The best stepper driver??? was Re: Stepper questions

Actually there is another, more significant effect. The most common
drive failure report with low voltage drives is "The drive popped
when I was decelerating my motor" or "The drive popped when my motor
stalled during a rapid".

Step motors are unique in that can develop a back-EMF much higher
than the supply voltage.

For your own personal edification, chuck-up a 1A, 5V NEMA-23 motor in
a drill-press, Put a multimeter set to AC volts across a winding and
run it up to 2,000 RPM. If you don't read over 100VAC (141 volts
peak), I'll eat my hat.

Yet you can put the same motor on a 24VDC powered drive and easily
spin it up to the same 2,000 RPM no problem.

What happens? When you stall the motor, the kinetic energy stored in
the moment of ineria is released and returned. It gets returned to
the drive as a current source with 100V+ of headroom. The power
supply capacitor absorbs this energy at the expense of a voltage rise
across it. If the rise is enough, it exceeds the breakdown voltage of
the drive and pops it.

Sound familiar?

Mariss



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffalanp" <xylotex@...>
wrote:

>
> Hi,
> The largest cause of 3977SED drives "popping", when a SLA7062

will

> not, is when a person disconnects a motor when it is under power.

As

> noted, the 3977 drive chip is specified for a max of 35VDC. As has
> also been stated in earlier post of this topic, when you disconnect

a

> live motor wire you can get high (double?) voltage produced.
> Running a 3977SED at about 30VDC would yield a voltage of around
> 60VDC. Very bad for the chip. On the other hand, the 7062 MUST
> handle the double voltage rating to cover the disconnected
> transistor, because that is how unipolar drives work. So, the guy
> who innocently (or not so) blows up his 3977SED wouldn't even know

he

> did something wrong with the 7062. There is nothing wrong with the
> A3977SED chip if it is run in its safe operating area. THE

*absolute

> largest reason* drives blow up is because people get excited at
> trying the new hardware, don't follow instructions and do something
> wrong. Allegro makes thousands and thousands of these chips. Most
> probably go in to commercial devices like printers. These NEVER

blow

> up because they aren't subjected to undue stress (like disconnects

or

> shorts or miswires or overheating, or...).
>
> The other main cause of a 3977 "popping" is when there is an
> overcurrent. This can be from miswires or short circuits. I don't
> think the 7062 is immune to short circuits either. Since I started
> selling the 269 oz.in. motors along with the power supply and drive
> board in a "system kit", "blow ups" have dropped even more, since
> people are not guessing at how to make motors connections or power
> supply connections; I provide instructions with each.

Unfortunately,

> people STILL don't read these sometimes, even though they are taped
> directly to the device :-(
>
> Anyway, both drive chips are good devices when properly

operated.

> The 7062 may however be more robust to user error than the 3977, so
> if you plan on making mistakes like disconnecting a live motor, go
> with the 7062. If you plan on following manufacturers guidelines
> either will be fine.
>
> Jeff
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <dave_mucha@> wrote:
> >
> > -
> > > IMO the early xylotex were not as robust in actual shop use, as
> the
> > > other two. There was also a noise problem in the step/dir

inputs

> > > which Jeff to my knowledge has fully corrected in present

boards.

> > > Saying they were not as robust may be an unfair assessment,

since

> > > their popularity meant a larger sample and response was

presented

> in
> > > these groups where much of my NON-personal experience is

gotten.

> > >
> >
> > The A3977 chip is listed as 35 volts and 2.5 amps.
> >
> > as I understand, the drivers on the Gecko are rated at something

one

> > the order of 100 volts, but the assembled unit has a manufacters
> > rating of only 80 volts. a 20% de-rating of the components.
> >
> > In the early days of the Xylotex, many people tried to supply

near

> 35
> > volts and with any back-emf, 36 volts was all to common.
> >
> > I find fault in the understanding of the parameters of the chip

and

> > Xylotex has since, as I understand, recomended 24 volts as the
> desired
> > power supply.
> >
> > Dave
> >
>