Re: Power Supply for 4-axis CNC stepper driver

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Weedy" <weedy@e...> wrote:

> Dave/Jon,
>
> So, are we back to:
> W = 4 x 60 x 6 x 0.66 or
> W = 4 x 60 x 6 x 0.66 x 1.8?
>
> The 1.8 is from Steve as quote below:
> "Transformer manufacturers generally recommend that you compensate

for this

> by applying a factor of 1.8 times the desired DC output current to

specify

> the RMS current rating needed for the transformer."
>
> Weedy

Hi Weedy,

we're getting there.

One of the comments that wizzed past that you might have missed was
with the type of machine.

A mill needs power to cut, but one can consider that all the cutting
energy to be on one axis. the reason is that if you are cutting at an
angle, the feed rate cannot exceed that of the tool, so you would have
to slow down one axis while speeds up thereby keeping the feedrate
constant.

So, for a milling machine, one might argue that one axis at full power
is the maximum the machine would need.

for some things like a punch, the X and Y have no real power needs as
they are stopped when the punch works.

Also, on a plasma table or router, the gantry is heavy and needs to
get pushed around as well as the cutter has it's power needs. These
type of machines have lower ratios, so the power to accelerate are
higher than on a mill. So, machines that have heavy axial loads to
start and stop will need more power overall than those exact same
motors on a mill.

Mariss has advised to design for the needed watts of power for the
machine, but most of us have no basis or reference to calculate just
what is needed, so we use the maximum of the motor.

Knowing you cannot possibly run a 4 axis milling machine with all 4
axes at full power, you can assume a lower overall power supply will
handle the machine completely.

One might argue that you cannot run a mill with anything more than one
axis at full power, but I don't think I'd go that low. I think most
people would design for the 3 axes and be content that they have a
balance between available power and unused surplus.

I'm guessing that many machines use much less than we design for, so
the 1.8 value Steve offered may be used when people design for 3 axes.
Consider your 4 x 60 x 6 x 0.66 to get 950 watts.

Now, consider you max out on actual use at two motors, adding the 1.8,
2 x 60 x 6 x 0.66 x 1.8 = 855

Even if you used 3 motors for design, 3 x 60 x 6 x 0.66 = 712, and
your machine never uses even 2 motors at full power, but rather uses
3/4 power, your power requirement is only 640, so you are still safe.

A lot of conjecture, but it may be why some people have steppers on a
Bridgeport that work well and others had a problem with them crapping out.

I figure I'd toss out my thoughts to allow them to be picked apart.

Dave