Re: G201s and BIG step motors

Stan,

Most of my step motor experience is with size 23 and 34 motors. I
have few size 42 motors owing to their size and cost. The
voltage "overdrive ratio" is based on empirical tests primarily with
these motors. Single stack 23s should be limited to no more than 20
times the rated voltage while triple stack 34s can exceed 30 times.
From this one can extrapolate size 42s should be even more.

This is a topic that requires further data to nail down and I will be
running tests to do just that when time allows.

The method will be to run the test motor beyond its corner speed to
eliminate I squared R heating. The motor is instrumented with
thermocouples to measure case temperature. The temperature is
measured when it reaches equilibrium. If the temp is below 85C, then
the supply voltage is increased until equilibrium is reached again.
This repeats until a steady state 85C is reached. The power supply
voltage is then noted and divided by the motor's rated voltage. This
ratio is then the maximum overdrive ratio for that motor size.

Big motors have long thermal time constants, so this test will take a
long time. The other problem will be having a drive capable of
driving the motor with enough wattage to heat it to its limits, where
one expects to get maximum power the motor is capable of.

There is good reason to expect the overdrive ratio will be much
higher on size 42s for the following reason:

If a 7A, 80VDC (560W) rated drive can extract 200W mechanical from a
motor, what should the drive rating be for a motor you expect to get
800W mechanical from?

If you work it as a ratio, then the drive's rating should be 4 times
greater, 2240W or so. This can then be parsed as a 7A, 320V rated
drive or a 28A, 80V drive and so on.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, "Stan Krumme" <skrumme@c...>
wrote:

> Hello Mariss,
>
> I am somewhat confused about G201s with really BIG step motors
> (double stack 42 and bigger I have double stack 42 steppers
> from API Controls Div, two winding bipolar, M422-12S, 3.6v 6.1

Amp.

> The 6.1 amp is lower than the 7A max capacity of the G201.
>
> Looking at the Gecko site, rule of thumb for overvoltage is about

25X

> maximum. This puts me at about 90 volts, slightly over the 80v for
> the G201. Do I really need to run these from 120++ volts, is the

25X

> value for size 34 motors and not 42 size?? I have noticed from the
> site links that double stack 42 steppers have torques of ~ 2000-

2500

> in-oz's. My steppers are rated at 1100 in-oz's. Are these M422-12S
> just older designs, of somewhat less power than current state of

the

> art? Will I get nearly full performance from the API M422-12S
> steppers when run by G201's @ 80v and 6.1A?
>
> Thanks , Stan K
>
>
> > Hi,
> >
> > Anyone using G201s with really BIG step motors (double stack 42

and

> > bigger) may need a modification to their Geckodrives to get

maximum

> > performance from these motors.
> >
> > It involves mid-band stability for these motors and requires
> changing
> > the value of a single resistor inside the G201. We will make this
> > change free of charge and return the drive within 24 hours.
> >
> > This change will make really SMALL motors work worse and have
> > absolutely no effect on all other motors.
> >
> > This modification will be called "-42", so ask for a G201-42 if

the

> > application will be a really BIG motor.
> >
> > Sorry for any inconvenience this may have caused.
> >
> > Mariss