Re: stepper drives and motor size

Carey, You should not have to worry if you 2 or more drives operating
from the same power supply.

This is only a problem if you have a large inertial load that is
decelerated from a high speed rapidly and only one drive connected to
the power supply.

What it has to do with is the rate of energy return. First you must
have a large amount of energy stored. This can only happen if you
have a large mass movining quickly; the old M * V squared / 2 thing.

Second you must return the energy quickly; consider a car braking to
a stop from 50 MPH at a stop light vs. the same car hitting a brick
wall at the same speed. The same amount of energy is involved yet the
results are quite different.

What makes the difference? The amount of time over which the stored
energy is released.

In the first case your drive will simply draw less current from the
power supply while the motor is decelerating, in the second case the
drive will turn into a power supply instead of a load.

Step motor drives cannot absorb returned energy; all they can do is
to convert it to electricity and return it to the power supply. Where
does the electricity go? Into helping power other step motor drives
you may have connected to your power supply if you have them.

The best way you can tell if you may have a problem is to monitor
your power supply voltage while decelerating your size 42 motor. If
your power supply voltage does not increase at the most rapid rate of
deceleration, you have no problem. Another drive is more than
sufficient to absorb returned power.

Mariss

-- In CAD_CAM_EDM_DRO@egroups.com, "Carey L. Culpepper" <mr.c@b...>
wrote:

> I got my new Warner drives today.I spent some time reading through

the

> instruction book. It has a caution: Do not use larger frame size

motor

> than those listed, or the drive may be damaged. If a larger frame

size

> motor must be used, consult the factory for recommendations.
> Well, I made that phone call. The recommendation was for a

different,

> very expensive(over $2000) drive. The problem with the NEMA 42

motors,he

> said, was a voltage increase in the buss when the motors are stopped
> quickly as in a high friction situation,which I certainly
> have(Bridgeport conversion).
> These drives are rated at 75Vdc and7A. I will be using only 5A and
> probably 56Vdc.
> Anything that I can do to protect these drives while running NEMA 42
> motors? Would microstep resolution make a difference as far as

induced

> voltage ? Anything that I can add to the cicuit to the motors for
> protection?
> Carey