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27th Apr 2018, 08:24 AM #16
Interesting topic.
I can think of various ways to convert single to 3 phase:
A few capacitors method: check you tube , not recommended but it works.
Rotary method: most common over the years; most points raised, I’m not a fan.
Have yet to see any video of phase balance from anyone, which always surprises me.
Transformer method: one of the best diy methods, check unique3phase on google.
It surprises me no manufacturer makes them.
VFD: for smaller machines 5kw and under this a great option.
Toying with the idea of a single phase transformer 240 to 400v 20kva a 30kw vfd to run the whole workshop; compressor, lathe a few other bits and pieces.
Finally the best a digital phase converter: see phase perfect. Out of my price range.
Maybe an electrical engineer could make one via arduino route?
My vote vfd
Good luck with your selection
Cheers pulpo
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27th Apr 2018, 12:34 PM #17Most Valued Member
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Apologies if its not the case, but from your post I'd say you don't actually have personal experience with any of these methods and what you've posted is just straight from the interweb.
I think if you understood how a RPC works and their limitations I don't think you'd be surprised why nobody posts phase balance videos. Likewise why the "transformer" method isn't something you can buy off the shelf.
Again, if that's not the case I apologise and would love to hear what you're running and how its performed for you.
Steve
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27th Apr 2018, 06:25 PM #18
I've never tried it so I don't know the answer to this, but is it actually possible to run "whole machines" (i.e. motor(s) AND control electricals) from a single VFD?
I've always been under the impression that normally the machine's control systems control the VFD (tell it to run/stop and maybe set direction) and the VFD simply drives a motor based on that control.
Have I been misled?Cheers.
Vernon.
__________________________________________________
Bite off more than you can chew and then chew like crazy.
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27th Apr 2018, 08:48 PM #19
Two versions nobody has mentioned yet: there are VFDs that connect to single phase 240V and put out 3 phase 415V. See Arc Euro in Britain. They cost around double the price of the cheapest Chinese VFDs. Still lot cheaper than an RPC.
Secondly, there are VFDs which are certified for motor-side switching. Again, about twice as expensive as cheap Chinese ones. Those will easily cope with auxiliary motors being switched on and off at will, though if their frequency is varied to change the speed of the main motor, then the speed of the auxiliary motors will change too. An RPC can't of course change frequency at all.
In the end, it's the buyer's choice. I would - and have - multiple VFDs on the same machine for a lot less money and much greater flexibility than an RPC.
Cheers, JoeCheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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27th Apr 2018, 11:11 PM #20Golden Member
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I use one of these to run the 5hp motor in my Colchester lathe - Light Horse Series | Phase Change Converters
Although it is the 5.5HP converter it did struggle to get the spindle up to speed in the 2 highest speed settings unless I slipped the clutch for a couple of seconds, after that it ran perfectly and there is no problem at other speeds,this characteristic is mentioned in the phase changer literature.
I have now overcome this problem completely by fitting a 5HP 3 phase input-output VFD between the phase changer and the lathe motor with the added advantage of variable speed.
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28th Apr 2018, 09:49 PM #21
That would seem to be the most expensive way to achieve VFD control...
Cheers, JoeCheers, Joe
retired - less energy, more time to contemplate projects and more shed time....
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28th Apr 2018, 10:17 PM #22Member: Blue and white apron brigade
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29th Apr 2018, 12:46 AM #23Golden Member
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VFD's are great but they are not a universal solution to running 3~ motors from a 1~ supply.
My Thiel mill has a Demag brake motor and based on a discussion I had with one of the automation & drives blokes when I worked at Siemens there was some doubt that the 3~ 240VAC output from a VFD could operate the brake clutch correctly, even with the spring backed off so I went with a Phase Changer 4 and have never had any problems.
I've got a spare 3~ 415VAC VFD and have been thinking about setting it up with the mill, based on What Lex has said I might move this up the project list a bit.
Cheers,
Greg,
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4th May 2018, 06:27 PM #24
Its interesting how others interpret ones post.
I thought my post actually contributed to the initial enquiry.
Yes a tremendous amount of my knowledge over the last 14 years on this topic has been from the web.
I'm not an electrical engineer.
I first saw a phase converter (rotary) around 20 years ago, home made and always wondered is that "right".
Yes the motor ran no problems but balancing the phases both in voltage and current from single phase is the key.
I bought a CD about 13 years ago from www.unqiue3phase.com Doug Arndt he sold a few into Oz.
I also bought his latest book on three phase converters last year; well worth a read.
Sent a few emails to him, very knowledgeable.
I built one of his transformer phase converters; after a few house and work moves I lost it.
It worked perfectly once running on a dust collector system.
As only one previous post mentioned about the phase balancing and the loss of power.
This matters for motor windings and efficiency.
For a second hand piece of machinery maybe not that critical but I have seen a water pump three phase destroyed from a phase converter.
Also with equipment electronics this could be an issue.
Once I discovered VFD I could not understand why any one would use rotary method.
I love VFD for smaller machines.
They can be a pain to get set up particularly if you buy with poor or no documentations.
However VFD have limitations.
VFD have harmonic distortion (Total harmonic distortion THD) which can be an issue and one should be aware of.
As best I know all VFD will convert single phase to three phase.
Finally a few years ago I discover Phase Perfect.
I thought it was game over for all other technologies; it is a game changer.
The price would suggest others still will have a big role to play.
So finally I realised that all methods have a place.
And Steve finally I am surprised why no manufacturer of rotary phase converters show on video how the phases are balanced.
Because this is the key to a phase converter, making a motor run from single phase is really only a small part.
They all have great marketing bs on their website telling the world how great the phase balance is but show nothing.
A rotary phase converter has change alot, with way more electronics, PCBs etc to years ago.
I own three 3 phase machines and have nothing running.
Low on my lists of priorities.
Thinking of also buying a 3 phase CNC machine, plasma cutter from China later this year (travel for work).
But am nervous due to electronics particularly THD if using vfd method.
Cheers
Pulpo
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8th May 2018, 11:21 AM #25Golden Member
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I'll chime in and share my experience in a home workshop just to illustrate my answer to what the OP was asking.
My first machine was a large (ish) 3-phase lathe. When considering the purchase, a friend gave me a VFD and told me I'd be able to run the lathe off it. I converted all the lathe switching to low-voltage signal for the VFD, this was great- I could vary the spindle speed from the VFD as well as setting the control parameters for soft-start, power braking on the emergency stop, etc. However, I had to set up a different input for the coolant pump, I use a 1ph 240v input and a bank of capacitors, there is a momentary switch that has to be held whilst switching on with another rotary switch. This works ok for a 1/8hp pump motor. Also, I was running a 3hp 3-phase machine off 3-phase 240volt- the VFD did not incorporate a transformer. I could do most of what I wanted to with the lathe but it would not spin the heavy chuck up to speed in top gear and would slow down with a heavy cut.
A couple of years later I bought a milling machine with a 4hp 3-phase motor. I was faced with going through the same process again of acquiring a suitable VFD, re-wiring the machine, having reduced torque capability etc. This did not appeal.
I built a RPC using a circuit diagram designed by a friend who was at that time building them for a living. The step-up transformer was the most expensive component, $450 iirc. 5kw idler motor from eBay for $80 and the friend got me all the switchgear and capacitors plus a cabinet for another $50. I suspect a realistic build cost without 'mates rates' would run close to $1k.
Plugged the mill into the rotary phase converter, solved a minor issue (see below) and started milling. Bought a 3-phase bandsaw, plugged it into the RPC and started cutting. Bought a shaper, plugged it into the RPC and started shaping. Bought a surface grinder, plugged it into the RPC and started grinding.
I found another VFD on eBay at a bargain price as it was 3ph input (those with 1ph in / 3ph out fetch high of bids as hobbyists without RPCs are clamouring after them) and my lathe now runs happily via this VFD downstream from the RPC. Now runs in top gear, also can take heavy cuts without stalling. The other VFD has been used to run a blower for my furnace, the power demand there is low so 240v 3ph works ok although I'll soon be running it off a treadmill motor and the VFD will be enlisted elsewhere.
The initial issue with the mill when I plugged into the VFD was that the contactor would not stay in- it was bouncing and arcing. Called my RPC expert mate and he told me I had the switching on the 'phantom' phase- rotate all the wires one position. I did this and have never looked back. The fact that this happened suggests to me that the 3-phase power produced by the RPC is not quite the same as the stuff the SEC used to make, but my machines do not appear to know the difference.
My RPC is push-button start & stop, with a single, switched 3-phase outlet on the side of the cabinet. I have an outlet on the wall behind my lathe, the plugs for the lathe, shaper and mill hang at that point and are plugged in as required. I ran another cable around the shed to where the bandsaw and surface grinder live. I can only plug one machine in at a time but that is all I need.
The idler motor is very noisy but it is mechanical (not electrical) noise, I guess it has square balls in the bearings and one day I will overhaul it. If it remains noisy I'll build a cabinet around it, or put it outside so the neighbours can listen to it. No reason why the idler motor has to be in the same place as the control panel.
I have a Bridgeport step-pulley J-head that I plan to graft onto my mill when time permits; I'll run this via the spare VFD with 3-phase input from the RPC, only because I happen to have one on hand and it may be a nice addition, speed variability without belt changes etc.
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13th Jul 2018, 09:58 PM #26
G'day Mr Joez,
I decided to get three phase power installed to my shed all up cost was $4,000 you could get it done cheaper than this price if you can get the materials yourself and install the cable yourself but as the sparky told me he can not prescribed Certificate of Electrical Safety only for the work he does, so i had him do the full installation. Now as for RPC i was quoted $4,500 plus i need to have a 30 amp outlet and i only had 20 amp. I can not use VFDs as my lathe has three motors same with the mill. I had the three phase power in for over a year now best thing i ever did.
Cheers,
Mark.
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13th Jul 2018, 10:35 PM #27Member: Blue and white apron brigade
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Not saying what you did was not the best option for you, but it's also worth knowing that $4000 buys a lot of VFDs.
I can not use VFDs as my lathe has three motors same with the mill.
This then not only solves the 3Phase issue but also provides all the other benefits provided by VFDs.
Typically on a mill or lathe only one large and one or two smaller VFDs are required and all 3 can be had for <$500.
I'm talking about rubbish VFDs but fully featured industrial strength type VFDs.
The smaller ones also only take up as much room as an old style contactor switch which are n longer required in VFD implementations.
I just completed a twin small VFDs installation on my small mill and to add another VFD to teh system would not have been a lot more work.
The twin VFDs fit into the same cabinet space under the mill where the old contactors and a 32V transformer was located.
tuckedawayVFDs.jpg
More photos and a bit of a WIP from about this point on in this thread
//metalworkforums.com/f189/t201...-2#post1935493
Like I said, it's not for everyone but it does mean it's not impossible.
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