Re: panel meters (why?)

At the risk of being accused of being insensitive to "things", I HAVE
to ask....why? Front panel meters on a CNC power supply may look
pretty and be impressive for show but what purpose would they serve?
The inherent latency of the meters are only going to show you an
integrated average of the values and once you have run the machine in
various conditions and speeds the readings will be the same. Seems
like a lot of trouble to go to (mounting, hookup, etc) to take some
test readings. It's not like you are going to run this from a
regulated variable bench supply. It might be informative to see the
initial readings of voltage and current (they may surprise you) but
after that it you will find you ignore the meters. While a current
meter could indicate the amount of average torque or cutting force it
would be a rough indicator.

I made the mistake of adding some nice commercial voltmeters on my
controller panel calibrated in IPM. Since my servo motors had DC
tachs I just took the basic 0-10DC movements and changed the internal
scaling resistor. They look REALLY neat but serve absolutely no real
functional purpose since I can look at the screen and see what the
speeds are if I am confused by the table movements.

Now, If you are dead set on having a front panel meter you could do
one of the following:

Use any standard meter movement and wind your own shunt from #12 bare
wire. It's easy if you have a way to put a known load on your supply
of several amps and with clipleads on the meter slide one along the
wire (probably 12 to 20" of wire) until the panel meter reads the
correct amount. Lets say you want 20A full scale, put a 10A load on
the supply and adjust the slider until you get 1/2 sacle on the
meter. Recalibrate the meter scale by turning the scale over and
using rub-on lettering or your laser printer to make a new scale. A 0-
20A DC meter will have an internal shunt and you will be forced to
run heavy wire to and all of the power through the meter.

Then just coil the wire so the turns don't short (I used to use a 1"
wood dowel as a form). The coil goes in series in either side of the
DC power with the meter measuring the "drop" across the coil. In
essence you have two resistors in parallel one very low and one much
higher (meter resistance) so the inverse proportion of current flows
through both.

If you use a DP 2pos switch you could use a single DPM to show both
volts and current and switch between them. You would need to be able
to scale the voltage with a series resistor externally to the basic
meter movement to read the volts. If you put the shunt in the ground
of the DC supply you would only have to switch the + side of the
meter between the upper end of the shunt to a scaling resistor
attached to the + DC to get either reading.

Then again if this is for show, separate meters for each motor would
be really COOL!