Re: [CAD_CAM_EDM_DRO] Re: Power Supply-- more questions

JanRwl@... wrote:

>
>In a message dated 1/4/2006 12:47:57 A.M. Central Standard Time,
>hjjohnson@... writes:
>
>I can't quite get 25 times my stepper voltage as that would put me over the
>Gecko 80v rating. So I'm shooting for 78vDC to the drives. Therefore
>78/1.4=56vAC 6.0A x 4 steppers =24A.
>
>
>
>CAREFUL! I discovered that the actual current drawn from the supply by a
>chopper drive is considerably LESS than the "motor current rating". It's the
>WATTAGE you use to do the math! If the coils are, say, 3V x 4A, then TWO
>windings draw 24 W. For 4 motors, you will have 96 W. total. So, if you have a
>75 V. supply, 96/75=1.3 A, so a supply rated for 1.5 or 2 amp would do!
>Amazing, yes, but I learned this by TRYING things myself, and it's true! You do
>NOT need a honking-big 24 A supply! I'd probably be conservative and go for
>4 amp supply just to be "safe", but MEASURE the actual current for various
>motor-RPM's and it will boggle your mind! JRR
>
>

This is for idle, only! When the motors are moving, and especially when
supplying
mechanical power to the load, then the wattage requirement rises. it
may, in fact,
rise close to the maximum he states above. But, this would have to be a
transient
condition in most CNC machines. (May be worse in systems where
sustained motion
is possible.) I would think in almost all cases half that would
suffice, or 12 A.
In a milling machine or lathe, probably a bulk supply rated for 6-8A
would work
fine, for a router the 10-12 might be a better choice due to the
sustained high
speeds on the router. These bulk supplies often have 1 Second peak ratings
of twice the continuous rating, but these peaks shouldn't be repeated
more than
a few times a minute.

Jon