Re: Voltage to steppers

Stan,

Because this seems to be getting OT, please feel free to contact me
off-list.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "iowaman50212
<stanlass@n...>" <stanlass@n...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis
> <mariss92705@y...>" <mariss92705@y...> wrote:
> > Stan,
> >
> > I like the way you think. Being inventive is to simply look a
> problem
> > from an unconventional perspective.
> >
> > Rather than limiting current (a current source takes care of that
> all
> > by itself), is to vary the supply voltage the current source has

to

> > work with. That is something you can predict based on the "steps
> per
> > second".
> >
> > What you are proposing is a closed-loop feedback to prevent the
> motor
> > from stalling by adjusting the power supply. That is a good idea.
> >
> > Unfortunately it requires overly complex circuitry to accomplish;

I

> > know because I spent some time with the idea before I abandoned

it.

> > The competing concept was to simply "brute force" it by having a
> high
> > voltage present at all times. Can't beat a simple solution,
> imperfect
> > as it may be.
> >
> > Mariss
> >
> >
> >
> > > Hi,
> > >
> > > It occurred to me that if the controller program kept track of
> the
> > > steps per second, it could also predict the current needed from
> the
> > > power supply.
> > >
> > > Also, one could write the controller program to limit the

current

> > > needed from the power supply by limiting the steps per second.
> When
> > > the steps per second approached the limit, the program could
> > stretch
> > > out the clock period such that the issuing of step pulses to

the

> > > stepper motors is slowed uniformly.
> > >
> > > Is this in any controller program?
>
> Mariss,
>
> I left out the motivation for the above. I need a power supply
> for some steppers. Worst case, I should allow for all 3 or 4
> steppers running at max steps per second. However, if the
> controller could limit the current used by limiting the steps
> per second, then I could likely get by with a significantly
> smaller power supply, like 50% less current.
>
> My stepper model is that for each step, there is an almost
> linear ramp up to maximum current in a winding, then followed
> by a chop mode. For the linear ramp, the current average is
> 50% of the maximum winding current. And for the chop mode,
> the current average is say 10% of the maximun winding current,
> assuming that the power supply voltage is say 10 times the
> voltage needed to get maximum current in the winding.
>
> Intuitively, I guessed that limiting the steps per second to
> say 1.5 times the max rate for one stepper, would degrade
> real world performance slightly, and allow using a smaller
> power supply.
>
> Newbie Stan