Electric OB conversion questions

Discussion in 'Electric Propulsion' started by Klinus, Jul 27, 2018.

  1. Klinus
    Joined: Jul 2018
    Posts: 2
    Likes: 0, Points: 1
    Location: Stockholm

    Klinus New Member

    Hello! I have a small, around 4 meters/13ft boat that I would like to put an electric outboard on. I have a cabin on an island, right now it takes about 10 minutes with a 20hp engine. I think an electric engine would be perfect for this purpose, since I only need power for max 30-60 minutes give or take.

    I have read a lot about outboard conversion of old gas engines, but I wonder if that project is too hard for me, I havent worked with motors or electrics a lot before, so I have some questions that I hope someone could answer:

    1) how does a controller work? Everyone just writes what controller they have, but not how they set it up. If I buy a controller, is it just plug n play (I suppose not?) or what type of configuration do I need to do, and how do I do that?

    2) When I researched electric outboards I noticed that for example the (super expensive) Torqueedo cruise10 (Electric powered outboards for boats - Torqeedo https://www.torqeedo.com/en/products/outboards/cruise/cruise-10.0-r/M-1240-00.html) has a maximum speed at 1400rpm, while most other engines are between 3000-5000 rpm. What does the low rpm give the torqueedo?
     
  2. alan craig
    Joined: Jul 2012
    Posts: 212
    Likes: 26, Points: 28, Legacy Rep: 14
    Location: s.e. england

    alan craig Senior Member

    As an enthusiast for electric propulsion I would say - don't change anything, you have the perfect set up! You only use your outboard for twenty minutes per visit.

    1. Controller depends on wether you have a brushed or brushless motor. A brushed motor can be run direct from a battery or via series/parallel switch for some speed control but better to use a pulse width modulated (PWM) controller which is very common. They pretty much just plug in. A brushless controller is more complicated but you do not need to know how they work, just follow the instructions. My experience is with controllers for model planes (see my post somewhere on this sub-forum) the controller is programmable for things like soft or hard start, minimum voltage before cut out (to protect the battery) and braking (useful for aircraft or car but not much use in a boat). You need some engineering skills and equipment to make the conversion.

    2. The Torqeedo turns a bigger prop than a petrol engine of the same power so the output is lower rpm/more torque.
     
  3. Klinus
    Joined: Jul 2018
    Posts: 2
    Likes: 0, Points: 1
    Location: Stockholm

    Klinus New Member

    Thanks for the answer! I won’t change the outboard I have as long as it’s working, I see this more as a hobby project and when/if I get it to work I make the switch. But I do feel like this would be the perfect opportunity for electric, so I dont need to buy gas all the time (which is a hustle since it’s quite a bit to nearest gas station).

    What type of motor would you recommend, brushed or brushless? I got the impression that brushless is preferable?

    If the torqueedo has lower rpm > better torque does that mean that I should look for a motor with low rpm as well?
     

  4. alan craig
    Joined: Jul 2012
    Posts: 212
    Likes: 26, Points: 28, Legacy Rep: 14
    Location: s.e. england

    alan craig Senior Member

    As a hobby project your biggest problem might be the expense; 20hp is the very top end of model aeroplane equipment and more than what is available for electric bicycles, which could also be a good source for motors and controllers - and things like twistgrip throttle. 20hp is roughly 15kW; 312.5A at 48v. Brushless and lithium batteries are more efficient and lighter and more expensive than brushed motors and lead batteries, and probably the only way to achieve equal performance to your petrol outboard. But, if you are prepared to travel at displacement speed and take longer you could get away with smaller and cheaper components.

    Choose a suitable outboard as a donor then look for an electric motor which approximately matches the power at the same motor speed.

    A good first step might be to find the price of a 7.5kWh lithium or lead battery (and the weight) and charger.
     
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