--- In electricboats@
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> I have a hypothetical question that I hope you electrical engineers out there can give me an answer to.
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> If we have a boat that takes 5kw of power to do 5kts in calm conditions, so this becomes a constant.
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> We have a 5kw motor providing the power at 48 volts.
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> Now my question is, if we change this motor to a 10kw motor at 48 volts would the draw from the batteries be the same to do the same 5kts assuming nothing else has changed.
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> Secondly if we used a 5kw motor at 96 volts would the power draw from the batteries again be the same to do 5kts.
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> I'm trying to get a better understanding of the consequences of using larger motors other than extra weight and cost.
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> Thanks for any help.
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> Colin Girvan
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> BC Canada
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Hi Colin,
I don't have much electric boating experience yet, but I am an electrical engineer. In the perfect world, the power would be the same, but as you know, the world isn't perfect. In your first example, the 10 kw motor would likely be less efficient running at half its rated power so the battery power would be used a little faster. It depends on the particular motors used, though. If you compare a more efficient 10 kw motor to a less efficient 5 kw motor, the opposite could be true. For your second example, the higher voltage system would be using half the current to achieve the same power. That would mean lower losses due to resistance of the wires and motor windings. In general, that's better, but again, it depends on the efficiency of all the particular components (motors, batteries, controllers, etc) being used. I hope that helps.
Pat
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