Motors controlled by vfd

Thread Starter

Thepallasbull1

Joined Jan 10, 2021
6
Hi guys, I need some help on this problem. I have at present a 5.5kw vfd running a 4hp motor 3 phase at 220v and works fine now I just purchased a 3hp, radial saw 3phase and would like to control both from the vfd . The vfd is a hunang 5.5 kw rated at 25amps. variable speed model. What are my options to control both at once but yet have their individual current protection on motors and at same time to be able to disconnect saw from vfd and swap out for another machine wood turning lathe to run from it with extraction . . Lathe has it's own vfd at the moment and I'm in the process of fitting the vfd's in a control box to protect from dust so I thought I might as well do it once and do it right . Thanks
 

jpanhalt

Joined Jan 18, 2008
10,933
Welcome to AAC.

Here's an interesting discussion: https://www.automation.com/en-us/articles/2011-1/vfds-can-control-multiple-motors

In brief, it is possible and may even be desirable to some extent. Be sure to read the third condition: Unless all motors are started simultaneously, the VFD needs to be upsized. That seems to be counterintuitive based on experience with rotary phase converters where it is desirable to start the motors sequentially. The reason: VFD's have slow-start, and that does not happen with any motor you add later. So, I would probably start the largest motor first, if simultaneous starting is not possible.

In my old shop (before VFD's were affordable), I used a rotary converter for a lathe and mill. As I worked alone, I never operated both at the same time for safety reasons.
 

strantor

Joined Oct 3, 2010
5,382
Hi guys, I need some help on this problem. I have at present a 5.5kw vfd running a 4hp motor 3 phase at 220v and works fine now I just purchased a 3hp, radial saw 3phase and would like to control both from the vfd . The vfd is a hunang 5.5 kw rated at 25amps. variable speed model. What are my options to control both at once but yet have their individual current protection on motors and at same time to be able to disconnect saw from vfd and swap out for another machine wood turning lathe to run from it with extraction . . Lathe has it's own vfd at the moment and I'm in the process of fitting the vfd's in a control box to protect from dust so I thought I might as well do it once and do it right . Thanks
It's not clear to me, whether you want to run these two machines at the same time, or one at a time. I assume it's an OR situation, not an AND situation. Either scenario is possible with most VFDs (I am not familiar with Hunang) although it is usually encouraged to find any other way. VFDs do not like to have the motor disconnected while running, as they can become damaged. It is much preferable to use the VFD's own overcurrent parameters to protect the motor, than an overcurrent device between VFD and motor. Most VFDs have digital inputs that can be assigned to different functions. I would consult the manual to learn if a digital input can be used to select between one current limit or another, then put a selector switch which you can use to choose lathe or saw.
 

Thread Starter

Thepallasbull1

Joined Jan 10, 2021
6
It's not clear to me, whether you want to run these two machines at the same time, or one at a time. I assume it's an OR situation, not an AND situation. Either scenario is possible with most VFDs (I am not familiar with Hunang) although it is usually encouraged to find any other way. VFDs do not like to have the motor disconnected while running, as they can become damaged. It is much preferable to use the VFD's own overcurrent parameters to protect the motor, than an overcurrent device between VFD and motor. Most VFDs have digital inputs that can be assigned to different functions. I would consult the manual to learn if a digital input can be used to select between one current limit or another, then put a selector switch which you can use to choose lathe or saw.
Thanks for your reply. As stated in my original post fla is r.5 for each motor maybe a little higher. Vfd is rated at 25 amps . 5.5kw. When I start the saw I need the extractor to start too . So from what I'm reading once both motors start together I'm fine . Yes
Then when I stop the vfd I want to switch power to the lathe so when I power up the lathe and extractor it should have no issues as not the saw is off line. Lathe is 1hp 0.75kw would that affect the setup running in conjunction to a 4hp extractor . I'm just looking for the best way to control all 3 from 1 single control box. .Thanks
 

Thread Starter

Thepallasbull1

Joined Jan 10, 2021
6
Thanks for your reply. As stated in my original post fla is r.5 for each motor maybe a little higher. Vfd is rated at 25 amps . 5.5kw. When I start the saw I need the extractor to start too . So from what I'm reading once both motors start together I'm fine . Yes
Then when I stop the vfd I want to switch power to the lathe so when I power up the lathe and extractor it should have no issues as not the saw is off line. Lathe is 1hp 0.75kw would that affect the setup running in conjunction to a 4hp extractor . I'm just looking for the best way to control all 3 from 1 single control box. .Thanks
Vfd will be powered down between motor switching due to high current draw issues
 

MaxHeadRoom

Joined Jul 18, 2013
21,984
I have ran two motors off of a VFD both simultaneously and alternatively.
In both cases it is desirable for both motors to be the same size. Particularly where the simultaneous condition exists.
In the case of alternate usage, the output can have two contactors fed from VFD output, one for each motor, but one of the outputs of the VFD must be set to 'At Zero Speed' in order to interlock and only allow the switching of contactors to take place when the running motor has stopped.
Are you running the VFD's off of 1phase?
If so that is about the limit of HP for 1ph VFD use.
Max.
 
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Thread Starter

Thepallasbull1

Joined Jan 10, 2021
6
Welcome to AAC.

Here's an interesting discussion: https://www.automation.com/en-us/articles/2011-1/vfds-can-control-multiple-motors

In brief, it is possible and may even be desirable to some extent. Be sure to read the third condition: Unless all motors are started simultaneously, the VFD needs to be upsized. That seems to be counterintuitive based on experience with rotary phase converters where it is desirable to start the motors sequentially. The reason: VFD's have slow-start, and that does not happen with any motor you add later. So, I would probably start the largest motor first, if simultaneous starting is not possible.

In my old shop (before VFD's were affordable), I used a rotary converter for a lathe and mill. As I worked alone, I never operated both at the same time for safety reasons.
Thank you for the link . Good reading
 

Thread Starter

Thepallasbull1

Joined Jan 10, 2021
6
I have ran two motors off of a VFD both simultaneously and alternatively.
In both cases it is desirable for both motors to be the same size. Particularly where the simultaneous condition exists.
In the case of alternate usage, the output can have two contactors fed from VFD output, one for each motor, but one of the outputs of the VFD must be set to 'At Zero Speed' in order to interlock and only allow the switching of contactors to take place when the running motor has stopped.
Are you running the VFD's off of 1phase?
If so that is about the limit of HP for 1ph VFD use.
Max.
Yes Max single phase but as you said both motors have to be the same that rules out my problem so looks like I will have to get another vfx as one motor is 3hp and the other is 4hp .just thought it might be possible
 
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