24v 120lb DIY brushless motor project

Discussion in 'Electric Propulsion' started by Catguy, Jun 7, 2017.

  1. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    4HP = 3Kw. As long as you get the same power, the boat will reach the same speed. Was it going 5 mph before?
     
  2. BertKu
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Gonzo, Actual I have a different view. I always understood that the Hp from a petrol/gas/diesel engine is given by the manufacturer as the power measured at the propeller shaft. However the power from people making brushless motors, there is the power actual the battery consumed power and is thus less by the factor of the efficiency of motor and controller together and is normally whatever people are stating and bragging, about 90% . Thus for me, 4 hp petrol is not the same as 4 Hp (2,983 Kw) electrical power. Except if 3,3 Kw ( 4,4 Hp) power is applied to the motor. Sorry to trow a spanner in a widely argued topic. The only advantage I see is, that a brushless motor has its maximum torque at 100% at very low revolutions to maximum revolutions, and that is not the case with a petrol/gas/diesel engine. Gonzo, I am not arguing, I just have a good laugh that we all have been tricked for the same conversion 1:1. Bert
     
  3. Caroute Motor
    Joined: Jun 2016
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    Caroute Motor Junior Member

    Bert, your explain is objective and unbiased. Same HP, petrol/gas/diesel engine use shaft power, but electric motor use input power. For same boat, petrol/gas/diesel engine surely will be quicker. But electric motor can thrust more heavier boat due to his larger torque. Brushless motor's advatage are its high efficiency which can over 65% and torque.
     
  4. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    I am a brushless motor lover and fan. I love brushless motors, but the manufacturers must go away from comparing HP with KW. Ocean Volt had the story that a substantial higher HP is the same as a much lower KW brushless motor. We should go away from that. One should indeed look at the size and weight and required speed of the boat and then give a KW rated and KV rated motor. In that case there will be no misunderstandings or open for arguments. Bert
     
  5. Caroute Motor
    Joined: Jun 2016
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    Location: CN

    Caroute Motor Junior Member

    Right, I agree. We had changed our advertising words. Now we only use Input Power and Thrust etc.
     

  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    I can see how that will create confusion. Probably I deal more with industrial motors that have both ratings: input and output power. Otherwise, they would be impossible to size for a machine.
     
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