# Rethinking My Approach with a VFD



## TNBen60 (Jan 21, 2022)

I am adding a new to me lathe in my shop. Its a Mazak with a 10 HP, 3 phase motor. I have used static phase converters, rotary phase converters and VFD’s in the past. I really like the utility of a VFD. But, when the electrical panel looks like this I question the viability of inserting the VFD so that it is directly connected to the motor. I also wonder about my ability to get in and out of 40 year old wiring without causing additional problems. This may just be a case where a rotary phase converter is the better option. I’m going to ponder on it over the weekend and was curious if anyone else had thought through this before.


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## den-den (Jan 21, 2022)

TNBen60 said:


> I am adding a new to me lathe in my shop. Its a Mazak with a 10 HP, 3 phase motor. I have used static phase converters, rotary phase converters and VFD’s in the past. I really like the utility of a VFD. But, when the electrical panel looks like this I question the viability of inserting the VFD so that it is directly connected to the motor. I also wonder about my ability to get in and out of 40 year old wiring without causing additional problems. This may just be a case where a rotary phase converter is the better option. I’m going to ponder on it over the weekend and was curious if anyone else had thought through this before.


I have installed several VFDs (none in a system like this).  In my opinion, if you want to keep the existing controls, a rotary phase converter is a better choice as it can supply 3 phase to the existing controls which would be a poor choice for a VFD.


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## matthewsx (Jan 21, 2022)

Yeah, probably a better candidate for an RPC. 

Do all the controls work properly as it sits? Does it have the required speeds for the work you'll be doing?

I love the VFD's on my lathes but they are older models without too much in the way of electrical in the first place (the Seneca Falls didn't even come to me with a switch). For a modern lathe (assuming CNC) it probably doesn't make sense to rewire it unless there are major issues with the controls to begin with.

@mksj would be the go to person for a real answer though.

John


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## Dabbler (Jan 21, 2022)

I have some (indirect) experience with this: a friend of mine rewired his lathe for a VFD/3PH motor from a single phase motor.  It tok him about a full-time week to get it done, and he has some experience with wiring.

RPC is your best bet, even if pricier.  You need to upsize your RPC because of the large starting mass of a lathe.  I use a 15HP RPC for a 7.5 HP lathe.  The manufacturers suggest 30% higher, but I prefer to have some 'breathing room'


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## Reddinr (Jan 21, 2022)

I went a different direction with my lathe because the lathe has a two-speed motor and I didn't want to deal with it.  I have a VFD that accepts single-phase input and can be set to output 240 VAC, 60Hz all of the time.  I wired in a sine-wave filter to its output and I have the equivalent of a rotary phase converter without all the spinning.  Typically to use most VFDs you should have about 1.5X the three-phase output rating.  My VFD is 200 Amp rated ... so no problem.  When I'm feeling jiggy I up the frequency to 66 Hz. for a little more speed.

I do want to revisit a real VFD for the lathe at some point but I don't know if it will really happen.  Maybe I'll do it when I get to the ELS project I've not gotten around to either.


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## JimDawson (Jan 21, 2022)

For 10 HP I would go with a RPC.  Up to 5HP a VFD with a single phase input works OK.  If you want a variable speed spindle, then a RPC feeding a VFD would be my choice.  This is how I run my 10 HP spindle lathe.


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## frugalguido (Jan 21, 2022)

JimDawson said:


> For 10 HP I would go with a RPC.


Or a Phase Perfect, especially for you are running any other machines like CNC's that the circuit boards are a lot of money to replace or repair. I use the a Phase  perfect for multiple machines like a 3 phase per supply for the shop.


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## TNBen60 (Jan 21, 2022)

Reddinr said:


> I went a different direction with my lathe because the lathe has a two-speed motor and I didn't want to deal with it.  I have a VFD that accepts single-phase input and can be set to output 240 VAC, 60Hz all of the time.  I wired in a sine-wave filter to its output and I have the equivalent of a rotary phase converter without all the spinning.  Typically to use most VFDs you should have about 1.5X the three-phase output rating.  My VFD is 200 Amp rated ... so no problem.  When I'm feeling jiggy I up the frequency to 66 Hz. for a little more speed.
> 
> I do want to revisit a real VFD for the lathe at some point but I don't know if it will really happen.  Maybe I'll do it when I get to the ELS project I've not gotten around to either.


You intrigue me and this is was why I posted this. If you don’t mind I will pepper you with a few questions.

1.) Do I understand correctly that the VFD runs continuously. You then power the lathe with a magnetic switch and use it’s controls normally?

2.) How do you get the VFD to power up without the motor load without complaining?

3.) Tell me about this sine wave filter of which you speak?

Like you I have no intention of varying the output frequency as there are more speeds in the gears than I know what to do with.

Thanks


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## mksj (Jan 21, 2022)

Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.




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						Phase Technologies
					






					www.phaseperfect.com
				




If you wanted variable speed, you could add a VFD, it would need to be oversized for single phase use, and you are pretty much looking at a complete new control system. I have done those for different individuals, but a lot of factors to consider and not a simple process. When all is said and done you are probably getting close to the cost of a Phase Perfect. You also need to figure in the ancillary costs and power source for any of the choices, as well as electrical code requirements. It has also come up that there can be issues with power companies if you are pulling large current draws that can pull down the line voltage of surrounding neighbors.


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## TNBen60 (Jan 21, 2022)

mksj said:


> Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.
> 
> 
> 
> ...





mksj said:


> Phase Perfect generates the third leg and passes through the the two single phase lines. It also filters the generated leg so it is very close to a sine wave, and it is not effected by the load. It is not a variable speed VFD, it is designed to provide fixed 60Hz 3 phase power from single phase. There have been issues with reflected electrical noise into the input line, I believe this is an issue with the older models. It has a very high efficiency (98.7) vs. say and RPC, so can be left on continuously, and newer models appear to have less physical noise than the older models. Downside is cost, but if you have multiple larger 3 phase machines then the investment may be worth it. They are rated to their specified output Hp/amps and are the output (all legs) are compatible with electrical control systems, multiple motors, etc.
> 
> 
> 
> ...


I really appreciate the information. I had a thought that I might have to place the shop light switch near the lathe. That way I could turn the lights out, start the lathe, then turn the lights back on. Don’t want to overload anything you know.


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## strantor (Jan 21, 2022)

TNBen60 said:


> I really appreciate the information. I had a thought that I might have to place the shop light switch near the lathe. That way I could turn the lights out, start the lathe, then turn the lights back on. Don’t want to overload anything you know.


When I start up my ADX30 (30HP) phase converter, it causes the lights to flicker in all the houses on my end of the street. So I don't turn it on and off all the time. Try to start it early in the morning and leave it on all day if I think I'm going to need it. Note that is just starting the phase converter itself with no load. Once it's running, starting 3ph loads doesn't cause much issue. 

The ADX30 is a bigger phase converter than you need, but not by much. You could probably do an ADX20 if you're looking at American Rotary products.


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## Reddinr (Jan 21, 2022)

> 1.) Do I understand correctly that the VFD runs continuously. You then power the lathe with a magnetic switch and use it’s controls normally?
> 
> 2.) How do you get the VFD to power up without the motor load without complaining?
> 
> 3.) Tell me about this sine wave filter of which you speak?



Yes.  The VFD runs continuously.  I do turn it on with a circuit breaker only when I want to use it.  The contactors on the lathe work normally.  The output filter protects the VFD from the switching of the contactors on its output.  I've been running mine for many years not this way.  The three phase actually powers multiple machines, not just the lathe.

The output filter seems to make the VFD happy.  My VFD is a surplus Yaskawa F-series drive.

The sine wave filter I use is made by MTE.  It has a three phase inductor with capacitors.  It takes the PWM "choppy" output of the VFD and makes the output look more like a sine wave.  I got the filter off of Ebay.

Also, I first tried a RPC with this lathe.  It has a 4HP motor so I got a 5 HP RPC.  It was an absolute DOG.  The lathe would start in lower gears but it spooled up slowly.  In higher gears, the RPC was overloaded and the CB tripped often during start-up.  I later found out that I should have used 2X the RPC size for the lathe load because of the inertia I guess.


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## TNBen60 (Jan 21, 2022)

Reddinr said:


> Yes.  The VFD runs continuously.  I do turn it on with a circuit breaker only when I want to use it.  The contactors on the lathe work normally.  The output filter protects the VFD from the switching of the contactors on its output.  I've been running mine for many years not this way.  The three phase actually powers multiple machines, not just the lathe.
> 
> The output filter seems to make the VFD happy.  My VFD is a surplus Yaskawa F-series drive.
> 
> ...





Reddinr said:


> I will look further into the things you brought up.  Thanks again.


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## strantor (Jan 21, 2022)

Reddinr said:


> The sine wave filter I use is made by MTE.  It has a three phase inductor with capacitors.  It takes the PWM "choppy" output of the VFD and makes the output look more like a sine wave.  I got the filter off of Ebay.



Not a rhetorical question or a veiled jab: 
Have you looked at the output of the filter with an oscilloscope to assess just how much more "like a sine wave" it makes it? I ask because I've contemplated doing this in the past, did some tests, and saw on my scope that the output with my filter was still a far cry from "sinusoidal." I did not have a buffet of filters from which to choose the one that worked best, but with what I had, I observed different levels of effectiveness in cleaning up the power depending on load and other things. It seemed like a crap shoot to me and I did not feel comfortable subjecting sensitive electronics to that kind of supply. It would have been fine for a shop full of manual machines but I use mine to power up CNCs and industrial control panels. But if you've verified that the output is "clean" from your filter I'd like to know the specs of that filter so that I can obtain one and give it another go.

P.s. just because a VFD doesn't complain about its input doesn't mean it's a clean input. A VFD will happily run on anything from DC to probably a few kHz, with +/- xxx variation in voltage. I just powered up a 480V 3ph VFD yesterday with 120V single phase to get the parameters out of it, and it didn't even fault out. I was curious if it would actually run a motor in that state, but didn't have time to test.



Reddinr said:


> Also, I first tried a RPC with this lathe.  It has a 4HP motor so I got a 5 HP RPC.  It was an absolute DOG.  The lathe would start in lower gears but it spooled up slowly.  In higher gears, the RPC was overloaded and the CB tripped often during start-up.  I later found out that I should have used 2X the RPC size for the lathe load because of the inertia I guess.


Yes, the stated HP of a RPC is almost always the "running HP" and there is a separate spec for "starting HP" which is close to half. This is why I recommend a 20HP minimum RPC for this 10HP lathe.


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## Reddinr (Jan 22, 2022)

Regarding "how sinewavy is it?".  I have looked on the output with a scope.  BTW It has to be an *isolated* scope channel to avoid damaging the scope.  It is not bad.  It is not perfect but good enough for a motor.  Probably about 10-15% THD or so.  I know some of the filters are just "dv/dt" filters to get rid of the sharp edges to avoid spewing EMI everywhere and reduce stress on insulation, especially in the case of long cable runs.  I have a DRO on the lathe and it seems happy.  I've had no trouble with that anyway.  It is important to get a filter that is designed for the job.  Tomorrow I'll go to the shop to find the make/model of the filter I have.

Regarding the input.   I added a series inductor to the input too in order to make it easier on the building power.  I didn't have too many worries as I run one machine at a time and have a separate 200A feed to the shop.  I bet your 480V VFD will fault out if you put a decent load on it.  The setting for the input voltage fault is adjustable.  Maybe yours is set to a low voltage setpoint for the trip-out.


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## mksj (Jan 22, 2022)

So a number of different approaches, given a big enough VFD, other individuals they have used it as a "fixed" 3 phase power source for their machines, but it is not just a factor of 2 for single phase input. You need a much larger VFD to deal with the high start up current of motors not being controlled by the VFD. You need significant filtering that it does not interfere with the control systems. Many VFD's will operate over a wide voltage range, but for the most part the output cannot be higher than the input unless you have a voltage doubler circuit.  On the 200-240V VFD's they will dropout at 120VAC, have had a few people connect them up incorrectly. Nice thing on some of the newer VFDs is they will program off of the USB power when connected to a computer.

I see no reason to need to turn off the Phase Perfect when not in use, they draw less than 100W at idle, RPC many individuals have it dropout when the lights get turned off. The Phase Perfect produces full sinusoidal three-phase output voltages balanced to within <2% under all load conditions. Because the output voltage is a sinewave with low harmonic distortion, all types of three-phase equipment can be safely powered per the manufacturer. RPC is the least expensive option if you build you own, if buying a turn key system, a 20 Hp RPC (which is recommended for a 10 Hp motor) is close in price to the Phase Perfect 10Hp which will drive the same load. One would probably want to go with a 15Hp Phase Perfect so you could power more than one machine, it is also unlikely that you will be using manual machines at anything close to full load for a sustained time frame. You could also buy a RPC box for not much and find a 20 Hp idler. If you want to run a VFD off of an RPC, I recommend going up one size in capacity, there is a small derating when running them off of an RPC.


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## Reddinr (Jan 22, 2022)

mksj - Do you know a rule-of thumb for sizing a VFD as a static converter?  I think you are right about needing to oversize due to start-up currents but I assume it depends on the design of the VFD as to what factor is needed, one designed close to the bleeding edge vs. a more industrial VFD.

TNBEN60 - I had a look.  The filter I use (surplus from EBAY) is an MTE SWAGA0030D.   mksj makes good points.  Using a VFD as a static converter takes oversizing.  Since I'm in it partly for the adventure and I got the big VFD very cheap, it worked for me.


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## frugalguido (Jan 22, 2022)

To add to the above, when I purchased my Deckel CNC, I was instructed that the Phase Perfect was the only way to power it off of my residential single phase . Why, because the Phase perfect was the "perfect 3 phase generator". It has really good balance between phases and is very clean power. You might ask why spend all that money one of these and not go with another means of obtaining 3 phase. Because when the old German CNC circuit boards are $2-3K per board at the time and there are multiples of these in the refrigerator sized control cabinet, I didn't want to take chance with bad power. I ran the Phase Perfect for over many years and when I moved into my new "Man Cave", which had 3 phase power, I sold the Phase Perfect close my purchase price,(high resell).


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## mksj (Jan 22, 2022)

I have only dealt with smaller VFD installs, mostly 5Hp and under, and not my background which is medicine. Where I have read others using the VFD as a fixed 3 phase power source, it has been older installs using much larger older style VFD's (surplus-cheap) and old style manual machines (not for CNC/electronics). If you figure that the startup draw of a motor is quite high like 8X the FLA, a VFD can provide probably 2-3X, and then factor in derating for single phase 2X. You are probably need 6-8X the the motor FLA for the VFD output, it would need to run in straight V/Hz, might be issues with THD which would trip it into an error mode. Larger VFD's usually have DC chokes which would be required, and then you would need some form of output filtering sized for the peak currents....  Discussions on it have mostly been over at the Practical Machinist, and more from years past, I have not seen it recommended as a general practice. You also would need a sizable service to the VFD, minimum would be 125% of the rated input, not what it is driving.  I cannot see it as a practical solution these days, when an RPC can be done for very little. 

Phase Perfect is what I see most people use if they have any type of electronics in their control system, or as a simple three phase power source for single phase input. Given the high efficiency and low standby power dissipation the service requirement would be much less than an oversized VFD. They appear to be reliable, and some of the previous issues seem to have been addressed with the newer models. Only issue that I recall reported from a reliability standpoint is the capacitors have a rated life and need to be replaced at regular intervals (years).


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## Firebrick43 (Jan 22, 2022)

TNBen60 said:


> I am adding a new to me lathe in my shop. Its a Mazak with a 10 HP, 3 phase motor. I have used static phase converters, rotary phase converters and VFD’s in the past. I really like the utility of a VFD. But, when the electrical panel looks like this I question the viability of inserting the VFD so that it is directly connected to the motor. I also wonder about my ability to get in and out of 40 year old wiring without causing additional problems. This may just be a case where a rotary phase converter is the better option. I’m going to ponder on it over the weekend and was curious if anyone else had thought through this before.


Is this a CNC mazak????  Where are the drives and existing spindle VFD.


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## strantor (Jan 22, 2022)

mksj said:


> If you figure that the startup draw of a motor is quite high like 8X the FLA, a VFD can provide probably 2-3X, and then factor in derating for single phase 2X. You are probably need 6-8X the the motor FLA for the VFD output


The starting current of a motor across the line is 8-10x the running current, because there is nothing to limit it except the resistance of the windings and the wires to the motor. It's that high because it _can_ be. The VFD monitors output current and regulates its duty cycle to prevent blowing itself up, so it won't (shouldn't) _let_ startup current go that high. So I think that half of the equation can be disregarded and we're back to the classic 1.7-2x derating factor. That said, I've never tried to start a motor off a VFD that was already running 60Hz. All the MFG guidance I've ever read, advised against doing this.

I agree with you that RPC ir phase perfect is the way to go.


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## mksj (Jan 22, 2022)

You have derating for single phase input which is 2X, and then you have derating in that the VFD will trip an over current error because it can't supply the needed current. It has no way to regulate the current demand because it is not adjusting the acceleration in V/Hz to control the current. You have it set at 60Hz.  There may also be additional safe guards in newer VFD's if they were to monitor the output, you may get an error with no motor attached, generally and issue with sensorless vector. I have had VFD's trip the over current error with sudden changes in speed. So I still think that you need a significantly larger VFD if you wanted to use it as a power source, I do not recall the numbers, but higher than a factor of 4.


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## JimDawson (Jan 22, 2022)

strantor said:


> When I start up my ADX30 (30HP) phase converter, it causes the lights to flicker in all the houses on my end of the street.


If you spin up the idler motor with a pony motor it won't do that.  I spin my 15 HP up with a 1/2 HP motor that is powered by a small VFD.  I spin it up to 1800 RPM over 10 seconds, and use the VFD onboard relay, programed to close ''At Speed'', to switch the main contactors in, and simultaneously drop out the VFD run signal.  The VFD is programmed for ''Coast to Stop''.  My shop lights don't even flicker.


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## TNBen60 (Jan 23, 2022)

Wow you guys are amazing! Thanks for the information. I spent some time looking at the options you brought up. While looking over the rotary converter option I called up the folks that helped me in the past with a rotary phase converter for a headsaw that needed a 75 HP idler motor with a really clean third leg due to its control system. Their customer service was excellent back then and was the same when I called them for this. In trying to balance everything I have decided to have them build a rotary converter for me.

I’m going to keep the VFD on my mill though.

I’m really impressed with the level of information. Thanks again.

Ben

EDIT: I came back to re-read this thread because there is some good information in it. In re-reading my last post it came across to me like an advertisement. That was not my intent.


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## strantor (Jan 23, 2022)

JimDawson said:


> If you spin up the idler motor with a pony motor it won't do that.  I spin my 15 HP up with a 1/2 HP motor that is powered by a small VFD.  I spin it up to 1800 RPM over 10 seconds, and use the VFD onboard relay, programed to close ''At Speed'', to switch the main contactors in, and simultaneously drop out the VFD run signal.  The VFD is programmed for ''Coast to Stop''.  My shop lights don't even flicker.


That's a pretty clever idea, and if I had built this RPC from a 2nd hand idler I'd be contemplating your suggestion pretty hard right now. But this RPC is conceived and born as a RPC, so it has no external shaft on which to couple something like that. Given its size and the fact put they controls in it with circuit boards, it seems a notable oversight that they didn't include any kind of soft start feature.

Although maybe I could use a VFD to spin up the idler iself...  maybe a few series RL circuits in the phases so the little VFD doesn't complain (if needed)?

Edit: you can see the shaftless motor in this video I recorded a few years ago:


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## JimDawson (Jan 23, 2022)

strantor said:


> But this RPC is conceived and born as a RPC, so it has no external shaft on which to couple something like that.


 No external shaft access at all?  The purpose built RPC idlers that I have seen basically had the shaft cut flush at the end bell, but was still accessible.  In my case I just turned the end of the armature down to fit the flex coupling I had, 12mm as I recall.  Adding a stub shaft to yours shouldn't be a huge problem even if the end bell is closed off.  That's what they make drill bits for.


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## strantor (Jan 23, 2022)

JimDawson said:


> No external shaft access at all?  The purpose built RPC idlers that I have seen basically had the shaft cut flush at the end bell, but was still accessible.  In my case I just turned the end of the armature down to fit the flex coupling I had, 12mm as I recall.  Adding a stub shaft to yours shouldn't be a huge problem even if the end bell is closed off.  That's what they make drill bits for.


Yep, no access at all. You can see 360 degrees around it in the videos on this page. Taking it apart and modifying it sounds fun, but there are a lot of fun things already on my to-do list and this would be sufficiently near the bottom as to ensure it almost certainly never gets done.


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## JimDawson (Jan 23, 2022)

Yup, that time thing is always a problem.


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## TNBen60 (Feb 23, 2022)

Well the rotary phase converter showed up today. A trip to the local electrical supply house and a visit from the electrician and I should be able to make lathe noises soon.


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## MikeInOr (Feb 24, 2022)

strantor said:


> That's a pretty clever idea, and if I had built this RPC from a 2nd hand idler I'd be contemplating your suggestion pretty hard right now. But this RPC is conceived and born as a RPC, so it has no external shaft on which to couple something like that. Given its size and the fact put they controls in it with circuit boards, it seems a notable oversight that they didn't include any kind of soft start feature.
> 
> Although maybe I could use a VFD to spin up the idler iself...  maybe a few series RL circuits in the phases so the little VFD doesn't complain (if needed)?
> 
> Edit: you can see the shaftless motor in this video I recorded a few years ago:



When I built my 10hp rotary phase convertor about 25 years ago I found that the ramp up time on the idler motor, hence its current draw, was directly proportional to the capacitance of the starting capacitors.  I remember the idler starting up near instantly when I first turned it on after building it and my shop lights did flicker.  I pulled a few of the starting capacitors out of the chain and the motor now takes about 1.5 ~ 2 seconds to start and it draws MUCH less current on startup.  My RPC uses an adjustable timing relay to cut the starting capacitors out so I just added a little to the amount of time the timing relay is energized.

I would be hesitant to change the starting capacitance on a factory bought RPC so I am not really recommending doing so to you.  I just thought I would mention it is possible.  I would not be surprised if a factory built RPC has a single starting capacitor of the needed value instead of a chain of them to get to the right value, so you potentially might have to pull the original starting capacitor and replace it with one of a lower value.




The round capacitors are the starting capacitors and the oval ones are the run (balancing) capacitors.

P.S. Running a VFD with a contactor between the VFD and the motor being powered is contrary to everything that I have ever been told about VFD's... but I have never actually tried it so I don't have any first hand experience.


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