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Old 10-27-2020, 11:35 AM
cliffrod cliffrod is offline
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Default VFD vs Rotary phase converter

I've spent recent months adding 3ph equipment- 1hp milling machine, 1hp 14x40 lathe and 3hp Gairu (pullmax)- to my 1ph metal shop. been doing lots of searching & reading but have not found good clear info about how to match a vfd to each machine or the realistic costs of doing so. I'm also not clear if I will need any additional components to accompany a vfd for each machine. some China/internet prices are dirt cheap. USA (preferred) prices are higher, Surplus USA units seem like the best deal but not sure how to match specifications to buy the correct units if I can find them surplus.

speed control via VFD would be nice on my Gairu, but the lathe and mill are probably not as big a deal. Not much interest or room to add many more machines.

So I'm leaning towards doing a proper 5hp rotary phase converter with capacitor-balanced output that will provide a 3ph circuit in my shop to run an individual machine as needed. That should keep costs around $200-$300 total, versus what seems like at least $200-$300 per machine for vfd. What have others experienced as real costs of installing a vfd on each machine? I'm not talking about once in a lifetime deals, but normal prices/costs to be expected. I would like to get my machines going this winter.
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  #2  
Old 10-27-2020, 11:55 AM
Overkill Overkill is offline
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Default Just went through this

My rotary phase converter is from American Rotary. They are very helpful and have a lot of information on the website. Including calculations on how large of a rotary phase converter to buy. From experience, go with 10HP or more. You can run two smaller 3ph machines at a time, or up to a 5hp.
Pros - you get full power out of your machine
Con - no speed control, and you have to go turn it on and off each time you use it.

VFD's - you'll need one per machine. I bought mine from Kent Martins, KMartins@valin.com (tell him John Alden sent you) and he was very helpful. I purchased VFD's that let me supply single phase power to the 3 phase machine. Only issues with VFD's are, when you slow the machine down, you do loose some power. However for me the control is worth it. I have VFD's on my Pullmax, Mill, bead roller, and I'm considering adding it to other machines. Overall, the expense is more, but for me, the speed control is worth it.
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  #3  
Old 10-27-2020, 01:04 PM
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mr.c mr.c is offline
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Clint: I use both rotary and VFD. There is no need to have a vfd for each machine. I bought my Mitsubishi years ago. It came prewired with a remote control box that gives me speed control via a rheostat, motor rotation(needed for Bridgeport if in back gear) and , of course, on off buttons.. I converted my old South Bend lathe from 120V to a 3 phases so that I could have speed control. I put plugs on the leads and just plug in whatever machine that I need to run.

The only precaution with the vfd is that I taped over my control switch at the machine. Cutting off the load on a running vfd is supposed to do bad things to the vfd. The control pendant is on a long cord that I move to whatever machine that I am running.
I still use the rotophase to power my P9 Pullmax and my Hardinge HLV-H lathe. There are so many parameters available on vfd's. Soft start,braking,etc. Not to mention speed control parameters. I have not gone beyong 60 cycle on mine. 400 cycle is available. That could be a good chance to grenade a motor.

So I use the VFD to run my Bridgeport, two of my lathes,my vertical bandsaw, my surface grinder. I use the rotary on the Hardinge lathe because the controls change to two speed motor and the power lever is necessary to use full capabilites. Plus it has a variable speed capability on its own. The pullmax has a five hp motor and a electrical shift four speed transmission. Pushing the limits on my VFD.

Size the vfd to the largest motor. Some require twice the rating when converting single phase to three phase. Something to check.
Also, the wild leg on a rotary can put up some interesting voltage. Probably conditioned on the capacitors. I have A 10hp rotary that I have never used. The wild leg was about 275v , as I recall. It had a capacitor bank that I could probably jockey arounf to get a lower wild leg voltage. Wild leg is the one generated by the 3 phase motor and the capacitor. Building your own rotary is doable. It is just a 3 phase motor sitting there running with a capacitor to pull the wild leg. I am sure there are YouTube videos on how to do that. Some are not self starting. My commercial rotary is. Homemade ones may require a rope start.
Also, when I first got my Bridgeport, It came with a static phase converter. Not the way to go. It made a momentary 3 phase just to start the motor. For it to be able to run the Bridgeport, I had to also turn on my surface grinder that was wired in. The 3 phase motor on the surface grinder helped generate the third (wild) leg. So I had two machines running while I was using one.
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Last edited by mr.c; 10-27-2020 at 01:21 PM. Reason: typo--and additional comments
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  #4  
Old 10-27-2020, 08:26 PM
Ryan in Melbourne Ryan in Melbourne is offline
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i have done a VFD conversion on my lathe.


the motor was originally 440v 3 phase in a Star configuration.
i had to open the motor up, find the star point in the winding, and bring that out to a terminal board so that i could connect it up in a delta (triangle) configuration.

After that i was able to bring the 3 phase leads of the motor up to a Danfos VFD microdrive. This is connected into a 240V 15a single phase wall socket. I have added a small electronics control panel to it. This allows me to control speed, direction, emergency stop overrides and also gives me access to a low speed jog function which is handy when threading up to a shoulder.
The Danfos mocrodrive also has the functionality to electrically brake the motor. You need to add an external high wattage resistor to it for this to function. It would allow the chuck to stop spinning a lot faster and prevent it running on when the motor is switched off. the excess momentum would then be converted into heat in the resistor.



I am yet to do this though. Another one of those jobs that i need to get around too. another $40 or so for the resistor. think the VFD was a few hundred. I just matched the VFD rating to the motor rating. think its a 3HP motor, cant remember.



Downsides is that the coolant pump is also a 3phase motor so i haven't got that running yet. your coolant pump may also require a 3 phase connection. So factor that into the calculation



Ryan
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  #5  
Old 10-28-2020, 06:09 AM
cliffrod cliffrod is offline
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Thank you, sirs. This all helps. I can envision the greatest benefit of a vfd on my Gairu. Wasn't sure about the details of using a single vfd for varying machines because of matching issues between the vfd and machines with different size motors. Planning for extra capacity makes complete sense, but the room for more equipment isn't there. A local motorcycle friend has a 10hp store-bought rotary converter, but still likes it too $$ much. The way he describes it, that 10hp unit alone will consume one more machine-sized footprint.

No worries, Ryan- My lathe is very basic, so no coolant pump issues. It's so old it doesn't even have a compound slide...

Any more info always helps.
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  #6  
Old 10-28-2020, 08:42 AM
metal manny metal manny is offline
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As others have mentioned, I too run a VFD around my workshop and run multiple machines off one drive (220V single in, 220V 3-phase out). A neat connector I utilise is the generator plug/socket combo as depicted below. I also use the original on-off switches situated on my two Pullmax's to operate the machines, and have suffered no adverse effects from not using the start/stop controls located on the drive to do this.
Get the VFD with the highest output your wallet can handle, or at least one that has an output matched to your biggest motor. Also preferably a VFD with a built in potentiometer which will allow you to manually vary motor speed on the fly. Most, if not all manufacturers support the retro-fitting of a potentiometer, so not having a built in one shouldn't be a deal breaker, but will need some elementary electronics knowledge.
Lastly, you should only run your motors in delta connection as someone else has previously stated.
Best of luck!




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  #7  
Old 10-28-2020, 10:35 AM
cliffrod cliffrod is offline
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Quote:
Originally Posted by Overkill View Post
. VFD's - you'll need one per machine..

Quote:
Originally Posted by mr.c View Post
There is no need to have a vfd for each machine. The only precaution with the vfd is that I taped over my control switch at the machine. Cutting off the load on a running vfd is supposed to do bad things to the vfd.

Quote:
Originally Posted by metal manny View Post
As others have mentioned, I too run a VFD around my workshop and run multiple machines off one drive (220V single in, 220V 3-phase out). I also use the original on-off switches situated on my two Pullmax's to operate the machines...
This ^^^ is the reason I'm asking for advice and still studying the solution. I have no reason to doubt or mistrust any of you. It's just the opposite. I value your opinions greatly and know that I can trust your experience & advice. No matter, I am more familiar with the likelihood of me choosing the one combination that will guarantee unwanted issues in the future.

Comparable differences have been found while studying the assembling of a rotary phase converter for the past year+, from the "all you need is a rope to start the spare 3ph motor for the third leg- i did it like that for years" to fine tuning the generated leg voltage and maintaining idler motor rpm with proper capacitors to protect the machines' motors and stabilize operation.

The input is much appreciated. I'll keep studying. Maybe this thread can help others as well.

Edit- I realize that this is China unit, but is something like this what I would use to use a single vfd to provide a 3ph circuit in my shop? https://www.ebay.com/itm/UPDATED-7-5...&ul_noapp=true? I can see a more modern lathe at some point, possibly in the 3hp range. A vfd to vary speed on my Gairu is the biggest benefit I see, but if it's going to be across the shop & back and forth to use it, that seems nuts. The current lathe and mill will probably be fine with a simple rotary converter.
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Last edited by cliffrod; 10-28-2020 at 10:58 AM. Reason: See edit
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  #8  
Old 10-28-2020, 11:08 AM
Ballantino Ballantino is offline
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Get both. Put the money in the VFD and build your own rotary from a used motor. I have my mill and bandsaw running off the same VFD. They are hardwired to a box on the wall containing the VFD, contactors and switches. I use switches to set which machine to use. Use 7-wire doorbell wiring (low voltage) for the on/off and speed control. Size the wiring for the motor appropriately. My Lathe is a clutch engaged machine which means the motor stays running while I use it. That made it easy to just run it on two legs and use capacitors to bump start it. I oversized the motor in it to compensate the loss - the original motor was toast anyway when I bought the lathe. I could also pull power off that machine to run other machines (with dirty 3 phase) if needed. Using run capacitors to clean up the power only works for the range that the machine will see the most. You will have to "tune it" for that range. I don't bother and everything works well.
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Old 10-28-2020, 05:03 PM
norson norson is offline
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I was faced with the same issue a number of years ago. My lathe had a 10 hp 440 motoring it also had a 440 lubrication pump. I bought a rotary phase converter KIT off eBay and found a 15 hp motor 220 to complete it. The motors on the lathe were nine wire so I just rewired them for 220. Since then I've purchased a Trumpf CS75 that is also 440, but with the main motor being a three speed and having two other motors plus ton of the electronics, I decided to use a transformer to adapt the 220 line to the 440 machine. I use VFDs on my Lennox nibbler and Bridgeport mill. I have several other 3 phase machines so the RPC is really necessary. I ended up not assembling the original RPC because I found a completed one on Craig's List with motor for $300. Still have the original if anyone needs it.
In my research I found that a 5hp RPC would power a 3hp motor, a 7hp RPC would power a 5hp motor, etc. If it was me I'd go at least 7hp.
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Old 10-29-2020, 07:44 AM
Refuse1 Refuse1 is offline
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I've have had great success with this VFD on multiple machines 3HP and below.

https://www.amazon.com/gp/product/B0...d6b1bfbee&th=1
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