Re: FS: New 4 axis microstepping driver $45.00 USD

I think regulating the power supply does not address the bigger
problem of returned energy and in fact, will make it much worse.

Those of you who have scopes may want to try a little experiment that
could destroy your drive.

1) Place the scope probe across your DC power supply. Set the input
coupling to DC, 10V / div vertical scale, 100 milliseconds / div on
the timebase. Trigger set to AUTO.

2) Spin up a NEMA-23 or NEMA-34 motor to 2,000 to 3,000 RPM.

3) Stall the motor while watching the scope.

You will see a significant voltage "bump" of at least 15 to 20 VDC on
top of your power supply voltage. This means a 35V supply will bump
up to 50 or 55 VDC for about 100 to 200 milliseconds.

What you are seeing is the mechanical energy stored in the motor
being returned as a regenerated current. If the supply is
unregulated, the filter cap will absorb it and give a smaller "bump".

With a regulator in place, this current has no place to go. A zener
clamp won't help either; a 33V, 5W zener (1N5364B) has a series
resistance of 10 Ohms. 2 amps of returned current turns this 33V
zener into a 53V zener. This kills L297/298 everytime; they go into
destructive secondary breakdown. I'm not as familiar what the Allegro
part would do.

What's needed is an active circuit voltage clamp to make it
unconditionally safe.

Mariss







--- In CAD_CAM_EDM_DRO@yahoogroups.com, John Johnson <johnatl@m...>
wrote:

> In figure 10 (Circuit for Increasing Output Voltage), the voltage

from

> the regulator's ground to it's input is the difference between the
> junction of R1R2 and the input voltage, not the full input voltage.
>
> In figure 13 (High Output Current with Short Circuit Protection), a
> TIP42 is used to up the maximum current. The TIP42 is rated at 6A.
>
> Regards,
> JJ
>
> On Monday, Mar 22, 2004, at 05:23 US/Eastern, Fred Smith wrote:
>
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, John Johnson

<johnatl@m...>

> > wrote:
> >> Using a couple of the circuits in the LM78xx datasheet available
> > here:
> >> http://www.fairchildsemi.com/pf/LM/LM7805.html
> >> It would be possible to build a regulator with short circuit
> > protection.
> >> See figures 10 & 13.
> >
> > JJ,
> >
> > I would think that the LM317 would be a better solution.
> >
> > http://www.fairchildsemi.com/pf/LM%2FLM317.html
> >
> > It is rated for 1.5 amps and *** 40 volts ***. Since a desktop
> > machine only needs about 4 amps @ 30 volts for a power supply, 3

of

> > these would seem to be a very interesting solution to the issue of
> > the 35 volt supply limit of the A3977. Pretty inexpensive too.
> >
> > Anyone ever play with creating a power supply with 3 LM317's in
> > parallel?
> >
> > Since we are going interesting places with this discussion,

anybody

> > ever run any tests on the A3977 to see if the same overvoltage

limits

> > were applicable at 1-2 amps (the limits on our board) instead of

max

> > current draw?
> >
> > Fred Smith - IMService
> >
> >> On Wednesday, Mar 17, 2004, at 17:40 US/Eastern, Fred Smith

wrote:

> >>>> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith"
> > <imserv@v... wrote:
> >>>>>> We have a limited edition, 4 axis, microstepping driver
> > available.Based
> >>>>> on
> >>>>>> the Allegro A3977 chip. The board is rated at 2 amps per axis
> >>> and
> >>>>>> maximum of 35vdc. This is a promotional item and is subject

to

> >>>>> prior
> >>>>>> sale. Quantities are very limited.
> >>>
> >>> Info at: http://www.cadcamcadcam.com
> >
> >
> >
> >
> >
> >
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