Re: Stepper Motor Driver

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:

> Blue wrote:
>
> >Hi,
> >
> >I was going to use this driver with 50oz motors of 1 amp using a power
> >supply of about 20 volts. The machine would be quite small for
> >drilling/routing circuit boards.
> >
> >
> Well, you would need to add resistors. A 1 Amp/winding motor would not
> have a 20 Ohm winding resistance, or it would go up in flames.
> So, you would need to add 2 resistors of about 19 Ohms (assuming the
> motor drops about 1 V at 1 A) at 360 W. Each motor/drive combination
> would need 720 W from the power supply, so a 3-axis system would draw
> over 2 KW!
>
> >Speed is not really an issue but I wouldn't want o wait all day for

it to

> >finish a job. I thiught it was a cheap alternative to proper drivers.
> >
> >
> Well, you will get your 50 Oz-In when standing still, but at 60 RPM, you
> might have only 5 usable Oz-In, because of R/L and resonance problems.
> The performance of such a drive is going to be so abysmally below a
> good bipolar microstepping drive that it is almost impossible for

someone

> who has not seen it with their own eyes to believe.
>
> The IRFZ44 transistors are not properly driven to saturation by a 5 V
> power supply, which is what the logic supply voltage is. The logic

signals

> are not opto-coupled, which may cause noise problems in a multi-axis
> system. There is no provision to control the inductive energy when one
> of the transistors is turned off, which may cause the transistors to be
> damaged by this energy.
>
> Yes, it is a cheap alternative. They left out the last 35 years of
> development
> in stepper drives.
>
> Jon

All this may be true, but for a cheap PCB driller type machine where
high performance is not needed, these would move the axes around.

Dave