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Running a big machine from a domestic supply

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SamI

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#1
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
 

Richard King 2

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#2
Back in the old days when shops were underpowered we would hit the start switch and shut it off and then start it again and again to get the motors coasting or speeding up slowly so all of the amps were not pulling from dead stop and blow a fuse. As the momentum was spinning up or RPM's were up there we would let it run.
 
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Cobranut

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VFD drives are available up to whatever power level you want.
We have them at work that can run 5000+ HP motors.
The only issue is cost, and the current capacity of your 240v single phase supply.
A 6 HP motor should draw around 4500 watts, so a 240v 20a circuit should handle it fine.

And yes, you'll want a separate VFD for each motor. A small one for the feed motor is dirt cheap
Motor leads should be connected directly to the VFD, and all the control done through the VFD's circuitry.
This allows you to program soft starts and stops, which minimize current spikes, and are also easier on gear-trains.

I installed 2 VFD's on my Rambaudi mill.
For the feed motor, I used the original drum switch to a remote input to start/stop the motor.
For the spindle, which I want to control speed via the VFD, I'm replacing the drum switch with a bracket for the VFD keypad, and will control it from there.
 

Cobranut

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#4
Also, you could probably run a 6hp motor on a 3hp VFD, but you'd have to program a very gradual startup, and of course, it would shut down on overload once you exceed approx. 3hp of load on the motor.
 

SamI

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Thank you both for your input. I guess the VFD programming is the more sophisticated version of Richard’s suggestion. Still trying to decide whether this will be a good buy or not. I suspect it is waaay to much machine for my current requirements and I am a little concerned about the max spindle speed of 1400 RPM – not sure how well that will play with small diameter cutters in softer materials such as aluminium.

Assuming the cost for a larger VFD wasn’t silly I’d probably choose to go down this route just to be on the safe side.

Thanks again for your help with this. Now I just have to wait and see how much they're wanting for it. It's an old toolroom machine from a company my employer has just taken over so I'm hoping the powers that be sympathise with my desire to fill my single garage with machinery top to bottom!
 

JimDawson

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#6
There are single phase input capable VFDs that will handle a 6 HP motor. A 10 HP VFD would do it. But given that you have several motors that require 3 phase, a rotary phase converter might make more sense.

My biggest concern is the low RPM of the spindle. It sounds like the machine is designed for some heavy duty milling with large cutters. 1400 RPM might be a bit light for small cutters in soft materials.
 

SamI

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That is good to know about the rotary phase converter.

I agree about the spindle speeds. I don’t do much work in aluminium but I probably care more about versatility than stock removal so it would be nice to have a larger range of spindle speeds. I have been told that there may be a Bridgeport going from our tool room and another mystery milling machine from another facility in the not so distant future so maybe I am better off holding out for that. I’ll still require a phase converter so this is all still really useful stuff!
 

ttabbal

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One option is to set up the VFD to supply higher frequency at the top end. I do this with my grinder and mill and it works great. The motor on the Bridgeport looks original and it handles it fine. The grinder is a modern inverter rated motor. 2x speed should work fine for most anything.

I don't know about your area, but around here rotary converters are stupid expensive. I just use the ebay Chinese VFDs. I have 3 of them now and they work great. The Bridgeport has the old gearbox power feed, so it needed its own.

I'm a noob, but wouldn't slower spindle speed just mean it would take a bit longer? Perhaps not ideal, but for a hobby user it wouldn't be the end of the world.
 

pacifica

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That is good to know about the rotary phase converter.

I agree about the spindle speeds. I don’t do much work in aluminium but I probably care more about versatility than stock removal so it would be nice to have a larger range of spindle speeds. I have been told that there may be a Bridgeport going from our tool room and another mystery milling machine from another facility in the not so distant future so maybe I am better off holding out for that. I’ll still require a phase converter so this is all still really useful stuff!
A vfd could allow you to overrate the motor by as much as 200% and also slow down to as low as 25 to 50%, that might take care of the spindle speed issue. If you have the room a big mill is very nice to have.With a modern DRO , rotary table ,spin indexer ,and dividing head there is a lot you can do.
 

benmychree

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There is nothing wrong with milling at lower speeds that production work may dictate, no need for high speeds for hobby work, and I'd just go with a rotary phase converter, for my shop, which has motors up to 7-1/2 HP, I made my own rotary, using a 5 hp motor and a static phase converter to start it, and added oil filled capacitors to balance to phases, it was cheap to make and works well enough.
 

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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.
 

Cobranut

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markba633csi

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#13
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
mark
 

Dabbler

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#14
-- 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.
 

SamI

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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
mark
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?
 

Cobranut

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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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TheArsonSmith

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#17
I used a really cheap VFD to get my Clausing 1500 up:

I'll post a more detailed video on how exactly I wired and programmed it in the next day or two.
 

NortonDommi

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#18
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.
 

Blackjackjacques

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#19
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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