Re: Voltage to steppers

Hi,

and I'm glad your interest brought you over here from the BasicStamps
list.

What I posted over there was something that many first time stepper
users don't know about.

Stepper motors have nameplates that list some basic information for
calculations which is unlike standard electric motors which put
maximums on the motor nameplates.

using ohms law, you need to know some basics. resistance, amps,
volts, watts, and inductance. with the basic lising of just a
voltage and current, you can figure out all the rest.

to charge the motor coil you need to pump current into it. higher
voltage means that current gets there faster. higher voltage means
faster motor speeds.

double the voltage and you double the speed. your 12 volt motor will
spin at 12 volts, it will do slightly more work at 24 and really
start to come into the power band at 70 volts. or 5 times the rated
voltage. If you want to run at 30 volts, a 1.5 volt motor would be a
better choice.

Power output increases proportionally with supply voltage. Losses in
the motor increase with the square of the voltage. At some point the
motor just gets too hot. This occurs at about 25 times nameplate
voltage. most hobbiests think a 5 volt motor needs to run at 5 volts
and 6 volts is too much.

also, stepper motor output power is independent of speed. Since power
is speed times torque, this means every time you double motor speed,
torque is halved. steppers appear to loose power at higher speeds as
on some machines the torque needed to move the assembly exceeds the
delivered torque and the motor starts missing steps.

One thing on the nameplate that should not be exceeded is the amps.
if you connect both sides of one coil of a 6 wire motor so they are
in parallel you use the full motor amperage. if you connect those in
series, then you half the current as you doubled the resistance and
4x'ed the inductance. this also means you get the same power, but
lose top end speed.

i'm sure others will comment on this or other questions you might
have.

Dave Mucha









--- In CAD_CAM_EDM_DRO@yahoogroups.com, "pwrcntrl <info@c...>"
<info@c...> wrote:

> I have a home-grown machine that uses small 55mm 12V steppers. I

have

> driven them with an embedded controler & Allegro driver chips,

which

> make it fairly straightforward. The setup uses round ground

thompson

> shafting and linear bearings and moves quite freely, however, the
> little motors only have enough torque to drive consistently in

either

> 1/2 or wave drive. I would more importantly like to see some more
> speed. during free moves...it doesn't need torque beyond what is
> required to move itself around.
>
> From what I have been reading here while lurking (from people like
> Dave M, of the Basic Stamp list - Hi Dave!) it seems that it is
> common practice to drive steppers above their rated voltage, is

that

> correct?
>
> If so, what will driving my 12V motors at say 24V do? It seems you
> guys were talking about 10X rated V, so I'm wondering what 2X will
> do....
>
> Perhaps I should just change motors. Of course they will have to be
> inexpensive say $20- and with 1/4 inch shaft. If I need to go over
> the V rating of the driver chips, I may have to re-think

everything...