RE: A 48 volt Freeway EV?

["Roger Stockton" <stockton@racalcanada.com>]

Hi Nathaniel,

I'm not sure I understand why you think there would
be a problem reaching highway speeds with a 48V system.

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.

One would want their 48V vehicle to operate near max.
RPM at the desired road speed to minimize current and
maximize efficiency, just as with any higher voltage
EV.  Your suggestion of holding it just under the rpm
where it leaves current limit will yield the highest
power, ~40kW for a 1000A controller and a 48V pack,
which is way more power than one needs to sustain
highway speeds on level ground... but the controller
would soon heat up and cut back to its lower continuous
rating anyway.

It is fairly common for a controller's continuous
rating to be about 1/2 of its peak, so a 1000A
(battery amps) controller might only sustain about
500A, which even assuming some sag from 48V is still
around 20kW, or at least twice the ~10hp required to
maintain the typical small car at ~60mph.

Cheers,

Roger.

 -----Original Message-----
From:	ev@listproc.sjsu.edu [SMTP:ev@listproc.sjsu.edu]
Sent:	Wednesday, June 30, 1999 2:17 PM
To:	ev@listproc.sjsu.edu
Cc:	Stockton@racalcanada.com
Subject:	Re: A 48 volt Freeway EV?

Hello.

Amps=torque
voltage=speed

If you used a 100amp + controller with 48 volts, you would have kick-butt
performance for around 1000 RPMs, max. then the performance would drop off
rapidly. Unless you use gearing that will make around 1000 RPM =65 MPH, you
will have problems reaching highway speed.

If you are looking for low voltage, but good commuting cars, try 96 volts.
Even with small 400 amps controllers they can do highway speeds.

 -Nathaniel Martin