Re: STEPPER MTR VOLTAGE SUPPLY HELP!!!

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:

>
>
> cnc6805 wrote:
>
> >
> >
> > How they regulate the current I have no idea. They use hexfets? I
> >dont see a large resistor on the board. This is one board

consisting

> >of 4 motion controllers integrated together. What is L-R type? Can
> >you expain the differneces between L-R verses chopper style

stepper

> >motor drives? How can one run at higher voltages and not the

other?

> >
> >
> The classic unipolar L-R drive from the 1960's used a motor with two
> center-tapped windings. The center taps were each connected to a
> huge power resistor and then to the positive motor supply. One
> NPN power transistor was attached to each end of each phase winding.
> When a transistor turned on, the current ramped up in an exponential
> curve based on the voltage, resistance and inductance. Once the
> current rose to a certain value, the resistance was such that it
> balanced the
> applied voltage. The resistor was selected, or often made

adjustable, so

> the proper motor current was delivered. This exponential rise in

current

> caused the torque to fall dramatically at low speeds, and the

resistors

> threw off hundreds of watts of heat. Generally, the DC power supply
> was put at the absolute lowest voltage possible to reduce the heat,
> meaning that the system was always on the edge of losing steps.
>
> A chopper drive uses some type of switching technology to sense
> motor current, and turn off the switch when the proper current had
> been reached. There are a vast number of ways to do this, fixed on-

time,

> fixed off-time, fixed frequency, and on and on. Microstepping

drives

> make the phase current match a varying current depending on the
> microstep the motor is supposed to be at that time.
>
> Jon

Is there a way to use this L/R stepper drive that I have to run
at two seperate voltages? at idle it holds the position
satisfactorily but, as soon as the axis begins to move the motor has
no power and is of little use. Is there a way to run the board from a
small transformer with the rated motor output then when the motor
starts to turn switch to another transformer of higher voltage? and
then back to the other transformer for idle current. The maker of the
board suggested that I use one of the on board relays to switch the
transformers via an M command in the program. Of course this would
only be successful until someone failed to put in the command when
the motor stopped and the board would be toast. Is there some simple
electronic device that would do this very same thing? I'm thinking
like something that senses the higher current at the board and
automatically switches it to the lower holding current. There has to
be a way to do it without getting too complicated. It works as is, I
just need a way to supply the motors with a higher current when
moving. I paid quite a bit for this board and the maker is not
wanting to give me a refund so, I'm ready to try anything. It's
useless to me as it is.