Re: servo voltage question ( regarding Steppers)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Peter Reilley" <micrio@m...>
wrote:

> A question on voltage. There must be a maximum voltage that
> can be applied a motor because of insulation breakdown.
> For a 4 volt stepper motor what voltage would be too high?
> What is the voltage rating of the insulation on the wire used
> in the average stepper motor? Are 30 year old stepper motors
> going to be significantly worse than new motors? Is there
> a voltage limit for the brush assembly used in servo motors?
>
> Do companies give these ratings? If not what are some good
> guesses?
>
> Pete.

The answer lies in the DRIVER MANUFACTURERES literature.

Gecko's are tuned to allow up to 25 times motor nameplate. Other
manufactureres go much higer, other go lower.

The key to understanding this is in the tutorial to steppers written
by Jones. Google Jones on Steppers.

Basically, the way I understand it, the amps and ohms and voltage of
the stepper NAMEPLATE, it for using Ohm's Law for the rest of the
calculations. This is NOT like your 220VAC motor where Nameplate is
Maximum.

The namplate offers 1,2 or 3 of these values, you can measure the
resistance to get that value, so you should be able to get at least 2
values pretty quickly.

The CHOPPER then pulses the charge into the motor, Volts and Amps,
until the chopper circuit see enough amps, then it chops the power.
Since SPEED is the issue, you can dump 10 amps with 100 volts MUCH
faster than 10 amps with 1 volt.

The motor never sees more than the nameplate current.

As for old steppers VS. new ones, the old round body are different
than the new square bodies. the new square bodies have
considderabley higher effiency and have considderably higher power.



As for SERVO's, like your AC motor, these are charged continually, so
the motor might have 50 volts on it to hold posistion, like when a
table is holding against the cutting forces.

And, like transformers, the motor insulation, wire size and spacing
is all based on voltage and current.

Over voltage and you can break down the insulation and short out the
windings. Over current and the motor overheats and damage occurs
there also.

IF (big IF) you can really cool the motor, you can change the
ratings, but since it is easy to cool the outside case, but not the
windings on the armature, that feat is hard to accomplish with any
predictability.

Considder that the motor costs will be a factor your project, and
project life.

I wrestled with a $35 servo and a $125 gear train of my own design to
handle the high motor RPM. so... if I found a decent low speed motor
for less than $155, things get much easier. and considdering my time
in building the gear reduction.....

Hope this helps somewhat.

Dave