Thursday, October 15, 2015

How I build my electric outboard motor

This blog post is an informational addition to the video I made about my electric outboard motor. If you haven't watch it yet, do so now(here on YouTube) and continue this after that :)
But first I have to make sure that you know what is my background in electricity and outboards. Year ago when I bought my boat I had no clue on electricity. I knew about plus and minus, but nothing about how voltage, amps etc. All I know and what I'm gonna talk about here is from googling stuff and trial/error experiments. Same goes with outboard motors. First time I opened a cover from a motor was when I had bought the my first "shell" for my project. So I had to improvise and figure out a lot of things. So take everything below this with little grain of salt and please feel free to comment and correct if there's a need for it. Thanks, now let's get started!
There are three main components when building an electric outboard motor: old outboard body, electric motor and controller. There are numerous options for each and even greater number of combinations. I did a lot of research on the internet before I chose the motor and the controller. I found some connections to these Kelly controllers from people who had build similar motors.
So I ended up with buying PM48301,300A,48V controller and MARS 0909 BRUSH-TYPE PM DC motor. I also bought some cables and a 0-5V throttle pot from ebay. The outboards that I converted were Evinrude 6hp and Terhi Valmet 15hp.
Because the motor top rpm is around 2100 in 24V the smaller propeller on Evinrude wasnt giving enough challenge for the motor(using only 40 amps) and going only 3,5kn I decided to go for a bigger body and the 15hp Terhi got me to 4kn and using about 60 amps. The motor got to the max rpm easily in 24 volts so I got the idea of doubling the voltage to 48V and doubling the rpm to 4200. This mode made a lot more resistant for the motor, so it ended up using more than 120 amps and i had to adjust the max amps from the controller down to 100 because the motor is rated only for 95 amps continuously. This double voltage mode I named Mörkömoodi(loose Finnish translation of beastmode :) and to be used only when I HAVE to get somewhere against some heavy resistance.
Heres some basic graph about the amps vs speed:
As you can see the consumption of electricity grows pretty fast as you get past 4 knots, so I my plan is to use 3 kn whenever I'm not in hurry and need to get far.
My battery bank is now 500ah in 24V and should give me a decent range. If not, then I buy more :)
I first thought that I could make the motor easely to also regenerate while sailing, but after many attempts I never got the controller to produce any amps. I tried many settings and turned the motor with a drill, no amps. But I know that the propeller starts turning when I hit around 5 knots. I'll get back to the regeneration after the winter...