Drinking from the VFD info firehose

[JENIUS]

I am begining the VFD knowledge process, having never used one and have a hopefully easy question.

1. In a non-clutch, 2 horsepower mechanical lathe, with only a drum switch and single electric drive motor (3-phase) and a small electric coolant pump with an on/off switch. Can and should i remove all of the legacy wiring/motor control electrics and run the 2 motors from an appropriately sized/rated for single phase vfd? Assuming i integrate an e-stop button and a fwd/rev switch into the vfd wiring? I have residential single phase power.

 

[jim rozen]

The 2 hp main motor might best be run off a 240 volt VFD. And yes, the motor is connected direct to the drive, no electrics in between, all control functions via low voltage logic on the VFD.

 

[JENIUS]

WOW, that is incredible, it almost sounds too good to be true. The legacy wiring in the lathe control panel is beautifully done, it almost seems a shame to remove it.

 

[JST]

You can leave it, or disconnect and label some wires, using the original switches to control the VFD.

also a possibility to use the aux contacts on existing relays to control the VFD. They are often better at low currents. Again, disconnect and label interfering wires. You would wire around the power connections, only leaving the control power to operate the relays.

 

[JENIUS]

An excellent idea, but the lathe has no switches except for the drum switch, which seems to be malfunctioning, and is buried inside the gear case actuated by a rod off of the handles on either side of the carriage. I was thinking of adding an e-stop, and fwd/rev switch in a small enclosure on the front of the lathe.

 

[mksj]

Actually you should not use an existing contact if it has been used to carry current, they build up resistance from arching and will not conduct the low voltage of the VFD signals very well which are a few mA. You still want some type of safety power relay system so if the power drops out and comes back on, or you press the E-Stop and then release it that the machine will not restart. In addition if you have a manual foot brake you will need a dual contact foot switch or have it tied into a relay to issue a free run command to the VFD and drop out the a power relay that prevents the lathe from restarting when you release the brake. The power relay is used to control the VFD inputs and not drop power to the VFD. E-Stop can be designed to do different things depending on its function. There are also a few other things to work out in the control system, depends on the VFD and what you want it to do, but I when I build my lathe control systems I use 2-3 levels of redundancy, should a run contact fail closed.

 

[JST]

Using any relay, even a new one you power from the control supply, will give the power off protection if wired in the control circuit.

The aux connections are much better than any power contact, as far as lower currents.

E-stop should be added, not re-purposed.

 

[Overland]

I've wired several 3 ph machines using a VFD powered from single phase. In my experience, always ensure there is no switch, contactor, etc between the VFD and motor.
Recently on a 21x80 Colchester lathe there is a simple rotary on/off switch on the headstock which was originally used to pull in the main motor contact. I took wires from the coil sid of this contactor back to my VFD and used the switch to start/stop VFD. Then took the motor power wires from this contactor and connected them back to the VFD.
I have no emergency stop switch in my setup.
Normally emergency stop buttons/switches are momentary, designed to drop out a contactor. You would probably need a contactor before the VFD, to power it up. The emergency switch could then be used to break the coil circuit on the contactor to drop it out, maybe.
Bob

 

[jim rozen]

VFDs are typically configured to prevent re-start of the motor after a power dip.

 

[Mark Rand]

Contrarian view:-
Buy a decent VFD (Teco, schneider etc.) sized to about 50% more than the main drive motor, set it to 60Hz, connectit to the incoming cable to the lathe's control box and just run it.

Works for me, except that I run the entire workshop of one VFD.

 

[eKretz]

I've wired several 3 ph machines using a VFD powered from single phase. In my experience, always ensure there is no switch, contactor, etc between the VFD and motor.
Recently on a 21x80 Colchester lathe there is a simple rotary on/off switch on the headstock which was originally used to pull in the main motor contact. I took wires from the coil sid of this contactor back to my VFD and used the switch to start/stop VFD. Then took the motor power wires from this contactor and connected them back to the VFD.
I have no emergency stop switch in my setup.
Normally emergency stop buttons/switches are momentary, designed to drop out a contactor. You would probably need a contactor before the VFD, to power it up. The emergency switch could then be used to break the coil circuit on the contactor to drop it out, maybe.
Bob

Most if not all VFDs have an input for an E-stop switch.

 

[Overland]

Thinking about it, I've wired VFD's two ways
1) with a "maintained" switch that can be either on or off. So when on, there is a small voltage from the VFD to switch, then back to VFD. When switch is turned off, the circuit is broken and the VFD stops.
2) the other way is 2 momentary switches, one sends a signal to start, and the other (STOP) sends a signal to stop. This requires some function codes to be set in the VFD. If a braking resistor is added, the STOP button can act much like an emergency stop and stop the motor very quickly, depending how the function codes are set.

I use Fuji VFD's and find them very good, with excellent support from Fuji tech direct.
Good luck
Bob

 

[JST]

E-stop is usually a switch which is normally closed and when activated for an emergency stop is opened and held open until reset by a an intentional action..

A momentary seems wrong for that use.

 

[mksj]

Some VFD's have a rapid or emergency stop, but it requires a sustained input not a momentary, at least the ones I have used. The on-machine E-Stops I use a NC contact block which either is directly wired to the run controls or operates a latched relay which drop out and prevents restart as well as drops the run controls. The second NO E-Stop block is wired the the to activate a fast/emergency stop. I always use a sustained type E-Stop, not a momentary. My regular stop is typically a momentary on the most machines, except lathes with a spindle switch on the carriage. The latter, I still wire it to run direction relays, which drop out if the latching power relay is tripped by a safety switch, power interruption, brake application, etc.. The power relay is energized if the faults are corrected and the stop control is active. Some VFD's like the Hitachi does not have a fast stop command, but one can set a fast stop brake rate to be engaged. Point being that you need to give some thought to the control system for the particular machine and VFD programming.

 

[JENIUS]

My lathe has no switches on it except for coolant pump on/off, the fwd/neutral/rev is controlled buy the handles on either side of the carriage actuating a rod that rotates a barrel switch (malfunctioning) which is covered by the drive gear cover.

Is there a list of components somewhere for building a vfd conversion? Is there a prefered vendor that sells switches, enclosures, and vfd's

Not sure what a NC contact block is.

 

[Mark Rand]

NC==Normally Closed

 

[rons]

Your VFD manual will describe the connections for 3 wire control.
That will have a start and stop switch.

Those small sized VFD push button pads and screens are ok for programming parameters. But not for normal ops.

 

[motion guru]

I recently installed a KB Electronics VFD into a small German Weiler Primus lathe. I created a truth table from the rotary switch (two speed forward and reverse), then moved a few jumpers around on the drum switch and wired it into the drives Forward and Reverse maintained inputs and configured a third input as a speed select. Wired it up using the original drum switch and the drive to the motors original low speed windings and it has been operating flawlessly since. It is right sized for the motor and fed from a 230VAC dryer socket.

drive - https://acim.nidec.com/drives/kbele...a-sheets/a42046_kbdf_rev_j_02_2022.ashx?la=en

I/O interface - https://acim.nidec.com/drives/kbele...s/product-manuals/kbdf_iodf_manual.ashx?la=en

The owner was into it for less than $330 plus a couple beers and an afternoon / evening of wiring and setup. We maintained OEM control levers and high voltage switches operating at 24VDC drive logic levels, added a single potentiometer for speed adjust and he has been very happy with the results. We set it up for gentle accels and slightly more aggressive decels . . . much better than the original across the line start and coast to stop.

Lastly the drive was exceptionally high quality with great documentation originally produced in English. I had never seen one of these drives before and it took me less than 30 minutes to read the pertinent details, install the I/O expansion card and hen-scratch a schematic together after determining what could be leveraged using all original controls.

 

[jim rozen]

I always thought it would be cool to retrofit a hardinge lathe with the two sticks, to run off a vfd. fwd/off/rev, and the other stick would be "speed up/ slow down" but not sure how it would default when it was first started up each time. I'd make the speed control stick be spring-loaded, center return.

 

[motion guru]

Jim, that would be easy using the MOP function . . . Otherwise known as the “motor operated potentiometer”. Set it up to default to some user set speed when powered up or when enabled and adjust from there.