Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.
A magnetic starter is not required with a VFD - the VFD is already a "listed motor starter". Even if you install one, heaters or other overload protection are not required and would have zero effect - that function is provided by the vfd. There is no "startup surge", more than the programmed time in excess of the programmed max current will cause the vfd to take whatever action is programmed (usually "stop"), and a locked rotor will cause immediate trip, followed by whatever action you programmed the vfd to perform (for example attempt restart "n" times).
I am not familiar with the setup of VFD units, and was only trying to clarify the purpose of magnetic starters and disconnects. I assumed a couple of things in regards to this setup, (my mistake).
Pat P.
Live for the moment!
Prepare for tomorrow!
Forgive the past!
While a contactor is not required, it is a darn good idea. In the case where a conversion/integration is being performed, the contactor would be surplus so why not use it?
Using contactors as a means of controlling power is common in new machines. Most of the new import machines use a contactor to control the main power regardless of motor type.
New IEC contactors are cheap. Something on the order of $15.00 or so.
The primary reason many import machines use contactors is that much of the world outside the USA requires low voltage controls anywhere an operator can touch them - like mains power on/off. Someone will no doubt correct me if wrong, but IIRC EU specifies a max of 24 volts for controls. Larger industrial machines have run "low" voltage control for years, although low is a misnomer - 115v was most common. Home shop machines don't usually run on three phase mains or 480 volts, but it wouldn't be good practice to have your panel switches directly connected
I use contactors, but not wired as a magnetic switch for epo or vfd control - just for single button on/off or all power to the machine and accessories. My 1980's lathe has a bank of contactor and motor starters. Two are starters for the motors, another for motor reverse, and the rest perform various logic functions for the safey interlocks. The control (coil) voltage is 115. With the VFD, much of this goes away.
I have occasional "flickering" of my power when it storms or is fairly windy.
I had the power flash on and off four times in the time it took me to get a machine shut off and it fried a contactor, burned a circuit board, and blew up a couple of capacitors.
I now use magnetic starters/contactors, so if the power flickers, the machine shuts down until I hit the start button again.
Glenn
Operating machines is perfectly safe......until you forget how dangerous it really is!
gleen w your observation of using a contactor to kill all machine power to protect during power drop out is a valid concern and the contactor should be controled with a two push button controller on/off not toggle switchs
the seconday controls of the vfd foreward-reverse-stop -e stop being in a series contact on the contactors stop button would give you max safety and protection
for clarification the e stop would have one contact for the vfd and 1 contact for the contactor
Glenn Wegman wrote:I have occasional "flickering" of my power when it storms or is fairly windy.
I had the power flash on and off four times in the time it took me to get a machine shut off and it fried a contactor, burned a circuit board, and blew up a couple of capacitors.
I now use magnetic starters/contactors, so if the power flickers, the machine shuts down until I hit the start button again.
Your magnetic contactor will drop on power loss, but won't help you in surge (likely what took out your boards). You can't assume there will be a power loss before each surge.
You may want to consider a "whole house" surge protector - wires to each phase and neutral at the panel. We don't get much lightning here, but the trees are over 160 foot tall - they toss branches and fall - bad power surges result. This all came back to me as we lost power this weekend - I raced down and turned of my new CNC BP.. A large surge protector in on it's way.
I don't wire my input contactors as "magnetic". I find a VFD is VERY tolerant of power loss - it takes a few seconds to empty the input caps at typical loads. The VFD is programmed how you want it to respond to power loss -mine is set to "stop". All VFDs I've looked at also have input protection, but that only works for simple transients - not high voltage applied to your feeder line.
Last edited by lakeside53 on Thu Oct 28, 2010 12:43 am, edited 1 time in total.
One thing not mentioned here is be carefull of the max speed setting you program into the unit. You possibly have the ability to run your motor at 2x rated speed. Your motor may handle this and it may not. I suggest that you set your max speed at just a bit more than 60 hz. This will help things intact.
Lots of experience, but I'm not sure what you mean
If you're talking about programing the vfd inputs to connect to the switches and potentiometer, then you'll need to explain exactly what physical arrangement you are using.
Check your manual for the various possibilites. My preference is "three wire" - separate momentary Start and Stop, toggle for forward/reverse.
Or .... do you you mean motor currents? If so, what does your motor nameplate specify?
Sorry, I meant setting the overloads. I can read and probably figure it out, but you guys are a ton of help with your experience and I don't want to smoke this thing in a dumb error.
They say a semiconductor will blow faster than a fuse.
The quickest way to trash a VFD (3 minutes or less) is to pickup a motor
that was manufacture'd prior to early 1990's and even though all plate
ratings look right, new or used from a surplus and or Ebay, there will be a
90 percent chance that it's a motor that is not frequency phase insulated
between the windings.
Ken.
One must remember.
The best learning experiences come
from working with the older Masters.
Ken.
A large surge protector in on it's way. 
