Re: A 48 volt Freeway EV?

[John Wayland <dat1200@europa.com>]

Hello to All,
      Jay  Wilson creatively writes:

>There's been a tendency in EV design to go to higher and higher 
>voltages in the battery pack. This is great for performance, but 
>also increases the problems with batteries.......Perhaps the ultimate >design for a day-to-day commuter (not a dragster) EV would be to >go to less voltage. 

        Amps x volts = horsepower. If you set a maximum motor loop
current at say, 1500 amps, with a 48v worth of L-16 batteries in
series/parallel, that would be a 1024 lbs. pack, but it will still sag
down to around 35 volts, so the most power you can see is 52 hp or so.
This would make for a pretty slow machine with lethargic acceleration
and a low top speed. 
        On the other hand, with a higher voltage pack of AGM batteries,
say 156v in series/parallel, even at lower currents of 1000 motor amps,
they'd  sag down to maybe 140v....you'd have 150 hp! Sorry, but there is
a huge difference here in available power.

>A 48 volt EV could use the massive Trojan L16 
>batteries, which will last twice as long as the toughest golf cart 
>batteries, judging from the experience from off grid "Home Power" >applications. 

     The big Trojan L16-HC (high capacity model) weighs in at 128 lbs.
for 395 ahrs @ 20 hours, and has a 700-900 cycle life rating. However,
that rating applies to its use as a house battery backup in an off-grid
application. The battery typically gets charged every day by either
solar power, wind power, water power, or generator. The batteries are
also never subjected to anything close to an EV load of 600-1000 amps.
The typical loads they do see are relatively light. 
     They also see very shallow discharges under normal use. Subject
these batteries to 60-100% discharges at very high currents, and their
cycle life will fall greatly. In an EV application, you can forget about
that "last twice as long as the toughest golf cart batteries" bit.
     These 'house batteries' are also not designed for high vibration
use, as are Trojan's golf car batteries, and as used in EV applications,
would be rattled and shaken apart prematurely.
     Finally, as pointed out, they have an extra reserve of water
capacity as well as extra space for sulfation deposits to fall into, so
pound for pound, you get far less ahrs in the L-16 than in a standard
T-105 battery. Compare two T-105 batteries at 121 lbs. and 432 ahrs, to
the L-16 at 128 lbs. and 395 ahrs.

>How about 40,000 miles on a set of batteries!....tougher cells makes >for a highly reliable battery pack. 

  My guess, is that you'd be lucky to get 10,000 miles out of them, for
all my above stated reasons.

>And maintenance problems would be reduced as well. Watering the >few cells in a 48 v pack would be easy,  and also infrequent because >of the huge water capacity of the cells. 

   This part is probably true. 

>Another benefit is that the shock hazard would be almost 
>eliminated at 48v.

  True again, however, in a properly designed higher voltage EV, shock
hazard is usually not a problem at all.

>Today's high power controllers can handle the 1000 amps required >to give a 48 volt EV good acceleration and freeway speed. 

  Yes, they can, however, as already pointed out, even those BIG wet
cells have problems with voltage sag under these kinds of currents, so
the 48v drops to under 40 at these levels....good acceleration and
freeway speed aren't going to happen!

>Could a 48v freeway-capable EV be built?

      Yes, using other kinds of batteries, such as Hawkers, Optimas, and
other high power AGM type batteries. These batteries will
 not sag so low under high currents. Also, with enough of them in 
series/parallel, 1000 amp discharges won't bother them a bit, 
as they certainly would to those behemoth L-16 batteries. 
         Even so, a 48v vehicle would still, be rather slow when
 compared to higher voltage EVs and ICEVs....it's still a matter 
of Amps x Volts = Horsepower. It's also still a matter of using
batteries that can handle high vibration, lots of deep cycling at 1 hr
rates, and that have a high amp to rate ratio.....this just excluded the
L-16.
       I had what some might call a '48v freeway-capable EV', way back
in 1980...an early version of Blue Meanie. Because my completed electric
car weighed in at a light 1800 lbs., with just 48v of Trojan 6 volters
and an aircraft starter/generator it did 81 mph flat out (clocked on
radar, mind you)! I used to take it on the freeway quite often, too.
However, in hind sight, it was still a lot slower than even the stock
fume-sniffing econobox '72 Datsun 1200 sedan it was based on, and on
steep hills it slowed down to where traffic had to go around me. Even
though 1000 amp speed controllers were the stuff dreams were made of, my
electric car did have a contactor controller that allowed unlimited amps
to flow into that poor 2CM77 GE motor.....at got hot as hell, the cable
and connectors got hot as hell, and the batteries got hot as hell...I
managed to fry one out of two 2CM77 motors, blow up one battery (they
make a big BOOM), and destroy the entire pack in 6 months.

See Ya........John Wayland