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

I think in this case it is not simply about exceeding the
manufacturers limits but rather that we are talking about
home built power supplies and that for the Allegro chip
35V cannot be exceeded. I think that Jeff can attest to
that as an expert.

My power is quite good and my provider (Hydro Quebec) says
that for a normal 120V supply the voltage can vary between
106V and 127V (marginal) and that normal would be between
110V and 125V.

Doing some math we can see that at 24VAC x 1.414 = 33.936VDC
But that would be based on 120VAC in - what happens when
it jumps to 127VAC? My DC could jump to 35.9156. That's
about 1VDC more than it takes to blow the drive and yet we
are still within the acceptable limits of service. Now
add back EMF.

Personally I'm running a 22VAC transformer and I feel like
I've pushed the limit (aprox. 32VDC). I think Jeff
recommends 30VDC as a limit.

There is a circuit around somewhere from Mariss (of Gecko)
that shunts overvoltage to ground. Great! But most
users of these drives are probably like me and haven't
built it. :-( Most of us want to snap the pieces
together and go, safer to recommend 18VAC or 24VDC and
leave the limits to those that are more daring.


-John

PS: Some UPSs allow you to set out voltage but many
cheaper UPSs I wouldn't trust to hold it 120V.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith" <imserv@v...>
wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffalanp" <xylotex@h...>
> wrote:
> > Fred wrote:
> >
> > >A 24 volt ac transformer is just
> > > about right for a power source (plus a bridge and a

capacitor).

> > > These transformers are readily available in 2-4 amps and
> contribute
> > > to a very inexpensive solution for a do it yourself project.
> >
> > Please be aware that 24VAC when filtered and rectified becomes
> > about 34VDC. If the transformer were rated for 110VAC to produce
> > 24VAC, and you used 115VAC or 120VAC (like I have), then you

would

> > surpass the 35VDC *absolute maximum* limit of the A3977SED driver
> > chip.
>
> Jeff,
>
> I agree whole heartedly. If local line voltage exceeds 120, it is
> probably a good idea to consider a step down transformer for any

CNC

> equipment, this is very common practice on commercial machinery. I
> would also recommend a UPS type setup on your computers as a UPS

will

> usually have some voltage regulation to maintain supply voltage
> within a narrow range. Surge protectors at a minimum.
>
> It's a good idea not to exceed the manufacturers limits on any
> electrical equipment.
>
> > 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