Re: Question on Power Supply

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Andy Wander <awander@v...> wrote:

> Well, 50V x 1.4 = 70V.
>
> 50V x 1.414 = 70.7V.
>
> Proably insignificant for most purposes.
>
>

There are so many variables that trying to calculate things out to
three decimal places is meaningless. The transformer itself can
exhibit several percentage points of loss (efficiency) based on the
core characteristics and winding geometry. The diode drops in the
bridge are 2X a single diode but once again can be from .6 to 1.2 (per
diode) based on current draw and temperature. Open circuit voltage
(no load) will be several volts higher than loaded voltage.

I have seen a lot of transformers rated at what I call JBBU (Just
Before Burn Up). When run at their full rating they get hot enough to
cook pancakes!

Then there is the AC line voltage itself. Most modern transformers
are rated at 120VAC primary as a nominal voltage but any PS engineer
will tell you that you plug in the numbers for 90 to 130 VAC to get a
"range". Some areas around big commercial buildings with heavy
machinery may see line sags and surges outside the 90 to 130VAC. I
once worked on a CNC punch press for 2 days that would intermittently
change accuracy. I took me a while to realize it was always around
noon and after 4:30....so a check of the 3 phase lines showed one
phase to be low during most of the day and would rise when other
plants went off-line. Sometimes it's the simple stuff.

The good news is that the current needs for most of the CNC
applications are grossly exagarated. The current power supply beta
testing we are about to start is going to yield some real world
measured numbers per motor under all forms of operating conditions. I
will be interesting to see in both stepper and servo systems how close
we come to the theoritical numbers we see offered.