Phase Conversion Only

[marrt]

I have a 5 HP 3-phase manual lathe. The lathe includes a 3-phase input VFD for variable speed control. The lathe also includes two other 3-phase motors for oil circulation and coolant. I don't have 3-phase power available at my location. I use phase converting VFDs to drive my other 3-phase equipment. However, in this case, I probably need a different solution. I already have a large American Rotary phase converter, but VFDs don't like to have frequent on/off input power cycles and I don't want to leave the rotary converter running all the time.

From my limited understanding, I have a couple options:

1. Supply phase converted power to the lathe using another VFD. I suspect this will not work, but want to confirm since this is the cheapest and lowest hassle option. I'm guessing you can't "string together" VFDs in this manner. I don't know, buy strongly suspect, VFDs are primarily designed to be connected directly to motors. However, if the frequency is "locked", could a 1-phase to 3-phase VFD be used to "drive" a 3-phase input VFD?

2. Replace the existing VFD with a phase converting VFD. That might be tricky due to the wiring. And, I'd have to address the other motors.

3. Purchase a stand alone phase converter of good quality, like a Phase Perfect. They seem to own the market based on my limited research. Do other companies produce similar products?

Of course, there are other options but the cost of the alternatives out way the benefits (i.e., it's cheaper to just buy a stand alone phase converter and be done with it).

 

[Doozer]

Safe method is to power your lathe motor directly connected to the output
of a VFD. You can branch (parallel) that output going through switches
or contactors, to your coolant or power feed 3ph motors. Keeping the
spindle motor connected will absorb any spikes from switching in and out
the other motors. Transistors should remain happy.

-Doozer

 

[mksj]

Items 1 and 2 will not work, the lathes will have internal power transformer, contactors and relays as part of the control system that won't be happy working off VFD power. Your current VFD is programed to operate with these controls and the main drive motor. The cheapest and easiest solution (other than running it off of an RPC) would be to get a small (micro VFD) to run the oil pump motor and replace the coolant pump with a single phase unit. KB, WEG, Hitachi, Teco etc. have small fractional Hp VFD's that work well for these applications. Oil pump would most likely be running continuously on power up, otherwise you can oil starvation on the gears and bearings if intermittent. Does not pay to put a VFD on the coolant pump if it is a standard type, although you can get simple KBVF for around $80. Overall far cheaper than a Phase Perfect, and at that point you wouldn't need an RPC. Other shops that I have done machine VFD installs in similar situations the RPC is kept on. I would also check that the lathe VFD is rated for single phase input, typically the 5 Hp factory installed VFD for lathes will come with a 7.5 Hp VFD to handle single and three phase input. So I would check the lathe/VFD specifications.

 

[crickets]

Yup. Either a big enough phase converter (rotary or static) to run all motors / 3ph VFDs, or individual 1ph VFDs sized for the specific motors and a bunch of rewiring.

 

[ignator]

I have a 5 HP 3-phase manual lathe. The lathe includes a 3-phase input VFD for variable speed control. The lathe also includes two other 3-phase motors for oil circulation and coolant. I don't have 3-phase power available at my location. I use phase converting VFDs to drive my other 3-phase equipment. However, in this case, I probably need a different solution. I already have a large American Rotary phase converter, but VFDs don't like to have frequent on/off input power cycles and I don't want to leave the rotary converter running all the time.

From my limited understanding, I have a couple options:

1. Supply phase converted power to the lathe using another VFD. I suspect this will not work, but want to confirm since this is the cheapest and lowest hassle option. I'm guessing you can't "string together" VFDs in this manner. I don't know, buy strongly suspect, VFDs are primarily designed to be connected directly to motors. However, if the frequency is "locked", could a 1-phase to 3-phase VFD be used to "drive" a 3-phase input VFD?

2. Replace the existing VFD with a phase converting VFD. That might be tricky due to the wiring. And, I'd have to address the other motors.

3. Purchase a stand alone phase converter of good quality, like a Phase Perfect. They seem to own the market based on my limited research. Do other companies produce similar products?

Of course, there are other options but the cost of the alternatives out way the benefits (i.e., it's cheaper to just buy a stand alone phase converter and be done with it).

What is the model number of the VFD you have on this lathe right now? It might be robust enough to use single phase input power.
If it will run on single phase input (some VFD's sense phase loss), I would use that. Yes, if the VFD diodes are not rated for full 5HP input current through single phase, it's possible they could be damaged. Typically you would use a 10HP VFD using single phase to drive your 5HP motor (so the input rectifier diodes are not damaged). Are you really ever going to use the full rated power? My experience with a 7.5HP VFD from single phase, driving a 7.5HP motor, I've never had it trip off on undervoltage. I've had overvoltage trip offs during deceleration for too short a time programmed into the VFD.

 

[marrt]

Apologies for posting this in the wrong forum initially (moved here by a Mod I assume). I did look for the proper forum but I just missed it.

Crickets: I was under the impression static phase converters are not well designed and probably won't work with a VFD expecting a clean waveform. I'll have to investigate.

Mksj: If I'm understanding your post, you are suggesting I could replace my existing VFD with another VFD rated for single phase input, then deal with the motors separately (i.e., thermite's suggestion)?

Thermite: I'm out toward Middleburg...small world. Power use isn't an issue because the lathe will not be used for production. Thank you for the detailed input.

Ignator: It's a Yaskawa CIMR-G7A23P7, rated at 3.7kw with 3-phase input. I'm pretty sure it will operate on single phase but would be derated of course.

Assuming I want to preserve full HP for the spindle motor, sound's like my two best options are to replace the existing VFD with a single phase input VFD or get a Phase Perfect converter. I don't know if the Phase Perfect converters need to be derated, but the smallest size looks to be "7.5 HP" in any case. An appropriately sized Yaskawa is probably the same or more cost. Also, I'm not positive I can wire in another VFD as needed. There's a number of contactors and other stuff in the cabinet that, per the wiring diagram, are expecting 3-phase input from the master power switch.

 

[marrt]

thermite: "In my wurld, that means not only fewer than 8 hours a day, but often long stretches with NO use AT ALL,"

Exactly correct. This machine may be used several times a day for several days, then not used again for a month.

Power to the VFD comes from a master power switch on the lathe. Are VFDs OK with fairly frequent input power cycling, like any other device? Or do they "expect" to be connected to input power full time?

I don't want to leave the rotary converter running full time because it's in my "office" and I don't like noise. I would turn the converter on, and provide power to the VFD through the lathe's master power switch, only when needed, and turn it off every night for sure. Does this sound like a problem for the VFD?

 

[marrt]

thermite: "the drop in annoyance is well worth remoting the buggers"

Mm-hmm. What if I told you I relocated the idler to its present location, to reduce noise, just before I decided to make that location my office...due to "unforeseen" circumstances of course. I could start a whole thread regarding how many times I've reoptimized my shop layout. Seems to be endless and a real headache for a "lazy perfectionist."

thermite: "You may be over-thinking the effect of ON/OFF cycling on service life".

Likely. I overthink everything. Been that way since a child. A benefit of being an only child with no local kids my age to serve as distracting friends.

As to the noise issue, I learned today the Phase Perfect "quite model" puts out 75db (measured at what distance? who knows...probably "close by"...standard model is over 90db). That's like sitting in a busy Starbucks. It's funny...I can't stand constant noise when trying to concentrate, but can't sleep without it...and some Sake of course.

This thread has been informative. Thank you. Sounds like there's no sufficiently compelling reason to not use the rotary converter in this scenario...so, I'll go that route.

 

[Overland]

I have have run many 3 ph machines using VFD's running on single phase. I like Fuji and have had great success and good s upport from their engineers.
It seems to me you could swap out the existing VFD with Fuji FRN0020C2S-2U. (or similar).
This VFD is rated, with single phase input, at 9.7 amps 3 ph output, or 3.9 kva.
As stated above, solve your coolant and oil pump problems separately.
This VFD is only $268. And the next size up is 14 amps for $499.

I think this is a much better solution than an expensive Phase Perfect or loud rotary converter.

FRN0020C2S-2U

AC DRIVE, 5HP, 230V, 3 PHASE, 19.1A,

www.wolfautomation.com

FRN0025C2S-2U

FRN0025C2S-2U quick delivery, authorized Fuji Electric distributor. Offers complete line of AC Drives . Easy online ordering, rewards program, and great pricing.

www.wolfautomation.com

This document gives single phase specifications:

https://www.wolfautomation.com/media/pdf/ac-drives/fuji/frenic-mini/fuji-frenic-minic2-1phrating-appnote-21.pdf

Bob

 

[mksj]

Your VFD is a 3 phase input model, that means that if (and also the Fuji's listed) you run it on single phase you would need to derate it by about 1.7 and add a DC choke to decrease the increased the THD. So your VFD would be rated for a 10.5A output with single phase power. A static converter makes no difference with driving a VFD, no free lunch here. Even with an RPC, there can be some derating for use with a VFD, but good enough in most cases. Switching out the current VFD for a bigger one to drive everything makes little sense, your VFD is programmed to work with your current lathe control systems and interlocks, it is also more than 3X the cost of the Fuji's. If one could just drop in a VFD as a 3 Phase power source, then it would indicate it as such and be significantly larger. You need to substantially increase the size of a VFD as a power source, it needs to run in a fixed volts/Hz @60Hz at a lower carrier frequency that will drive you nuts, and it still may not play nice with your control system.I have not heard of using a VFD to drive a VFD, exception is a Phase Perfect which just generates one of the phases. Single VFD's in some cases can drive dissimilar multiple motors, you loose many of the benefits of using a VFD and requires each motor to have it's own oveload device that works with VFD's. This is not the type of application that it would be used in that manner, and most likely will not work with the lathe control system. Bad choice.

The simplest and least expensive approach from an install/cost perspective is to run it off of an RPC, it can be relocated if noise is an issue or get a quieter idler. Since your VFD is not sized to run on single phase for the output current required, it is off the table to add other VFD's for the pumps. This leaves you with running it off of a Phase Perfect if you do not want to use the RPC. Replacement of the lathe's VFD with a single phase input model or a larger 3 phase input Yaskawa VFD unit would be quite expensive. You then need the space to install it, program it and make sure everything works with your lathe control system (or design a new one), then figure another couple hundred dollars for a VFD for the other pumps. A lot of time and money. I have done quite a few VFD installs for 5Hp lathes with complete replacement control systems, I size the VFD(s) often so they can run off of either single or 3 phase input, it is a time consuming and costly install.

Phase Perfects are designed to run off single phase and the output is model specific. There is no derating.

 

[jim rozen]

Recap: you have a rotary converter that can run this lathe. If it were run on utility 3 phase power you would be unlikely to leave it powered 24/7/365 so I see no substantial reason to simply continue using the rotary and simply shutting the rotary off when not in use. Is there a specific manufacturer's statement in the manual to avoid shutting the machine off when not in use, or is this anecdotal from the internet?

 

[JST]

I............................................ I already have a large American Rotary phase converter, but VFDs don't like to have frequent on/off input power cycles and I don't want to leave the rotary converter running all the time.
................

What is "frequent"?

As a designer of VFDs, the main issue I see is the possibility of the inrush protector not protecting when the VFD is turned back on right after being tuned off (power removed).

That is not an issue if there are several minutes between off and back on.

1) For short times like that, you would just stop the VFD, and if necessary (and available) open the "safe torque off" switch. No need to remove power. There is little reason to shut off an RPC for short periods, you save very little electricity.

2) it is standard to turn on the RPC when you start work with the machine(s), and leave it on until you are done.

3) If you have any other machines that would be connected to the RPC, they would have switches as well. An RPC normally does not get started under load. You start the RPC, and then switch on whatever machine(s) you are using.

4) A VFD that is used to power a rectified load, like another VFD, needs to be de-rated a bit due to the nature of rectified loads. They tend to take power in as short very high current pulses, and VFDs do better with constant loads like motors. You would likely need a larger VFD to power the 5 HP VFD you have, while an RPC would do the job better in most cases.

 

[Overland]

Look at the Fuji document I posted showing the rating for single phase supply.
The first one I posted has an output rating of 9.7 amps, 3.9 kVA.
Plenty for a 5 hp motor.
Keep it simple.

 

[marrt]

jim rozen: "Is there a specific manufacturer's statement in the manual to avoid shutting the machine off when not in use, or is this anecdotal from the internet?"

Good question and I wondered that myself. I looked and couldn't find anything definitive. Only a warning to avoid disconnecting power to a VFD under load.

I also recall reading about an operator that didn’t like the continuously running VFD fan (loud) and so installed a switch in front of the VFD. I think this was a drill press. Each time he used the machine, he cycled power to the VFD. The VFD didn't last very long. My recollection is people in the thread warned that VFDs should be powered continuously. But this is an extreme example and not what we’re discussing here.

 

[marrt]

JST: What is "frequent"?

My question was open ended because I’m curious as to what is acceptable (what is the design spec). Frankly, if it’s an issue, it should be stated in the manual. I called Phase Perfect and asked this power cycling question. They said it’s fine to cycle their inverter each day. Ok. What about every hour, or every 10 minutes? No, that’s not acceptable. Further, he said I should wait a few minutes after turning the unit on before applying a load. Ok, how many minutes? Two, ten or what?

I’m not trying to be an armchair expert here. But it’s common for some devices to suffer premature failure due to frequent power cycling (e.g., larger electric motors that start under load…but that’s simple to understand). I “imagine” most VFDs are designed for industrial applications and are “expected” to be powered at least throughout the work shift. These Yaskawa drives aren’t cheap. I called the company and the technical representative indicated he definitely did not recommend frequent power cycling to the VFD. But, he could not tell me exactly why or what was acceptable.

Again, I AM overthinking the issue. I can get around my concern using the advice suggested here. I’m just a little frustrated that, if this is an issue at all, it would be nice to know the design spec. I’m left to “assume” it’s not an issue because it’s not addressed in the manual. But I don’t like making assumptions when the information is “out there” somewhere.

I have a Kubota tractor that recommends a 10 minute warm up each time the tractor is started (cold). This is to avoid pump cavitation. I’m pretty sure no one follows this recommendation. But it’s good to know best practices and why. At the very least, I can “go easy” on the variable displacement pump until the tractor is warm.

Sorry for the rant.

 

[marrt]

thermite: "Can work. But AFAIK, the main reason -> VFD -> VFD is not often done is that there is seldom any NEED to do, nor any significant gain, even if you throw 'extra' money and clever configuration settings at it."

True. But times, they are a changin’. I have 5 or 6 VFDs in my shop, all connected directly to motors. They are ALL reputable brands. All but one (Korean) are Japanese or US made.

The other day, I ran across a 10HP 7.5KW VFD for $170 shipped! Yes, it comes from a country many of us don't like. And the brand itself won't get me banned...but it's definitely from the same family I assume. If you look inside a Phase Perfect inverter, there's not much there. The cost is not in the materials and labor. It's in the engineering. And if you steal the engineering, you can manufacture and offer the product at a very compelling price. Funny how that works.

So, now, it’s at least possible to buy a VFD cheaper that a POS static phase converter. Yes, the VFD may be a POS too. But, it may not. As many have warned for years, the big country in the east (west really, but let's use the British orientation) is improving their stuff every day (thanks to western machinery and know how). And with cheap labor (that’s changing…but slowly) and favorable artificial exchange rates, they will kill us eventually (metaphorically) unless the status quo is changed. Just yesterday, the heads of MI5 and the FBI warned about this very issue in an extraordinary joint press conference. Twenty years too late, but hey, they are bureaucrats and don’t react until there’s no other choice.

Back to the issue of the OP, it’s absolutely possible to economically use a VFD strictly for phase conversion only. Unfortunately, for me, I’m not an EE and don’t even own an oscilloscope, or know how to use one. A Fluke is as far as I can go. Which is one of the reasons I asked the original question. I would buy the equipment and test it myself if I knew how. If there’s someone here who does know how, I will fund a couple cheap VFDs in the interest of science.

Full disclosure: I did buy that cheap 7.5KW VFD (yes, I feel a bit dirty). I have a 3 phase USA made dust collector that also needs frequent restarts. I’m not hooking that VFD to my Yaskawa…but I will connect it to a USA motor…I have a spare anyway.

 

[marrt]

I have have run many 3 ph machines using VFD's running on single phase. I like Fuji and have had great success and good s upport from their engineers.
It seems to me you could swap out the existing VFD with Fuji FRN0020C2S-2U. (or similar).
This VFD is rated, with single phase input, at 9.7 amps 3 ph output, or 3.9 kva.
As stated above, solve your coolant and oil pump problems separately.
This VFD is only $268. And the next size up is 14 amps for $499.

I think this is a much better solution than an expensive Phase Perfect or loud rotary converter.

FRN0020C2S-2U

AC DRIVE, 5HP, 230V, 3 PHASE, 19.1A,

www.wolfautomation.com

FRN0025C2S-2U

FRN0025C2S-2U quick delivery, authorized Fuji Electric distributor. Offers complete line of AC Drives . Easy online ordering, rewards program, and great pricing.

www.wolfautomation.com

This document gives single phase specifications:

https://www.wolfautomation.com/media/pdf/ac-drives/fuji/frenic-mini/fuji-frenic-minic2-1phrating-appnote-21.pdf

Bob

Overland, thank you for the post. Those Fuji's are certainly affordable.

In my case, a RPC is the way to go because I already own a “15 HP” American Rotary and I don’t want to rewire the lathe control panel. If driving the motor only, the VFD would be the way to go.

 

[mksj]

Manufacturers usually recommend at least 5 minutes to cycle a VFD ON-OFF-ON, and not doing it repeatedly as the resistive element will heat up and cause higher current draw. A DC choke decreases the current peaks, and is often used when running a 3 phase input VFD off of single phase, and also for larger VFD's. Turning a VFD on and off 2-3X a day should not have an appreciable effect on service life, but when I am working in the shop I turn mine on when I start working and off at the end of the day or I leave (4-8 hours). The Yaskawa VFD's have a very good reliability, MTBF is something like 27 years. You have plenty of margin with your current VFD to run it off of an RPC.

 

[JST]

JST: What is "frequent"?

My question was open ended because I’m curious as to what is acceptable (what is the design spec). Frankly, if it’s an issue, it should be stated in the manual. I called Phase Perfect and asked this power cycling question. They said it’s fine to cycle their inverter each day. Ok. What about every hour, or every 10 minutes? No, that’s not acceptable. Further, he said I should wait a few minutes after turning the unit on before applying a load. Ok, how many minutes? Two, ten or what?

I’m not trying to be an armchair expert here. But it’s common for some devices to suffer premature failure due to frequent power cycling (e.g., larger electric motors that start under load…but that’s simple to understand). I “imagine” most VFDs are designed for industrial applications and are “expected” to be powered at least throughout the work shift. These Yaskawa drives aren’t cheap. I called the company and the technical representative indicated he definitely did not recommend frequent power cycling to the VFD. But, he could not tell me exactly why or what was acceptable.

Again, I AM overthinking the issue. I can get around my concern using the advice suggested here. I’m just a little frustrated that, if this is an issue at all, it would be nice to know the design spec. I’m left to “assume” it’s not an issue because it’s not addressed in the manual. But I don’t like making assumptions when the information is “out there” somewhere.
.........................................

You will probably never tie anyone down to a specific number. That is mostly because there is no magic number, no point at which it flips from "bad" to "acceptable".

The 5 min is a good number, but of course, 4min and 59 sec is not "bad", and there is nothing magic about the exact number "5 minutes" that makes it good when 2 sec before that is bad.

There are two common types of inrush protection. I don't KNOW what Yaskawa uses, but I bet they use the relay type. I seem to recall seeing a relay in the right place when looking in one once, but I was wrong once before, so it could happen again.

What is protected against is a high current surge when the VFD is powered up. The capacitors have to charge up from zero volts, and so if connected immediately to full voltage, a very large current would flow, potentially damaging them somewhat, shortening life "some amount" (anywhere from instant failure, to cutting the life by some small amount per turn-on event.

Type #1 is a "thermistor" type. A heavy-duty version of a thermistor is in series with the input. It starts out with a given higher resistance, often between 1 and 20 ohms. When you turn on the unit, the resistance limits current to whatever the designer thought was a good idea (hopefully with a decent reason). That surge heats the thermistor, which (with this type) causes the resistance to decrease. The normal current draw of the VFD then keeps the thermistor hot enough to stay low in resistance, which may be 10 or 20x lower than the "cold" resistance.


Type #2 is a resistor and relay. The resistor limits the inrush current, allowing the bus capacitors to charge up. At some certain voltage, the control circuit shorts the resistor with a relay, allowing a small surge as the capacitors charge the rest of the way to full voltage, but providing essentially no resistance to incoming power. That second surge is not limited, so the designer has to pick the trigger voltage and resistor value for best protection and least stress.

The type #1 needs to cool down in order to resume normal protective action. That may take several minutes.


Type #2 is variable... if re-powered quickly, the capacitors may not have dropped in voltage enough to re-engage the resistor, so switching "on" causes another surge.

All turn-on events are stressful, so you want to minimize them. And you want to make sure that each one starts from the normal power-off state, so that you do not catch the VFD before it "resets" to power off condition.

Essentially, turn the VFD on, leave it on while you are working, and shut off when done. Don't turn off the VFD for every tool change, or to change parts, etc. Turn off when you are done working.

It's fine to leave the VFD on, which I would do over lunch, etc.

 

[marrt]

mksj and JST, thank you for the comments. I understand the issue much better as your posts complement nicely. Recommended cycle times of 5 minutes (as one example) enable the inrush control circuit to "reset" essentially. This reduces the heat damage caused over time by frequent large current spikes. Since VFD's have large capacitors, the current draw to "fill" the capacitor is sufficient in duration and degree that it should be avoided on a frequent basis. In addition, frequent power cycling can cause unwanted harmonic issues for the grid if done at scale (e.g., industrial) and not properly addressed.