Re: Shunt field motors

["Jon \"Sheer\" Pullen" <sheer@brassrat.net>]

The problem is they're still shorting out active feilds - whenever they're
touching the commutator. Reread Lee's excellent post about how a commutator
is essentually a mechanical inverter, and I think you'll understand the
objections people have.

Personally, I think you all are missing the boat. By the time you get to the
mechanical complexity of having the brushes mechanically advance [either
through the brush cage rotating or through two sets of brushes and solenoids
to lift & lower] it's going to be cheaper to build a AC motor and inverter.

S.


----- Original Message -----
From: "Victor Tikhonov" <vtikhono@lsil.com>
To: <ev@listproc.sjsu.edu>
Sent: Thursday, February 28, 2002 1:15 PM
Subject: Re: Shunt field motors


> Rather than lifting the brushes you electrically disconnect them
> (contactors, IGBTs,...).
>
> Sorry, I didn't think it needed mentioning...
>
> Victor
>
> Paul G wrote:
> >
> > Victor wrote:
> > >I guess I didn't explain my thought very well.
> > >
> > >The idea was to have extra set of identical thickness brushes,
> > >so they still short two bars.
> >
> > Yes, but the unused brushes would have to be lifted when not in use. The
> > regen brushes also must cover 2 com bars, but not the same 2 as the
> > traction brushes (one forward of neutral one aft of neutral). So, when
in
> > traction mode an armature turn is being shorted by each regen brush (in
> > each brush location, generally 4 total).
> >
>