# Single VFD with 2 motors



## Jairus (Feb 19, 2014)

Hello experts,

Before I will implement this in our factory I need a consultation from you guys here in this forum.

My issue is:
I have 2 motors for 2 conveyors; this will run and stop at the same time.
1st motor rated at 1KW/380V/3-phase/cosθ=0.8. 
2nd motor rated at 0.75KW/380V/3-phase/cosθ=0.85
Both motors are in Y-connection start and run.
I have single VFD available rated at 2KW.

Now my question is, it is possible to let this single VFD to drive these 2 motors? If ever yes then shall I need to get the average of the PF for these motors and key in this to VFD PF parameter? Pls. help me.

Thank you in advance…


--Jairus---


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## MDShunk (Jan 7, 2007)

It's done all the time. No worries.


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## JRaef (Mar 23, 2009)

Jairus said:


> ... If ever yes then shall I need to get the average of the PF for these motors and key in this to VFD PF parameter? ...


not sure where you came up with that, but no, PF has nothing to do with it.

One thing that is true however is that the single drive can no longer protect the separate motors for overload, it has no way of discerning the separate current values. So you must provide individual overload relays for each motor, and wire the trip contacts into the VFD to shut it down, which means shutting down both motors if either one overloads. Make sure that whatever overload relay you use specifically says it is OK to be used down stream from a VFD.


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## Safari (Jul 9, 2013)

Jairus said:


> Hello experts,
> 
> 
> I have single VFD available rated at 2kw
> ...


does this vfd at the terminals have position to input two motors ?

or it's just a normal vfd with with a single u v w terminal

we have a drive altivar that runs two motors but its designed in a way that you can input two motors. 
am just concerned. i realised jraef and MD shunk didn't ask. or is it ok in either case 

Sent from my HUAWEI Y210-0100 using Tapatalk 2


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## erics37 (May 7, 2009)

JRaef said:


> not sure where you came up with that, but no, PF has nothing to do with it.
> 
> One thing that is true however is that the single drive can no longer protect the separate motors for overload, it has no way of discerning the separate current values. So you must provide individual overload relays for each motor, and wire the trip contacts into the VFD to shut it down, which means shutting down both motors if either one overloads. Make sure that whatever overload relay you use specifically says it is OK to be used down stream from a VFD.


Can you give me an example of a particular make & model of overload that is suitable to be placed downstream from a VFD? And where would you find the info for that? On the overload relay spec sheet or something?


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## Jlarson (Jun 28, 2009)

A lot of the basic self powered electronic OL relays can't be used on drive outputs. The fancier electronic OL's that require an external control PS can usually though.

Bi metal and melting alloy OL's and MMS's are good too. 


Using the MMS's gives you bi metal OL, short circuit protection, and a disconnect for the individual motor in one package.


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## JRaef (Mar 23, 2009)

Melting alloy overload relays are all insensitive to frequencies up to 400Hz, bimetal overloads are typically only rated to be used on 40 - 60Hz, which makes them unsuitable for use on VFDs, and most people are unaware of that. It is done all the time I realize, but there is clear evidence that using bimetal devices down stream of VFDs causes nuisance tripping beyond their stated operating range. Nuisance tripping is not something that UL and other testing agencies are concerned with, because the failure mode is not inherently unsafe, so there is no prohibition. But some VFD mfrs have begun issuing warnings to this effect. Rockwell is one of them, and I can post a link to the technical note stating this when I get to my PC later, but you will have to be registered on the Rockwell Knowledge Base to see it. Registration is free (as long as you don't work for a competitor), you just have to do it.


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## Jlarson (Jun 28, 2009)

We just started to hear the same thing with the bi metals but they are still the standard pretty much here for mult motor installs like fan wall stuff.


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## tates1882 (Sep 3, 2010)

Jlarson said:


> We just started to hear the same thing with the bi metals but they are still the standard pretty much here for mult motor installs like fan wall stuff.


are you using bi metallic for new installs or just add a VFD ahead of the existing mags? I don't think I've installed a non electronic ol in 2 years unless it was an existing retro.


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## JRaef (Mar 23, 2009)

If you already have a logon ID for the Rockwell Knowledge base, log in and go here:
https://rockwellautomation.custhelp.com/app/answers/detail/a_id/18270

If not, go here to set up a user ID (it's free, but you must have an email address)

https://rockwellautomation.custhelp.com/

Then when logged in, use the link above, or do a "Search for public records" using the search term "18270"


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## greenman (Apr 20, 2012)

JRaef said:


> not sure where you came up with that, but no, PF has nothing to do with it.
> 
> One thing that is true however is that the single drive can no longer protect the separate motors for overload, it has no way of discerning the separate current values. So you must provide individual overload relays for each motor, and wire the trip contacts into the VFD to shut it down, which means shutting down both motors if either one overloads. Make sure that whatever overload relay you use specifically says it is OK to be used down stream from a VFD.


 Carlo Gavazzi offers a comprehensive range of monitoring controls for monitoring of phase loss, incorrect phase sequence, phase unbalance, over/under current, over/under load, over/under frequency, and over/under voltage.

:thumbsup:


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## erics37 (May 7, 2009)

Jlarson said:


> A lot of the basic self powered electronic OL relays can't be used on drive outputs. The fancier electronic OL's that require an external control PS can usually though.
> 
> Bi metal and melting alloy OL's and MMS's are good too.
> 
> ...


Gotcha.

Now that you mentioned that, there is a new machine they got recently at the shrimp plant; it is a big blast freezer thing with a large control cabinet built on to one end. It has 2 drives feeding four separate MMSs each feeding a big blower fan. I haven't dug into that control cabinet too much because it is new enough that no one has had a chance to break it yet.


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## Jairus (Feb 19, 2014)

nickson said:


> does this vfd at the terminals have position to input two motors ?
> 
> or it's just a normal vfd with with a single u v w terminal
> 
> ...



It just a normal vfd with with a single u v w terminal.
Omron JX 2.2KW vfd.


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## Jairus (Feb 19, 2014)

JRaef said:


> not sure where you came up with that, but no, PF has nothing to do with it.
> 
> One thing that is true however is that the single drive can no longer protect the separate motors for overload, it has no way of discerning the separate current values. So you must provide individual overload relays for each motor, and wire the trip contacts into the VFD to shut it down, which means shutting down both motors if either one overloads. Make sure that whatever overload relay you use specifically says it is OK to be used down stream from a VFD.


Thank you.

I'm almost out of time now i need to run the line as soon as possible.
I will implement as what you have suggested. I will install individual schneider (GV2ME series) thermal circuit breaker for each motor since i have this on stock. As what i have read GV2ME is not designed for short circuit protection, it's some sort of overload relay with disconnecting switch. anyway it have adjustable current setting so i can set this to times 125-140% with respect to nameplate current of the motors. By the way I am running @ 50 to 60 hz. but if you all guys out there still have any suggestion pls. tell me, i really appreciate it... Thank you so much.


---jairus----


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## tates1882 (Sep 3, 2010)

Jairus said:


> Thank you. I'm almost out of time now i need to run the line as soon as possible. I will implement as what you have suggested. I will install individual schneider (GV2ME series) thermal circuit breaker for each motor since i have this on stock. As what i have read GV2ME is not designed for short circuit protection, it's some sort of overload relay with disconnecting switch. anyway it have adjustable current setting so i can set this to times 125-140% with respect to nameplate current of the motors. By the way I am running @ 50 to 60 hz. but if you all guys out there still have any suggestion pls. tell me, i really appreciate it... Thank you so much. ---jairus----


What are you using to protect said drive? Normally short circuit protection is handled by the ocpd ahead of the drive, then individual motors just require ol relay/safety mag. The breaker you specified above, is it listed for load side of a vfd?


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## Jairus (Feb 19, 2014)

tates1882 said:


> What are you using to protect said drive? Normally short circuit protection is handled by the ocpd ahead of the drive, then individual motors just require ol relay/safety mag. The breaker you specified above, is it listed for load side of a vfd?


This is how i wired it; a single VFD for 2 motors.

I installed 3 FUSES for each line in the line side of the VFD for the short circuit protection, then in the load side of the VFD are follows:
-> GV2ME(overload relay 1) -> motor 1
-> GV2ME(overload realy 2) -> motor 2

If any of the two GV2ME will trip, then the VDF will stop.

So far now the line is running with this type of setup. I'm not completely sure, but i think I'm not violating any of the electrical code particularly for NEC, because that's what they usually implement here.

Thank you so much

---Jairus---


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## JRaef (Mar 23, 2009)

The GV2ME is only rated for use at 50/60Hz.You should check with Schneider on whether they say it is safe to use behind a VFD.

Even if they say it's OK, the 125% of the motor nameplate FLA is ALREADY built-in to the design of the thermal trips, you *set them to the motor nameplate FLA*. If you set the dial to 125-140% of the nameplate FLA, you are in effect setting them to not begin to start the thermal monitoring until the motor current is from 156 to 175% of FLC, well into the damage curve of the motor.


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## Jairus (Feb 19, 2014)

JRaef said:


> The GV2ME is only rated for use at 50/60Hz.You should check with Schneider on whether they say it is safe to use behind a VFD.
> 
> Even if they say it's OK, the 125% of the motor nameplate FLA is ALREADY built-in to the design of the thermal trips, you *set them to the motor nameplate FLA*. If you set the dial to 125-140% of the nameplate FLA, you are in effect setting them to not begin to start the thermal monitoring until the motor current is from 156 to 175% of FLC, well into the damage curve of the motor.


You mean to say, i need to adjust the dial to exactly the same as the nameplate FLA. Ok i will try it. i had measured the actual current of the individual motor during full load of the conveyor, and it appeared to be 35% less than the nameplate FLA. SO i think your suggestion will work.

THANK YOU SO MUCH BY THE WAY...

---JAIRUS---


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