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Vfd Drive Question

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jamesarnold26

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Dec 28, 2016
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#1
I'm just a hobby Machinist. I have three lathes, a BP J-head mill all with 3ph motors.
This is what I'm thinking of doing.
Getting a 5hp vfd drive and putting a disconnect box under it. Run the wires from the vfd in the top. Then run conduit from each machine to the bottom contacting all of them to the terminals. Use the machines on/off switches.
It's only me working in the shop. So I can't see running two at a time.
The largest motor is 3hp with the longest 3ph wire length being 20 feet to the BP 1hp.
This would keep me from buying one vfd per machine.
Would this setup work ?
 

stupoty

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Dec 2, 2012
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#2
I belive most vfd's dont like running without a motor connected and may detect it as a fault condition and switch off.

You could have a vfd with a three phase socket wired on the output and plug the diferent machines in, the motors would have to be simmilar in spec (poles, rpm, desired start stop speed) to play nice without changeing vfd settings.

Stuart
 

Eddyde

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#3
No, at least not easily. You cannot have any switches between the VFD and the motor. All control, direction, speed etc., must be done by the VFD so the machines control wiring must also go to the VFD, that would be difficult to do with multiple machines. The only way I could see such a scenario, would be to have the VFD connected to a receptacle and have a plug for each machine, so that only one machine could be connected at a time. Control would be via a pendant on a long cable that you would have to bring to the machine you want to use. Not very convenient IMHO.
 

jamesarnold26

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Dec 28, 2016
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#4
Well aren't y'all just full of good news. Lol
I was afraid that would be the answer. Thank you for the information and keeping me from wasting the money setting it up for nothing.

Sent from my SM-G930V using Tapatalk
 

mksj

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#5
You would be better off with a single RPC (and probably less overall cost). These does not stop you from running a RPC and then using a 3 phase VFD on a particular machines if you need the speed control. A smaller VFD on a single machine would be more cost effective, but it needs to be wired into the controls. Three phase VFDs run fine off of RPCs in most cases. The limiting factor between a single phase and three phase VFDs is the ripple generated in the DC conversion process, single phase generates more ripple and needs higher rated diodes and capacitors. The ripple can also be minimized by the use of input or bus chokes which store and release energy (smooth the ripple). So an RPC uses the motor coils to produce a similar affect to generate the third leg.
 
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