[Bob La Londe]

I seem to recall reading somewhere that G540 can only handle about 7amps total.

If that is the case, is there any point in using a power supply capable of more than that?
(Unless you are also running other things off that power supply of course.)

There are outfits routinely packaging the G540 with higher torque motors than one would expect. 495, 620 oz/in etc. Never mind that a stepper motor is incapable of high torque and high speed at the same time. I am quite aware that the torque drops off very dramaticly after its peak at a pretty low RPM.

Is the G540 capable of driving those motors at the peak they are claimed to be rated for?

Can it drive more than one at the same time with that much torque?

[morestuff]

The 7 ampere number refers to the amount of current that
the G540 will draw from the power supply. The G540 actually
has a 7 ampere fuse internally.

This does not mean that the motor outputs are limited to
any particular current. Because the switching technique
used in modern drivers effectively converts a higher voltage
at low current into a lower voltage higher current, much like
a switching power supply, the sum of the motor currents can
actually exceed the power supply input current.

Regards,
Steve Stallings
www.PMDX.com

[Bob La Londe]

The 7 ampere number refers to the amount of current that
the G540 will draw from the power supply. The G540 actually
has a 7 ampere fuse internally.

This does not mean that the motor outputs are limited to
any particular current. Because the switching technique
used in modern drivers effectively converts a higher voltage
at low current into a lower voltage higher current, much like
a switching power supply, the sum of the motor currents can
actually exceed the power supply input current.

Regards,
Steve Stallings
www.PMDX.com

Thanks Steve, I kind of obliquely knew that and its usefull to solidify that, but it didn't really answer the questions.

[morestuff]

To answer your specific questions:

There is no reason to use a power supply capable of more
than 7 amperes. A 48 or 50 volt regulated supply will provide
the best performance available from a G540. Some switching
supplies may not be happy feeding stepper motor drivers and
this includes the G540, so you may have to pick and choose.

The G540 can provide 3.5 amperes to all motors at once,
but that does not assure that the motors will provide the
rated torque at anything other that zero RPM. The motors
that claim high torque at modest current are going to have
higher inductance and therefore lose torque faster as the
RPM increases. This is because 48 or 50 volts is not enough
to overcome the back EMF developed by these motors when
turning at speed and therefore less actual current will flow
into the motor. A higher voltage drive system could force
more current and get more usable torque at speed.

Regards,
Steve Stallings
www.PMDX.com

[Bob La Londe]

Ok, thanks Steve. That does help. My specific reason for asking was that I am working on a servo driven mill conversion.

~ segway

I have a couple stepper driven 4th axis chucks. One came with a cheap system and the other I modified from a manual rotary table. I have used them with moderate success on mini mill and stepper driven router, but more stationary holding force would be better. A higher pulley gear ratio would help, but so would stronger motors. In addition I have considered removing the current limiting resistor from these so that they have full current when stationary for obvious reasons. My concern with that was the total current limit of the G540.


~ segway back

In addition if this would work well enough I would probably setup a single G250 on one set of step direction outputs on the motion controller on my big mill so if I want to use one of the chucks there all I have to do is plug it in. If not then I'll look at setting one of my 4th axis chucks up with a servo motor instead.

I have a small mill and a small gantry router currently run with G540s, and another small mill that will probably get one.