Electric outboard drive for small cruisers

  • 03 Jun 2020 18:41
    Reply # 9012767 on 9006703
    I wrote:

    Yay, my 24V 190Ah LiFePO4 bank has finally arrived! Now I just need to wait for the 150A breaker to arrive and I can go and give the electric motor a go.

    They arrived well balanced, as advertised, with voltages all between 3.267-3.269V.

    Grab your own at AliExpress! Price for the above cells is €1325 right now, I paid €1180 back in April.

    Oops, I was checking the price shipped from Poland. If you can wait longer (2 months vs 2 weeks from Poland) and order from China instead like I did, then that package is €574.05 + 574.05 = €1148.10. Add a BMS for €112 and you have a 4.5 kWh battery bank for a total of €1260.

    I also got a Victron temperature sensor (~€50) as I won't have other charging methods than solar so I don't need low temp cutoff on BMS level.

    Cells are held together in two groups of 4 (for easier handling, 2x14 kg) with double-sided tape (gives a bit of spacing between the cells) and hose clamps. BMS cleared through customs yesterday so should arrive any day now. I'm getting excited here!

  • 01 Jun 2020 14:14
    Reply # 9006703 on 8809939

    Yay, my 24V 190Ah LiFePO4 bank has finally arrived! Now I just need to wait for the 150A breaker to arrive and I can go and give the electric motor a go.

    They arrived well balanced, as advertised, with voltages all between 3.267-3.269V.

    Grab your own at AliExpress! Price for the above cells is €1325 right now, I paid €1180 back in April.

  • 30 May 2020 21:40
    Reply # 9003608 on 9002534
    Anonymous wrote:

    While surfing the web looking for website "looks" that might suit the JRA, I happened upon this:

    https://www.temofrance.com/en_GB/

    Maybe not applicable to small cruisers, but I've been thinking for some time that this is what electric propulsion for a small dinghy ought to look like - more like the "longtail" motors. Having tried unsuccessfully to get a small inflatable off a beach with a regular electric outboard, I was thinking of converting it to the longtail format.


    Bonjour

    I've seen the prototype at the Paris Boatshow in December 2019. It looks impressive.

    I was thinking about it for Mingming.

    Eric

  • 30 May 2020 07:55
    Reply # 9002534 on 8809939

    While surfing the web looking for website "looks" that might suit the JRA, I happened upon this:

    https://www.temofrance.com/en_GB/

    Maybe not applicable to small cruisers, but I've been thinking for some time that this is what electric propulsion for a small dinghy ought to look like - more like the "longtail" motors. Having tried unsuccessfully to get a small inflatable off a beach with a regular electric outboard, I was thinking of converting it to the longtail format.

  • 28 May 2020 21:08
    Reply # 8998853 on 8809939
    Anonymous member (Administrator)

    Darren, I am really impressed by that 2kW motor. It just reminds me og that technology has left me behind.  Anyway, I was never a whale on motors.

    Cheers,
    Arne

    Last modified: 30 May 2020 08:33 | Anonymous member (Administrator)
  • 28 May 2020 20:07
    Reply # 8998731 on 8809939

    David, 

    The big prop makes your new motor very much like a modern British Seagull.  They were one of the few manufacturers that got outboards right for displacement boats, with a large slow turning prop.  Of course, you'll now do it without the trailing cloud of smoke, crazy exposed flywheel, or incredible racket.

    Glad to hear it is working out well.

  • 28 May 2020 19:59
    Reply # 8998708 on 8809939

    Arne, 

    Given that we may have some difficulty convincing David to dissect his new motor, I'll take my best guess.  100A actually seems pretty tame from what I was used to with model airplanes, where it was not unusual to pump 100A through a very small controller and a much smaller motor than what David has.  Maybe an electrical engineer can step in with the details on mosfets, but my experience is that power mosfets are certainly capable of handling those currents.  Also, remember, even at full RPM the mosfets aren't continuously on.  I'm working from memory (thus there is good reason not to trust what I'm saying), but for example if you had a twelve pole motor you would switch the FET's 36 times in one full rotation.  At part throttle the Mosfets are on even less of the time.

    As for the motor, this could be done a couple of ways.  First the wire can be smaller than you would use for continuous rating, because it is only energized part of the time.  Also, you can do things like use two parrallel wires when a single large conductor would be unwieldy.  I've seen motors for models where there were only two or three wraps of wire on a stator.  It looks comical, but yeilds a very high KV motor (one that spins very fast at lower voltage).

    So, my guess is that there is no voltage boosting taking place in the controller.  Here's an example of a much tinier model airplane motor that could handle 2400 Watts @24V.  This motor would have much better cooling, but it is tiny compared to what is likely inside the Haswing.  The Haswing, really is just at the upper end of what would be used in large radio control models.

    Last modified: 28 May 2020 20:09 | Anonymous member
  • 28 May 2020 12:43
    Reply # 8997560 on 8809939

    Whatever is going on inside the motor and its controller, it's clear that the behaviour of both of them together is exactly what's wanted for motor-sailing. Full throttle = full RPM, but with current draw proportional to the load on the prop.

    The big prop certainly moves a lot of water around. Yesterday, during static testing with the boat not quite floating, full throttle resulted in a mighty whirlpool being formed, with occasional cavitation. There is an argument for always setting the motor at maximum depth when in use. Maybe there is also an argument for a home made anti-cavitation plate? Today, at LW, I see that there is a big scour in the seabed where the water flow has moved a lot of sand away.

  • 28 May 2020 09:46
    Reply # 8997313 on 8809939
    Anonymous member (Administrator)

    Darren,
    now I have slept on it. I certainly am no expert on electric motors, but I begin to doubt if they produce a 5hp motor running directly on 24V. That would result in very thick windings, and there would not be room for many of them. They may have chosen to do it that way, but I doubt it. Then the transistors turning on and off the coils, would have to handle 100A each.

    It would therefore not surprise me if the 24VDC first has been either stepped up to a hi-voltage DC, or even inverted to AC, and thus driving an AC motor.

    Arne


  • 27 May 2020 20:40
    Reply # 8996177 on 8995940
    Anonymous wrote:

     To reduce the torque and thus power of the motor, I guess the coils are fed with shorter and shorter pulses as the user of the motor reduce throttle.
    Neat.

    Arne


    Given your background Arne, you could very quickly come to a better understanding of this than me.  One of the great parts of the JRA is that it is populated by a bunch of very intelligent and creative folks who are very generous in  sharing what they know.  Glad I could contribute this time.

    Yes, the motor speed is controlled by Pulse Width Modulation (PWM).  One thing that might make this discussion useful to David and Oscar, is that depending on the winding of the motor, the frequency of the PWM controller, as well as some other variables, the system is not equally efficient across the entire throttle range.  Very low throttle settings can be particularly inefficient.  If your motor makes a harmonic "singing" sound at low throttle this is particularly so.  When you also consider the exponentially increasing power demands as you approach hull speed, there is likely to be a sweet spot somewhere at an intermediate throttle position that would give the maximal range.  Some tests in non-tidal water using a gps, and keeping an eye on the amp-meter could be informative for helping maximise range.  

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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