Ben Goren via EV wrote:
once I started driving it, I realized I hardly ever used the
brakes... the amount from regen is not worth it (I am going on the
assumption that regen in DC traction motors causes undue arcing of
the commutator...)
A DC motor needs to be designed with regen in mind. The optimum brush
position to minimize arcing *changes* at different currents. Changing
from motoring to generating reverses the current, which is a very large
change indeed!
Standard DC traction motors have their brushes positioned for pure
motoring operation -- not regen. To use it for both motoring and
generating, the brushes need to be in a compromise position that reduces
(but does not minimize) arcing for both types of operation. This is
acceptable at lower voltages, and when you aren't using it to its
maximum current capability.
100 years ago, motors had adjustable brush rigging, so you could change
it while the motor was running to suit the mode of operation.
50 years ago, they added interpoles to DC motors. These a small
compensating windings, which automatically cancel out the brush position
differences between motoring and generating.
But since these added cost, these options have been left out of almost
all modern motors. :-(
I'm still anticipating regen as being very helpful in my wacky hybrid
Mustang... what I'm *really* looking to use it for is to maintain a
minimum charge in the batteries in hybrid mode.
An easy way to get modest "engine braking" style regen is to add a
second small generator, optimized for regen. This can be as simple as
rewinding the stock ICE alternator to work as a high voltage generator.
Use the field to control the voltage and current it generates, as usual.
With the field off, the alternator just freewheels. With the field on,
it generates.
Though automotive alternator efficiency is low, they are capable
generating amazingly large amounts of power for short time periods (like
regen).
--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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