# Vfd & Safety ?



## dlane (Jun 4, 2015)

Hi all,  Got to thinking , I'm taking off a perfectly working mechanical drum switch and installing a vfd in its place . 
Teco  7300 cv is going on a 2hp supermax mill . 
My concern is the electronics that the 6 yr old chi kid put together for < 10c an hour, And ghost starts with my hands in the danger zone. 
My plan is to use vfd to control machine , thinking I'll mount it under dro shelf  so it's easy to get at , will that interfere with dro readings?.
Any how me and overseas electronics don't always get along real good and ied like to keep all my fingers 
Seems all the popular known brand vfd s are made in china nowadays.
Should this be a concern ?.  
Thanks
Derrick


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## bosephus (Jun 4, 2015)

i just went a vfd on my lathe ,  with some very minimal help from another member i was able to keep my original  e stop button , drum switch , and on button 
and use them exactly as intended  . all it took was rewiring them for low voltage , and a few simple programming changes to the vfd  .
both very simple and easy to do .  i am fairly ignorant on electrical  and i got threw it easily .  
 if there is a reason you can not use your drum switch i am sure a more knowledgeable member will let you know


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## dlane (Jun 4, 2015)

Thanks bosephus, That would be nice to have a real switch but it would still relie on electronics in the vfd to keep machine stopped , no switches between vfd and motor. Short of putting a disconnect on main power in and using it as a stop I don't know how else to be sure machine won't ghost start. I don't have vfd yet it's in transit, I looked at online manual and it seems pretty complicated to me. Any suggestions much appreciated thanks
Derrick


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## RJSakowski (Jun 4, 2015)

dlane said:


> Hi all,  Got to thinking , I'm taking off a perfectly working mechanical drum switch and installing a vfd in its place .
> Teco  7300 cv is going on a 2hp supermax mill .
> My concern is the electronics that the 6 yr old chi kid put together for < 10c an hour, And ghost starts with my hands in the danger zone.
> My plan is to use vfd to control machine , thinking I'll mount it under dro shelf  so it's easy to get at , will that interfere with dro readings?.
> ...



Having an E-Stop or other positively acting switch is always a good idea.  Especially if you are putting your body in harm's way.   One section of the drum switch controls the power and could still be used as a convenient positive disconnect.    My Tormach has a relay controlling the power fed to the the spindle vfd so that any time the do0r to access the spindle drawbar is open, the vfd is disconnected.  It also has a separate keyed spindle lockout switch feeding the relay to disconnect the spindle vfd should there be other operations such as adjusting a boring bar setting where you would not normally open the access door.
In terms of safety, having switch like a drum switch where there is no question as to whether the connection is broken is preferable to a relay where contacts could weld shut.  Installing a pilot light to indicate live power would be another belt and suspenders option.


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## JimDawson (Jun 4, 2015)

I understand your concerns.  In 25 years of working with VFDs I have not seen one self-start or not shut off when told to.  Having said that, a hard stop (disconnect) wired ahead of the VFD would provide the margin of safety that you want.  You could use the original drum switch for this purpose.  You do not want a break between the VFD and the motor.

Normally the DRO is well shielded, and with proper grounding I would not expect any interference.


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## mzayd3 (Jun 4, 2015)

If these vfds were made here, they would be made of Chinese parts anyhow.  To answer your question about safety, a vfd will not turn on on its own.  It's an electrical circuit which will only do what you tell it to do.


Sent from my iPhone using Tapatalk


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## JimDawson (Jun 4, 2015)

dlane said:


> Thanks bosephus, That would be nice to have a real switch but it would still relie on electronics in the vfd to keep machine stopped , no switches between vfd and motor. Short of putting a disconnect on main power in and using it as a stop I don't know how else to be sure machine won't ghost start. I don't have vfd yet it's in transit, I looked at online manual and it seems pretty complicated to me. Any suggestions much appreciated thanks
> Derrick



A number of members have installed Teco VFDs, so there is a lot of support for them on this forum.  At first look, the manual can be a bit overwhelming, but it's not that complicated once you actually start the installation.


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## dlane (Jun 4, 2015)

Thanks for the reply's I guess I'll hurry up and wait for the vfd to arrive, did some cleaning on it and the way wipers. 
So here it is waiting on power. The drum switch is hanging 
	

		
			
		

		
	



Derrick


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## mksj (Jun 4, 2015)

Just a follow-up on a simple way to add a second layer of safety to your VFD controls. Most VFDs have an emergency stop command which will override all other commands, also if a for/rev command was given at the same time, the VFD will go into a stop mode. You can get an E-Stop with multiple switch blocks, with a NC and a NO switches in the E-Stop default non-engaged position. The NC contacts connects the VFD input command power (usually 12 or 24VDC; P12 or P24) and then goes to you forward/reverse (command) switches. The other NO switch is also connected to the VFD input command power and connects to a emergency stop input on the VFD. When the E-Stop is engaged, if breaks input power to the forward/reverse command and signals the VFD to do an emergency stop. So there are two separate command structures operating. As other have mentioned, there are addition redundancies in safety NC switches  for open electrical cabinets, etc. between the E-Stop and the forward/reverse switches,

Alternatively you could use a contacter before the VFD and have the E-Stop break power to the contactor coil when engaged, depending on the VFD the motor will either cost to a stop, or in some cases brake from the continuing regenerative power from the motor as it spins down. Lots of possibilities, but I would think a switch failure is more likely to occur then a VFD malfunction. There are many well made VFDs with companies having a presences in the US, with our litigiousness society, it is highly unlikely that these manufactures would build a faulty VFD product. The flip side of the coin, if you buy a VFD from offshore through noname electronics on eBay, you may be in for a real surprise. Then try deciphering the manual or getting any support. 

Very nice looking mill.


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## dlane (Jun 15, 2015)

Here is what I come up with
	

		
			
		

		
	



	

		
			
		

		
	
the disconect on left is mounted to a bracket that is bolted to the lifting eye hole , there is room for the head to tilt.
The vfd enclosure has a front cover
Time will tell
Thanks
	

		
			
		

		
	



	

		
			
		

		
	
 Derrick


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