# Small boats and Solar Power

Discussion in 'Boat Design' started by TomCat58, Aug 31, 2014.

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### TomCat58Junior Member

I wonder how many post I need to start posting pictures ?

TomCat

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### YobarnacleSenior Member holding true course

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Both "outrunners" and "inrunners" are three phase motors. You will need a special controller that is capable of chopping up the single phase input voltage. At present the controllers cost more than the motors. No matter, the three phase motors seem to deliver better performance for a given watt input than the brushed types.

For folks who are not up to speed on how the calculations are done........You need only two laws of electricity; Ohms law and Watts law. Ohms law states that Amperage is the quotient of voltage divided by resistance. For whatever reason the three factors have letter symbols to represent them. Amperage is represented by the symbol I, voltage is E and resistance is R ....We write the simple equation.....I=E/R That is not the most useful equation for motor analysis. That one needs Watts law. which is P=I x E where P is to be thought of as power. We can transpose that equation any way that we like. P/E = I and P/I + E and so on.

One electrical horsepower is ...lets use round numbers...750 watts. Close enough. If a motor is to produce one HP then we can plug in voltage and amperage to determine what the wattage is. We can transpose that equation to suit our convenience. Say you are using 24 volt batteries, what will the amperage be to produce 750 watts of potential power? Plug in the numbers. 750=24 x I Transpose to get......750/24 = 31.25 amps. Say that you wanted to contain the amperage output to 20. You will need to increase the voltage to get the one horsepower. 750/20 = 37.5 volts.

Electric motors are also generators. Electricity can be produced with three simple requirements. They are: A magnetic field, a conductor to cut through the magnetic field, and relative motion between the field and the conductor. Either the conductor coils or the magnetic field is whirling around inside the motor. Sure enough the motor generates some electricity that opposes the input electricity. That is called Back EMF. The back voltage is determined by the speed of the relative motion between the conductors and the magnetic field.

When the motor runs slowly, like when you over load it with too much prop, the back EMF is diminished. That means that input voltage goes higher. But the input voltage has a limited threshold and so the amperage increases to satisfy Watts law. You can then smoke off the controller which has a limited ampacity. Avoid weed tangles which may stall the prop.

The bottom line is that it is prudent to install an inline fuse between the motor and the controller. Fuses are cheap, controllers are not cheap.

I am aware that many of you know all about the laws of electricity. I did this brief explanation for the benefit of those who are not quite as familiar with the two laws and their implications.

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### TomCat58Junior Member

Gauges I use on my solar canoe. Amps in from solar panels and Amps out to the electric trolling motor. total cost \$15.

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### portacruiseSenior Member

I wonder why controllers and motors on troll motors didn't come wired with fuses or circuit breakers already? Is it because the fast blow type are too sensitive to typical current variations and the slow blow type to slow to provide protection?

PC

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### gonzoSenior Member

Motors on trolling motors do come with a fuse. If the fuse is not installed the warranty is voided.

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### TomCat58Junior Member

I have Minn Kota Max Endura and it has no fuse. Bought it new (2013) and they recommend a 50 amp breaker as close to the battery as possible. I have not had the motor apart to see if there is a fuse in it but the manual should of stated if it did.

What trolling motor are you running that has a fuse and where is it located ?

Tom Cat

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