Thread: kiss a VFD a good bye . now you can run 3 phase motor on your normal 240v main

Originally Posted by thorens

I found this to be very interesting.
love to give it a try.
How to do it: run a 3 phase motor on single phase supply. part 1 - YouTube

Peter

The only problem with that, if I remember correctly, is that you lose something like half the motor power. However, it certainly works, I have a monstrous old 3hp 3 phase running in this fashion on my linisher (someone else had already wired the cap to it).

Originally Posted by thorens

I found this to be very interesting.
love to give it a try.
How to do it: run a 3 phase motor on single phase supply. part 1 - YouTube

Peter

The title is maybe a bit misleading. A VFD is really for things like variable speed, soft start, electric braking etc etc. And as an added bonus, it lets you run a small horsepower 3-phase motor from single phase power.

The method described in the video is only a "quick and dirty" shortcut. You loose much if not most of the motor power, and the motor is likely to vibrate quite a bit. Definitely not something you want for a lathe or a mill. It may work ok for something like an old grinder at the end of its life, where the choices may be to toss or to connect it by a shortcut method such as this.

You are FAR better off with a real single phase motor. Or else, keep the existing motor and get a VFD, if its only a small horsepower motor it may not even cost more than a good single phase motor would.

That is fantastic - thanks for posting.

However having not played with 3phase machinery previously, the question is realistically, how safe is it?

Its safe if you wire it correctly.....but as Chris points out it is not really that great. Sure you can wire 2 caps in to split the phase into 3, but they will never be exactly or maybe even close to 120 deg from each other, meaning the motor will run rough, and lack power. Better to get a VFD or RPC.

Ew

Greetings Peter,

I'd consider this a quick and dirty way to get your motor running.

Given that the recommendations for good motor life involve things like phase currents all in balance to within 3% or better, minimum of harmonics etc, I would not expect a motor so wired to have a long life expectancy.

As others have said the vibration levels would be nothing to write home about, and one of the reasons for running three phase motors is the reduced vibration so a bit self defeating??

I'd like to know what the motor start currents are. Single phase motors can have quite high starting currents. I looked at replacing a 4kW three phase motor with single phase. The starting current was quoted at 129 amps. I'd also be interested in the starting performance on heavy static loads like a compressor.

VFD's are pretty cheap these days. Why would you give up their advantages for a jury rigged system?

Originally Posted by thorens

I found this to be very interesting.
love to give it a try.
How to do it: run a 3 phase motor on single phase supply. part 1 - YouTube

Peter

Its the 'old' way of running 3 phase motors on a single phase supply. I' ve done it with a few motors in the past. My mate Peter is still running his Sheraton lathe on caps since about 1990 or so. Works fine, but growls a bit. Not something you would do in 2013 unless you had no options. New run and start caps for a 3 hp motor cost about as much as a cheap VFD, by the way....

Cheers,
Joe

It's an old quick and dirty trick BUT.

As he points out, the value of the capacitance is reasonably critical, too small, poor starting, to big, smoke. What he doesn't say is that it is also load dependant, in the videos he is stuffing around with the motor off load, put the motor under load and the winding currents change, so the required capacitance changes. You can buy static converters that do exactly what he is doing in his videos, but they come as a wall mounted unit with switched capacitors to try and match the capacitance used to load applied, viable if you can set something up and run near continuously with steady load, but a right PIA for variable loads that we normally find.

A few other points about his presentation or style:

From the outset of vid 1 he is into the jbox on the motor, having already removed the earth. At 8 minutes in he tells you to make sure that you have the machine fully isolated. Thats a fair chance for someone to wipe themselves out with a hot wire before the warning.

Once he starts demonstrating the mods he has made, he is doing it with an open j box, and no earth connection from his plug to the machine.

He refers to 240VAC mains active as positive more than once, this is typical of someone who obtained his limited knowledge of electricty playing with low voltage battery power, and has scaled up his practice without scaling up his knowlwdge base.

He uses open twisted connections to add and subtract capacitance, and worse still secures his caps by clamping them between a couple of strips of wood with an F clamp. Looks maybe viable if you don't know, but compress/ squash the case of those caps and there is a high risk of perforating the the delectric in the cap and shorting it and all the other caps in parallel with it out, instant smoke from the motor.Suppose then you would have an excuse to go to the finance director for permission to buy a ney sngle phase motor for the machine.

Personally I am starting to think $250 for a decent VFD would be a better idea. As presented, it really is a case of a little bit of knowledge is a very dangerous thing, and this guy appears not to know much, but very keen to share his limited knowledge to cohort who probably know less.

Many good points raised by the previous contributors, that video does not impress with the level of competence shown, nor the work practices either. Besides removing the earth connection, and just twisting wires to connect or disconnect capacitors, he says nothing of the need to bleed capacitors to discharge them before handling them, - I hope that he never gets one without a built in bleed resistor. If he does he could be in for a real shock.
His best advice or rather the best point was the mention of Jim Coxes book "Electric Motors" from The Workshop Practice Series, and I would add one other, "Three Phase Conversion" by Graham Astbury, No.47 in the same series.
Astbury does go into the necessary calculations, for both static converters, (the subject of this thread) and rotary Phase converters, which are basically static converters, with a 3 phase motor added, and you run other 3 phase motors by wiring them in parallel with that one. As always the devil is in the detail, and there is much to do to get it right, but if you carefully digest his explanations, Graham Astbury covers it pretty well. There is much more info on American sites, Practical Machinist comes to mind, they seem more popular over there whilst in Australia you will struggle to find an electrician who has heard of an RPC, let alone built or even installed one. Having said that, there is lots of misinformation too, and the American power system differs markedly from ours in various ways, frequency and voltage being 2 of them which will need to be factored into any design you come up with for static (or rotary) converters.
One advantage of a Rotary Phase Converter, is that you only need one which can drive your biggest motor, and it will be able to drive smaller ones also, so a mill with separately powered feeds, coolant pumps etc can run from it, and other machines can also be run simultaneously, which can't usually be done with a VFD.
I'm not sure that a 3 phase motor fed with imbalances in the power would necessarily perform worse than a single phase motor, and balance to within 3% may be necessary for some CNC equipment, but most stuff I've read on the subject, seems to aim for about 10% balance and from what they have reported, it seems to be satisfactory.
Summing up, I would say that there are times when static converters, are a good choice, when power loss can be tolerated, and costs need to be kept low, but more times when the simple static converter with the addition of a 3phase motor to make a rotary phase converter, would be a good choice. VFDs are more capable again with programmable features like soft starts, ramp up /ramp down, speed control and emergency braking, all of which makes them desirable from an operations view, but you usually need one VFD for each motor which can get expensive. If you are a good scrounger, with access to useful bits, and have workshop access, you may build a great RPC for a low cost, but if you pay full retail for everything it will cost lots.
Finally even if you think you know all about it, get your work checked by a licensed electrician before applying the power. Electricity is a great servant but a deadly master. Just my 2¢ worth.
Rob

Originally Posted by malb

It's an old quick and dirty trick BUT.

As he points out, the value of the capacitance is reasonably critical, too small, poor starting, to big, smoke. What he doesn't say is that it is also load dependant, in the videos he is stuffing around with the motor off load, put the motor under load and the winding currents change, so the required capacitance changes. You can buy static converters that do exactly what he is doing in his videos, but they come as a wall mounted unit with switched capacitors to try and match the capacitance used to load applied, viable if you can set something up and run near continuously with steady load, but a right PIA for variable loads that we normally find.

A few other points about his presentation or style:

From the outset of vid 1 he is into the jbox on the motor, having already removed the earth. At 8 minutes in he tells you to make sure that you have the machine fully isolated. Thats a fair chance for someone to wipe themselves out with a hot wire before the warning.

Once he starts demonstrating the mods he has made, he is doing it with an open j box, and no earth connection from his plug to the machine.

He refers to 240VAC mains active as positive more than once, this is typical of someone who obtained his limited knowledge of electricty playing with low voltage battery power, and has scaled up his practice without scaling up his knowlwdge base.

He uses open twisted connections to add and subtract capacitance, and worse still secures his caps by clamping them between a couple of strips of wood with an F clamp. Looks maybe viable if you don't know, but compress/ squash the case of those caps and there is a high risk of perforating the the delectric in the cap and shorting it and all the other caps in parallel with it out, instant smoke from the motor.Suppose then you would have an excuse to go to the finance director for permission to buy a ney sngle phase motor for the machine.

Personally I am starting to think $250 for a decent VFD would be a better idea. As presented, it really is a case of a little bit of knowledge is a very dangerous thing, and this guy appears not to know much, but very keen to share his limited knowledge to cohort who probably know less.

I agree 100% .
get a decent VFD is the way to go .
the mod is interesting in the way that if you have no choice then it should help you get going thought.

regards
Peter

Hi Thorens,
I'm not sure what these other Chaps are on about, & I'm not an Electrician.
I bought a SEW EURO DRIVE Inverter, that wood take 2HP, but not knowing how much power I wood loose, I only bought a 1HP 3Phase Motor. Also, it doesn't have an RPM Readout, so I just use the Hertz Readout. Works fine for me.
For the work I do on my Tough Wood Lathe, it is OK. In hind sight I should have bought 2HP. motor.
Don't know what these others are about, as I definitely have no Vibrations what so ever.
Yes, it wood have been better to have bought the recommended Product, but at the time, they were $800+ & I got mine for under $500.
Another point to consider, is that these new motors are so Powerful, if something goes wrong, you can't stop them, were as I have the older V Belt & mine will slip.
It hasn't missed a beat for just on 5 years now, since I have had it, & BTW it was wired in by an Leccie.

It comes down to application when discussing vibration. Turning timber, which already has wildly varying hardnesses throughout, would show little to no evidence of rotational vibration. On a precision metal lathe or a surface grinder, it could have enough effect to significantly reduce the machines usability. Even in my worn hercus 260 thats had a 1ph motor put on it has been more difficult to get really really nice surface finish over the original 3ph motor.

Personally, I find all this interesting because my next purchase will probably be a drill press. And being a complete tightarse, I probably will avoid buying a vfd if I know that this sort of option is available. Hell, id have a play with this just for the experience, but I dont have any 3 phase motors handy here.

Originally Posted by Ropetangler

snip.........One advantage of a Rotary Phase Converter, is that you only need one which can drive your biggest motor, and it will be able to drive smaller ones also, so a mill with separately powered feeds, coolant pumps etc can run from it, and other machines can also be run simultaneously, which can't usually be done with a VFD....... snip

snip......VFDs are more capable again with programmable features like soft starts, ramp up /ramp down, speed control and emergency braking, all of which makes them desirable from an operations view, but you usually need one VFD for each motor which can get expensive. ........snip
Rob

Hi Rob. As a rule, you CAN run several motors simultaneously from a VFD, but:

- the VFD must at least be rated for the sum of all motors to be run simultaneously.
- if fitted, the "sensorless vector" feature must be turned off. Hence you can buy the cheapest VFD there is (it is the sensorless vector feature that makes VFD expensive). Even an older obsolete or used VFD will do perfectly well. You must use the simple V/Hz characteristic that all VFD's offer.
- you can not use the VFD features related to "motor protection" - you must instead use separate motor protection for each motor.
- you cannot use variable speed, unless it is ok that all motors run simultaneously at the same higher or lower speed. If you are the only user in a workshop, that may be perfectly fine. But if there are multiple user, it is not practical if the spindle of the mill changes speed with the lathe spindle.
- you cannot use ramp up / ramp down or braking, unless all motors connected are started and stopped simultaneously.


Example 1: you have a 3ph lathe, and this lathe a 3ph spindle motor and a 3ph coolant pump. No problem run them all together from one VFD. It will not matter if they start/stop together, and it will not matter if they change speed together.

Example 2: you have a mill and a lathe and a grinder and a bandsaw (all 3-phase), and you want to turn them on or off at random, and you want to use them sometimes simultaneaosly. In this case you must use the VFD exactly as if it was a phase converter, eg no variable speed no ramps etc etc.


By the way, some VFD manuals explain in detail how to attach several motors. The better VFD brands have quite thick manuals, and you can additionally download application notes etc. Whereas the cheap Chinese VFD's found on eBay are just a few condensed pages, and there is no application notes or the like that you could download, and if there was then maybe only in Chinese. But these too can by default be used toi drive several motors at the same time.

Regarding "motor torque vibration", this is a problem of single phase motors. It does not exist in 3-phase motors, provided these are connected to a reasonably symmetric 3-phase supply. 3-phase electricity as supplied to a house is reasonably symmetric, as is electricity supplied by a VFD.

Electricity supplied by a static phase converter depends very much on how the device has been designed and matched to the particular motor in question. Electricity supplied by a rotary converter depends how big the "master" motor is in relation the sum of all "slaves". Both will have some degree of inbalance, but not enough to be as bad as in a single phase motor.

Electricity supplied by shortcut means like shown in the video, is essentially a primitive / badly matched static phase converter, and I would expect some considerable torque vibration, possibly even worse than what one would expect from a good single phase motor.

Originally Posted by issatree

Hi Thorens,
I'm not sure what these other Chaps are on about, & I'm not an Electrician.
I bought a SEW EURO DRIVE Inverter, that wood take 2HP, but not knowing how much power I wood loose, I only bought a 1HP 3Phase Motor. Also, it doesn't have an RPM Readout, so I just use the Hertz Readout. Works fine for me.
For the work I do on my Tough Wood Lathe, it is OK. In hind sight I should have bought 2HP. motor.
Don't know what these others are about, as I definitely have no Vibrations what so ever.
Yes, it wood have been better to have bought the recommended Product, but at the time, they were $800+ & I got mine for under $500.
Another point to consider, is that these new motors are so Powerful, if something goes wrong, you can't stop them, were as I have the older V Belt & mine will slip.
It hasn't missed a beat for just on 5 years now, since I have had it, & BTW it was wired in by an Leccie.

I think you will find your SEW is a vfd. The basic workings of these units are all the same, they turn the 240v 1ph into DC and then split it into 3 120deg opposed AC phases at 240v. Early units didn't do much more except Hz control, but these day they will do just about anything you want.

Cheers,
Ew