# Considering switching to VFD from Rotary



## Investigator (Jun 25, 2019)

Im in the planing stages of a new shop building at home, just for home hobby use.  I currently have a RFC built around a 5hp 3ph idler, it is not balanced just simple direct wired.  I built it because at the time I owned 2 lathes, a 16" Southbend and a 12" Logan.  I have since sold the Southbend, so the phase converter only runs the Logan, my mill is single phase.  In planning for the new building, I'm playing with layout and am considering going to a VFD for the Logan to save the space now used for the converter.

Right now the only advantage I see of switching to a VFD is the space savings, but that is a really big advantage in my mind.  The Logan has the Reeves drive as well as a 2-speed motor, so speed adjustments are not an issue.  I have infinite speed adjustment from around 20-2000rpm.  If I swap to the VFD I would only program it to run on 60hz and either have it on or off, not using the VFD for speed adjustments.

I'm leaning toward switching and keeping the idler motor 'just in case' I run across any good deals on 3phase equipment I can't pass up.  Have I missed anything?  Is there any reason to not do this?


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## MikeInOr (Jun 25, 2019)

One of the nice things about a VFD is that you can plug your machine into any 220v outlet.

If you are building a new shop and you are planning on using a RPC I would recommend wiring your shop for 3 phase then run the 3ph from your RPC into the 3ph breaker breaker panel.  You will then be able to run your 3ph machines where ever you put a 3ph outlet.

It is awfully nice to bring a new machine home, plug it into a 3ph outlet and go!  I have a RPC with a 10hp idler... eventually ALL of my machines will be converted to run of VFD's.


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## cathead (Jun 26, 2019)

Yes, a VFD is nice and I own one of them myself.  FAST FORWARD 20 YEARS:  The RPC will still likely be in running shape but
the VFD will likely be in scrap electronics pile probably in Agbogbloshie.  I would hang on to the RPC.


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## Crank (Jun 26, 2019)

I'll put in my 2 cents worth for arguing both ways.

 I have three pieces currently set up with VFD's, a 5hp motor in my Takisawa TSL-800D, a 2hp motor for my Schaublin 102 and a 1hp on my Bridgeport. I used to have a 5hp Graziano SAG14 that I ran off of an RPC. When I went to the Takisawa, I found that VFD's were finally available that could produce a full 5hp and by going that route, I was able to strip out all of the contactors and electrical controls from the lathe and consolidate all functions to the VFD panel. I also have been able to program the VFD to ramp the motor to speed and ramp to a stop. I still need to add a braking resistor to have an emergency instant stop, but with the ramp down I programmed, it will bring the spindle to a complete stop in well under 2 seconds. I have absolute control over spindle speed and the ramp up doesn't slam the gear train. The 3ph output is smooth and shows in the surface finish of the parts, with no loss of power. I recently wanted to see how it would respond to a heavy cut and on a 2.5" round of stainless, I wound up taking .100" DOC with a moderately heavy feed and the lathe never slowed at all. The VFD is about the size of an old time lunch box and weighs about 6lbs. Which is much better than an RPC that was over 100lbs and ate up a sizable footprint in my crowded garage/shop. 

The Schaublin was a case where I had to replace the motor since the options to run a 380V motor were limited and bulky.

 The Bridgeport was my first piece of 3ph equipment and with only a 1hp motor, the VFD's from back then were adequate to do the job. 

Pros: Compact, programmable, cost is constantly dropping and versatile.
Cons: Does not play well with switches (if downstream from VFD) control switches must be connected to VFD to prevent confusing VFD (oversimplification but you get the idea). Cathead has a reasonable point, longevity is debateable. You get what you pay for, my 5hp VFD was around $700, but it was designed to do what I bought it for, it wasn't a repurposed industial unit.

As for an RPC, I just sold off mine last weekend, it did a stellar job powering the Graziano and never had any issue other than popping one fuse in my master switch panel on a single leg of the phases. It was not terribly loud and only a minor task to turn it on before powering up the lathe. My Graziano had a raft of contactors, switches and other electrical wizardry stuffed into it and as I tend to harbor ill will towards electrons, the RPC was the simple way to avoid grief. If I had a large shop area that I could leave an RPC stashed out of the way and had multiple machines of various complexity in regards to electrics, the RPC is simplicity and durability epitomized. It just wasn't my ideal option. Personally, I always felt the power didn't allow an ideal surface finish.

Pros: Simple, durable and reasonably understandable for most people to wire up.
Cons: Weight, noise, no adjustability and less than ideal wave form that may or, may not impact final finish. I will admit that the last comment is just a personal observation YMMV. 

Each option has it's benefits and if your budget allows you flexibility, you won't be forced to go only one route based on what your stuck with. if you have the opportunity to play with a quality VFD, it might help swing your decision.
 BTW, my RPC was a Cedarberg 5hp.
Good luck!

Mark


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## Investigator (Jun 26, 2019)

MikeInOr said:


> One of the nice things about a VFD is that you can plug your machine into any 220v outlet.





cathead said:


> Yes, a VFD is nice and I own one of them myself.  FAST FORWARD 20 YEARS:  The RPC will still likely be in running shape but
> the VFD will likely be in scrap electronics pile probably in Agbogbloshie.  I would hang on to the RPC.





Crank said:


> I'll put in my 2 cents worth for arguing both ways.
> .......
> Pros: Compact, programmable, cost is constantly dropping and versatile.
> Cons: Does not play well with switches (if downstream from VFD) control switches must be connected to VFD to prevent confusing VFD (oversimplification but you get the idea). Cathead has a reasonable point, longevity is debateable. You get what you pay for, my 5hp VFD was around $700, but it was designed to do what I bought it for, it wasn't a repurposed industial unit.
> ...



Let me ask a question to clarify.....

Can I run 220 1ph to the VFD, then wire the Logan to the output of the VFD, and still use the mechanical "on/off" switch on the Logan?  Could I go to the VFD, turn it on to be just standard 60hz, then go and use the Logan with the manual switches like I do now while the RPC is running?

It sounds like folks are saying that with the VFD the machine is left on and the VFD controls the on and off.  Is that correct?


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## Crank (Jun 26, 2019)

Investigator,
In a nutshell, NO!
That's what I meant in regard to "Does not play well with switches ". The key is that you want to run the output of the VFD staight to the motor, not the cord running into the machine because there tends to be a number of bits that all want a piece of the action electrically. It's not a monstrous task, all you do is run your ON/OFF switch and FWD/REV switch to the bank of connections for that very purpose on the front of the VFD. You will disconnect the contactors (if you have them) so that the switches merely pass a low voltage control signal though and "tell" the VFD what you are wanting to do. The VFD handles the rest. I eliminated the contactors (relays) that switched the 220V 3ph to the motor and directly wired the VFD output to the motor. Otherwise, you could bypass the controls entirely on the machine and make them useless and control all functions directly from the VFD panel. 

It really is that simple to take 220V 1ph and what comes out of the VFD is 220V 3ph. In their purest form, a VFD works perfect for a driven motor with no form of control (fan motors, pumps, etc,,,), but they have advanced and now work with ouside control signals to start, stop, control speed, E-stop, FWD/REV, etc...

I'm no videographer, but here is what I did. All of the guts you see for wiring in the lathe are now gone and this is before I programmed it.





Here are the runs with the motor for the Schaublin and it running on the lathe.









Hope this helps!

Mark


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## MikeInOr (Jun 26, 2019)

Investigator said:


> Let me ask a question to clarify.....
> 
> Can I run 220 1ph to the VFD, then wire the Logan to the output of the VFD, and still use the mechanical "on/off" switch on the Logan?  Could I go to the VFD, turn it on to be just standard 60hz, then go and use the Logan with the manual switches like I do now while the RPC is running?




*NO - Definitely not!  Rule #1 is there should be no switches or other controls between the VFD and the motor!  The VFD IS the controls for the motor.  Sorry if I made that confusing previously.  *

Once you have converted (rewired) your machine for it to be controlled by the VFD it is ready to be plugged into a single phase outlet... any 240v single phase outlet that is handy.  You no longer have to have a  3 phase outlet near by or a long 3 phase extension cord to plug the machine into your RPC.  For me this makes moving my machines around easier as I wired plenty of 1 phase 240v outlets in my shop... but I did not wire a separate 3 phase infrastructure in my shop.

In contrast one of the pluses for using a rotary phase converter and wiring your shop for 3 phase with multiple 3 phase outlets is you can bring your new acquisition home, plug it into one of your 3 phase outlets, turn your RPC on then you are good to use your new machine with its existing controls, no rewiring required.  You don't have to wait until you have purchased the VFD, enclosure, misc switches and wiring items and rewire the machine to use it.  The 3 phase shop wiring and RPC give you the instant gratification of using your new machine we all crave!  LOL!

I recently bought a used 3 phase mill.  I brought it home, unloaded it, positioned it where I want it... then used a 3 phase extension cord to plug it into my 10 hp RPC in the other room.  I got to play with my new toy as soon as I got it unloaded.  I will rewire the mill to use a VFD eventually so I don't have to have that heavy 4-10g extension cord running through the middle of my shop... I will be able to use a 240v single phase outlet that is right next to the mill.

Does this make more sense?


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## Investigator (Jun 26, 2019)

Ah, I understand now.  I'm not liking the idea of motor control via the VFD.  I think my best plan will be move RPC to a quieter space and leave things as they are.

Just for giggles, tell me what happens if I try to use the switches on my machine downstream from the VFD


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## Crank (Jun 26, 2019)

You could curve your spine, develop an allergy to whales and your babies will be born naked. 

Other than that, it may not work, or you might release the "majic smoke". Never tried and don't want to find out. I think the sudden load change can wreak havoc with the light electronics in the VFD. However, my Bridgeport has a separate factory motor for the table feed and I have used it without incident. I keep waiting for it to cause problems, but so far the little$100 Teco is still holding up.

Mark

Sent from my ONEPLUS A6013 using Tapatalk


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## mksj (Jun 27, 2019)

VFD's in certain modes need feedback from the motor (sensorless vector) to determine the rotational speed of the motor as well as tuning the VFD to the specific motor parameters. When you interrupt this function it can have unpredictable effects (VFD will go into a fault mode and shut down) and can result in failure of the output section of the VFD. The VFD expects and is designed around driving only a motor, and the VFD does not output smooth  sign wave 3 phase, so it is not designed to be used with any other load other than a motor. There are phase inverters (Phase Perfect)  that basically generate a fixed 3rd wave at 60Hz and can be used with machinery needing 3 phase input from single phase. They are expensive, but work well with shops that have multiple machines/CNC machines.

A properly designed RPC can be very quiet and represent a small space. I recently saw a portable RPC "AMP" from American Rotary Phase Converters, when on you had to be close to the unit to tell if it was even running. Nice that it is portable on rollers, just plug the single phase on one side and your machines in the other side. Not inexpensive, but an alternative for those individuals that do not want to deal with building an RPC/electrical wiring.








						AMP - Mobile Phase Converter - American Rotary
					

AMP Mobile - The AMP Mobile rotary phase converter is plug-and-play ready for a quick and cost-effective installation. Equipped to run 208-250V equipment in three tiers:     Tier 1: 1 Breaker and 1 Receptacle Tier 2: 2 Breakers and 2 Receptacles Tier 3: 3 Breakers and 3 Receptacles     These...




					www.americanrotary.com
				




My recommendation, as others have also indicated, is stick with an RPC in this setting.


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## MikeInOr (Jun 27, 2019)

Investigator said:


> Ah, I understand now.  I'm not liking the idea of motor control via the VFD.  I think my best plan will be move RPC to a quieter space and leave things as they are.
> 
> Just for giggles, tell me what happens if I try to use the switches on my machine downstream from the VFD



A standard feature of VFD's is "soft start".  The VFD spins the motor up over a period of time instead of near instantly.  This GREATLY reduces the amount of current needed to start the motor.  The inrush current from hard starting a motor near instantly is many times that of the motors typical run current.

By engaging a motor with a switch between the VFD and the motor you are doing a hard start instead of a soft start.  Modern (inexpensive) VFD's are not designed to handle the full inrush current of hard starting the motor.  Most likely the VFD will just throw an error and turn off.  If the VFD's over current detection doesn't kick in you will likely fry the power transistors in the VFD.  Repeatedly tripping the VFD's over current circuit is probably not very healthy for the VFD and will most likely take its toll on the VFD over time.

If you wire your shop for 3 phase and plan for your RPC you can always add VFD's to your machines later if you want to make use of the variable speed control or electronic braking capabilities of a VFD.


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## AGCB97 (Jun 27, 2019)

I've had an RPC and I can't see why anyone would want one over a VFD. VFDs give you so much control so easily and can be right next to the machine so everything is at arms reach.

This is how mine is set up. The breaker to the left controls power. I never touch the VFD panel controls, 
only the added on stuff below. Machine lights are controlled by switch in upper left corner.



This is my added control panel. Simple on/off, forward/reverse and frequency pot.
 I have never used the jog feature. So many other things are available with VFD also.




With VFD you get motor protection (over current, temperature, stall and others), ramp up/down speed control, emergency stop and instant reversing.

I also run my surface grinder off this same VFD (similar motor chacteristics) by just plugging in the proper 3-phase plug (one machine at a time).


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## davidcarmichael (Jun 28, 2019)

I agree completely. I just fitted a Fuji Frenic mini VFD to my 3-phase PM-835S mill. It has remote control via a panel I built, soft start, very fast braking thanks to the cheap (and huge) finned resistor I got from Ebay, and as an added bonus, when I put it in back gear it automatically reverses the controls so forward still means forward. Programming is not very simple but you soon get the hang of it. Many complain of the possibility of induced motor noise but judicious setting of the switching frequency and the use of ferrite beads on input and output leads and a 240V input filter appear to smooth everything out and, so far, I have detected no issues with it.


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## AGCB97 (Jun 28, 2019)

What did you use to tell it it's in back gear?


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## davidcarmichael (Jun 28, 2019)

A reed switch and a magnet. The reed switch is simply wired to one of the multi-purpose inputs (pull-down) to reverse direction and the magnet is on the back gear control lever. Took a bit of time to find the best place to put the switch as my mill has a complex, home-brew power drawbar, but neodymium magnets are so strong they can work over a goodly distance.


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## Flyinfool (Jun 29, 2019)

One more thing to consider with a VFD is that some of the VFDs do not have well filtered outputs and can only be used on inverter duty motors. If you have an old machine it likely does not have an inverter duty motor. Not all new motors are inverter duty either. If the output of the VFD is well filtered and is giving a true sinusoidl output then it will be fine on the older motors.


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## davidcarmichael (Jun 29, 2019)

Flyinfool said:


> One more thing to consider with a VFD is that some of the VFDs do not have well filtered outputs and can only be used on inverter duty motors. If you have an old machine it likely does not have an inverter duty motor. Not all new motors are inverter duty either. If the output of the VFD is well filtered and is giving a true sinusoidl output then it will be fine on the older motors.


No VFD produces a "true" sinusoidal waveform. It is an approximation created by high speed switching. While it is true that some motors may be less tolerant of this than others, altering the switching frequency can have a dramatic effect, as can output filtering to reduce higher frequency harmonics.


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## Flyinfool (Jun 29, 2019)

With enough filtering you can get the PWM output darn close to a sinusoidal output. Not perfect but close enough.

A very layman explanation of a VFD.
A VFD works by taking the 240 1ph in and converting it to 340V DC, a bunch of transistors then take the 340VDC and by switching on and off real fast sends an output that to an inductive load like a motor resembles a 3ph wave form.

It is that constant barrage of 340VDC peaks in the output that will break down the insulation of the motor winding in a non inverter duty motor. An inverter duty motor simply has an insulation package that is designed for the 340 volts.


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## davidcarmichael (Jun 29, 2019)

Flyinfool said:


> With enough filtering you can get the PWM output darn close to a sinusoidal output. Not perfect but close enough.
> 
> A very layman explanation of a VFD.
> A VFD works by taking the 240 1ph in and converting it to 340V DC, a bunch of transistors then take the 340VDC and by switching on and off real fast sends an output that to an inductive load like a motor resembles a 3ph wave form.
> ...


At a high enough frequency the inductive elements of a motor offer almost infinite impedance to a high frequency electrical impulse. 
It's like music. A CD samples the musical waveform at 44KHz and that is high enough that a human cannot hear that it is not a sinusoidal frequency (or at least a component of it).  This does not prevent some people preferring the distortion induced by RIAA correction of the pre-distorted signal applied to vinyl records.
Please back up your proposition that some motors cannot by driven by a VFD with some empirical evidence. The use of ferrite beads on the 3-phase output leads is done to prevent RF interference with external electrical equipment like tuners and amplifiers, not to protect the motor.
I cannot see a mechanism for any harm to be done to the motor unless an unnecessarily low sampling frequency is chosen. 
What exactly is the definition of a "non-inverter duty" motor?


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## Janderso (Jun 30, 2019)

The beauty of a quality RPC is, all your 3 phase machines plug into the disconnect or outlet and operate as designed.
Simple, clean install. My 10hp American Rotary is very quiet. When I turn on my mill or lathe, I don’t hear the RPC.


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## Flyinfool (Jun 30, 2019)

Where I work we design and build our own custom VFDs for our product line. In the early stages of us doing this we did let the Magic blue smoke out of a bunch of new motors. When we went to try to get warranty, as soon as the motor manufacturer looked at the burnt up motors the very first thing they asked was if we ran them on a VFD, When we said yes the warranty was void, and then they explained the Inverted duty motors that have a higher voltage rated insulation to withstand the PWM vs sinusoidal wave forms that are hitting them. So yes I have seen it happen first hand. This was a long time ago, most motors today are inverter duty just because it is prevalent. Many people on this site have old machines from before all this fancy electronics even existed, so the motors may or may not handle the voltage. For instance my mill has dual voltage motors that can run on either 220 or 440. This means that my motors are perfectly safe to run on a 220 VFD because the insulation system was designed to handle 440.

Here is a good explanation. https://www.automationdirect.com/products/motors/index


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## davidcarmichael (Jun 30, 2019)

Flyinfool said:


> Where I work we design and build our own custom VFDs for our product line. In the early stages of us doing this we did let the Magic blue smoke out of a bunch of new motors. When we went to try to get warranty, as soon as the motor manufacturer looked at the burnt up motors the very first thing they asked was if we ran them on a VFD, When we said yes the warranty was void, and then they explained the Inverted duty motors that have a higher voltage rated insulation to withstand the PWM vs sinusoidal wave forms that are hitting them. So yes I have seen it happen first hand. This was a long time ago, most motors today are inverter duty just because it is prevalent. Many people on this site have old machines from before all this fancy electronics even existed, so the motors may or may not handle the voltage. For instance my mill has dual voltage motors that can run on either 220 or 440. This means that my motors are perfectly safe to run on a 220 VFD because the insulation system was designed to handle 440.
> 
> Here is a good explanation. https://www.automationdirect.com/products/motors/index


Thanks for the explanation and link.


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