On Mon, 06 Oct 2008 14:46:50 -0500, "Pete C." wrote:
David Lesher wrote:
Vernon writes:

"Depending on the VFD, maybe it has a shutdown function, but don't
depend on it. I'd have a direct 3-phase pushbutton, the latching
kind. [Push in, it stays in until unlatched.] Use an aux contact for the
VFD."

I did not understand this. The VFD manual says to have a disconnect
device but not to use it except in an emergency. Obviously, getting
entwined in rotating machinery is an emergency and trumps trashing the
VFD.

Get a pushbutton, a big industrial one. Allen Bradley comes to mind. They
are basically Legos; you start with the basic button and add contacts of
the type needed.

It should have 3 contacts rated for the full current of the motor. They
will be closed in OUT mode, but open when pushed in. Wire in series
with all three legs going to the motor..

Have a low current 4th contact going to the VFD shutdown connection.

This will break the power feed to your mill when hit, AND send a shutdown
to the VFD. [It may take a while to turn off, however, as compared to the
button. Maybe even as much a second or two; see what the VFD Fine Manual
says.]

This way, even if the shutdown command does not work, the power *is* off.

The shutdown pushbutton will be expensive new. There are millions surplus
but it will be tricky to mail-order same. If you have a surplus place
nearby....

The E-stop switch belongs on the power feed *to* the VFD, *not* on the
motor leads from the VFD, otherwise you just have a "VFD destruct"
button. The diagrams in the VFD manual should show the proper wiring for
an emergency stop.

The proper way to rig a Panic Button (Emergency Cutoff) IMHO is with
a motor starter type dedicated purpose contactor sized for the motor
current, wired into the power feed to the tool before the VFD. Get
real contactor with internal magnetic arc chutes (not just a relay) to
make sure it can interrupt heavy loads, you can draw a pretty good arc
at 240V and really nice ones at 480V.

You do NOT want to open the line between the VFD and the motor,
period - the odds of smoking the VFD are rather high. If you want to
wire the factory switches to something, hook it to the remote start
and remoter stop leads of the VFD.

Put your ECO Panic Button near the operating position with a classic
Big Red Mushroom Head operator, and if this is a large tool where you
might get in trouble while standing on the back side out of range of
the main controls, put a separate ECO back there, too. The switches
are Normally Closed loop wired, so any switch breaks the power to the
contactor coil and shuts it down.

Big equipment like web-fed color newspaper printing presses can have
dozens of ECO switches scattered all over, they place them wherever
someone might have to go make an adjustment exposed to moving parts
with the press running. You always want one within easy reach.

And if you want to get fancy, you can rig Safety Shutdowns into that
ECO loop. For instance you can rig a microswitch or two for a contact
shutdown if the stock in an automatic swiss screw lathe bar feeder
bends and start whipping. They can do a LOT of damage before you get
there to slap the button.

-- Bruce --