Otto Smiths patent for 3 phase motor running on 1 phase power

Discussion in 'General Electronics Chat' started by machapungo, Jan 21, 2014.

  1. machapungo

    Thread Starter New Member

    Jan 17, 2014
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    I'm looking at Figure 1 at this address: http://www.google.com/patents/US4792740
    Fig 1 shows Otto's simplest circuit to a 3 phase motor on 1 phase power and contains two wye circuits. I have an old 15 hp 3 Ph. dual voltage motor and would like to use this circuit assuming it is the best among the population of simpler circuits to accomplish the task. If you have a better candidate please suggest it. One reason I latched onto this circuit is that I think it will allow the motor to actually function as a 3 phase. An even simpler circuit can be found here: http://www.freepatentsonline.com/4745348.pdf
    BUT It has the 3 Ph. motor acting like a 1 Ph. motor. Any opinions on how these two circuits would compare in my application are welcome. My application is making a small log ripping mill using a 26.5" diameter circular carbide tipped blade that cuts a 0.25" swath. OKAY, back to Otto's circuit.
    Since my 220/440 volt motor is dual voltage I could construct two wye circuits with the 9 available wires and connect them, I hope, according to Otto's circuit. Q1. Do you think this is possible? His circuit also has 4 capacitors and 1 switch. (probably spring loaded momentary to function as a a motor starter) The other 3 capacitors along with the unique wye connections, I think are supposed to maintain a reasonably balanced rotating magnetic field once started. The current rating for the motor is 46 amps when connected with 2 wye's in parallel for 220 volt operation and 23 amps
    when connected with the 6 coils connected in one wye for 440 volt operation. The 3 coils with 3 ends labelled 7, 8, & 9 are permanently wye connected with ends 10, 11, & 12 which are not accessible. My chore is to determine the values of the capacitors using only the known data. Oh, the resistance of each coil is about 1 ohm and two in series gives about 2 ohms, of course. Because of this low resistance, I think it will not play a role in determining capacitor values. CAN YOU HELP?
     
  2. tcmtech

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    Last edited: Jan 22, 2014
  3. tinkerman

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    http://www.freepatentsonline.com/4745348.pdf

    The one shown here is the simplest. They do not produce true three phase. I've built two capacitor static phase converters which have been in use for several years. They have limitations though. The motor must be derated to about 60%. Also phase currents are difficult to balance and change with loads applied. Unbalanced phase currents can cause heating of the affected phase winding and motor failure. A better system is a rotary phase converter. I've built one of those and it too has been in steady use for many years. It produces a better 3 phase power and motors attached perform at closer to rated hp. Basically my rotary system is a static capacitor unit which starts and runs a large three phase motor which is connected to a main three phase buss. It has nothing attached to the shaft. It just acts more or less like a huge flywheel spinning. All the other smaller motors operate off that buss. As motors are added to the system more capacitors must be added to help keep the phases balanced. The sum of the small HP motors shouldn't exceed the size of the "spinner". My static converters run 1 1/2 and 3 HP motors. The rotary unit has a 15 HP motor as the "spinner" and about equal HP in small motors attached most of the time. (small cleaning plant)

    Neither system is plug and play. You have to mess with them to get them operating reasonably well. IIRC the rotary unit did have a couple of small motor failures since constructed but I can't say if that could be attributed to unbalanced currents. I know that system gets a LOT of use. Sometimes days of continuous use.
     
    Last edited: Jan 21, 2014
  4. machapungo

    Thread Starter New Member

    Jan 17, 2014
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    The link goes to a discussion of "Grid tie inverter" stuff. I don't see the relevance to my task of operating my 3 phase motor on 1 phase power. ????
     
  5. machapungo

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    Jan 17, 2014
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    have a friend that apparently did a similar phase converter using a 3 phase motor (with no mechanical load) with one or two legs of the wye connected to the 1 phase line. Thereby he is driving it as a 1 phase motor. He did not mention using any capacitors to start it spinning. Then he connected that converter motors 3 phases to drive a 3 phase motor on a lathe. The only thing between the two motors electrically is a 3 Phase switch with 3 fuses. It's been working for 15 years, he says, without any problems. I think there must be some imbalance in his configuration that gets the converter motor spinning. Anyway, I understand I could follow your example BUT I really would prefer NOT to have to use a second motor to do it.

    My effort to figure out what size capacitors to use in Otto's simplest circuit Is to simply use ohm's law to estimate my motors approximate inductive reactance in the high voltage configuration. I figure I can justify using Ohm's law because the winding resistance is so low as to not contribute more than about 16.6 % of the total opposition to current flow. The motor's high voltage operation is at 416v & not the 440v originally stated in my post. Dividing 416 by 23 amps gives me 18.087 Ohms. I roughly figure that any single moment the motor wye circuit presents two legs in parallel then one leg in series. Since each leg has 2 Ohm's of resistance then 2 in parallel gives 1 ohm added to 2 ohms of the third leg gives 3 ohm's. So, I subtract the 3 ohms of resistance from the calculated 18.087 and get roughly 15 ohms of total inductive reactance. So that works out to be a nice even 10 ohms of reactance in each leg. Each leg has two coils so that's a 5 ohms of reactance and 1 ohm of inductive resistance per coil.
    Now, I need to come up with some smoke, mirrors & a crystal ball to conjure up Otto's intentions when he placed those TBD capacitance values where he did in the circuit of fig. 1. I will initially omit from the analysis the switch and it's series capacitor (#110) that are intended to start the motor spinning. Since Cap. 110, when used, is in parallel with Cap 109 it will result in a lower total capacitive reactance of the two individual reactances. Blah, blah, blah!!! Now I need to glean some help from Otto's words. More help from all here at "circuits" is welcome.
     
  6. tcmtech

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    Nov 4, 2013
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    Sorry. :p

    Wrong link to wrong person. (Too many windows open on my laptop at once.) :eek:

    It's fixed. ;)

    Here is the quick and basic diagram and values to work from.

    3ph converter.png
     
  7. tinkerman

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    Jul 22, 2012
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    To the best of my knowledge you CAN'T get good 3 phase from a single phase supply. I work with a company that did extensive research on the subject and got copies of a lot of their results when I delved into building these three converters. The problem arises from the fact that single phase applied to any two legs of a three phase motor are 180 degrees apart rather than the normal 120 degrees. The third phase at best is 90 degrees from either of the main legs and that isn't constant. I believe this is called a T connection. With large motors as you're hoping to use the problem increases with the high single phase currents. The utility won't like the starting currents as it will disrupt other customers. One setup this company tested they used a small motor to get the large rotary "spinner" up to speed and THEN applied the single phase power just to avoid "bumping the system".

    It's a challenging problem, has been researched for decades and I don't think anyone has truly come up with a reliable properly functioning system. Nothing matches real 3 phase supply.
     
  8. machapungo

    Thread Starter New Member

    Jan 17, 2014
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    Thanks!!! Please, pardon my my following bit of confusion and requests for confirmation. Am I correct in thinking that this circuits 3 Phase motor (shown) is used as a converter to drive other loads such as my motor /saw application?
    In other words, this solution will require me to have another 3 phase motor in addition to my 15hp motor, on hand, and that it should be 15hp or greater. Correct?

    If so, then I assume that the input line voltages mentioned must be supported by the wye motor used in the converter circuit as well as my 15hp load motor (and In my case, being a typical home, you understand, all I have to offer my 15 hp load motor is 220Vac as an input voltage) Correct?

    Also, I'm not familiar with that type of automated switch used but I'll check it out.
    Am I correct in thinking that after it performs its function the associated capacitor will be, in effect, totally removed from the circuit? If so, then a less sophisticated method would be to use a spring loaded normally open switch to insert the capacitor to manually bring the motor up to speed. Correct?
    Those green lines are unfamiliar and therefore confuse me!!!


    [​IMG]
     
  9. mcgyvr

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  10. tinkerman

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    Jul 22, 2012
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    That drawing is a static converter design and could be used to operate your 15 HP motor, BUT it would reduce you output HP to 60 % of nameplate. It could be changed to a rotary design by using that circuit to start and run a 15 HP preferably larger 3 phase motor and then connecting your 15 HP. That's the way I went with the rotary unit. It also needs a starting circuit using large start capacitors similar to single phase induction motors to get the unit running which are switched out after it's near full rpm. Running capacitors must be left in the circuit to provide the phase shift for the third leg. So you will need to design a starting relay system and adjust the number of capacitors for both starting and running. You could do this process manally but large starting caps required are short duration and can easily be destroyed if left energized too long. That problem is common to large single phase starting capacitors. I've seen quite a number of single phase motors with blown start caps simply because the starting load was to heavy and too slow to come up to speed.
     
  11. machapungo

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    Jan 17, 2014
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    My 15 hp 3 ph which I paid $80 for does not justify a $596.95 ea additional expenditure.

    Thanks anyway. Information is good!
     
  12. machapungo

    Thread Starter New Member

    Jan 17, 2014
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    I thought he was trying to do the rotary converter type that you recommend! OOPS!!!
    Apparently, the wye in his diagram was intended to represent my 15hp motor.
    Sooo...this "static converter" looks a lot like Otto Smiths patent, therefore, are you saying that Otto's simplest ckt. is a static converter? Now I'm going to return to your previous post that I need to comment on. Thanks for sticking with me on this quest.
     
  13. machapungo

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    Jan 17, 2014
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    WOW! You say" The problem arises from the fact that single phase applied to any two legs of a three phase motor are 180 degrees apart rather than the normal 120 degrees."
    That is interesting but I can't say I understand why. I've read (maybe here) that connecting 1 Ph to two legs of the wye ( like L1 & L2 which would put their coils in series) and then putting a capacitor and a spring loaded normally open switch in series with the L3 leg and then to either L1 or L2 to act only temporarily to start the thing rotating would be using the motor as a single phase motor. Your statement about two legs being 180 degrees apart makes me question the other guy's statement about simply acting as a single phase motor. What's your take on that? How much would that cut into my motors 15hp? and would there be other problems? Perhaps I really should get more serious about buying another cheap 3Ph. motor to play the converter role. You are obviously not an amateur in these motor issues. My naturally stubborn nature makes me want to persist in trying to get away with just the one motor but I feel my resolve weakening in the face of reality. If there were no other significant problems I would be willing to latch onto a simpler solution if it just meant losing 2 or 3 hp. Apparently, I'm searching in vane for a solution that does not exist. I'd be reluctant to get something bigger than 15 hp because I'm guessing mine probably weighs in the neighbourhood of 225 to 250 lbs. I've seen 20 hp units at about 500 lbs and more. Would the converting motor have to be the same rpm as the driven motor?
    I think I have a squirrel cage type because the data plate does not speak of an armature current. It was made by Lincoln Electric in 1977. Regal bought Lincoln's motor business in the late 1990's. I called both company’s. Lincoln could only point to regal and Regal had paperwork that contained the motors metal tag data as well as currents and the year of manufacture.
     
  14. tcmtech

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    Nov 4, 2013
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    The green lines are the wiring. It's what my circuit drafting program uses for line color. Imagine them black or red if that helps.

    It's a direct drive system not a two stage rotary unit running a second motor however they can be made to work that way if a number of smaller motors are being used in a highly cyclic application or if a machine like a welder needs a full three phase source with reasonably balanced phase angle and voltage.

    Contrary to common belief if the two phase balancing capacitors are correctly matched to the motor all three phase lines feeding the motor will have equal voltage and current readings and the motor will handle operating loads at its full rated running capacity.

    The odd relay is a common voltage sensing (Potential) relay normally used for single phase well pumps and air conditioner compressor start circuits and as you are seeing the motor start capacitors are only in the circuit to get the motor started and up to speed . Once there the two phase balancing capacitors are what keep the induced three phase balanced properly. For motors under 5 HP the relays can be used directly but over that I recommend using the relay to drive larger contactor for the starting circuit.


    I have built more of these units than I can recall with several in the 15 HP range and so far other than having to replace a few bad potential relays (they do wear out) and the relating fried start capacitors I have never had one burn up a motor or fail while running whatever load the original three phase powered motor ran in stock form.

    Starting power wise the inrush currents are as proportional to the motors size as any single phase unit would be so all primary power wiring from the utility service entrance to the motor has to be able to handle the size of motor you intend to run.

    My main shop compressor is a 15 HP system that starts and runs off of a normal 60 amp 240 VAC line and can do so even at - 15 F without tripping the breaker. However while getting up to speed it does draw about 140 - 150 amps but being my farm and shop are on a 200 amp service it really not noticeable. :)
     
    Last edited: Jan 22, 2014
  15. tinkerman

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    Jul 22, 2012
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    L1-N and L2 to N are 180 degrees out of phase. That's a factor of the utility transformer bringing power to the house. Far as I know that can't be changed. All the capacitor does is change the phase angle to the third leg just the same as the starting winding in any cap start/cap run single phase motor. I experimented a lot with my setups, adding caps to balance currents and voltages to the three legs and was never successful getting them perfectly equal. All the motors run and have been for perhaps 30 years but I know I don't get full power out of them. My drill press is 1 1/4 inch and I can stall it with the large drills. With real three phase that wouldn't happen very easily. The rotary system isn't mine. I built it for a friend and while we spent considerable time initially trying to size capacitors to numbers of motors and varying loads I know it too never was perfectly balanced. He got pretty good at running his system but I'm quite sure he lost a couple small 3 phase motors.

    No you shouldn't need the same rpm motor for the rotary converter. I believe it would be best to have one that has lots of copper and iron though. One of the old old style that weigh a ton, 1750 rpm. That's what we used.

    The system can be made to work if you like to experiment and are prepared for less than optimal performance. Perhaps a commercial unit would be an easier route. I have no knowledge of what is currently available on the market. With the great advances in solid state technology they may be able to get far better performance.
     
  16. tcmtech

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    Nov 4, 2013
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    I prefer the high RPM 2 pole type 3450 RPM motors for stand alone rotary converter duty. The higher rotor RPMs seem to give a better carry through on high amp bursts like when welding and a rod sticks for a second.

    As the phase balancing goes on a variable load all three phases will never stay 100% exactly the same. I consider anything within the motors designed amps and volts specs to be more than sufficient.

    The biggest balancing problem is when the line 1 to the generated line 3 and line 2 to the generated line 3 capacitive values are not equal. Running all the motor run capacitance on just one input line ot the third phase is what causes so many current and voltage instability problems.

    For full mechanical power output all three phase lines on the motor need to have fairly close average numbers being that the spinning rotor in a three phase motor is more than just the power source for the mechanical load. It's also the stabilizing device that keeps the phase to phase angles pulled up to 120 degrees instead of how in a normal static LC circuit the phase angles would be 90 degrees to each other. A three phase motor suning off of a single phase source is working as a 1:1 rotary phase shift transformer and not just a electrical energy to mechanical energy converter.

    I have spent enough years designing and refining the circuit value I posted to know that if done right any good three phase motor can do its job just fine on a single phase power source without overheating or drawing excessive current on any of the phases.
     
  17. tinkerman

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    Jul 22, 2012
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    I have spent enough years designing and refining the circuit value I posted to know that if done right any good three phase motor can do its job just fine on a single phase power source without overheating or drawing excessive current on any of the phases.

    Interesting. That's good. At full HP? It's not supported by the research of the company I work for. The only design that came close was the rotary unit which was close to 100% IIRC. It also begs the question why would anyone install 3 phase power which is quite costly if a fairly simple and economical single phase converter system could achieve equal results? For me it was impossible to get three phase and for my friend it would have costs thousands of dollars. My system works but I know what it's limits are. My friend has learned how to adjust his sytem as he changes the number of motors in service. From my experience they work but they are not a replacement for real three phase.
     
  18. tcmtech

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    I've been around a lot of people and places that looked into doing things and came to the conclusion it was not possible even though I had found otherwise. ;)

    Grid Tie Inverter system design is one of them. This type of passive three phase motor driver is another.

    Mostly it has to do with the power consumption issues. Past 10 HP on single phase the power demands for starting an electric motor start to get beyond what most older single phase systems are designed to handle for peak loads.

    The other main reason is once a person's average power consumption goes above a few tens of KWh's or has to run single motors larger than 15 HP putting in a full three phase utility service make more sense. It divides up the loads three ways so the peak loading events are much smaller per phase.

    It's not that running larger motors on single phase by this simple method can't be done. It's just that the utility sources and related wiring start going beyond the typical mass produced home owners service systems limits. :(

    Even with my 200 amp service I am limited to about 20 HP. Above that the starting currents are pushing 200 amps plus.

    I have done a number of 15 HP systems and so far everyone of them has worked and worked well. Past that so few people have the service capacity available to a single circuit or the knowledge to make a larger custom circuit that the install costs and logistics just don't warrant running that large of mechanical load off of their electrical services. Going to a gas or diesel engine for the power source is cheaper.
     
  19. machapungo

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    Jan 17, 2014
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  20. machapungo

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    Jan 17, 2014
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    I TOO, HAVE A 200 AMP SERVICE BUT THE LEG I INTENDED TO USE CURRENTLY HAS A 50AMP BREAKER ON AN 8 GAUGE HIGH QUALITY MADE FOR UNDERGROUND USE CABLE. PERHAPS I SHOULD STEP UP TO A 60AMP BREAKER TO HANDLE THE STARTING CURRENT?

    [​IMG]
     
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