Re: power supply size [was: Where to buy transformers?]

On sizing transformers....


a stepper will draw about 2/3 of the rated current so you need to
provide enough current for the total of all steppers.

also, series wiring of 6 and 8 wire will use half of the nameplate
current.

providing more is neat and gives you bragging rights to how big yours
is. providing less offers problems when you loose power.

Running a stepper at less than the proper amp setting with Geckos
will start to bunch the microsteps and cause problems.

above data gathered from the White Paper on Steppers from the Gecko
site.

Personally, I think if you get what you need, maybe a little for
reserve or sized for those 600 in/oz units you are buying next year,
you are in good company. buying less will always make you wonder
if 'that' is the problem.

Dave

--- In CAD_CAM_EDM_DRO@y..., "ds_hutchins" <hutchins@m...> wrote:
>
> My machine is an Enco mill-drill, with maybe 300lbs of tables &
vises
> on the table at any one time. So I'm not really expecting to hit
full
> load on the motors except for brief periods of time -- I was just
> wondering what the experiences of others in the group were.
>
> As to hitting the wrong button -- if the motor controller limits
> voltage to the motor, then all I need to do is make sure I hard-
code a
> reasonable maximum feed rate to make sure I don't accidentally break
> things. I doesn't take 20A to accidentally cut through my vise with
> bad g-code, and I'm not hooking the motors directly to the supply,
so
> I'm not quite sure why a small power supply would really offer much
of
> a safety advantage. If I have enough power to run three motors at
> moderate rates, than I still have enough power to break something
with
> one motor at high load, right? On the other hand, I don't want a
> high-power transformer to overheat in my garage because I misjudged
> how much power I require.
>
> I'd guess that an least a few people on this list have broken
> something with big, high-power, home-made chunks of spinning steel,
> and I'd like to benefit from the mistak... I mean experience of
> others. :-)
>
> > It depends on the size of the machine. 14 A at 60 V is 840 W, or
about
> > one HP output from the motor. That is a lot of power, probably
good for
> > a Series II Bridgeport machine to get up close to the same
performance
> > as the EZ-Trak control. On a much lighter machine, you would
likely
> > break something or get hurt by pushing the wrong button. If you
DO have
> > a Series II, I would go for the 20 A transformer. If a smaller
machine,
> > I think 10 A will probably be sufficient. The servo drive limits
> the voltage
> > to the motor, so a higher voltage DC supply will not harm the
motors.