Re: A 48 volt Freeway EV?

["Peter VanDerWal" <peter_v@primenet.com>]

>At 16:56 30/06/99 -0700, you wrote:
>>Many lower-voltage motors (12, 24, 36V, etc.) are
>>rated for operation near 4000rpm, so 1000rpm needn't
>>be an inherent limitation for a 48V motor.
>>
>I didn't say it wouldn't be able to get above 1000 RPM, I just said the
>torque would drop off steeply after around 1000 RPM. Maybe you would have
>usable torque to the 3000 range, but I don't know.
>


    From your statements it appears that you are assuming that they would be
using a high voltage motor at 48V.  If you were to use a motor designed for
48V then your statements are basically incorrect.

    Take for example two motors that are basically the same except one is
designed to produce 10hp @ 144V; 60 amps; 4000 rpm and another that is
designed to produce 10hp @ 48V; 180 amps; 4000 rpm.
    If you were to compare the torque charts from the two motors they would
be very similar except the 48V motor would need 3 times as much current.

    In other words if you had a controller that could handle three times the
current for the 48V motor, then the torque would drop off the same for both
motors.

    The only real problems (that I see) with 48V setups are: three times the
I2R losses; your cables have to handle three times the current; and in order
to handle these huge currents the motor is going to be much heavier (maybe
three times as heavy?)


>According to :  HP=(Torque*RPM)/5252
>18=(54.5*RPM)/5252
>RPM=1734
>
>(note torque is based on Prestolite 7" motor)
>


Ah ha!  See this is what I was saying, you were assuming that they would use
a high voltage motor at 48V.