# VFD question



## Great white hunter (Feb 4, 2014)

I have a teco JNEV-202-H1 VFD. I have one simple question. Can I run the 3 phase out put directly to the switch on the lathe. The switch is just an forward/off/reverse switch. I know the manual says directly to the motor but I have seen this done before and would like to do it this way if its not going to blow up the VFD. I don't understand why it wouldn't work because it is still a direct feed to the motor. If I can -  do I always have the switch on the forward position and use the VFD to control the forward/reverse? I have also done this in the past with a cheap chineese VFD and it seemed to work fine till the VFD exploded on me. I do not think the VFD blew up because of my wireing, I think the VFD was garabage.  I feel like I'm going to go crazy with this VFD stuff. Thanks Jason. :whiteflag:


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## AlanR (Feb 4, 2014)

jason nosse said:


> If I can -  do I always have the switch on the forward position and use the VFD to control the forward/reverse?



Yes or turn the power TO the VFD off before you use the machine's switch. 

The issue is that the motor presents an inductive load to the VFD and disconnecting the motor while the VFD is powered up will result in very large voltage spikes to the output semiconductors in the VFD and they're not rated for that.


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## Ray C (Feb 4, 2014)

Jason,

 Placing a switch in that location is not common practice and it should only be used as an emergency switch.  Using the switch while the VFD is energized will burn out the VFD.


Ray


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## Great white hunter (Feb 4, 2014)

Ray C said:


> Jason,
> 
> Placing a switch in that location is not common practice and it should only be used as an emergency switch.  Using the switch while the VFD is energized will burn out the VFD.
> 
> ...



But as long as the machine switch is always on it should be ok? Right?


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## AlanR (Feb 4, 2014)

jason nosse said:


> But as long as the machine switch is always on it should be ok? Right?



My machine is two speed, 8 / 4 pole so I don't want to remove the switch. I removed the knob so that switch can't be easily used, I'd have to pick it up and hold it in place to use the machine switch. Pretty safe that way. So you could say it's always on.


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## Great white hunter (Feb 4, 2014)

AlanR said:


> My machine is two speed, 8 / 4 pole so I don't want to remove the switch. I removed the knob so that switch can't be easily used, I'd have to pick it up and hold it in place to use the machine switch. Pretty safe that way. So you could say it's always on.



Ok, so I will turn the switch on and will remove the knob so it is always on. That sounds way better that cutting into the wiring and getting rid of my switch. I just want it to be easy to switch from the VFD and go back to my phase converter if I want to with out rewiring the whole machine.


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## Ray C (Feb 5, 2014)

Correct.

Once a VFD is energizing a load (such as a motor) you should never suddenly break the connection between the VFD and the load.  Technically speaking, it's fine to have the switch there -as long as you never use it while the VFD is powering the motor.

Ray





jason nosse said:


> But as long as the machine switch is always on it should be ok? Right?


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