VFD ...yea or nay

[sf67n20]

Greetings to All,
My question is a straight one so please be direct. My new Bridgeport J mill (actually an old machine) has a 2 hp w/3 phase. I have no 3ph in my new shop & I want to skirt around the costs of a rotary converter. Can I use a good VFD w/230vac input for my 2hp/3ph mill motor ? The costs between a good VFD and a rotary is staggering . If I am reading the forums correctly, I can. So , if yes, please suggest a real good VFD. I will read diligently .
Thank You Gents (or Gentets) !!

Sincerely
Philip

 

[madaussie]

Philip,

Yes it can be done. As for picking a VFD to suit your motor, a bit more information off the name plate is required. Post a photo and someone should be able to suggest a model and size.

To stop/start your motor, the stop/start button will need to be wired as a DI into the drive as you will pop the transistors if you open the circuit load side of the VFD.

Allen Bradley make good industrial motor control gear that has been around for many years, though I think they can be a bit expensive. They should have a model to suit your needs. Some models have a braking feature as well.

If your country requires it, a licensed electrical contractor will need to perform the work.

Hope this helps,

Matt

 

[KenErickson]

I run 3 different pieces of equipment with vfd. 2 knife makers belt grinders and a horizontal 9 inch disk.

If I was putting in a step pulley Bridgeport I would go vfd for sure.

I have had good luck with KB drives.

http://www.kbelectronics.com/Variable_Speed_AC_Drives_Inverters.html

 

[Hopefuldave]

Hi Phil,
A VFD is a much better idea than a rotary converter, if only because the rotary will drive you mad, droning away in the corner of your shop...

Advantages (other than the quiet) are control of spindle speed, reduced power consumption compared to a rotary, and best of all for a mill quick reversing, which will make power tapping a possibility ( ideally pick a VFD that has or can have an external brake resistor for the rapid stops, to save pushing reset too often).

Disadvantages... Unlike a rotary, it's relatively difficult to run more than one machine from a VFD, if you want to run a 3-phase lathe or such as well it'll be easiest to give it its own VFD. Installing and setting up the VFD isn't difficult if you have some idea of electrical work but isn't trivial, you will need to read the manual a few times and spend an evening or three head-scratching!

Good VFDs... Basically avoid no-name boxes from China.
Allen-Bradley, ABB are good, as are the American and Japanese brands whose names you'll recognise. Check your motor plate for current required, and the VFD's own power requirements - some will want 3-phase in or may need to be derated on single-phase...

I have an ABB VFD on my lathe (£25 English from eBay second-hand, lucky there!) but it was a complicated installation as it has a 3-speed 415v-only motor and I only have 240 single-phase, achievable though with some head-scratching! It's a big improvement, speed control means I can hit the sweet spot for a job easily or ramp up the spindle speed when facing or parting off, and the rapid stop/reversing is even more useful on a lathe, e.g. Metric threading with inch leadscrew where I have to keep the half-nuts engaged.

Hope this helps,
Dave H. (the other one)

 

[madaussie]

One more point to be cautious about with VFD's is the harmonic interference that can be transmitted to other electronic devices.

With the right precautions it can be avoided. Look for C tick rated drives and use shielded cable to block the interference. Can play havoc with TV, radios etc.

Matt

 

[kvom]

I use a VFD on my step pulley BP (GS2 from Automation direct). I have the front LED programmed to read the RPM, and leave the pulley on the 2nd sheave.

I also removed the power switch from the mill and use the VFD for on/off/reverse. VFD output is wired directly to motor leads.

 

[Sshire]

Kvom
I replaced the motor on my lathe with a 220v and a VFD. One of my smarter decisions. Mine is a TECO-Westinghouse.
Selection guide is here
http://www.tecowestinghouse.com/PDF/Drive Selection Guide D-SG 07-06.pdf

Hope this helps
Stan

 

[Mainer]

IMO the only way to fly. I have a TECO-Speecon from Automation direct that I bought several years ago. It's great.

 

[dman]

the answer is simple. if you have one machine go vfd. of you have several that are 3-phase and can't afford a vfd for every machine go with a rotary converter. vfds cost has everything to do with current handleing. for a 2 horse motor it'll cost a bit. also if you find an ebay deal on a used one you can sometimes use one for a slightly different application but it will be de-rated in some circumstances.

you can use a 3-phase input converter with single phase power but if it's not rated to use single phase input it will be de-rated, so if oyu find a deal on one for 3phase buy one with twice the hp. it works on single phase because it is just rectified to dc then a new signal is generated, the control circuits are regulated down to a low dc voltage. you can also use a higher voltage converter for a lower voltage input but again the horse power will be de-rated by a factor of the difference in voltage ratings.. this is why a 460v vfd for 4hp is barely more expensive than a 220v vfd for 2hp. the only difference is usually the input stage which is tuned for the voltage/phase count but will work in other applications as long as you don't fully load it.

 

[sf67n20]

Thank You so much Guys.....this group is always a treasure trove of important info/help !!

Of course, now I have to actually choose a good unit....whew !!!!!!



Thank You All !!!!!!

 

[123RWO]

An excellent source for VFD's and super tech support is automationdirect.com. They offer their own house brand as well as Hitachi . I have had one of their house brand GS2 1 hp units on my BP step pulley mill for about 9 years and it has been perfect.

RWO

 

[MachineTom]

Another Yes for the VFD, when thinking of costs, after buying the VFD there are other things needed as well and not cheap. An enclosure is needed to provide chip protection to the VFD, at the same time the enclosure has to be vented as a fair amount of heat is generated by the VFD. The controls are low voltage, but need to be robust enough for where they will be used, I use the Square D brand as my favorite source is Ebay and there are lots there, at minimum there are two needed, Push/pull for on/off and a maintain switch for fwd/rev, and contact blocks to match. These need another enclosure near the mill as you don't want to be jumping around to shut off the mill that just picked up a birds nest of stringers.

Some folks like a start button, a stop button, and a E-button. I suggest keeping it simple, a single mushroom headed switch for on/off, and a fwd/rev switch, as well as speed control knob. Mount them on the knee, and make chips.

The Hitachi units have been great for me, they offer single phase input models, of just get a 4hp 3 phase unit to run a 2hp and input sihgle phase.

 

[sf67n20]

If I can pick your thoughts a little further, I have one more piece of equip. I got from this liquidation sale .
It's a Ingersol Rand T-20 compressor. 5 hp / 3 ph. It was built in 1987 and the 5 hp runs at an amazing 3490 rpm . Double v-belt pulley...but they been running just one belt with a sheave pulley ( 5.5" on a 1.125 shaft) on the motor side .
Question : can a VFD run this compressor with less amps, better efficiency, less cost, than a rotary p/c....OR....would it be better to just get another 5hp motor with 1ph (230v). Eaton compressors has 5 hp for 325.00 plus shipping...but they can't guarantee me it would be USA motor or southoftheborder motor(aluminum windings for sure). 5hp's are spendy and I would have to get a 3400 rpm to keep the pump oiled properly .
Any thoughts ??
If you're wondering why I got such a huge compressor for a home shop, it was a steal @ 150.00(load in my P/U)....and it runs smooth .
Thank You for your input !!
Philip

 

[dreeves]

I use a phase-o-matic static box to run my mill and lathe. Each has its own. They both run great.

Dave

 

[kvom]

5HP is too big for a 1PH VFD. You will need a rotary to power it, or a motor swap as you suggest.

WRT Tom's comments on the VFD, I mounted my VFD in a Nema enclosure for protection, and used a remote cable to connect the detachable control panel, which I mount near the mill. The panel has the LED readout, a rotary speed control, and three buttons: start, stop/reset, and fwd/rev. In back gear, the spindle is geared backwards and the VFD must be set to reverse. I've been running this for 3+ years with no issues.

 

[dman]

I use a phase-o-matic static box to run my mill and lathe. Each has its own. They both run great.

Dave

i have one on a van norman valve seat and guide machine but the phase shift isn't as even as a rotary or vfd, there is an audible 60 cycle hum in the motor and it leaves very slight but visable chatter marks, the marks are regularly spaced and the spacing changes with the gear you are in, the marks are too slight to effect the valve seal and easily lap out but sometimes cause problems cutting spring seats. i want to replace it with a vfd.

 

[123RWO]

If I can pick your thoughts a little further, I have one more piece of equip. I got from this liquidation sale .
It's a Ingersol Rand T-20 compressor. 5 hp / 3 ph. It was built in 1987 and the 5 hp runs at an amazing 3490 rpm . Double v-belt pulley...but they been running just one belt with a sheave pulley ( 5.5" on a 1.125 shaft) on the motor side .
Question : can a VFD run this compressor with less amps, better efficiency, less cost, than a rotary p/c....OR....would it be better to just get another 5hp motor with 1ph (230v). Eaton compressors has 5 hp for 325.00 plus shipping...but they can't guarantee me it would be USA motor or southoftheborder motor(aluminum windings for sure). 5hp's are spendy and I would have to get a 3400 rpm to keep the pump oiled properly .
Any thoughts ??
If you're wondering why I got such a huge compressor for a home shop, it was a steal @ 150.00(load in my P/U)....and it runs smooth .
Thank You for your input !!
Philip

This is not a good application for a VFD because of the high peak torque requirement as each cylinder comes up to TDC on the compression stroke. Once up to speed the whole machine acts as an effective flywheel to smooth out the torque peaks to a value that the motor can handle. An induction motor can handle the torque peaks better than the same motor driven by a VFD. Load torque is directly translatable to motor current and a motor running across the line is not usually limited very much as to peak current as long as the motor doesn't stall and cause a tripped motor protective device. A VFD has a peak current limit set by the output circuitry rating and the control logic will try to hold the peak current to a value below the damage point. As long as the current limit is above that required by the load's torque requirement, all is well and good ( theoretically).

In this case, the only way to use a VFD would be to delay loading the compressor until you accelerate the compressor to at least 3/4 speed before allowing the unloader to kick out and load the motor. How long it would take to achieve 3/4peed would depend on the rotating and recip mass of the whole machine. Once up and running, you could not expect to vary the speed of the compressor below about 75% speed if that much ( educated guess).

If you just use the VFD as a handy single-phase to 3-phase converter and keep it running at full speed, it should work OK provided you get around the starting problem mentioned above.

RWO

 

[sf67n20]

Thank You All again....so very helpful !!

I almost expected the responses received...VFD seems just not the right application. But nothing is lost here from this thread. I have learned a room full of info .
Probability will be to check on pricing for one 10hp rotary phase converter to run both the 2hp & 5hp mill/comprsr.. as one hook-up . My talley looks like this : (1)5 hp motor @ 325.00 plus shipping....(1) VFD 2hp(actual 3-4hp) @ 255.00 plus shipping....versus (1) rotary phase converter 10hp @ 600.00 plus shipping(maybe local pick-up).

So if this looks typical & doable...I'll go ahead in this direction.

Thanks Gentlemen !!!



Philip

 

[kvom]

I would still use a VFD for the mill. Changing the pulley sheaves for speed control gets old after a while.

 

[dman]

Thank You All again....so very helpful !!

I almost expected the responses received...VFD seems just not the right application. But nothing is lost here from this thread. I have learned a room full of info .
Probability will be to check on pricing for one 10hp rotary phase converter to run both the 2hp & 5hp mill/comprsr.. as one hook-up . My talley looks like this : (1)5 hp motor @ 325.00 plus shipping....(1) VFD 2hp(actual 3-4hp) @ 255.00 plus shipping....versus (1) rotary phase converter 10hp @ 600.00 plus shipping(maybe local pick-up).

So if this looks typical & doable...I'll go ahead in this direction.

Thanks Gentlemen !!!



Philip

before i give my input a little insight into motors and phase converters may help you in alternative solutions. 1) a rotary phase converter is nothing but a 3 phase motor with a start circuit for a single phase motor attached to it on either a momentary switch or a relay that senses current or voltage differential. 3 phase motors run on single phase as long as you have some method to start them either mechanically or with a phase shifted signal (like a single phase motor) but will have some derating. since a rotary converter and a 3phase motor running on single phase are the same thing all 3 phase motors in the circuit can act as supplementary phase converters so for this reason the phase converter only has to be rated for the largest motor you plan to start so you don't need to size the converter for the 7 hp of motors to support, only the 5hp of the compressor you want to start so maybe you could get away with a 7.5 hp converter instead of 10hp.

2) many motors are built on very standard dimensions and have parts interchangeability. the difference between a single phase and 3 phase motor are a.) the windings are arranged differently. b.) single phase motors tend to have a centrifugal switch that kicks out the start winding so the external controls can be simple. so it is possible to convert a 3phase to a single phase by having the housing rewound or replacing the housing from a similar single phase motor (i did this once but the machine has a unique output shaft making an oem replacement motor cost prohibitive.) but without the centrifugal switch you will have to use a potential relay since it has automatic start so a momentary switch is out of the question. this is probably not a good solution for you as the relay selection is hard to find information on. but maybe a local rebuilder knows or will do an exchange of the old motor towards a rebuilt single phase.

3) you haven't considered a static converter for the compressor. a static converter can run as cheap as $50 on ebay but i'd budget $100-$150 and should be fine for a compressor. i just don't like them on machine tools.

a $125 static converter for the compressor (or maybe the same for a motor exchage towards a reconditioned motor) and a $255 vfd may be a good idea but the rotary offers future support for more machines. so i'm not suggesting one or the other but i think i would like a vfd for the mill so even if it didn't make sense i might do it anyway.