On Mon, 6 Oct 2008 10:08:56 -0700 (PDT), Vernon
wrote:
1) Do I remove the mill's on-off switch completely or otherwise wire
it permanently in the ON position?
If this is simply a switch in the incoming line, use it to feed power
to the VFD.
2) Do I similarly wire around the wires going to and from the mill's
FORWARD - REVERSE toggle switch and re-route these wires to the VFD's
programmable inputs/outputs?
Yes, though I prefer three pushbuttons -- FWD/OFF/REV.
Plan on setting up a pot for speed adjustment. If you use the drive's
keypad for speed changes you'll lose much of the convenience the drive
offers.
There was previously some discussion here about whether a VFD can
adequately handle the mill's instant reverse. However, upon careful
reading of the manual the VFD does seem to have a programmable "node"
that allows for this. Apparently this can be tweaked a couple of
ways. One of these involves installing additional resistors. Another
SEEMS to provide for programming the injection of a DC current into
the motor to stop it from coasting. I think these two things are
related but I'm not sure.
You'll have to experiment to see what works for you. On many drives
the accel and decel settings are set in seconds even though the actual
effect is "seconds per 60 Hz." The result is that at low speed
settings the reverse is very quick. The most obvious application is
for power tapping, where it's often convenient to drill at high speed,
then turn the speed down to tap, and reverse to back the tap out. If
your drive is one that behaves as I've described above, the tap
reversal will be almost instantaneous at 10 Hz with, say, a 1 second
(at 60 Hz) accel/decel setting. If your drive's manual is silent or
vague on this point, you'll have to experiment to determine its actual
behavior.
I think I can get the thing installed this weekend so that it will at
least start and run. However, my brain is a lot murkier as regards
these programmable controls.
Thanks to one and all.
Vernon
This is a block diagram of how I'd recommend you wire you mill. (View
with a fixed pitch font.)
(Line In) - (Main Power Switch) - ( VFD ) - (Motor)
^ ^
| |
(FWD/OFF/REV) (Speed Pot)
Here's photo of that setup on my mill:
http://www.suscom-maine.net/~nsimmons/news/MillVFD.JPG
--
Ned Simmons