Re: G201 modifications/update

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:

>
>
> ballendo@y... wrote:
>
> > Ballendo,
> >
> > The G201 is a STEPPER drive. No fault indicator. No "braking"
> > necessary. Duh. Sorry list.
>
> This is not necessarily true. Stepper motors can take advantage of
> braking. If you have a large machine, with a lot of moving mass,

it can

>
> continue traveling quite a distance if the drive is simply shut off,
> without
> a dynamic braking mode. It won't make much difference on a

Sherline.

> Stepper motors can be easily braked in a controlled manner by

connecting

>
> a braking resistor where the DC power supply normally feeds the
> full-bridge
> switches (for a bipolar drive). The regenerated voltage from the

motor

> will be rectified by the freewheeling diodes and fed to the braking
> resistor.
>
> Jon

Hi,

This happens automatically in a full-bridge drive because each pass
transistor has a diode across it. Usually with bipolar transistors
this diode is a discrete component, with MOSFETs it is intrinsic to
the transistor. Furthermore, a MOSFET can "assist" the diode if the
MOSFET is turned on because they are perfectly happy to carry current
in either direction, unlike bipolar transistors.

During deceleration kinetic energy must be removed from the motor and
load. If the rate of energy removal is moderate, (gentle
deceleration, and/or small load, low speed) the returned energy
merely lessens the power supply load. If a large inertial load is
rapidly decelerated from a high speed, (high rate of energy return),
then power supply current can actually reverse direction and flow
from the drive to the power supply.

This "return" current will charge an uregulated power supply filter
capacitor above the supply's rated voltage, and possibly above the
drive's breakdown voltage.

A while ago I posted in the "files" section of this group a circuit
called "energy dump.pdf" which safely deals with this problem.

Mariss