[ausev] Regen for brushless DC

[Sarah & Erik]

Paraphrasing someone much more knowledgable than myself, all motors
are AC motors at heart. Some are supplied with DC, and some are
supplied with AC, but in order to create motion a varying voltage (AC)
has to be seen inside the motor. In a brushed, series wound, DC motor
like used on many EV conversions, the commutator creates the varying
voltage. In an AC induction or brushed DC motor an inverter creates
precisely timed varying voltage, instead of a mechanical commutator.

Check out: http://en.wikipedia.org/wiki/Electric_motor

I believe all motors can regen, but there are a couple of reasons why
this is difficult on series wound DC motors:

- The current in the field or armature needs to change direction, this
can be done with another contactor
- Brushes are often advanced, so if the motor is run backwards with
more than a little voltage or current you can get a lot of sparking
and brush and comm damage
- The same current is in the field and armature (since it is a series
motor). This makes controlling the regen more difficult than other
motor flavors.

I'm pretty sure that since a BLDC motor already has a fully electronic
inverter the regen is free, much like an AC induction motor (the type
used on the EV1 and many other OEM EVs)

Erik

On 10/6/07, Donovan Becker <dbecker215 at hotmail.com> wrote:
> We just had a discussion about why regen isn't used in spiral wound DC
> motors but I was wondering how the regen in brushless DC differs from the
> regen in the AC motors.
>
> The Vectrix scooter (www.vectrix.com) for example has regen with a brushless
> DC motor. Is that a risky endeavor such as with other DC's? Is the regen
> built in like in an AC motor or does it require a special controller such as
> the Zapi? Most importantly is it practical?
>
> Thanx,
>
> Donovan
>
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