Re: SLA7062 technical stuff - supply voltages

Mariss,

Your info is very interesting!

Would you be willing, if you have the time, to sketch out a drawing
what it takes to construct a "snubber" and how one would add it to
an existing stepper drive using a 7062?

I think this would be a valuable accessory for those of us who have
7062-based drives and are operating with power supplies over 30vdc.

Regards,

Tom

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
<mariss92705@...> wrote:

>
> I hope nobody minds me sticking my nose into this.
>
> For fun I took a G201 and turned it into a unipolar drive by

removing

> the top MOSFETs in each full bridge. The motor center-taps went to
> the +supply, otherwise everything is the same. The drive actually
> works that way.
>
> Run this way (kind of like an SLA7026 with 33A-rated MOSFETs) it
> avalanches on each on-to-off output transition. The avalanche

voltage

> is 112VDC, the current is 3A and the time is 250nS. The energy is
> 84uJ. This results in 8.4W dissipation due to avalanche heating.
>
> Avalanche operation should be avoided no matter what mfg.

literature

> says. Monolithic power ICs usually "pop" during that condition.
>
> I calculated an RC snubber to eliminate this behavior (I = 3A, V =
> 42V, 750nS time constant gives 15 Ohms and 0.05uF). The snubber

was

> built and applied to each output; it limited the voltage "spike"

to

> 12V.
>
> The SLA7062 claims 100V MOSFETs. This gives 44VDC as the absolute
> maximum supply voltage (Vds = (100V - 12V) / 2). Throw in a sane
> derating of 80% and you get 35VDC as the max rated voltage for the
> drive.
>
> These snubbers and 35VDC max should stop the "popped SLA7062"

effect.

>
> Mariss
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turyga1963" <TIntruder@>
> wrote:
> >
> > Dave,
> >
> > You're right...I wish I hadn't spent so much time looking for a
> > transformer that would supply those extra volts!
> >
> > I think this is valuable information, but I also wonder what the
> end
> > effect is on how the steppers operate?
> >
> > If a board is rated to 42vdc and you supply only 34vdc or even
> > 24vdc, what happens? If you still have the amperage, do the

motors

> > still turn as fast with as much power? If not, is the effective
> > decrease linear?
> >
> > Tom
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> > <dave_mucha@> wrote:
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turyga1963"

<TIntruder@>

> > > wrote:
> > > >
> > > > Dave,
> > > >
> > > > Good to know. Problem in my case and I suspect that of many
> > others
> > > > who have had similar problems is that we were expressly told

by

> > HCNC
> > > > that we could use up to 42vdc and the circuit board is even
> > > > silkscreened to show that voltage. Further we were told the
> > closer
> > > > to 42vdc we got, the better as that would insure maximum
> > power/speed
> > > > from the steppers.
> > > >
> > > > Oh well, live and learn...
> > > >
> > > > Tom
> > >
> > > I found that many of the parts seem to fit well with existing
> > > transformers.
> > >
> > > a 24V transformer times 1.414 to get 34 volts fits well to a

44

> > volt
> > > maximum unit.
> > >
> > > 48 volts to the Gecko offers about 66 volts to the drive.

Again a

> > > nice fit without leaving too much room for improvement.
> > >
> > > Some time ago, Mariss posted some results of life expectancy

of

> his
> > > drives. at 114 volts the life expectancy was something in the
> > minutes
> > > range. at 80 volts it was in the years, at 90 it was in the
> months
> > > and only got worse as the voltage increased.
> > >
> > > I suspect that this is the case with all drives. there is a

sweet

> > > spot that offers a very long life and a bleeding edge where one
> > > mistake, one time results in that sinking feeling you get when

you

> > > smell that magic smoke.
> > >
> > > Dave
> > >
> >
>