Re: Voltage, Current, Resistance and Heat?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
<lcdpublishing@y...> wrote:

>
> Hello,
>
> Forgive my ignorance, I am learning all about the electronics on

the

> fly here.
>
> My CNC Router - phase one, started with a Stepperworld Fet4 driver
> board and the Sanyo Denki stepper motors provided by them. They

are

> old surplus, unipolar, 6 wire, 4.5V, 1.5 Amp, 160 Oz In motors.

This

> particular driver is an L/R driver. As such, I used the power
> resistors as specked by Stepper world for these motors. The power
> supply provided by them was a computer power supply, so I used the
> 12V side of that supply to drive the motors.
>
> That board had a setting for "High Torque" which is full step and I
> believe 2 phases on all the time. This setup provided good torque
> and moderate speed. However, the motors, especially the Z axis (as
> it is not moving much of the time) would get very hot. Almost too
> hot to touch.
>
> Recently, I changed out that driver board for the Hobby CNC driver
> board which is a chopper driver. I set this unit up at 1/4 step

and

> it runs very smooth and I could achieve higher RPMS which is cool.
> But, in playing around with it for the last 2 days, I noticed
> another COOL thing, the motors barely get warm to the touch - they
> run very cool.
>
> After some tuning, I believe I have the torque pretty close on the
> new board as the old board. But still, the motors run cooler.
>
> This got me to thinking about something I read somewhere.
>
> "Torque is directly related to current"
>
> If this is the case, then, if I have the same current I should have
> the same torque. Also, I believe the motors should run at the same
> temperature.
>
> So, I am wondering if I could run more current (Amps) into these
> motors than what is given on the spec sheet. Eventually, I will be
> running them at about 40 volts when I get the parts for the new
> power supply. But, I am VERY tempted to crank up the current to

see

> if I can get more umph out of them. Now I know I am not suppose to
> do that, but if the motors are running cool, I am wondering if I
> would in fact hurt them by running up the current while keeping a
> very close eye on motor temps.
>
> Any thoughts on this?
>
> Again, forgive my ignorance, I know lot's about software and CNC,
> but very little about the electronics.
>
> Chris

Chris: You will not gain much by running the motors in overcurrent
condition. Almost all of the added current will go up in heat
dissipation. Rejoice over the fact your motors are running cooler.
Since you are using the entire winding in bipolar mode you can get
more torque with the same current. In a chopper drive the coils are
not on for the full duty cycle of the pulse (except at full speed) so
under different speed conditons the dissipated power will change.
Raising you *voltage* will increase the max RPM and the torque (up to
a point). You will see a marked improvement at 40VDC vs 12. Do not
exceed the nameplate current specs. It's not worth the added strain
on the motors versus the added torque.