Building a Rotary Phase Converter. Part 1: Theory, initial testing and proof of concept

[Music] [Music] hello and welcome back to the shop so this to my left is a 20 horsepower three-phase electric motor I sourced it from one of my plants recently it was no cost to me and I'm fairly confident should work like a charm I have no use for a 20 horsepower motor might lay this three horsepower my mill is three horsepower and I already have a five horsepower rotary phase converter that's powering them having said that a 20 horsepower rotary phase converter is about the largest size that the that anyone in a home shop setting would have any use for and as such it is right at the sweet spot of someone who has a large home shop could power pretty much anything that they're going to come across so it seems a shame to scrap it for its raw materials and I thought that I would go ahead and turn it into a rotary phase converter let's talk for a minute about how a rotary phase converter works but before that we have to address why as a rotary phase converter needed and to get to the bottom of that we have to understand the difference between a single phase and a three-phase electric motor but first let me give a disclaimer what I'm about to say is true but not accurate in every technical detail I'm not making things up but I am greatly oversimplifying things in order to make them understandable all the physics nerds and engineers may want to plug their ears for the next few minutes the first practical AC electric motor was patented by Nikola Tesla in the late 1800s and his patent drawing gives us a good place to start what we have on the screen is a generator on the right side and an electric motor on the left all generators and electric motors operate because of two principles the first principle is that moving a coil of wire through a magnetic field induces an electric current in that wire so in the generator on the right there are two magnets north and south and on the rotor in between the magnets are a series of electric coils that I have indicated with blue scribble as those blue coils spin in the field between the North and South Poles of that magnet it induces a current in the wire inside those coils the coil wires are connected to the wires leading to the motor and for simplicity sake we'll say that the current flows towards the motor on the bottom wire and returns from the motor on the top wire the second principle is that electrical currents passing through a coil create a magnetic field around that coil these two principles go hand-in-hand if you move a coil through a magnetic field you get a current and if you push a current through a coil you get a magnetic field as the current passes through the coil in the motor it creates a magnetic field around that coil the coil effectively becomes a magnet during the instant that the current is flowing now let's imagine that in the middle of the motor is a magnetized rotor that has a North and South Pole while our coil is energized we'll say it has a North field magnet there is an attractive force between the South Pole of the rotor and the North Pole of the coils magnetic field that magnetic force will cause the rotor to move in the direction of the pole here we see a diagram of the current flow through a 60 cycle AC electric motor AC is short for alternating current which is to say that the current flows one direction and then instantaneously flows in the other direction 60 times per second notice that the coils are specially wired so that as the current passes through them the current flows clockwise in half of the motor and counterclockwise in the other half this causes the motor to always have opposite magnetic fields between its axes so each time that the current passes through the motor the twelve and six portions of the motor will be for instance a northfield while the three and nine portions of the motor will be a Southfield and since the current is constantly reversing direction each of the coils alternates between being a north and south magnet sixty times per second when we place the rotor which has permanent magnets embedded into it in between all those coils then the magnetic fields produced by the coils are going to act on the rotors magnets depending on the rotors position some coil fields will be pushing it while other fields will be pulling it let's take a look at a single instant in this process as the screen looks right now the rotor is at its strongest point in the cycle there's a strong attraction between the north magnet of the rotor and the south polar magnetic field coming from this coil at the same time there is a repulsion between the north magnet of the rotor against the north polar magnetic field coming from this coil this process of alternating pushes and pulls traveling in a circle causes the rotor to spin around if you use your imagination and watch the big green North fields as they hop around the circle you can almost see them pulling the rotor around behind them so what's different about a three-phase motor three-phase motors have six sets of internal coils rather than just four and those coils are energized in overlapping waves of current called phases for any given phase of current the current travels into the motor on one of the three wires and returns by way of the other two wires as before the coils are wound in such a way that for each instantaneous phase two coils are energized as strong north magnetic fields and the remaining coils are energized as weaker south magnetic the here we see the rotor spinning as the alternating North and South fields hop their way around the coils it's not hard to imagine the rotor being pulled around the circle by the strong North fields and being pushed around the circle by the weaker South fields so why do we have both single-phase and three-phase motors well because single-phase motors are relatively cheap and because they utilize the same simple to wire residential wiring zazz all of our lighting and other electronics single-phase motors are all around us powering everything from power tools to hair dryers but where torque and efficiency are critical three-phase motors have a substantial advantage over single-phase motors in this diagram we see our single-phase motor at its strongest possible moment the South fields of the rotor are very close and exerting their highest attraction to the North fields of the coils but in the very next instant the fields have moved at this point the south pole of the rotor is being pulled towards the North field at the 12 o'clock position but it's a long way away so the magnetic attraction is weak meanwhile the repulsion force from the South field coil is very strong but it's being directed straight toward the center shaft of the rotor so despite its strength it's not providing any rotational push now let's examine a three-phase motor at the same instant again the rotor is at its greatest point of torque where the closed north polar field of the top coil is strongly attracting the South Pole of the rotor in the next instant the magnetic fields move on but notice what a better situation the rotor is now in in this case the distance between the rotors South Pole and the North coil field is much smaller so the attraction is much greater and though the 12 o'clock coil field is useless to us right now since it's directed straight towards the center shaft of the rotor we also have ten o'clock oil field and that field is providing a nearly perfect rotational push so our three-phase rotor has both a pull towards a rotation and a push towards rotation so a three-phase motor has much stronger attracting forces and it has both attractive and repulsive forces at all points in rotation as a result for the same voltage and current a three-phase motor can transmit three times more power than a single-phase motor we can use a physically smaller motor to accomplish the same task and we use less electricity to accomplish the same task so what happens if we hook up a three-phase motor to a single-phase power supply well for two out of the three fields the rotor will tend to have some induced movement but one of the fields is completely dead and doesn't provide any pusher pull at all so when the rotor reaches that dead zone it'll come to a stop and when the magnetic fields move on to the next cycle the forces acting on the rotor actually tend to make it hold still not rotate so if you just hook up a single-phase power supply to your three-phase motor it will not spin up now it is actually possible to run a three-phase motor from a single-phase supply because of the flywheel effect if we can get the rotor to come up to full operating speed before we apply power then though the rotor slows down a bit as it passes through the dead zones its inertia will pull it through the dead zone and the remaining coil fields can exert enough attraction and repulsion to keep it spinning at essentially full motor speed and this is where a rotary phase converter is so ingenious remember we discussed earlier that if a coil moves through a magnetic field it induces a current well as the rotors inertia carries it through the dead zone the movement of the rotors magnetic fields past the faces of the dead coils induces a current inside those coils for every revolution of the rotor it behaves as a motor for two-thirds of the and as a generator for the other third of the time in this diagram the bright green North coil fields are the normal fields created by the electricity flowing from the current source while the dark green north coil fields are the result of the spinning rotor creating what's called the generated leg as the spinning poles of the rotor passed through the region of the otherwise dead coils it generates a voltage from those coils as indicated by the dark green arrow coming out of the motors third leg so to get a working rotary phase converter all you need is to get a three-phase motor spun up to speed so that its operating on single-phase supply at that point the leg that's not connected to source current will actually provide generated current this will make all three legs of the motor effectively live and we can draw three-phase power down stream from there for optimum efficiency will also be balancing the three legs of our system by adding capacitors across the three poles of the motor the generated legs voltage tends to be lower than the supplied legs voltage the balancing capacitor served to boost the generated leg up to the same voltage as the supplied legs so we need a method to connect and disconnect our idler motor to both source and output current we need a method to get our idler motor to spin up to speed before we connect the source current and we need two capacitor balance our idler motor so that the generated leg has the same voltage as the supplied legs to do all this I'll be using a set of plans that I found on the web I've made a couple small changes and there's a link in the video description to both the original and updated plans and schematics now my first rotary phase converter was what you might refer to as field expedient I got it minimally working because I couldn't wait to use my lathe and as soon as I got the thing up and running I'd put it right into service and it's worked fine ever since there's a couple things that I wish I had done that I'm going to do with this one one is to fully capacitor balance the leads my phase converter works fine but I don't have the leads balanced out capacitor wise and I'm sure it's not supplying as much power to the motor as it could and it's using more electrical current while it's in use than is necessary secondly I have to use a momentary switch to start my phase converter I have to flip it to the start position and listen for the motor to spin up and then flip back to the run position that works fine but there is a more polished and professional way of doing it where you use a mushroom button and you just pull to turn the unit on and it starts by itself and when you're done you push to turn it back off and that's what I'm going to do with this one so this thing weighs about 400 pounds so the first thing I'm going to do is I have a design in my head for a practical way to move it around a bit of a frame that it can be bolted to they'll have wheels on it so that it's portable then I will minimally test it to confirm that I can actually start it and bring it up to speed without spending a lot of money I have most of the parts to make this happen the only parts that I do not have are the various capacitors I'm gonna need something like six or seven 50 micro farad capacitors and I'm gonna need a single thousand micro farad capacitor to get it to start the cost for all that's going to be around $100 maybe a little more before I sink a hundred bucks into it I want to hear it spin at full speed and just confirmed that the motor does work the way I expect so I hope you enjoy the journey I'll be learning as I go and you'll be watching the learning as it happens I will use as the wheels for the base that the rotary phase converter will be attached to shoot a little liquid wrench to break the grip of the rust for what it's worth liquid wrench is the best at breaking rust especially when you consider cost per ounce it's better than wd-40 it's better than a lot of the very expensive products if you go over to the project farm channel he did a test of like eight or perhaps ten different products for loosening rust liquid wrench performed second best the one that performed the very best I forget what it was but it was twenty dollars a can liquid wrench is under three dollars a can and performed almost as well no this is not a paid endorsement yes I really like their product this is why so sometimes you just need a big vise because I could not break these nuts loose just holding it on the bench probably a hundred foot-pounds to break them loose put it in the big vise and broke them loose so back to the normal bench but sometimes you just need a big bench vise voila so another dumpster stores treasure was this nice three sixteenths angled plate and what I'm gonna do is gain a couple of these together and make an object that is somewhat like a two-wheeled cart so I'll have two of these side-by-side the motor will sit here there will be a vertical here and the wheels will sit and this general kind of orientation so that you can tilt the thing back and roll it around I'm going to be deciding if I should just do a straight shaft into here or if I should actually use this bracket and just weld the bracket in place and go from there so here's what I've decided I'm gonna drill through here and bolt the bracket through here and perhaps provide a little bit of weld if necessary I'm welding these two angle brackets side by side to a single angled plate kind of will join them together as one unit this is electro galvanized angle and as such I do have positive ventilation going to recycle the air through here so that I'm not breathing this stuff it's tempting to paint this before I put it all together but I really don't want to get too much time and effort sunk into it before I know for sure that it's gonna work why not the wheels I went ahead and bolted Yoona strut through those bolts so these now act as the lever arm this is a piece of 5/16 angle iron that is cut off here and then so this is drilled and threaded down here and then so we're screwed in here we're screwed in there so now this bar is solid and the motor can sit right on that plate and the unit will be mobile meanwhile the control box will sit right here so having attached it to the cart it's now much easier to move around so the next thing I did is I have taken the motor apart check the varying clearance looked for signs of abrasion looked for problems with the wiring everything in there looks good clean then I um doubt all the terminals to each other and confirmed that there is only continuity within the six actual motor coils that are inside of there and confirm that there is no continuity whatsoever between any of those leads and the frame so I now have it wired up for 208 / 230 operation and I'm going to attempt to start it up using this drill which is about 2500 rpm the motor is actually rated at 1750 so this can bring it fully on speed to where it should really only be drawing about 25 26 amps as far as starting it up goes I have a temporary a number 6 wire coming in here that's backed up to a hundred amp breaker over in the corner I have a 250 amp contactor here the contactor is driven by standard 120 volts so as soon as I push this button it will close the contactor supply voltage to the motor I should be able to spin the thing up to speed and then disengage the drill get the drill back out of the way and then close the contactor and the motor should start up the polling [Music] the answer about right just check it one last time to make sure there's no voltage at the motor casing means that the motor itself works so now we know I'm not just throwing money away their capacity that I need by the time you see this I'll already have the capacity but in real time is going to be two or three [Music] right so it is about five weeks later and the start capacitor has come in so the start capacitor they say it should be seventy micro farad's per horsepower and that's an approximate number so twenty times seventy would be fourteen hundred this one is twelve hundred it was affordable to go above that kind of went logarithmically expensive so we're going to hope that at twelve hundred will work so what we have here is the same test rig we had before hooked up to a hundred amp breaker I have two hots coming in and they're going through the contactor and they're wired straight into two hundred the motors three leads the third lead is just a jumper from one of the leads through the start capacitor back into the third lead so as a result the third leg gets this leg but on kind of a time delay because the charge and discharge cycle of the capacitor is in between like it receives a charge and then when this leg has gone dormant because we're going you know forward backward forward backward we're doing the alternating current when this one approaches the zero point then the the capacitor fires and discharges and sends it to this leg so this leg kind of gets a time-release it's been my experience with these three-phase motors that when they're done right when you have the the time delay the capacitor right it does seem kind of effortless and of course what I've been doing is a rotary starting it which i think is really kind of the hard way so if I push in this contactor then we will put the motor in the start condition that's not it's long term condition it only needs that until it spins up hopefully something far less than one second but this state is just to get the rotary motion induced so let's find out how well it works okay that was very satisfying clearly was not too much of a power load let's try it again okay that's excellent all right so now I'll work on the timer okay so now I have added into the circuit or the starting capacitor this hundred amp solid state relay the solid state relay is activated by a five volt wall walk so if I push in this momentary switch it becomes active the idea is that I only need this starting capacitor to be on for just you know whatever partial part of a second so I'm just going to manually try it and confirm that it works the way I expect so what I'll do is I will activate the contactor while at the same time activating this button and as soon as I have seen that the motor spun up I will let go of this button that will kick the starting capacitor out of the circuit this will remain on and the motor should then remain spinning this is the fundamental circuit that we'll be using on startup every time we'll just be using a timer to perform what I'll be doing visually [Music] alright let's do another star alright so let's say relay is active so now we'll just put the automated to mechanized timer into the circuit okay so the next step so this is a one-second adjustable timer adjustable down to a tenth of a second or whatever I'll be honest I've played around a little bit with it I've started the motor three or four times and I have it running around three point-two tenths of a second and here's how it works the timer is sensitive to 240 volts so as soon as the timer receives 240 volts it starts say 3 tenths of a second countdown at the end of the countdown it throws the relay the relay has two positions one is it can close a switch after 0.3 seconds or it can open a switch in our case we're doing an open so this solid state relay is currently sitting here energized it has 5 volts the 5 volts is running through this timer and is energizing the relay 3 tenths of a second after I apply power to the motor this will activate and remove the voltage leading to the solid state relay which will take the start capacitor out of the circuit so when I activate the contactor for 3 tenths of a second this capacitor is in the circuit and helps the motor to spin up at after 3 tenths of a second this light will go out and the start contactor will be out of the circuit and the motor will be running let's see how it works [Music] the goal of all of this is to be able to start this unit with a single button push so what we'll have is a big red mushroom button and when you pop the button out it will feed 110 volts to the contactor and that will start the entire unit up so I'm about to emulate here comes 110 volts to the contactor so we now have the motor reliably starting that is kind of step 1 [Music]

Channel: The Buildist

Views: 13,193

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Keywords: thebuildist, the_buildist, the buildist, rotary phase converter, rpc, single phase, three phase, ac motor, nikola tesla, phase converter, pony motor, idler motor, capacitor balance, automatic start, single button rpc, generated leg, motor testing

Id: h9XzczTN1IQ

Length: 28min 3sec (1683 seconds)

Published: Thu Nov 28 2019