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

I "stacked the deck" to illustrate this behavior. It assumes a single
drive per power supply which is not entirely unfair.:-)

This phenomena is of no practical consequence if 2 or more drives
share a common power supply and all motors don't stall simultaneously.

All that happens then is the energy from the stalling high-speed
motor gets used to power the drive/drives. There is no power supply
voltage change at all then.

Mariss


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

>
>
> Hi,
>
> I did chuck up a stepper once, but I used a battery powered drill
> made for torque, not speed, and never got it close to 2000 RPM. I
> don't remember the voltage I did produce, but I'll take your word

on

> the stepper's emf capabilites.
>
> For the most part, people that use Xylotex systems are not

spinning

> their motors 2000 RPM. For a 20TPI machine (like a Taig or
> Sherline), this would equate to 100 IPM. Even faster for a 10TPI
> machine. These speeds typically are not achieved on most of the
> machines the Xylotex system go into due to both the limited power

of

> the drive to get it going that fast, and to the limited travel of

the

> machine. I did get my Sherline X axis up to over 100IPM running at
> 24VDC. When it did finally stall (I think the max I got it to was
> around 110 IPM) the drive didn't go 'pop'. The other axes weren't
> running so there was only the on-board caps, and supply caps to

take

> the load. They did so without any problems - that I know of :-)
>
> While what you suggest certainly is a possible problem if the

drive

> is run closer to its 35VDC maximum limit. I recommend a 'running'
> maximum of 30VDC. The typical supply voltage used is 24VDC. This
> does leave a good amount of "room".
>
> One of the bigger problems I had in the past (before I started
> selling the 24VDC power supplies along with the system) was people
> looking at the mpja 24VAC/10A transformers for $18.00+/- and

thinking

> it would work great. Slap it together with a diode block and a big
> cap and ready to go, right? Well, as you know, wrong.
>
> The original 3 axis drives also did not have the on board DC-DC
> converter for +5VDC like the new drives have. There were a
> reasonable number of failures back then simply due to mis-wiring up
> the 5V. Yep, it's true.
>
> Finally though, some of the few "unknown pop"s cetainly might be
> attributed to what you mention. Generally though, the users

actually

> know what they did, and it usually turns out to be a wiring error

or

> some other mistake they wish they could take back.
>
> So hold on to your hat, you probably will not be eating it any

time

> in the near future. Mine's a cowboy hat, and I certainly wouldn't
> want to eat it (though I have had my fair share of crow as food for
> thought).
>
> Jeff
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> <mariss92705@> wrote:
> >
> > 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
> > > >
> > >
> >
>