Choosing a VFD

[MushCreek]

I'm going to be buying a 3 phase mill soon, and need to power it at home. Rather than going with a phase converter, I figured a VFD would be a better option. I like the idea of being able to change speeds without changing the belt on an older Bridgeport. I'm assuming that a VFD and 240V, single phase is all I need, right?

How do I choose one? In searching, I'm finding a lot of options. Constant torque, or variable torque? I looked at one, and the manual was 420 pages! Too much info; I just want to plug 'n play. Will they power most standard 3 ph motors? Is there any way to make it show the actual spindle RPM? In low gear, the motor RPM doesn't tell me much. Can I use the device for different machines (one at a time, of course)? I have a 3 ph surface grinder that I'd like to use from time to time. Can I put the VFD near my panel, and just wire up several outlets for different machines? I see you can get a remote to mount right on the machine- are they hard-wired, or wireless?

What else do I need to know? Is there any harm in going big, such as a 5 hp unit for a 2 hp motor? Do you instant reverse with the switch on the machine, or with the VFD? Or either? Obviously, I have a lot to learn- I know one of you guys have experience here. Thanks!

 

[bad_idea]

Mind if I tag along? I am curious about the subject.

 

[manwithtools]

A lot of questions in that post. Have you read the sticky in this forum regarding VFD's?.

https://www.garagejournal.com/forum/showthread.php?t=320064

Take a look there for lot's of good info.

 

[Davefr]

I'm going to be buying a 3 phase mill soon, and need to power it at home. Rather than going with a phase converter, I figured a VFD would be a better option. I like the idea of being able to change speeds without changing the belt on an older Bridgeport. I'm assuming that a VFD and 240V, single phase is all I need, right?

How do I choose one? In searching, I'm finding a lot of options. Constant torque, or variable torque? I looked at one, and the manual was 420 pages! Too much info; I just want to plug 'n play. Will they power most standard 3 ph motors? Is there any way to make it show the actual spindle RPM? In low gear, the motor RPM doesn't tell me much. Can I use the device for different machines (one at a time, of course)? I have a 3 ph surface grinder that I'd like to use from time to time. Can I put the VFD near my panel, and just wire up several outlets for different machines? I see you can get a remote to mount right on the machine- are they hard-wired, or wireless?

What else do I need to know? Is there any harm in going big, such as a 5 hp unit for a 2 hp motor? Do you instant reverse with the switch on the machine, or with the VFD? Or either? Obviously, I have a lot to learn- I know one of you guys have experience here. Thanks!

1. Buy a name brand unit (ex: Teco, Hitachi, etc) and make sure the documentation is thorough and readable. Download the documentation before you buy the unit. Avoid the no name Chinese VFD units on Ebay for this very reason. The documentation is absolutely terrible and will leave you frustrated and guessing. For the most part these come pretty much plug and play but there's a gazillion setup options.

2. Put the VFD where ever you want, but keep in mind most VFD's are not rated for NEMA washdown type specs. A harsh environment will require a separate enclosure to protect the unit from fluid spray, chips, etc. The enclosure may need to provide ventilation via a fan.

3. I don't see why you can't choose one unit and use it for multiple machines as long as the capacity is chosen for the machine with the largest current draw and then use it for only one machine at a time. Keep in mind VFD pricing goes up exponentially after about 1 HP.

4. A remote control at the machine is very convenient. (start/stop, speed, forward/reverse). It's super easy to make one yourself. The add on's from the VFD manufacturers are over priced IMHO. I'm not aware of wireless.

5. You can read RPM direct from the VFD as long as you map the frequency to a known RPM given the machines belt configuration. (It's one line in the setup code.) If you change belts then the RPM will no longer be accurate. There are also very inexpensive stand alone RPM indicators out there like this one:
https://www.ebay.com/i/322307752760?chn=ps

Search the Tubal Cain you tube series and he shows setup of one of these units.

6. For more VFD reading go the the GJ VFD thread:
https://www.garagejournal.com/forum/showthread.php?t=320064

 

[manwithtools]

I'm going to be buying a 3 phase mill soon, and need to power it at home. Rather than going with a phase converter, I figured a VFD would be a better option. I like the idea of being able to change speeds without changing the belt on an older Bridgeport. I'm assuming that a VFD and 240V, single phase is all I need, right? Mostly correct.

How do I choose one? In searching, I'm finding a lot of options. Constant torque, or variable torque? You want constant torque I looked at one, and the manual was 420 pages! Too much info; I just want to plug 'n play.

Will they power most standard 3 ph motors? Yes
Is there any way to make it show the actual spindle RPM? Yes
In low gear, the motor RPM doesn't tell me much. Can I use the device for different machines (one at a time, of course)? Possibly

I have a 3 ph surface grinder that I'd like to use from time to time. Can I put the VFD near my panel, and just wire up several outlets for different machines? Depends on the machine horsepower and if you can locate plugs / receptacles that are HP rated.

I see you can get a remote to mount right on the machine- are they hard-wired, or wireless? They are hard wired

What else do I need to know? Is there any harm in going big, such as a 5 hp unit for a 2 hp motor? VFD's up to 3 hp are typically available without de-rating when supplied with single phase, above 3 hp you need to de-rate the VFD, you'll need to investigate the specs closely to understand that part.

Do you instant reverse with the switch on the machine, or with the VFD? Or either? Instant reverse would be handled in the VFD, switching the output leads of the VFD is a no-no.

Obviously, I have a lot to learn- I know one of you guys have experience here. Thanks!

See my comments above in red.

 

[J king]

I agree on buying a name brand. I have 4 ac drives. I sold my bp and included my toshiba with mill since the new BP had a larger motor. The old drive was 15 years old. No problems. The new Chinese drive I bought lasted a year and is acting up. I figured that since they are all built in China I may as well get the off brand.. don’t

 

[Norcal]

Don't buy a no-name drive from China, bad manuals & little to no support for them, buy cheap, you get cheap. A 3 HP single phase input drive will require no derating, over 3 HP plan on derating 50%, so a 5 HP motor would require a 10 HP drive, a lot of people use TECO drives. One thing to note, switching between the drive & the motor can result in failure, controlling the motor functions should be only done through the VFD. There is more to be added..

 

[laser3kw]

Put the VFD where ever you want, but keep in mind most VFD's are not rated for NEMA washdown type specs. A harsh environment will require a separate enclosure to protect the unit from fluid spray, chips, etc. The enclosure may need to provide ventilation via a fan.

Be aware that some VFD's have exposed terminals. That can be an issue if your mill is throwing chips and cutting fluids. Mounting it in an enclosure is good insurance. Typically you don't need additional ventilation or fans. You will probably never work the VFD hard enough to heat it up. I have cabinets with three 5 or 7 hp vfds and have never had an over temp alarm and they are running at rated power for full shifts.

 

[MushCreek]

Great info- Thanks! Given the nature of milling machines, I guess I'll mount the VFD a little bit away, and buy (or make) a remote to mount directly on the machine. Being as they don't cost that much, I just might get a separate one for the grinder.

I'll remove the switch on the machine to prevent being tempted to use it- force of habit, and all that. From what I've been reading, there's no reason to go big on the VFD. The cut-off price-wise seems to be 3 hp; above that, they go up in price steeply. I'm getting a 2 hp mill, but you never know when a 3 hp one might drop in my lap.

Good to know about name brands, too. I might have been tempted to buy an ebay cheapie. I'm seeing TECO and Hitachi ones for not much over $200.

 

[txvwnut]

www.surpluscenter.com has both Hitachi and Teco in the $200 range. I have a Teco that I got from there and it has been great. You can wire the drum switch on the machine through the VFD to give switchable directions at the machine or just wire the VFD up and use it like a phase converter and leave the machine wiring as is. This is how I did mine as I have a variable speed machine and don't need the VFD to control my speed.

 

[manwithtools]

www.surpluscenter.com has both Hitachi and Teco in the $200 range. I have a Teco that I got from there and it has been great. You can wire the drum switch on the machine through the VFD to give switchable directions at the machine or just wire the VFD up and use it like a phase converter and leave the machine wiring as is. This is how I did mine as I have a variable speed machine and don't need the VFD to control my speed.

If you are using the drum switch to reverse the motor by swapping the phases going to the motor, be prepared for that VFD to fail at some point, they don't like having their outputs switched. You really should wire the drum switch to the FVD's direction inputs, not use it in the way you have described. If you are not reversing your motor at all, then disregard my post.

 

[MushCreek]

In reading the sticky thread, many guys casually talk about wiring up their own remote, such as using the original drum switch for F/R, and a pot to control speed. Is it pretty easy to wire up such accessories to a VFD? Do the instructions tell you how to wire this stuff up? I know you don't want to actually switch the motor downstream of the VFD; it is rewired to control the VFD, and thus the motor. After running a Bridgeport for over 40 years, it would be nice to have the old switch still control direction.

 

[Davefr]

In reading the sticky thread, many guys casually talk about wiring up their own remote, such as using the original drum switch for F/R, and a pot to control speed. Is it pretty easy to wire up such accessories to a VFD? Do the instructions tell you how to wire this stuff up? I know you don't want to actually switch the motor downstream of the VFD; it is rewired to control the VFD, and thus the motor. After running a Bridgeport for over 40 years, it would be nice to have the old switch still control direction.

Yes, it's inexpensive and easy.

All you need is a switch, potentiometer and some wire. In the case of Teco, the manual is very clear as to how you wire it up and made the necessary programming changes.

The control inputs are all low voltage/low current. I also recommend having another switch that disconnects the VFD from the main power source.

Example

 

[matt_i]

Just wanted to throw out Lenze/AC Tech as what I consider to be a "good" manufacturer of VFDs.

It will take reading sections of the manual about 3 times to fully understand what's going on. One of the "worst drives" I own is an Emerson Electric VFD, while functional the manual really made it hard, the microscopic electrical drawing for the controls section made it tough.

There may also be some competitive drives at AutomationDirect.com. I forget if those are Fuji or Hitachi or (?)

I've always used 1 drive per 1 motor and have no breaks in the "secondary side power wiring" other than the bare minimum, screw terminals at the VFD and wire nuts or ring terminals at the motor. I'm sure there's a way to switch between motors but making it foolproof so it isn't switched under load is going to take some thinking. Also telling the drive which speed reference to use would take some work. One could use a typical 3-wire motor control strategy for multiple start/stop stations, wire all of the starts in parallel and all of the stops in series. The low voltage carrier signal (could be 5 to 24vdc with limited amperage) could be a problem if machines were far away from each other....

 

[mm08822]

Just wanted to throw out Lenze/AC Tech as what I consider to be a "good" manufacturer of VFDs.

It will take reading sections of the manual about 3 times to fully understand what's going on. One of the "worst drives" I own is an Emerson Electric VFD, while functional the manual really made it hard, the microscopic electrical drawing for the controls section made it tough.

There may also be some competitive drives at AutomationDirect.com. I forget if those are Fuji or Hitachi or (?)

I've always used 1 drive per 1 motor and have no breaks in the "secondary side power wiring" other than the bare minimum, screw terminals at the VFD and wire nuts or ring terminals at the motor. I'm sure there's a way to switch between motors but making it foolproof so it isn't switched under load is going to take some thinking. Also telling the drive which speed reference to use would take some work. One could use a typical 3-wire motor control strategy for multiple start/stop stations, wire all of the starts in parallel and all of the stops in series. The low voltage carrier signal (could be 5 to 24vdc with limited amperage) could be a problem if machines were far away from each other....

I agree, Lenze does make a nice dependable drive. I have used 3 of them over the past several years at work for cheap prototypes. All of our production equipment is AB($$). Lenze is not the cheapest, but at least you can read the manual and get good support.

If you want a reversing feature, the drive must change the motor direction. You can not open and interchange the t leads as you will quickly blow the the output stage. I learned that in the late '90's on servo motors just opening the output ckt for lockout purposes! What a great way to blow up output contactors.

If you still want to use the drum switch to do so, it has to be rewired as a CONTROL circuit. Meaning forward runs the drive forward input, off stops the drive and reverse runs the drive reverse input.

If you plan to run the equipment with fast reversing, you should use a drive with a "flying start feature" as that allows the drive to synch to current motor speed and direction before it runs to the the commanded speed and direction.

 

[manwithtools]

Also, if you want rapid reversing with any frequency, you may have to add an external braking resistor. Info in the manual about that.