Running a big machine from a domestic supply

At somewhere around 6HP, depending on your source, begins the transition where rotary phase converters begin to make sense. If you are bujying 2 VFD untis to power the machine, then a RPC is clearly a way to go - but -you lose the ability to control the speed directly or do overspeed. It easy hobby way is to VFD the main motor, ans use it wothout the power feed for a while, gaining the advantages of a VFD. THEN you can add a second VFD when you cna afford it, allowing the power feed.

A word of caution: It can be tricky to run two motors on one VFD. I would shy away from running your 6HP motor on anything less than a 6HP VFD. The impedance and the inductance are our of spec for the VFD, and can affect its operation. I'm not saying it can't be done, but it can be expensive if you damage your VFD.
 
Hi Sam: finding a VFD with single phase input/ three phase output with 6 HP (or higher) rating might be a challenge- do some online shopping first before you decide
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-- Cobranut, I was referring to all US sourced equipment. A Westinghouse TECO VFD at 7.5 HP is about the same price as a Rotophase at a similar HP rating... at least it saves the cost of a second TECO.

I've never purchased any electronics from aliexpress, so I'm not the right guy to comment on that option.
 
Hi Sam: finding a VFD with single phase input/ three phase output with 6 HP (or higher) rating might be a challenge- do some online shopping first before you decide
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I have seen a few available however all bar one is of Chinese origin from Ebay sellers. I’m not saying that they’re no good because of that but I do worry if they’re claiming that their units can do something that reputable brands cant.

Looking into it a rotary phase converter does seem to make sense and it looks as though these units are plug and play so there would be no fettling with the machine (a bit of a bonus for me as while I have the mechanical skills to be able to do this I am at a loss when it comes to electrical knowledge!). The down side to these is that they are quite expensive – likely to be more than I am hoping to pay for the machine.

As for the spindle speeds – some have mentioned that it’s OK to run a little slower. I’m not sure if the same applies with milling but I turn a lot of stainless on the lathe and BUE is a major problem for me if I’m not running the machine at a high enough speed. Inserts can fail to give acceptable finishes after only minutes of cutting. If I predominately used HSS cutters on the mill this would be less of a problem but presumably if I were using small diameter end mills then this could presumably lead to rapid tool breakage, or am I just making a mountain out of a molehill?
 
Thanks Dabbler,

If I were running these machines commercially, then I'd certainly look into higher quality electronics, but it's only for hobby use.
Both the 3HP VFD's I have work fine so far.
I'll be adding a third one on my lathe, so if one burns up in the middle of a project, I can always swap in another and order a replacement, considering they're under $100 each.

I don't particularly like purchasing stuff from China, but when the cost of US parts is multiples of the Chinese stuff, it's hard to justify.

For major stuff like vehicles, that I depend on every day, I do buy American, or at least from US based companies.
 
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I am picking up some Transformers next week to rewind as auto-transformers to power some 3~ machinery. This is my first foray into this but I have read a bit about it in the Workshop Practice Series of books particularly #47'Three-Phase Conversion'. I have done the capacitor hook-up one 240 V 1~ but from what I have read doing it with 415 V works a lot better. I have also seen a book that I will purchase soon from Unique 3-Phase.com
https://unique3phase.com/ They have an interesting website. I'd love to be able to just go and buy a few VFDs but the budget is very tight.

TheArsonSmith, Nice video, you make it look so easy.
 
Hi all,

I am hoping some one can offer some advice. It may have been asked before but I can't seem to find a simple answer!

I have the opportunity to buy an Ajax Cleveland No 2 mill which I am very tempted by if the price is right. The only thing I am not sure on (other than how to get a 2000 Kg machine into my garage) is how to power the thing.

I am led to believe that it has a 6 hp motor plus a 1.5 hp motor for the power feeds. I have a 240 volt single phase supply to the garage. A (very) quick google would appear that a VFD phase converter on a 240 v supply is only capable of powering a 3 hp motor. Would this mean that the motor won't run or that it would simply be under powered? Or am I missing something all together? Would I need two separate phase converters, one for the motor and one for the power feeds?

Thanks in advance for your help. I've been putting off looking into three phase for a while now due to fear of the unknown but this machine has the potential to be an offer too good to miss out on!

Sam

Long before VFD's, Reduced Voltage Motor Controllers (RV) were used to address the problems caused by motor inrush currents. They used either tapped inductors or resistors to permit the motor to start and minimize voltage dip and sag that would affect adjacent systems. They do make solid state RVs and that can also be used for speed control as well. Once the motor starts and is running, timed contactors close to put the motor across-the-line. If you are looking to minimize inrush currents, then you need a RV. If you are looking for speed control as well, then you need to make sure the motor is VFD rated. You should easily be able to start and run 6 hp single phase motor with 240 single phase using a RV appliance. The 1.5 hp motor you can start across the line. The primary stipulation you need to insure when selecting a RV device for your 6 hp motor is that you can meet the starting torque of the motor and the RV's reduced tap.
 
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