Thread: Hercus 3 phase lathe, single phase supply

I think I would need a 3hp single phase to replace the 2 HP 3 phase though .
from what I have been told single phase dosen't have the torque that 3 phase does ,so I would need to up the horse power.(I assume)
And I'm not after the variable speed , just single to three phase power step up.

Pics of the brute

Kev.

Originally Posted by Woodlee

I think I would need a 3hp single phase to replace the 2 HP 3 phase though .
Kev.

The saw is looking real good Kev.
A 3HP single phase motor should do the job nicely.
Like this one http://cgi.ebay.com.au/Crompton-3HP-...742.m153.l1262

Hey guys, I pulled the motor out and modified to Delta, fortunately the star point was easy to get to on the stator. The VFD arrived and it works just fine, I'll put it all back in the lathe tomorrow.

The only issue I presently have is that the VFD trips the RCD so that's a shame. I'll have to work out what I'll do about that, maybe an isolation transformer. The only other thing I noticed is the high frequency pulses to the motor make a very distinctive noise. I guess I'll get used to it. Once again a very cool way to control a motor in my book.

Edit: I've since learnt that VFDs will quite often be incompatible with RCDs. Apparently there are special RCDs available for use with VFDs but I doubt I'll bother going down that track. I may try floating the VFD itself and keeping the lathe and motor earthed for operator protection.

Kev, personally for something like a hacksaw I'm not sure I'd be bothered with a VFD unless you want to do it for the exercise. If it were me I'd just throw in a single phase motor and be done with it. In my case I wanted to be able to vary the speed more than the lathe's pulleys allowed and also reverse the lathe, the soft start is nice and I could keep the original motor if I do finish up doing a complete restoration.

Pete

NC ,
Thanks for the link ,I will consider a single phase as well , that 3 ph motor may be too old for a vsd .

Kev.

When choosing an option it comes down to a few things.

1. How much power you have available
2. How much it costs to connect to utility 3 phase
3. What machines you want to run

It is often a very viable option to change to a single phase motor rather than buying a VSD (VFD) or a Rotary Converter. It is dangerous to use plans to make rotary converters if you havent got the electrical and electronic background and I would advise against this.

VFD's can only be used for one single motor, whereas a rotary converter can be used to power multiple loads. Therefore, if you had a converter rated to 22kW you could run as many machines as you wanted up to that load rating, and probably more if you start them at different times.

It all comes down to your personal application. If you have bought something cheap second hand as a hobby, you might as well change the motor, but if you need power and reliability, then rotary converters are the way to go.

The best thing to do is to look at all the options and decide which is best for you.

Tom
www.phasechanger.com
[email protected]

VFDs are very different animals to phase converters. Sure they may ALSO convert single phase to 3 phase but their main function is to CONTROL the motor. Something neither phase converters nor changing the motor will do.

Following the experience of fitting the VFD to my lathe, unless there was absolutely no advantage in soft start/stop, variable speed, fwd/rev, etc etc, when faced with a situation in future of needing to power a 3 phase motor off a single phase supply I'd once again fit a VFD in a heartbeat and leave the phase converters for the ark!

Originally Posted by Woodlee

I think I would need a 3hp single phase to replace the 2 HP 3 phase though .
f

Hare & Forbes have a 3.2hp 240V motor on special at $209

Sorry I forgot.

By the way, for those of you who decide to change their motor from three phase 415V to single phase before buying anything make sure that you ramp up the rating of the motor a little bit. If you use a 3 phase 415V machine rated to 3HP, you would need to at least above 4HP single phase motor. If you simply put a 3HP single phase motor on, you will get a third of the torque that you had on the three phase motor. This will result in eventually burning out your motor, which you can't have too often

Also, a little extra advice. If you are buying a new single phase motor that is a bit bigger in HP than the three phase you were going to use, you must make sure that the flange (the area at the front of the motor that bolts on with the shaft) is the exact same size. If the shaft is different, it will not be able to run that machine. Sometimes changing across to a single phase motor can be a lot harder and trickier than you would think. Please make sure you get the flange right if you decide to do this, it will save you a lot of trouble.

Kind Regards,

Tom Fraser
[email protected]

Originally Posted by Vernonv

Hi Pete,
I also responded in your other thread in the reno forums. I assumed the VFD outputted 3 x 240V (240V phase to neutral) and Fossil is assuming it's 240V 3~ (240V phase to phase). I'm not sure who is right, but I think you will need to check out the VFD specs a bit more closely to determine what they mean by "3 x 240V".

If my assumption is correct then the motor will work without modification. If Fossil is correct then it will need to be modified as he mentioned.

As an aside (and as everyone else is mentioning phase converters) - I built a static phase converter for my workshop that cost much less than $100 (I had a lot of the parts). It runs off 240V split phase (480V) and can run my saw (7.5HP) scriber blade (1HP) and dust extraction blower (3HP) all at the same time ... and I didn't need to reconfigure the motors to run 240V 3~.

Static Phase Converters work for some machines like saws where it doesn't matter how smoothly the machine runs. Because a static converter uses no pilot motor, and instead uses the motor of the machine itself to produce the third phase you will end up with a third less of the power from the machine. This results in very poor balancing on the application, and a very very rough run whilst using the machines. As outlined, your saw would handle this rough running with no issues, as a lot fo woodworking machines would. But if you are looking at Mills, Lathes, etc. that need to have a smooth run you would be very silly to contemplate using a static converter.

Originally Posted by PhaseChangeConv

Static Phase Converters work for some machines like saws where it doesn't matter how smoothly the machine runs. Because a static converter uses no pilot motor, and instead uses the motor of the machine itself to produce the third phase you will end up with a third less of the power from the machine. This results in very poor balancing on the application, and a very very rough run whilst using the machines. As outlined, your saw would handle this rough running with no issues, as a lot fo woodworking machines would. But if you are looking at Mills, Lathes, etc. that need to have a smooth run you would be very silly to contemplate using a static converter.

Woodworking machinery or not, I have not noticed any significant rough running of the motors - I find my 7.5hp table saw (with a 300mm blade) a hell of a lot quieter than my old Triton table with Triton saw fitted. I might have to try the "glass of water" trick to see what sort of vibrations I am getting.

Here's something to contemplate - if I run both the saw (which includes 2 motors) and the dust extraction all off the one static phase converter (which I do), doesn't it effectively become an RPC? If so, which motor is generating the 3rd phase?

Originally Posted by Vernonv

Woodworking machinery or not, I have not noticed any significant rough running of the motors - I find my 7.5hp table saw (with a 300mm blade) a hell of a lot quieter than my old Triton table with Triton saw fitted. I might have to try the "glass of water" trick to see what sort of vibrations I am getting.

The Triton saw uses a completely different type of motor called a "universal" motor. A universal motor is the 2 stroke of electric motor; revs high, doesn't have a lot of torque, and makes lots of noise Your 3 phase table saw is more like a diesel motor, slow revving and very torquey. A single phase induction motor is like a bog standard 4 stroke; find them everywhere and they do the job, though not as efficiently as is possible. Each type of motor has its place, universal motors are small and light, 3 phase induction motors smooth and efficient. Depends on what you're trying to achieve.

Pete

Hi Pete,
True and I realise they are different types of motors, I was merely trying to make the point/comparison that the noise/vibration from the panel saw (running on the phase converter) is significantly less than the noise/vibration from a standard hand held saw.

With the panel saw running, I don't even need to have hearing protection on - it is that quiet.

I personally think the vibration issue is a bit of a furphy (even with metal working machines). Most decent machines use a lot of cast iron and are heavy. The vibration caused by the (relatively) slow speed of the motor would have minimal (if any) effect of the accuracy of the machine.

Hi Vernon and other subscribers,

Tom has been having his input on this forum and asked for me to do the same.

I am assuming your static converter has been made to start your 7.5hp saw. In this case the capacitors required to create phase offset/motor start ability must be sized to suite that motor. Are you able to use your static to start just the dust extractor? Or do you have to start the large saw motor first and the other motors after this? Again I assume this would be your procedure and this 7.5hp saw motor is essential acting as the pilot motor. The other smaller motors are simply feeding off this system to operate. Please correct me if I'm wrong.

There are a number of draw backs using static converters, one being their inability to offer any phase balancing resulting in poor voltage symmetry. Measuring voltage between phases both when your static is running just the saw motor and when running the other motors with it will show the effects of multiple motors being run.
As I said static's will have poorly balanced phases supplying the motor they been 'sized' to run which is usually made worse by each additional motor run with the same static. Static converter manufactures data shows they build a static to suit a certain size motor, i.e. a 4kw static converter is designed to run a 4kw motor not a 1kw motor. However if you are willing to test the limits of this design you could possibly start the 4kw load and then start 1kw load too, it may work but the phase balance will end up as I've mentioned above.

Metal workers who are aiming for a 'smooth' high precision finish on their work will not have the luxury of ignoring any imbalance in phase's being produced by there converter. There is a good chance that work will not be as well finished as it would with a well balance mains power or rotary converter supply. Worst case scenario poorly balanced phases can be damaging to three phase motors, although they're tough they're not indestructible.

The reason I've covered all this is because although the static converter design may meet your needs Vernon it is a long way from the 'best' solution available, and will definitely not be a good option for all.

I'm all for DIY when it comes to using wood or metal work machinery... But if it hasn’t already been mentioned converters use high voltage capacitors not to mention 240V/415V mains power, anyone considering the home built converter should consider if they value their life enough to save a few dollars over buying something professionally built and safety tested. I would not recommend anyone who is not a qualified electrician to be building any type of power converter, it is illegal. Anyone who jumps on a forum and assists someone in risking their life playing with electricity should consider their own liability let alone their conscience if something goes wrong!

Many hobbyists and most small home business's are going to add to their equipment at some point so it's good to have a solution which will allow for this. Unfortunately a static converter will offer little to no flexibility on different motors or machines it will run.
A quality designed and manufactured rotary converter will offer not only this flexibility but the ability to balance phase's under any, even changing load conditions. For example a 4kw power converter will have the ability to start and run motors from .1kw to 4kw as well as the ability to run any number of motors up to is rated output (i.e. 4 X 1kw motors).

I could make comments about the VSD/VFD solution not being everyone (or ideal for some) but will save that for now as my post is already too long.

I look forward to everyone's comments.

Kind Regards

Ben
[email protected]

Hi Ben,
The 3 motors I have in the system are a 1HP scriber motor (in the saw), the main saw motor (7.5HP) and the DC motor (3HP). Note that I run the static phase converter off 240V split phase (i.e. 480V).

I originally sized the capacitors for the 7.5hp motor, but I can start either the 3 or the 7.5 motor first without a problem. The 1hp normally gets started after the saw is running, so have never started it first.

Yes, I agree that the static phase converted is a trade-off in regard to voltage balance, but from my experience this has not caused any issues, such as vibration, overheating, breakdown, etc.

What I'm getting at though, is that once the first motor is started my system effectively becomes a rotary phase converter. Any additional motor that is started also becomes part of the rotary phase converter "system" and it is my understanding (which could very well be flawed) that all motors in the system share the job of generating the 3rd phase, not just the "pilot" motor.
This "sharing" is as true in my system, as it is in your system?
Note that I don't dispute, and recognise that your systems would be producing a higher quality result than mine ... I just trying the learn/understand and maybe help others.