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



## CanFire (Aug 26, 2013)

Hi.  I noticed in the Huanyang VFD documentation that it states: 

_"Electromagnetic contactor:__Note: Do not use the electromagnetic contactor as the on/off button of power supply for_
_the inverter."
_
I was planning to do exactly that.  Another fellow has already done it here: http://www.5bears.com/vfd02.htm

The manual does not say 'Do Not use on/off switch', but specifically states not to use an electromagnetic contactor as the on/off switch.   Does anybody know why?


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## Ray C (Aug 26, 2013)

Don't know the answer and this is precisely why I'm not a big fan of Huanyang VFD.  -The manual sucks and gives no useful information.  I'm still trying to figure-out how the jog settings are supposed to work for both fwd and rev mode.  One slight problem though, is they are one of the very few VFD makers that output 5HP from single phase input.  Most others only go up to 3 HP.


The Hitachi documentation is very good and informative.  You might want to track it down and see if you can glean information from it.


Ray





CanSir said:


> Hi. I noticed in the Huanyang VFD documentation that it states:
> 
> _"Electromagnetic contactor:__Note: Do not use the electromagnetic contactor as the on/off button of power supply for_
> _the inverter."
> ...


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## CanFire (Aug 26, 2013)

Ray C said:


> I'm still trying to figure-out how the jog settings are supposed to work for both fwd and rev mode.



Ray, this guy has jog working on his lathe: http://youtu.be/4YOZHcoSNfQ?t=1m51s .Maybe you could post a comment asking for more info?

I just can't understand the reason behind wanting jog though.  On a mills power x,y, or z feed I can see it being useful for positioning, but then you could always just use the speed potentiometer for the same thing.  Would you mind explaining how you intend to use the jog function and on which machine?

Regards,
Dean.


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## righto88 (Aug 26, 2013)

Use a 2 pole disconnect switch installed after the fused L1 and L2. Or a fused disconnect switch and feed it.
Still use the Run/Off switch but if the contactor fails, ie, contacts stick together, you still have a means of shutting power off.
 Keep it (the disconnect) with-in sight of your machine.


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## righto88 (Aug 26, 2013)

A key point:
"_Do not use the electromagnetic contactor as the on/off button of power supply for the inverter"
Where is the supply coming from? 
L1 and L2
 via the run/stop, on/off, start/stop, (whatever it is called) switched contactor.
Tech talk for having a place to remove "applied power". Or should I say "the source of power"?_


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## Ray C (Aug 26, 2013)

Thanks... I'll check that info about the jog.Jog is really handy for changing gear setting on some lathes.  To change the gear speed on my machine, it must be stopped first then, the gear levers are manually changed.  Sometimes, the gears do not line-up and you blip the motor for a split second to move the gears just enough so you can move the lever.  This happens to me 10 times a day at least.  For now, I just manually spin the chuck by hand but sometimes that's almost impossible to do if the gears are in a very low ratio.Also, all my chucks have witness marks to align with a mark on the spindle.  It's darn hard to grab the spindle and turn it by hand to rotate it to a desirable position so a chuck can be installed in the preferred position.-Many other examples too.  Especially when setting up a shaft for re-threading on the lathe.  -Especially if it's a metric thread where you cannot let the halfnuts loose.Ray





CanSir said:


> Ray, this guy has jog working on his lathe: http://youtu.be/4YOZHcoSNfQ?t=1m51s .Maybe you could post a comment asking for more info?I just can't understand the reason behind wanting jog though.  On a mills power x,y, or z feed I can see it being useful for positioning, but then you could always just use the speed potentiometer for the same thing.  Would you mind explaining how you intend to use the jog function and on which machine?Regards,Dean.


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## CanFire (Aug 26, 2013)

righto88 said:


> A key point:
> "_Do not use the electromagnetic contactor as the on/off button of power supply for the inverter"
> Where is the supply coming from?
> L1 and L2
> ...



Thanks for the reply, but I'm not sure what you're getting at.  I was planning to wire it almost exactly like 5bears did in the link I posted in my first message.  I intend to use an electromagnetic contactor as a means to turn on & off the power (L1 & L2) that supplies the VFD.   The manual however, seems to say that this is a bad idea.  I just don't understand why an electromagnetic contactor is singled out as bad, but other types of switches seem to be OK.  I can't leave the VFD running all the time and turning it on & off via a 50-amp breaker is a bad idea.  

Cheers!


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## righto88 (Aug 26, 2013)

CanSir said:


> Thanks for the reply, but I'm not sure what you're getting at.  I was planning to wire it almost exactly like 5bears did in the link I posted in my first message.  I intend to use an electromagnetic contactor as a means to turn on & off the power (L1 & L2) that supplies the VFD.   The manual however, seems to say that this is a bad idea.  I just don't understand why an electromagnetic contactor is singled out as bad, but other types of switches seem to be OK.  I can't leave the VFD running all the time and turning it on & off via a 50-amp breaker is a bad idea.
> 
> Cheers!



You must not be reading your PM, ie private messages.


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## righto88 (Aug 26, 2013)

I can't leave the VFD running all the time and turning it on & off via a 50-amp breaker is a bad idea.  


Where is this located at with respect to "your machine"?????

the 50 amp breaker? I never said to use that as an on/off switch but as a means, a source, a place to stop all source of implied power, ie voltage or cause of,,,,,


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## CanFire (Aug 26, 2013)

righto88 said:


> the 50 amp breaker? I never said to use that as an on/off switch but as a means, a source, a place to stop all source of implied power, ie voltage or cause of,,,,,


I didn't mean to imply that you had suggested it.   The outlet that I use for my mill will be the same outlet that I occasionally use for my welder and it is a 50-amp circuit.  From the manual, it almost seems like Huanyang wants the VFD hardwired in and left running 24x7 or to use the circuit breaker as an on/off switch - which in my mind is a bad idea.

My apologies for the confusion.  You were right - I hadn't noticed that I had been getting PM's.


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## Ulma Doctor (Aug 26, 2013)

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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## Ray C (Aug 26, 2013)

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


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## CanFire (Aug 26, 2013)

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).



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.


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## Codered741 (Aug 27, 2013)

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


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## CanFire (Aug 27, 2013)

Codered741 said:


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



Just recycling the components that came with the mill.  )    

I appreciate the tip about not wiring the contactor coils in series.


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## 577 stu (Jul 26, 2021)

Who carries emergency shut of switches.
577stu


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## 577 stu (Jul 26, 2021)

Where do you put, emergency shut off on a small horizontal mill so you can always reach it.
577stu


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## hman (Jul 26, 2021)

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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