It is actually worse than that. If he cuts the voltage to 1/2 and does not change anything else, the current will also drop by 1/2. That means the power will drop to 1/4 of the original value. As you and others have stated, using a 48 volt motor at 24 volts does not have the same effect as lowering the speed with belts & pullies or gears.
--- In electricboats@yahoogroups.com, thomas stoll <stollte@...> wrote:
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> Your going to reduce the power output of the motor by lowering the voltage(cutting it in half!). By using a gear reduction(or pulley) you will increase torque at a lower RPM.
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> Power (in watts) is ~745.7 watts per HP. Watts = current times voltage. so If you cut the voltage you get half the watts of power. A good electric motor is very efficient giving as much as %98 output!
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> Say you go with a 2:1 gear ratio, you will double the amount of torque at half the RPM. If you cut the voltage you will just lose power. Now It's not a good idea to run most motors at maximum power draw (heat=power loss).
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> Belts really aren’t that inefficient ether although their will be some friction loss, this will depend on the setup, a good bearing etc will limit this loss.
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> --- On Sun, 4/10/11, Jak Mang <jak.mang@...> wrote:
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> From: Jak Mang <jak.mang@...>
> Subject: [Electric Boats] Pros and Cons of Lower Voltage
> To: electricboats@yahoogroups.com
> Date: Sunday, April 10, 2011, 11:19 AM
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> I am looking at a Mars motor that turns at a high RPM (2400@48v). The supplier suggests a gear reduction with a belt drive to decrease RPM at the prop. What are the drawbacks of just lowering the voltage to 24 rather than the extra hardware? It seems that there would be some inefficiency from the belt. How does this compare to less than maximum efficiency at 24 volts?
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> Thanks,
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> -jak
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