On/Off switch (magnetic contactor) for VFD power supply

My 2 cents...

There is absolutely nothing wrong with using a magnetic contactor as your power cut off.
the VFD has no idea what the cutoff device is or how it's wired in and really doesn't care as long as power is uninterrupted to the VFD during it's intended operation.
A contactor is the primary means that larger hp motor operating currents are switched on and off.

I have 30 Packaging machines that get their source of power from a circuit that is directly supplied with power from magnetic contactors and have not had a single failure from their use.:thumbzup:
the 30 food packaging machines have been in continuous operation for 10- 14 years if that makes you fell any better......

Their thinking may be as a safety precaution should the contactor's contact tips should weld together, there would be power flowing through the contactor even if the contactor's control circuit was de-energized.
But if you were to wire in an overload relay, it would provide an excellent way to provide as much safety as possible and still accomplish what you wish by using a magnetic contactor.

There is one other alternative i could suggest that is quite cost effective and even simpler to install...
an emergency stop switch....
there are many manufacturers of switches for that purpose. I use a lot of Telemecanique and Square D
the only draw back is the E-Stop switches are for control purposes and generally can't carry much current.
but they can be used in conjunction with the contactors control circuit and provide a higher degree of safety as well, should you wish to entertain that type of circuit.

i can help you with the project if the need arises, shoot me a PM if i can assist in any way.

mike:))
 
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Here's my guess in the matter...

If you wish to power off the motor, it's best to use the on/off switch built into the VFD as it is no doubt a solid-state device that does not bounce. I believe all power coming into a VFD should have a shut-off switch for emergency and maintenance purposes. That said, if the VFD is already powered off and if you then shut off the incoming power with a switch of any type, there will be no problems. If however one were to get into the practice of turning the VFD on/off by way of the switch on the incoming power lines while the motor is being driven, it can cause problems. All mechanical switches bounce and with dual line (or 3 phase) switches, all the lines will not be shut off (or turned on) instantaneously. The timing difference between the legs could be on the order of milliseconds to deciseconds (thousandths up to tenths of a second) or perhaps even more. In terms of electricity, a millisecond might as well be a million years and during the time the supply lines are not fully engaged, one or more of the lines is getting drawn upon and it will surge on that line. Eventually it stabilizes but in the mean time, the electronics in the unit is going bonkers trying to figure-out what the heck is going on.

On the matter of "switch bounce". All mechanical switches do not immediately and fully open or close but rather, during transition, they may bounce open/shut many times until they stabilize. "Many times" depends on the type of switch but it's not uncommon for a typical switch to bounce (roughly) 3 to 10 times.

When you add these combined non-steady-state conditions together, it wreaks havoc with the solid state circuitry and could lead (presumably) to failure.

Moral of the story: I have switches on all my VFD power lines and are only used for emergency purposes and/or, when the VFD's own power switch is in the off position. As a matter of safety, your particular model of VFD should be checked to verify it will not power-up a motor when it is first turned on. I can hardly believe UL/CSA would approve such a device that operated with "instant-on" at power-up. It's possible this is a programmable feature though...

That's my guess with my EE hat on.

Ray
 
Here is a schematic of how I intend to wire things (except the transformer will be moved to after one of the breakers).

One VFD for the 3hp spindle (protected by 15A No Fuse Breaker) and one VFD for the 1hp power X feed (protected by 10A NFB).
78d1723d-8d2f-4e50-b38e-a335ae705813.jpg

I will be using momentary NO push button for RUN and a momentary NC for STOP.

The purpose of this is not as an emergency stop, but rather as a regular power on/off switch which the Huanyang VFD's don't have.
 
Generally what the manuals are talking about when they say not to switch the VFD on and off with a contactor, is not to regularly cycle the VFD on and off by switching the main power. This is very hard on the capacitors, and will eventually destroy the drive. Once you shut off a VFD, you should not re-apply power for 5-10 minutes, or you risk reducing the life of the drive.

There is technically nothing wrong with this setup, (I would not recommend wiring the relay coils in series, but rather in parallel to avoid voltage drops) but only use the buttons to start the VFD at the beginning of a project, and off at the end. This is why most installations use a knife switch or other disconnect to start-up and shut down the VFD, and use push buttons wired to the drive to control the speed, direction, and start/stop.

It is also not necessary to use a transformer as contactors are made with 110vac coils, just to simplify the process.

-Cody
 
Codered741 said:
It is also not necessary to use a transformer as contactors are made with 110vac coils, just to simplify the process.
Click to expand...

Just recycling the components that came with the mill. :))

I appreciate the tip about not wiring the contactor coils in series.
 
Where do you put, emergency shut off on a small horizontal mill so you can always reach it.
577stu
 
Who carries them? You can search for "emergency stop switch" on eBay and find lots of inexpensive ones that come from China, perhaps a NOS (new old stock) domestically produced one on occasion. Or else go to Grainger or McMaster-Carr.

Where to place it? I tend to place E-stop switches on "the other side/end of the machine" from where the normal run/stop control is located ... just in case I'm at that end of the machine and don't want to cross in front of when the hoo-raw starts happening. I guess the best answer is for you to imagine what can go wrong, and where you're likely to be when it happens. That's where to locate the E-stop. You can't always locate such a switch "so you can always reach it," but between the normal start/stop and the E-stop, you can usually cover a wider area.
 
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