# VFD question



## Wheresmywrench? (Aug 29, 2014)

_*I have rewired my Emco Maximat V10-P Mentor Lathe/Mill for 220V single phase. I'm going to change the connections on the mill head from 440v to 220V 3 phase. Now I'm thinking of using a 220V single to 3 phase VFD for the mill. Can I run the power through the control box from the Maximat? Or does it have to be a direct connect to the motor?*_


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## Hawkeye (Aug 29, 2014)

If a connection between the VFD and the motor is opened while the VFD is powered up, it can damage the VFD. It's important that no switching devices (switches or relays) are installed in that circuit unless there is no way they can be operated while the VFD is powered up.


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## JimDawson (Aug 30, 2014)

+1 what Hawkeye said.

Having said that, you can power up the VFD from the control box.  The only problem that I see is the Maximat has two motors and the best way would be to use two VFDs.  It is possible to use one VFD for the two motors and use a transfer switch to switch between them.  A standard 3 phase, FOR/OFF/REV drum switch would work for this.  But you must never switch over under power.

This is the way that I am going to run my T&C grinder and the surface grinder.  I am going to have one plug on the wall, from the VFD,  that I can plug either machine into and I'll have a service disconnect just ahead of the VFD.  I will just have to be careful that I have one or the other plugged in at all times.


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## compressorguy (Aug 30, 2014)

JimDawson said:


> +1 what Hawkeye said.
> 
> Having said that, you can power up the VFD from the control box.  The only problem that I see is the Maximat has two motors and the best way would be to use two VFDs.  It is possible to use one VFD for the two motors and use a transfer switch to switch between them.  A standard 3 phase, FOR/OFF/REV drum switch would work for this.  But you must never switch over under power.
> 
> This is the way that I am going to run my T&C grinder and the surface grinder.  I am going to have one plug on the wall, from the VFD,  that I can plug either machine into and I'll have a service disconnect just ahead of the VFD.  I will just have to be careful that I have one or the other plugged in at all times.



The OP said his lathe is wired for 220v *single phase*.  Kind of an odd arrangement.  Single phase on the lathe and three phase on the mill head.


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## JimDawson (Aug 30, 2014)

compressorguy said:


> The OP said his lathe is wired for 220v *single phase*.  Kind of an odd arrangement.  Single phase on the lathe and three phase on the mill head.



Yup, you're right.  I guess I can't read.


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## compressorguy (Aug 31, 2014)

JimDawson said:


> Yup, you're right.  I guess I can't read.


Actually, I read it 3 times before it struck me.  I am having a hard time understanding why this one unit would have both three phase and single phase motors and controls.  Something doesn't make sense.


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## lens42 (Aug 31, 2014)

You can try to use the switch block, but it's probably not worth it. I added a control box on top of the old switch location and sold the old switch on eBay for $100.

You can find more details on V10 switch conversions on the Yahoo Maximat lathe group.


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## Jim Nunn (Sep 1, 2014)

lens42 said:


> You can try to use the switch block, but it's probably not worth it. I added a control box on top of the old switch location and sold the old switch on eBay for $100.
> 
> You can find more details on V10 switch conversions on the Yahoo Maximat lathe group.



Lens 42,

Is the VFD on the left a Reliance Drive? if not could you tell me the name of the brand of the drive.

Jim Nunn


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## lens42 (Sep 1, 2014)

It is, but don't take that to mean that Reliance is better. I just used what I got cheap off eBay or already had. Both motors are pretty low HP so almost any VFD will work. Per the help I got on the Yahoo Maximat board, I just connect the high speed winding and use the VFD (and still the gearbox) for the rest. The box is a junk store alarm box.


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## Wheresmywrench? (Sep 5, 2014)

Thanks for all the input on my options. The reason there are two different powered motors is that there is no 440V 3 phase available but I can wire the Mill head motor to 3phase 220v and I have a 220v single phase motor to replace the 440v 3phase motor on the lathe.


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