Re: A 48 VOLT FREEWAY EV?

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

>
>>The only real problems (that I see) with 48V setups are: three times the
>>I2R losses; your cables have to handle three times
>
>At three times the current, the I2R losses would be 9X for the same
>wire thickness.

    If you are using the same size wire for a 144V setup as you are for a
48V then you are either using way to much copper on 144V or your looking for
a meltdown at 48V.  But yeah you're right,  I forgot  about the geometric
effect of I2R losses.

>As for the motor being 3X heaver, that is not
>quite correct.  The scaling is such that the length of the wire
>decreases with it's increase in thickness, so the losses stay the
>same, and the amount of copper stays the same.  Reference: earlier
>discussions on rewinding motors.
>


    Well I haven't bothered figuring out the physics of it, but it has been
my experience that high current motors tend to be larger than low current
motors.
    For example let's compare a ADC X89-4001 to a ADC FB-4001, the FB-401
can handle 1.7 times as much current as the X89 and it weights (hmmm...) 1.7
times as much. Note: both of these motors have identical voltage ratings.
    It has also been my experience that similar motors with similar current
rating but different voltage ratings weight about the same.
    Therefor it is my conclusion that a motors weight depends mainly on the
current rating and not the voltage, 3x the current equals roughly 3x the
weight.

    Of course, as always, I could be wrong.