Re: MircoStepping Drive Which One?

The PMDX-150 does provide galvanic isolation of the PC ground from
the motor power. Our documentation convention is to refer to the
motor supply as Vpos and Vneg. The logic Ground signal is on the
control interface, and is isolated from Vneg. In addition to the Step
and Direction inputs, we also isolate the Fault output (the Gecko
drives do not).

Aside from added functions that you may or may not need, the greatest
improvement offered by the PMDX-150 is protection from the inductive
voltage spikes that result from disconnecting a motor with power
applied. These will typically kill the A3977 chip but the PMDX-150's
Schottky clamp diodes prevent this from happening.

Regards,
Steve Stallings
www.PMDX.com

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@t...> wrote:
>
> I'm confused here. The PMDX card has opto isolators but states
step
> and direction are ground referenced. Which ground? Is the motor
DC
> share the same ground with the PC ground? I don't see anything on
the
> board that would indicate that there are split grounds. If they do
> share the grounds why bother with Opto's? Yes, they will increase
the
> noise immunity some but don't isolate the grounds where a lot of
the
> noise develops.
>
> There is nothing wrong with a common ground driver for smaller
> applications but just having opto's to isolate the signal does
little
> to offer true galvanic isolation like the Gecko's.
>
> The Xylotex card uses the same exact chip and rates their card at
2.5A.
> 30V. The only difference appears that the PMDX was a more efficient
> heatsink design. There are definitely more features on the PMDX.
I
> think the price is reasonable with the added features, but from an
> operational perspective I doubt there is a lot of difference when
you
> get down to spinning the motors.
>
> On a cost basis the Xylotex is still the winner at $175 for 4 axis
VS
> $260 for PMDX and $456 for Gecko's.
>
> From a servo perspective Fred's 30V 5A servo cards are the best
deal
> for smaller servos.