Re: regen on a heavy EV (range ~ lbs)

[XURQ03A@prodigy.com ( LEE A HART)]

> Lee - give us a circuit diagram of your PWM / contactor 192V controller
> where the PWM controller only sees 96V or tell me why I'm wrong.

         _______________________
        |                 M+   _|_
       _|_ +                 /     \
      _____  96v            |       | motor
        |  -       diode     \ ___ /
        |___________|/|_________|
        |      B+   |\|   M-    |
       _|_ +                  |_|
      _____  96v           --||_  transistor
        |  -                  | |
        |_________________B-____|

The diode(s) and transistor(s) are in the controller. B+, B-, M+ and M- are
the terminal names on a Curtis controller. The batteries are shown connected
in the series position. In parallel, both 96v packs are in parallel, and
connected to the controller normally, and the motor can be controlled from
0-96v. In either series or parallel, the controller never sees more than 96v.

Notice that there is always a path through the upper pack, motor, and diode.
Therefore, the upper pack always carries full motor current, and the motor
always sees at least 96v. The lower pack is selectively switched in series by
the controller. Depending on the duty cycle, it adds 0-96v, so the motor sees 96-192v.

Battery balancing:

  lower battery    100% |---------         /
  current as a          |         |      /
  percent of            |         |    /
  upper battery         |         |  /
  current           0% _|_________|/____________ motor voltage
                        0       96 97      192

Below 96v, both packs are in parallel, so they automatically stay balanced.
When you switch to series, the two packs have different currents depending on
throttle position. At full throttle, they are again the same.

To keep the batteries balanced, the simple answer is to avoid spending much
time driving at just over 1/2 throttle (just above 97v). If the batteries are
in parallel most of the time (cruising speed doesn't require over 96v), then
the pack will re-balance itself to compensate for the times when you are at
97v (going up a slight hill, for example). Sudden bursts of high-current full
accelleration also will not imbalance the pack.

Lee Hart                     If you would not be forgotten
4209 France Ave. N.          Soon as you are dead and rotten
Robbinsdale, MN 55422 USA    Either write things worth the reading
phone (612) 533-3226         Or do things worthy of the writing
e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)