Re: Stepper motors and increased Amps

--- In CAD_CAM_EDM_DRO@egroups.com, "John Guenther" <jguenther@l...>
wrote:

> Tim,
>
> The motors have 6 wires, red, red/white, black, green, green/white

and

> white. Black and white are the common between 4 coils according to

the

> document supplied with the motors. Black and White are not used

currently.

>
> I am basically curious as to whether increased current increases the

torque

> provided by the motor. These are rated at 59.7 oz/in holding torque

and 34.7

> oz/in pull torque.

Hi John, I think I can help. I am using surplus
Sanyo Denki 5.1v 1.0A size 23 (2 stack motors
which are 2" long) in my home mini mill, and I
have just done a lab test on them last week.

Running bipolar full-copper (ignoring centre tap)
at 1A was 10.2v. This is ok, and is the same
dissipated heat power as "two windings on"
unipolar drive at 5.1v 1.0A.

If you plan to run bipolar two-phase-on mode
you have to de-rate current to 0.707A per
phase to give the same heat dissipation.

I measured torque for one phase on bipolar
1A 10.2v at 5.3kg/cm (about 75 oz/in).
If your motors are 2" long this will be
very close to your figure too.

Now you won't gain much from increasing the
current as 23 frame motor current ratings
place the motor very close to core saturation.

For example, here are some torque and heat
dissipation figures I measured:

1A 10.2v 10.2w 5.3kg/cm (one phase on)
0.71A 7.6v 10.2w 5.95kg/cm (two phase on)
0.57A 5.9v 6.7w 5.3kg/cm (two phase on)
1.2A 14.0v 16.7w 5.5kg/cm (one phase on)

The last one, the over-current test is what
you are asking, increasing current from 1.0A
to 1.2A gave ONLY a 4% increase in torque,
but dissipated 64% more heat and wasted power.
This shows the official 1A rating of the motor
is very close to magnetic saturation. Most
23 frame motors are rated this way.

If you are interested I put up the chart of
the exact phase currents needed to reach all
8 microstep values at exact angular position
and the same torque. See:
www.ezy.net.au/~fastvid/stepper8.gif

(the dots are theoretical standard current
values the crosses actual current values).
I think this motor is almost identical to
yours, I have 2" length 5.1v 1.0A motors
in my junk box from a few manufacturers.