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View Full Version : Hercus 3 phase lathe, single phase supply



Pete F
21st Jul 2008, 10:47 PM
G'day Guys, I FINALLY got my lathe, an ex high school Hercus. I don't have 3 phase to my property, and after investigation found it too expensive to consider. So with the lathe I could either put a single phase motor on it or I believe I can get a VFD off ebay and use that.

I have plenty of experience with electrons but absolutely zero with VFD. Is there any tips or advice available on using a VFD as a single to 3 phase converter on a lathe like this? I'm also wondering about the ability to reverse the lathe as it's imperial and any thread cutting I'd do would be metric.

Thanks,
Pete

Woodlee
21st Jul 2008, 11:36 PM
I am in the same situation at my place ,as far as 3 phase goes. I have been looking at a rotary 3 phase converter. It would be better to keep the lathe 3 phase from what I under stand they are smoother running with less vibration than a single phase ,some thing to do with phase balance or some thing.
I don't think a VFD is is the right device.
I have done some reading online regarding rotary phase converters and they are also commercially available .Not being a sparky ,I haven't really fully understood the concept.
I'm not into electrickety so I might be spouting BS here
What I have gathered is you feed 240 volt power into the 3 phase motor and use a single phase motor to get it spinning and the 3 phase motor out puts 3 phase.

There are discussions and instructions online to build them and how they work , some wiring diagrams as well.
Some one on this forum has also built one if I recall correctly .
Just do a Google for phase converter.

Kev.

pipeclay
22nd Jul 2008, 09:05 AM
Not knowing the cost of phase convertors or VFD's why not just go with the single phase motor and reverseing drum switch.

In regards to the mention of vibration of 3 phase / single phase wouldn't have a clue either.

In my opinion I would go for the cheapest allternative,but would try to have at least 1HP.

Pete F
22nd Jul 2008, 12:36 PM
As I understand it, the VFD converts either single or 3 phase input (depending on the model) to DC then back to 3 phase AC with variable frequency to control the speed. So I can't see any reason why not to use a VFD for 3 phase power.

I'm uncertain about whether the motor fitted will be suitable however. It looks to be the original, branded GMF. I have no clue about star and delta windings but the 3 wires from the "guts" of the motor into the terminal box on the motor simply terminate at standoffs, ie there is no possibility to change connections there that I can see.

As for the motor size, they are remarkably small, the standard motor is 0.5 hp

Cheers,
Pete

DavidG
22nd Jul 2008, 05:02 PM
If it is only 1/2hp then the cheapest option would be a 3/4 hp single phase motor with reverse.

(3 phase has more torque than single phase so you need a bit bigger motor)

Other options are as given above and the old faithful, a seperate 3 phase generator which is always useful. :;

NCArcher
22nd Jul 2008, 07:08 PM
Not all motors are suitable to use with a single to 3 phase VFD conversion.
In this case the cost of either a VFD or a rotary phase converter would be significantly more than a 3/4 or 1 HP single phase motor.
If possible find a motor that has the same size shaft as the old motor so you can reuse the pulley.

matthew_g
22nd Jul 2008, 07:29 PM
Hi there,Phase changers are the way to go.As mentioned above the best choice is a rotary phase converter.These range in price according to the size you buy. I have just bought one and the costwas $4800 this includes having a sparky come and wire it in.My pase converter will run my lathe and mill as well as my 350 amp welder.the best place to go is phase change converters australia they have a good website with all you will need to get started.I hope this helps you a little

etd
22nd Jul 2008, 09:20 PM
G'day all
Agreed the Phase Changer rotary converter is good, and gives approx 415 volts per phase, so standard 3 phase motors can be used. As I understand it, VFDs put out 240v per phase, so the motor needs to be 415/240. However, unless you will be using several machines with 3 ph motors the price of the converter probably is a bit much. I would go with the single phase, my old Model A has a half horsepower and will slip the belts before the motor is distressed. The belts flapping around and runout on the pulleys will give far more vibration than the single phase motor.

Evan

Greg Q
23rd Jul 2008, 12:17 AM
I have a homemade 7.5kw rotary phase converter...less than $500 to make yourself which is of course illegal here or something. Plenty of plans and info online.

Three phase power on a lathe or any machine tool is a good thing. You do get better surface finishes because the torque is more evenly produced as the shaft rotates...kind of like a three cylinder radial engine compared to a one cylinder engine, if you pardon the crude analogy.

VFDs seem to me to be the best way, hands down, of converting single phase to three. The current biggest three phase that you can power with an easily purchased VFD is 3 hp, although Polyspede in the US have 5 hp and greater models.

Phase converting VFDs come in 240v single phase input. This you need a 240v three phase motor. (A motor that is 415volt star connected can be configured 240 volts via the delta windings. The biggest motor that you are likely to find in Australia connected 415 star is maybe 5 hp or so. (Not a factor for you).

Since the modern VFDs can drive a motor at very slow speeds some alternate cooling method for the motor must be provided...the shaft driven fan obviously does not do an adequate job at low speeds. Hence the point that not all motors can be used with a VFD. They can't, but fitting a separate fan takes care of that.

VFDs also allow you to select speeds via a potentiometer which can be mounted in a convenient place. Reversing can be done using any old low voltage switch wired through the vfd's control terminals. They also have provisions for variable stopping time on the spindle...a nice thing to have with a screw-on chuck.

I am in the process of restoring a toolroom lathe and I have to use a VFD for reasons unrelated to this topic. So far the best prices are ex-USA (even shipped) I find it difficult and stupidly, wildly expensive to find a 240v VFD here.

Some brands that I would consider are: Teco (Westinghouse) Ac Tech (Lenze) and Hitachi. Sometimes eBay will yield a Danfoss, Allen Bradley or Sew Eurodrive. SEW make very good units.

It won't be a factor for you, but other readers should note that when powering higher power motors you need an over sized circuit because the inrush current is higher than nameplate current owing to capacitor charging requirements internal to the VFD. Those same capacitors dislike sitting on a shelf for years. If you purchase an old unused VFD it pays to Google "reshaping capacitors". Generally giving power to the unit for 12 hours or so without running the motor will do it.

Good luck with your decision!

Greg

Pete F
23rd Jul 2008, 11:20 AM
G'day Greg, I took a chance and purchased a SEW single to 3 phase VFD. The specs suggest matching VFD to motor size so this 0.5hp one should fit the bill. However I'm just got a bad feeling it won't be that easy :U

The motor is the original and have confirmed it is definitely star configured (with no option for delta). The output from the VFD is quoted as 3 x input voltage ie 230V

I'd definitely like VFD with not only the variable speed part but soft start/reversing etc. I'd much rather do that electronically than starting and stopping a motor at full voltage as I'm sure it must put a strain on not only the motor but also the gear chain etc etc. Bit like taking off from the lights with your foot flat to the floor, sure the car can do it but would you .... hmmm, I take that back, I live in Sydney and the answer is definitely YES from the way some people drive here :P

Cheers,
Pete

Fossil
23rd Jul 2008, 12:00 PM
Hi Pete.

Your little motor will be 415v star I suppose.
I also assume your vfd will output 240v 3~ which means that your .5hp motor will not run in it's current config.
Don't despair though. You will need to pull the motor apart and dig out the star connection. Solder three separately wires to these three and bring out to the terminal box. You now have the six wires necessary to wire it up as 240v delta 3~

I built a 4kw phase converter last year for my lathe, saw drill press etc. I wired my .5hp drill press motor as described above, and it works beautifully.

Here is a link to a thread discussing the build of the unit.
http://www.woodworkforums.ubeaut.com.au/showthread.php?t=52259&highlight=pahes+converter
Please read carefully though, and disregard some information that I posted that was incorrect. It was huge learning process for me, and I had a few teething problems with the technical side that were clarified by another forum member later in the thread.

I have recently upgraded the final unit as shown in the thread. I now run a 4kw 3~ motor from this unit to my bench saw. I installed another contactor in the unit, and controlled the cappacitance to start it from the starter at the saw. The extra caps only switch in to the curcuit while the saw is running, and the converter runs without these extra caps for my smaller machines. This way, I have balanced power over all three phases for each machine.... within 3% phase to phase.

Good luck. :)

Fossil
23rd Jul 2008, 12:10 PM
Hi again,

Below is a quote from Chris on another board. The instructions he gives in this quote is very close to how I went about the brain surgery on my drill press motor.


Hi Tim,

I've done this twice too (or once on a dual-wound two-speed machine in
fact). Firstly, you need to make sure that you have a machine which is
star connected for 415 V. If your machine is delta connected for 415 V,
you can't convert it to 240 V operation, but I'm sure that you already
knew this. Usually the star point is fairly visible once you've removed
the end bells and rotor. It will normally be inside some glass fibre
sleeving, tied and varnished to the windings at one end of the stator.
Get the motor off the machine and into a comfortable, well lit
location. When you've got plenty of time and are feeling patient,
carefully cut the cords which tie the windings together and identify
which length of sleeving has three wires leaving it (two from one end
of the sleeve and one from the other). This will be the star point.
Carefully slit the sleeving with a sharp knife and remove it to reveal
the soldered joint. You may or may not be able to neatly desolder the
joint. If you can't, cut the lacquered wire as close to the joint as
you can. Try not to nick the windings with your knife or nippers,
although if you do it isn't a complete disaster because you can paint
over the nicks with insulating varnish. Now take some emery paper and
draw it along the ends of the wires to remove the lacquer. Be very
careful not to bend the wire, or it may break. I broke a wire doing
this and only just had enough to solder onto. If it breaks near where
it enters the windings you'll have to get a rewind, so it's worth
taking your time here. Now tin some lengths of stranded wire to use as
your lead-outs. I used 105 C equipment wire from Farnell, but I
understand that the temperature rating should officially be higher. It
worked fine for me, though. I'd attach one lead-out to each of the
three wires at the star point, and take all six wires out of the motor.
I don't think it's worth trying to create a delta connection internally
when you can just attach two wires to each of the three terminals in
the terminal box. I fitted heat-shrink sleeving over my soldered
joints, tied everything together with thick cotton and painted it with
a bit of glass fibre resin. You can get proper insulating varnish from
Farnell if you want. My motor probably isn't quite standards-compliant
but it has been working fine for six years now. The whole job took me
about 3 to 4 hours as I remember.

Good luck!

Best wishes,

Chris

Vernonv
23rd Jul 2008, 12:57 PM
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~.:2tsup:

Pete F
23rd Jul 2008, 01:21 PM
Yeah exactly, I think it's quite confusing. As I read it, the VFD outputs 3x230V measured phase to neutral, which as I understand it, bit grey in these areas is just standard 3 phase????

Here is a link to the operating instructions http://sew-eurodrive.com/download/pdf/1056411x.pdf

The unit I have ordered is MC 07 A004-2B1-4-00 ie the smallest VFD they do.

Thanks for your time guys, much appreciate the input.

Pete

Penpal
23rd Jul 2008, 01:31 PM
I fitted a VSpeed controller to a 2 1/2 hp motor on my Woodfast Lathe, great, easy,Adjacent to the Lathe I had a 20 amp circuit 240 volt so it was uncertain what the start run current would be so I measured it at 7.5 amps start and run.
A single phase normal motor on start gives a short but nasty surge of thirty to forty amps ie a 21/2 hp one. The VS unit has a soft start that enables that frugal current on startup.
Now in America two things are different single phase is 110 and also 60 cycles, now a single phase motor run on 240 volts 50 cycles can be used on 60 cycles however a 60 cycles motor used here will overheat very quickly.
Two considerations when buying from the great USA then are current ratings and then cycles.
Another requirement in Aussie Law is a form of suppressor that is now included in the price here but not always to prevent a trouble locator knocking on your door with an irate neighbor with them to locate the souce of interference on their appliences such as Radios and T.Vs interference is against the law, mine cost me an additional 80 bucks at the time.
Have fun Peter:2tsup:

Vernonv
23rd Jul 2008, 01:55 PM
Hi Pete,
I've had a read of that manual and although it does not make it 100% clear, I'm now leaning to it being 230V 3~ i.e. 230V phase to phase and NOT 230V phase to neutral. maybe you should ring or email the Australian office to get confirmation.

Pete F
23rd Jul 2008, 02:12 PM
No it's not clear at all in my book. Thanks for looking at the manual. I sent an email to SEW but once sent see it actually went to Germany so who knows if/when I will get an answer nor if they'll understand what I'm on about. Will see.

I was trying to figure it out from the basics of how I understand they work from the block diagrams I've now seen. Taking the single phase input and converting it to DC you don't get 230V DC, I vaguely recall there's some formula for what it will be but more vividly recall goofing off in AC theory so wouldn't have a clue what it is. Anyway, converting that BACK to AC unless there's some transformers involved (and there isn't) you can't get the full 230V waveform, the maximum is just whatever that DC rail is. Soooo I'm thinking that it will be 240V phase to phase.

Having said that, I change my mind as to whether it will work about twice per hour. At the moment I sitting with "yes it will probably run but the motor will not achieve full power". Ask me again in 30 minutes and I'll have a different opinion however as the instructions DO say 3 x 230V and I would expect them to specify if that was between phases. The mystery continues ...turning into quite a saga this isn't it ;) May continue this over in Electrical thread as people there may be more interested in my waffle.

Fossil
23rd Jul 2008, 02:48 PM
I think you will find that it puts out 240v ~ to ~ and not ~ to N.

If it put out 3x240v ~ to N, they would advertise the unit as 240v single ~ in and 415v 3~ out.

Digging out the star point and hooking a motor up delta, only takes an hour or so. That's what it took me anyway. :)

DavidG
23rd Jul 2008, 03:58 PM
Sorry but all this seems like overkill.

A 1hp single phase motor will cost far less.

KISS. Keep is simple s.......

Vernonv
23rd Jul 2008, 04:08 PM
Sorry but all this seems like overkill.

Yes maybe, but having access to 3 phase (either directly or through VFD's, phase converters, etc) opens you up to being able to use/purchase other 3 phase machinery. So for extra initial outlay you may save/benefit in the future - that's been my experience, anyway.

NCArcher
23rd Jul 2008, 04:32 PM
The output of the VFD is 220V phase to phase. This is the standard American 3 phase voltage whereas ours is 415V phase to phase.
The VFD is able to take our standard single phase 240V supply and effectively split it into 3 phases 120 deg offset from each other using solid state switching. The VFD then varies the frequency of the switching sequence to alter the speed of the connected motor.
The star configuration of the windings draws a much higher current with heaps of torque.
The delta configuration keeps the current draw within acceptable limits for the VFD but at reduced torque. (Although it doesn't make much difference once it's up and running.)
Simplified VFD operation but that's the bare bones.
Some motors are designed for operation on either voltage and will have the nameplate marked 415V star/220V Delta. Not too sure how they differ in construction but it could just be marking to cater for the American and Rest of the World markets.

Pete F
23rd Jul 2008, 04:57 PM
Sorry but all this seems like overkill.

A 1hp single phase motor will cost far less.

KISS. Keep is simple s.......

G'day David, sometimes what seems simple isn't so much so once you start getting into it. If I were to get a new motor I would firstly need to ensure it is approximately the right speed, not generally a problem but may eliminate some "candidates". Since I would like to be able to reverse this lathe it also needs to be a reversible single phase motor. A new motor almost certainly will need the mount modified or a whole new one constructed to take it. If the spindle size is different the existing pully won't fit, and so it goes on. When I compared, the price difference was about 20-30 bucks, and that was a NON reversing motor! A new variable speed, reversible motor from H&F is 600 bucks!!

As mentioned a VFD has a huge number of advantages (hey you're talking to somebody who modified his espresso machine to take a PID controller, some people are satisfied with instant coffee :) ) so even if I can't use or modify the existing motor I'd probably still go 3 phase eventually.

How odd they're quoting an America standard for 3 phase, given that I understand it's a German company. Anyway, since posting SEW returned my email (can't complain about the service) and the existing motor will definitely require the "Fossil Mod".

Cheers,
Pete

DavidG
23rd Jul 2008, 05:30 PM
Having just looked up VSD's on EBay from $240 up and seeing one for 3hp for $350.00 Buy Now, I will shut up and retract what I said.
I was imagining a VSD at $1000 up. Wow they have got cheaper. :B

Edit. For only $495.00 gets a 5hp 3 phase 415v unit (http://cgi.ebay.com.au/3-7-KW-5HP-415V-NEW-VSD-with-Build-in-Brake-chopper_W0QQitemZ280244047828QQihZ018QQcategoryZ154951QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262)

Pete F
23rd Jul 2008, 05:35 PM
Yeah it's amazing how cheap these are now, I paid about $170 for mine. Figured if it couldn't get it to work I could always sell it again.

Woodlee
23rd Jul 2008, 06:32 PM
I think I will go this route (VSD) for my power hacksaw ,rather than try to find a single phase motor that runs at 1425rpm ,last time I checked it was around $700.00.
It will also save the headache of finding a new pulley and drilling more holes to mount another motor.
I think a strip and clean and some new bearings will be quite adequate.
The three phase motor that was on my hacksaw is 2hp and is wired star according to the plate.
Its a CMG made in Melbourne .
Just to pick your brains what rating VSD would I need for this?

Edit : thanks for the link David ,Ive just e-mailed them with some questions regarding the above.

Thanks

Kev.

Pete F
23rd Jul 2008, 06:42 PM
Well from what we can determine so far, if you want to use an existing 3 phase motor on the VFD it needs to be Delta. Also check somebody like Hare and Forbes (or similar), the single phase motors I checked were around that speed and about $140ish as I recall.

If you REALLY want VFD for the hacksaw then SEW for example suggested just matching the VFD size with the motor size ie no need to over-rate as they become a matched pair and bigger doesn't always mean better.

Cheers,
Pete

damian
23rd Jul 2008, 08:54 PM
For what it's worth H&F have a 1 hp 1440 induction motor for $150. That would bolt straight onto your lathe and run it perfectly. On ebay you can get 1, 2 and 3 hp induction motors 2880 rpm for about $100 delivered.

If you go phase converter that's all good, just pointing out the other options.

Woodlee
23rd Jul 2008, 11:49 PM
Well from what we can determine so far, if you want to use an existing 3 phase motor on the VFD it needs to be Delta. Also check somebody like Hare and Forbes (or similar), the single phase motors I checked were around that speed and about $140ish as I recall.

If you REALLY want VFD for the hacksaw then SEW for example suggested just matching the VFD size with the motor size ie no need to over-rate as they become a matched pair and bigger doesn't always mean better.

Cheers,
Pete


Got a reply from that seller on Ebay ,he says that the motor will be ok with out converting ,just wont have as much torque ,which for a power hacksaw wont be a problem really .If it is I have a sparky as a neighbour ,I can recruit him to help convert the motor to delta.

Kev.

zuffen
24th Jul 2008, 09:41 AM
I picked up a new (unused) 2hp 1425/925rpm single phase motor for $75.00 of eBay.

It bolted straight on to my drill press and the shaft size was correct.

Couldn't get much cheaper than that.

The drill doesn't tend to stall too easily and if it does the lights go dim!

schwartzy
24th Jul 2008, 04:51 PM
Gentlemen,

Not all motors are suitable for running on a VFD. It should be VFD rated, greater insulation on the windings. I would not advise running any old motor via a VFD. I changed my lathe to three phase running on a VFD for speed control, but I purchased a new VFD rated 3 phase motor. Also be aware of reduced torque at low speeds and the need for additional cooling.

KISS single phase motor with a reversing switch.

beetle
24th Jul 2008, 06:42 PM
I bought a plug in 1hp motor from HARE & FORBES bolts straight on no problem.around $265

Woodlee
24th Jul 2008, 08:26 PM
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.

NCArcher
24th Jul 2008, 08:51 PM
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-2-2kw-1425rpm-240V-Electric-Motor_W0QQitemZ200158385590QQihZ010QQcategoryZ11752QQcmdZViewItemQQ_trksidZp1742.m153.l1262

Pete F
25th Jul 2008, 09:39 PM
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

Woodlee
26th Jul 2008, 10:57 AM
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.

PhaseChangeConv
3rd Sep 2008, 02:46 PM
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 (http://www.phasechanger.com)
[email protected]

Pete F
3rd Sep 2008, 07:00 PM
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!

Big Shed
3rd Sep 2008, 09:46 PM
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 (http://www.machineryhouse.com.au/Products?stockCode=E112) motor on special at $209

PhaseChangeConv
4th Sep 2008, 09:30 AM
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]

PhaseChangeConv
4th Sep 2008, 09:43 AM
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~.:2tsup:

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.

Vernonv
4th Sep 2008, 11:26 AM
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?

Pete F
4th Sep 2008, 11:36 AM
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

Vernonv
4th Sep 2008, 12:09 PM
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.

PhaseChangeConv
4th Sep 2008, 12:52 PM
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]

Vernonv
4th Sep 2008, 01:30 PM
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.

PhaseChangeConv
4th Sep 2008, 02:05 PM
Hi Vernon,

Do you have a step down transformer to correct this 480V?

If you are using your static to start say your 3hp motor can you then start your 7.5hp motor after this?
I do not think that we can call this a rotary system because with a normal rotary converter you could not have a 3hp pilot motor starting a 7.5hp motor.
Either way we look at it the system "sharing" you refer to will be far less efficient in your static converter then it would be with our rotary converters. If all your motors are contributing to creating the '3rd' phase they will still all loose power output. Any rotary converter becomes less powerful, less efficient and unbalanced when you apply a physical load to the pilot motor.

Kind Regards

Ben
[email protected]

Vernonv
4th Sep 2008, 03:28 PM
Do you have a step down transformer to correct this 480V?
No. I was planning to, but during testing I found that it didn't cause any overheating of the motors. Also only being 15% over-voltage, it shouldn't over-stress the insulation of the motor's windings (and I use good quality motors).


If you are using your static to start say your 3hp motor can you then start your 7.5hp motor after this?
Yes.


I do not think that we can call this a rotary system because with a normal rotary converter you could not have a 3hp pilot motor starting a 7.5hp motor.
I still think that once running an SPC is effectively an RPC. However, I do understand your point about the 3hp RPC not starting a bigger hp motor, but isn't that because the RPC would be setup to start a 3hp motor and therefore would not cope with starting the 7.5hp. As I said my SPC is setup to start the 7.5hp so can easily start the 3hp. If the 3hp is already running then it is already generating the 3rd phase and this together with the overall capacity of the SPC allows the 7.5hp to start.


Either way we look at it the system "sharing" you refer to will be far less efficient in your static converter then it would be with our rotary converters.
Agreed - my setup although effective is a bit "rough and ready" and certainly doesn't produce the most efficient output (especially compared to a good commercial unit).


If all your motors are contributing to creating the '3rd' phase they will still all loose power output. Any rotary converter becomes less powerful, less efficient and unbalanced when you apply a physical load to the pilot motor.I agree that the more load placed on the "system", the less efficient and more unbalanced it gets. I think it applies equally to SPC's and RPC's. The capacity of the RPC is more to do with starting a load motor, rather than keeping it going. It seems logical to me (knowing how RPC's in general are configured electrically) that once running, the load motor would share a proportion of the 3rd phase "generating" with the pilot motor and the more motors that are running, the better the whole system performs (i.e. more spare capacity it has). I guess as the RPC pilot motor is unloaded it is able to provide a fair bit of that spare capacity.
This is an area I would love to find out more about.

Pete F
5th Sep 2008, 11:16 AM
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.

I'm not so sure that's true when talking about high accuracy work. While setting up the lathe to which the VFD mentioned in this thread was fitted, I noticed it was cutting a noticeable cam on the work when using the leadscrew. Turns out the gear on the spindle contacting the gear train had a ding in it which was enough to push the spindle ever so lightly off and create a noticeable ridge. For someone like myself from woodworking it was eye opening into how unforgiving metal is and even seemingly insignificant faults can produce poor results. I certainly wouldn't rule out "pulses" from a single phase motor degrading the work, particularly if they happened to be a harmonic of the spindle speed ie they fell at the same spindle position with each rotation.

Pete

Woodlee
5th Sep 2008, 05:00 PM
Hare & Forbes have a 3.2hp 240V (http://www.machineryhouse.com.au/Products?stockCode=E112) motor on special at $209


I just had delivered up a 3hp 240 motor from Royce Cross Agencies in Adelaide ,for $231.00 which include freight to Katherine ,its a 28mm shaft 1410rpm , just what the doctor ordered.

Its second hand ,but has been serviced and has a 3month warranty.Just a few scratches on the paint around the foot mounting holes other wise it looks brand new and no marks on the shaft .

Just need to bore and key the pulley and alter the mounting plate on the saw.

Kev

Big Shed
5th Sep 2008, 05:15 PM
Good one Kev, hope that completes the project:2tsup:

Turner2608
16th Jan 2009, 04:10 AM
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~.:2tsup:
Hi, just wondering if you have any info on building a phase convertor, as i need to run a panel saw (7.5HP) from a single phase supply, and can't warrant spending $5,000 on a bought one. cheers luke.

Vernonv
16th Jan 2009, 10:15 AM
Hi, just wondering if you have any info on building a phase convertor, as i need to run a panel saw (7.5HP) from a single phase supply, and can't warrant spending $5,000 on a bought one. cheers luke.

Hi Luke,
The converter I am using is running off 240V split phase i.e. 480V, and not 240V. If you only have 240V single phase then you need to either run a 240-415 step up transformer or configure your motor to run 240V Delta (that is if your motor will allow it).

Static phase converters are pretty simple to configure - all you need are some motor run capacitors and a contactor (and a few other minor bits and pieces).

I gleaned a lot of info from the net and also these forums (I think Fossil posted about his build). So your best bet is to do a bit of reading and research first, so that you have an understanding of what your options are and what best suits your situation.

Let me know if you need more detail on anything.