP or more.

Supplying the necessary battery power for boats of this size is easy. By putting enough 12 volt batteries in series, voltages of 120 to 240 volts can be obtained. Efficient 3 phase AC induction motors of any horsepower can also be obtained off-the-shelf. The missing component is a 3 phase inverter capable of controlling the speed and direction of these powerful motors.

To my knowledge, the only off-the-shelf inverters available for the control of large 3 phase motors cost several thousand dollars. They require 230/460 volt 3 phase input which is then rectified into DC and then inverted back to a variable 3 phase AC power to control the speed of the motor. Such a device could probably be modified to accept the DC from the battery instead of the rectified DC, but considering the cost of these devices, I never experimented with them.

Control Box for the Honda Inverter

With the advent of the Toyota Prius and the Honda Insight hybrid cars, 3 phase inverter/controllers for motors in the 20 HP range are readily available at junk yards, at E-Bay and on the Internet for less than $200. In the case of the Honda inverter, the device can be turned into a motor controller without any changes whatsoever to the inverter.


Electric Propulsion for Boats book
1st Edition: Electric Propulsion for Boats