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A 3 phase AC (Alternating Current) question

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donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sun Feb 14, 2021 12:00 pm Post subject: A 3 phase AC (Alternating Current) question

Looking for some solutions on a project.



I have a lathe/mill combo.  I'm going to be upgrading it by replacing the motors and controlling them with VFD's.  Space is tight and it occurred to me that if I could use one VFD to control the motors (never at the same time) that would simplify the installation.  It would also save money since I would only need one VFD.  



But now the question is how to switch the VFD between the two motors? 



My first thought was a 3P2T switch.  But I have not been able to find one rated for 230VAC and 1HP.  It was suggested to use a contactor.  But then I would need a low voltage source for the contactor with a switch for that power source and now it's no longer simplifying things. 



Any ideas?

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Ceengland

Joined: 11 Oct 2020
Posts: 381
Location: MS

Posted: Sun Feb 14, 2021 12:33 pm Post subject: A 3 phase AC (Alternating Current) question

On 2/14/2021 2:00 PM, donjohnston wrote:

 	  Quote: 	
		   



 Looking for some solutions on a project.



 I have a lathe/mill combo.  I'm going to be upgrading it by replacing the motors and controlling them with VFD's.  Space is tight and it occurred to me that if I could use one VFD to control the motors (never at the same time) that would simplify the installation.  It would also save money since I would only need one VFD. 



 But now the question is how to switch the VFD between the two motors?



 My first thought was a 3P2T switch.  But I have not been able to find one rated for 230VAC and 1HP.  It was suggested to use a contactor.  But then I would need a low voltage source for the contactor with a switch for that power source and now it's no longer simplifying things.



 Any ideas?

Contactors with 120VAC coils are used in thousands of devices.
	




1 HP should be easy to find; here's one rated at 30A per contact with a 

120V coil:

https://www.galco.com/buy/Deltrol-Controls/21011-84?source=googleshopping



The vendor's spec sheet says '30A  (at) 30V DC', so it should handle 30A AC 

with no problem at all.



I started by searching for '3pdt 30a 110v relay'



Charlie

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Charlie

donjohnston

Joined: 13 Dec 2009
Posts: 231

Posted: Sun Feb 14, 2021 2:08 pm Post subject: Re: A 3 phase AC (Alternating Current) question

Would I use one leg of the 230v supply to power the coil? 



(I haven't used a relay like this before)

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user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Sun Feb 14, 2021 2:08 pm Post subject: Re: A 3 phase AC (Alternating Current) question

How about one of these switches: 

https://www.mouser.com/Electromechanical/Switches/Toggle-Switches/_/N-5g2jZ1yzvvqxZgjdhub?P=1z0z296Z1z0z20xZ1z0z2qcZ1z0yqrwZ1y8pmr4Z1y8ziurZ1y8ziusZ1z0z63x&Rl=5g2jZer5eZ1z0x8gwZ1z0x87nSGT&Ns=Current%20Rating|0

I assume that your VFD has an on-off switch controlling input power.

Turn the input power off before switching the output power from one motor to the other.

Then the switch will not even know that an inductive load is connected.

If you operate a switch with no load on it, then it will handle a lot more current 

without damage.  Even if a switch carries more current than its rating, it will 

not self destruct.  But its life might be shortened, for example from 100,000 cycles to 5,000 cycles.

A 3 phase, 240 volt motor will draw less than 4 amps according to this table:

https://twcontrols.com/lessons/motors-horsepower-and-amps-of-230vac-and-460vac-3-phase-60hz-electric-motors

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Joe Gores

echristley(at)att.net
Guest

Posted: Sun Feb 14, 2021 4:10 pm Post subject: A 3 phase AC (Alternating Current) question

connect the switch to relays?  But, now you're talking six relays, so more complication.

                  

                                                                    On Sunday, February 14, 2021, 03:02:43 PM EST, donjohnston <don(at)velocity-xl.com> wrote:                 

                 



                 



                 --> AeroElectric-List message posted by: "donjohnston" <don(at)velocity-xl.com (don(at)velocity-xl.com)>



Looking for some solutions on a project.



I have a lathe/mill combo.  I'm going to be upgrading it by replacing the motors and controlling them with VFD's.  Space is tight and it occurred to me that if I could use one VFD to control the motors (never at the same time) that would simplify the installation.  It would also save money since I would only need one VFD.  



But now the question is how to switch the VFD between the two motors? 



My first thought was a 3P2T switch.  But I have not been able to find one rated for 230VAC and 1HP.  It was suggested to use a contactor.  But then I would need a low voltage source for the contactor with a switch for that power source and now it's no longer simplifying things. 



Any ideas?



Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=500688#500688



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