Mike,
I agree that using a 100A motor when you'll never run more than 30A it probably overkill. If, however, your normal cruise is 30A and you want good efficiency plus some reserve for maneuvering then the 100A motor makes good sense. There is no real disadvantage to going over-sized (to a point) other than cost. A 100A motor operated at 30A will be more efficient and last longer than a 30A motor run at it's limit. I don't see motor inertia or weight being a significant factor on a boat. I say go large if you can.
This is not to say a motor can't be operated near it's limit, but when you start "pushing the envelope", efficiency starts to drop and things like component sizing, thermal management, gear ratios, and all the other engineering choices become more critical.
Jim
--- In electricboats@yahoogroups.com, Michael Mccomb <mccomb.michael@...> wrote:
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> my original thoughts centered around no belts to break, being able to decouple the motors in the case of a problem 50% of the time and direct connecting because of the constant torque that a motor provides.... others reminded me that the motors would operate more efficiently if they were allowed to reasonably spin up and that cooling would be better served by spinning up.... just thought it interesting that motors had been doubled up
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> as a sort of corollary question to my original one, IF an electric motor can, for arguments sake, utilize 100 amps at a given voltage but never uses more than 30amps because that provides so acceptably close to hull speed then isn't that motor over sized by more than two times? Wouldn't it be better to have half the motor as such a motor only only being able to absorb 50amps would be no detriment at all at the same power level of 30amps. Isn't 30amps at a certain voltage delivering the exact same power regardless of whether the motor could ultimately handle 50, 100 or 500amps. I realize that inertia and other factors would have a part to play but don't these other factors all tend to point to the use of the smaller motor rather than the larger?Â
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