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  1. #21
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    Quote Originally Posted by rons View Post
    You would only know about that if you removed the case from the scope chassis.
    I did. I got put in the instrument room with an old timer who wound his own resistors and rewound meter coils, taught me to use resistance bridges, mirror galvanometers and meter movement work. Then he moved away and I had a boss who was a good mechanical guy but knew little about electronics. As long as there were instruments within calibration date, I could do whatever I wanted. Talk about a kid in a candy store.

    Besides the coax coil, we had a Tek scope with a delay line made of a series of inductors and capacitors. I have never heard of a phase converter working that way, but it is at least theoretically possible.

    Bill

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    I quickly went through most of the references, they all basically say the same thing. However, there was one little pearl of knowledge that has been brought up occasionally that is worth noting, that is the use of a flywheel with a RPC. (If a Dynamic converter is a RPG then what is an Autoformer?). Of course if one has a commercial RPC motor than this would not apply as these units do not have extended shafts.

    So what do I (or we) get out of all this.

    Transformer method: Theoretically very good for a constant load application, expensive and difficult initial installation, long life, low maintenance. Choice for the average machine shop, poor.

    Static convertor method: Simple, cheap, very limited application to one motor and where more than 50% motor rating is not required. Possible uses, a three phase pedestal grinder in an otherwise single phase shop.

    Rotary convertor (RPC): Probably the most widely used method of getting 3 phase power from single phase supplies. Relatively inexpensive to install and operate, usable over a wide range of loads, for most applications the phase balance is acceptable, somewhat noisy, maintenance required for bearings, capacitors. Third phase is supplied by a combination of rotating magnetic fields inside the convertor motor and transformer action.

    Variable frequency drive (VFD): Good choice for single motor applications, low cost for small motors, may be difficult to incorporate into existing control cabinets (rewiring start/stop/reverse controls), programmable for motor control, requires cooling that may not be suitable for use in an enclosure.

    Phase Perfect: Probably the most expensive source of three phase power, closest to true three power. Maintenance costs can be high. Cooling is required. Third phase is manufactured by switching transistors. First and second phase wires pass through the unit and other than supplying power for convertor to function, act the same as on an RPC.

    Please make additions, subtractions or corrections as needed.

    Tom

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  4. #23
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    Quote Originally Posted by TDegenhart View Post
    ...

    snip an excellent compendium...

    Rotary convertor (RPC): Probably the most widely used method of getting 3 phase power from single phase supplies. Relatively inexpensive to install and operate, usable over a wide range of loads, for most applications the phase balance is acceptable, somewhat noisy, maintenance required for bearings, capacitors. ...
    Tom
    Capacitors - what capacitors? None needed!

    As an aside, the discussion of flywheels in the past has resulted in smarter people than me, saying they harm rather than help rotary converter performance.
    I seem to recall that the manufactured phase relies on slip, and if the dynamic behavor or the rotor is slowed down, this suffers.

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    Hi Jarrett,
    I hope I can steer this post back to what you were asking.
    I have built several of this type of converters. If you search for my previous posts you will find they are mostly on transformer converters I have built, with many pictures.
    I will answer any of your questions, if I can.
    With the information you have already supplied, I think this method would be your best choice.

    Jim

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    Quote Originally Posted by jim rozen View Post
    Capacitors - what capacitors? None needed!

    As an aside, the discussion of flywheels in the past has resulted in smarter people than me, saying they harm rather than help rotary converter performance.
    I seem to recall that the manufactured phase relies on slip, and if the dynamic behavior or the rotor is slowed down, this suffers.
    Most of the ones I have seen use caps to both start the RPC and balance the voltages. Yes, a simple three phase motor will supply three phase power but there will be a degree of unbalance. This will lead to heating and loss of output.

    As to the flywheel, I have no personal experience but it seem reasonable that maintaining the rotor speed would be beneficial as in the limiting case of a stalled rotor there is no third phase.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    .. in the limiting case of a stalled rotor there is no third phase.
    "Stall" an idler's rotor, you prolly lose all three ... off the back of tripping the breaker!


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    i did a rather crude experiment and discovered that the rotor slows down far less than the slip that would be expected from a mechanical load,

    I performed a number of experiments on my 4 ton scroll compressor.

    it works great as an RPC, similar in impedance to a 5-6 hp 3 phase motor.
    The run winding is connected across the 120/240v line and the auxiliary winding is connected to the neutral.
    A 50uF capacitor is connected from the other end of the aux winding to the 120v line.

    It self starts with the 50uF capacitor, and open circuit is 240 volts across the auxiliary winding with 4.5 amps flowing through the neutral (due to the 50uf cap). voltage across the capacitor is 270 vac, voltage from the third leg to the other 120v line is 265 when the mains are at 250 volts. so the open circuit 3 phase voltage is 250/265/270 volts.

    The input current is 9.6 amps, and 11.2 amps. (with the capacitor removed these would both be about 16 amps, and the auxiliary coil would generate 225 volts instead of 240)

    When the rpc is loaded with a 16 ohm resistor connected across the auxiliary coil, the voltage drops from 240 to 207 volts*, 12 amps flow into the resistor or about 2500 watts.

    The input current increases from 9.6 to 18.6 amps, and from 11.2 to 16.7 amps. the current flowing through the neutral decreases from 4.5 to 3.9 because the voltage across the capacitor decreases from 270 to ~240 volts.


    I placed a magnet on the shaft and at no load it takes 34 seconds for the rotor to fall behind 1 revolution. so its running at about 3598 rpm.

    When the load is placed on the rpc the rotor takes 13 seconds to lag behind 1 revolution. or about 5 rpm short of 3600. this is a lot less slip than i expected. i can repeat the test again with a heavier load later.

    *(207 is what it should be for 240/240/240/208 3 phase)
    10 ohm load drops generated leg from 240 volts down to 190 at 19 amps. (3600 watts of power extracted from the motor at unity power factor)

    amps on line side increase from 10 to 27, and from 11.7 to 25.

    i couldn't get as good a count this time on the revolutions but on the order of 7 seconds per revolution, or 8-10 rpm short of 3600.

    There appears to be no discernible voltage drop due to the rpm dropping. there is a bit of a ripple in the first 5 cycles, but after 5 cycles or 80 milliseconds, the voltage is stable and appears to have no fluctuation. so the first two cycles might be slightly higher voltage with the third cycle slightly lower. (need a better than 8 bit oscope to measure this)

    the rpm drop is fairly quick, within 18 line cycles or 1/4th of a second the magnet is 45 degrees behind where it was at initially, which would correspond to one revolution every 2.3 seconds, or 26 rpm. i know it isn't that much slower so i think the current drawn is influencing my coil pickup on the magnet. (edit: or its possible it does slow down that quickly initially)
    this is a 4 ton single phase scroll compressor with a 24 amp full load rating, which includes the ~6 amps that would be flowing through the auxiliary winding.) instead, 19 amps is flowing out of the auxiliary winding and 25 amps is flowing into the run winding in the recent test.

    needless to say it heats up real quick at such loads.

    anyhow, from my experiment regarding a 4 ton scroll compressor which mechanically is similar to a 3 hp motor, or a 5 hp rpc (regarding impedance which is not the same as mechanical shaft power): if you want to add a flywheel i think it will do no good unless you can somehow setup another prime mover to dump torque into the rotor during high load.. on the order of the same amount of power as is required by your loads. which is on the order of 2-5 times the normal running load.

    the energy stored in even a large 3600 rpm motor is mostly nothingcompared to starting a small motor from zero rpm, when the difference in slip under load is only 10 rpm. (though the rate of change during the first few line cycles may be a lot higher than that)

    and its not hard to understand this when you work the math out.. count from zero to 1 while understanding your locked rotor torque is sucking up 6 to 7 times full load amps at 50% power factor. that's equivalent to 3 seconds of full load torque applied to a 3600 rpm motor. and if in that first 1.0 seconds the driven load accelerates from 0 to 600 rpm, the energy it sucked out of the 3600 rpm idler was worth 36*3 times as much inertia. so to just get your driven load to the first 600 rpm as the idler slows down from 3598 to 3590 rpm requires an idler with on the order .. if my math is right.. 6.2 times as much rotational inertia as the load. 95% of which will be burned up as heat in the driven load. (im not including the 50% efficiency of the rpc under such a load)

    does it take 3 seconds to accelerate your RPC flywheel from 3590 to 3598 rpm when starting the idler? if not.. the flywheel isn't going to do you any good, as it will have already slowed down and dumped its available energy long before your driven load started moving.

    anyhow, if you have a flywheel that can deliver 20KW for 3 seconds while its rpm drops from 3598 to 3590, or from 1749 to 1745 rpm.. you can get a lot more data more quickly than i can, attempting to start a 5 hp load motor from a 10hp rpc idler to see if a flywheel makes a damn bit of difference.

    5 hp idler assuming it pulls 80 amps at 50% power factor.. that's 16KW at startup.

    I don't even like being around my 2500 joule capacitor bank. the idea of a ~3 foot diameter 3600 rpm flywheel kinda scares me, and its going to need to store 60,000 joules of energy (in the difference between 3598 and 3590 rpm) which means you need 13.5 million joules stored total, or 3 kilowatt hours!!! to even begin to make a significant difference to starting a 5hp load.


    on the other hand a dc motor, or a hydraulic motor, applying torque to the idler, assisted with a flywheel, through a differential driven could let you momentarily supply all the torque you need to keep the idler running above synchronization while the load motor starts without a lot of work being done by the auxilarary prime mover.


    or you could just buy a vfd and be done with it. add some batteries to the dc bus.

    i had good results with AA nimh cells. 40 cents each at 1 amp hour, works out to 400$ a kilowatt hour. much cheaper than flywheels.

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    Quote Originally Posted by johansen View Post
    i did a rather crude experiment
    Crude or not-really, that was good work.

    Thanks for sharing it!

    There is a "parallel" with similar "physics" at-work for long years out in the critical power bizness wherein costly but desperately needed flywheel storage is done with either of:

    - low-tech BFBI mass at modest RPM. The form taken is long shafts so the diameter is kept small enough to not have to spend on dealing with excessive stress at the rim.

    - high-tech and smaller "oil drum" or washing-machine sizes, where the flywheel is near-as-dammit "ALL rim" but made of extremely strong material - Aramid/Kevlar fiber, etc.

    In-use, when primary power loss is detected on the BFBI long-shaft ones, the flywheel / shaft it had been spinning is clutched to a Diesel - starting it near-as- dammit "at once", Diesel thereafter on-duty as primary power input. Generator at the other end sees very little drop in Hz or power through the transition.

    "Farms" of these rigs exist. We've explored that, with links, on PM in prior years, other threads.

    The take-away - that larger body of work, or this experiment, just posted - is that stored-energy "lunch" is neither free nor even cheap.

    To do any good, a flywheel has to store far more energy than we might gain from stacking 1, 2 or 3 boneyard-salvaged GMC 350 V8 auto flywheels onto the idler's shaft. Easy approach as they are dirt-common and have known safe max RPM's

    That said, I can't see even the modest work of doing that as any gain from it is smaller yet!



    As to secondary-cell (AKA "rechargeable") storage batteries?

    Labs are already pushing beyond Lithium tech. Those will go into hand-helds, hand-tools, and "wearables" where space and mass vs storage density really, really matters.

    Back where we HAVE space and mass is less of a factor? Longevity and "life cycle cost" will still rule.

    I'm keeping an eye on "saltwater" batteries to displace lead-acid and Edison // Nickel-Iron, not on Lithium.

    Safer as well as cheaper, potentially longer lived and/or rebuildable in-place cheaply, even if they are waaaaay bigger.

    Worth a bit of reading if yah give a damn.. while so much of the world is not able to go to our "usual" jobs in any case.



    3 1/2 CW

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    Quite reasonable considerations about flywheel. Similar to what I came up with.

    It's a balance......

    The generated leg is made by "generation" as the rotor, with its magnetic field, is "motored past" the coils of the generated leg.

    The speed of that passing, the RPM, is a factor determining the output voltage. So is the rotor current.

    The only way the magnetic field exists in the rotor is that it rotates slower than synchronous and has current induced in it continuously. The difference in rpm vs synchronous determines how much current is induced.

    Bottom line is that a flywheel would work better if the rotor had permanent magnets, BUT, as Johansen points out, you need a lot of mass to store enough energy to make a difference.

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    Quote Originally Posted by JST View Post
    Quite reasonable considerations about flywheel. Similar to what I came up with.

    It's a balance......

    The generated leg is made by "generation" as the rotor, with its magnetic field, is "motored past" the coils of the generated leg.

    The speed of that passing, the RPM, is a factor determining the output voltage. So is the rotor current.

    The only way the magnetic field exists in the rotor is that it rotates slower than synchronous and has current induced in it continuously. The difference in rpm vs synchronous determines how much current is induced.

    Bottom line is that a flywheel would work better if the rotor had permanent magnets, BUT, as Johansen points out, you need a lot of mass to store enough energy to make a difference.
    I would like to try a synchronous motor, one with a externally excited field.

    But hard to find them in the smaller (under 50 hp) sizes.

    I'm thinking a simple voltage regulator circuit could be built to vary the excitation on the field, to keep the 3rd (generated) leg in spec.

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    Quote Originally Posted by digger doug View Post
    I would like to try a synchronous motor, one with a externally excited field.

    But hard to find them in the smaller (under 50 hp) sizes.

    I'm thinking a simple voltage regulator circuit could be built to vary the excitation on the field, to keep the 3rd (generated) leg in spec.
    By the time you doo all that, it gets reasonably effective to go full-scale to a motor-generator and just "deal with" the inherent losses.

    EG: If I HAD to have power any better balanced than what an ignorant RPC gives me cheaply and compactly, I could rig a largish single-phase motor through an ignorant Lovejoy coupling to a 3-Phase generator head.

    As happens, I have a form of that.

    The "single-phase motor" driving the Marathon generator head just happens to be a Lister- Petter 4-cylinder Diesel instead! (Fermont's NATO/OTAN "Tactically Quiet" MEP-803A).

    Running off the 10 HP Weg idlered RPC is FAR the better deal. Simple reason. Dominion Virginia Power's grid via a 200A service entrance has far deeper pockets than the valiant little Diesel, gen head, and breaker can match for starting loads "always", or transient heavy cuts "only sometimes".

    It will become more advantageous yet as the recently arrived 7.5 HP Reliance Duty-Master supplementary idler is added, then a 5 HP I am still scouting for as to a good brand, model, and price, net of delivery.

    "Selectable" RPC if you will.

    Six power levels, 5, 7.5, 10, 15, 17.5, 22,5 HP of "net" idler resourcing off the "array" of only three idlers, 5, 7.5, and 10 HP - switched as needed.

    Not a great deal of spend, actually. One shared starter. Two extra idlers, each with one stout contactor. Nor even all that much space consumed, given it is soon to go camp-out well away from the shop - and my damaged ears.

    Also easily as durable as dirt.

    Annnnd.... for-sure I can START anything under roof, "no drama". then also run with less waste as they can be a closer match to actual running loads.

    Not a lot of magic to that, just Old Skewl "BFBI" adopted from the experience of OTHERS.. see Dave Kamp's basic drawing... then applied at bargain rates.

    Well.. mostly "bargain".

    LazyIyam, so I buy NEW idler motors to avoid need of cleaning the dirty buggers or fitting new bearings!

    If yer TIME is worth anything, I think that might actually be cheaper than used idlers - if only off the back of old, dirty - even now-and-then "risky" - motors costing as much as clean, new ones, (or more) to ship-in ELSE go-fetch?



    "Transformer (only) Phase conversion?" Similar challenge as the Diesel has.

    Takes a lot of mass and spend on Iron and wire to deal with a STEADY load.

    Hit it with our common machine-tool variable loads?
    "Variable" applies at the tool-tip, too.

    EG: The "naked chicken rule" applies:

    Yer plucked!.

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    Quote Originally Posted by Jim Kennedy View Post
    Hi Jarrett,
    I hope I can steer this post back to what you were asking.
    I have built several of this type of converters. If you search for my previous posts you will find they are mostly on transformer converters I have built, with many pictures.
    I will answer any of your questions, if I can.
    With the information you have already supplied, I think this method would be your best choice.

    Jim
    Agreed, A 15hp 42 amp hi pressure compressor is a chore for any converter. Definitely doable without any wind-it- yourself transformer.

    Jarrett check your PM's , private messages

    Joe

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    Quote Originally Posted by thermite View Post
    By the time you doo all that, it gets reasonably effective to go full-scale to a motor-generator and just "deal with" the inherent losses.

    .
    Thinking more on this, purchase a bog standard 40-50 hp motor, pull the rotor.

    make a new custom rotor (I think the slot numbers need changed, need some guidance here)
    Wind that rotor, make a slip ring (or rotating xformer) could even drill the shaft and put a purchased unit on the end (no need for a pulley out there, so use it for the fields)

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    Quote Originally Posted by Joe H View Post
    Agreed, A 15hp 42 amp hi pressure compressor is a chore for any converter. Definitely doable without any wind-it- yourself transformer.
    Given a transformer, by its nature, is also a "choke", where "the physics" say a given HP translates to a certain KW/KVA, we often have to DOUBLE that figure in ordinary AC to AC power-tool transformer selection, no phase conversions involved, simply to insure we have the reserve for periodic peak loading and/or sustained hard working.

    Even adding the task of phase-conversion and ALSO starting that sort of load may look dead-easy - in in theory, on paper and with "solid numbers" according.

    Get into the "physical" realm? The size, mass, and cost of taking those "numbers" off the screen or paper and selecting - or custom implementing from scratch - into actual metal for significant loads get's serious-hairy.

    We live in a world where any opportunity of any kind to make and sell a product gets PLENTY of attention, and globally so.

    That one cannot "just buy" and at competitive pricing (or ANY price..) an all-transformer phase-converter to operate 15 HP motors with challenging loading tells a tale all by itself.

    But there you have it. Tell a person there exist some huge and unimaginable number of stars in the universe? Most folk take the number unchallenged.

    Put a "wet paint" sign on a handrail? There WILL be a fingerprint adjacent in short order. Most of the time? It will match the finger of he who himself had just finished painting it an hour earlier, too!

    You'd have to know pesky humans - ever in search of a "freebie" - even if it costs them dearly!


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    Quote Originally Posted by thermite View Post
    Given a transformer, by its nature, is also a "choke", where "the physics" say a given HP translates to a certain KW/KVA, we often have to DOUBLE that figure in ordinary AC to AC power-tool transformer selection, no phase conversions involved, simply to insure we have the reserve for periodic peak loading and/or sustained hard working.

    Even adding the task of phase-conversion and ALSO starting that sort of load may look dead-easy - in in theory, on paper and with "solid numbers" according.

    Get into the "physical" realm? The size, mass, and cost of taking those "numbers" off the screen or paper and selecting - or custom implementing from scratch - into actual metal for significant loads get's serious-hairy.

    We live in a world where any opportunity of any kind to make and sell a product gets PLENTY of attention, and globally so.

    That one cannot "just buy" and at competitive pricing (or ANY price..) an all-transformer phase-converter to operate 15 HP motors with challenging loading tells a tale all by itself.

    But there you have it. Tell a person there exist some huge and unimaginable number of stars in the universe? Most folk take the number unchallenged.

    Put a "wet paint" sign on a handrail? There WILL be a fingerprint adjacent in short order. Most of the time? It will match the finger of he who himself had just finished painting it an hour earlier, too!

    You'd have to know pesky humans - ever in search of a "freebie" - even if it costs them dearly!

    Thermite,

    You bring up some interesting points:

    These converters, up to 125 hp, have been commercially available and used since the 1950's, originally developed for oil pumps in S. Il. where 3 phase power was lacking.

    Type S - ADD-A-PHASE - Static Phase Converters - Ronk Electrical

    The previously posted operating instructions, or better yet click on the user manual in the link I provided above for the Add-a-Phase showing it is essentially a static with a run cap plus an auto transformer to increase the voltage to the run cap. The voltage to the run cap provides the required power factor so that the device will operate a motor at rated HP.

    A tapped auto transformer is not required if you set it up for your specific motor, A dry power transformer can be used and wired as an auto transformer. The KVA is far less than you suspect since you are only transforming one leg of single phase power in the case of a 1800 rpm motor about 120v. The commercial ADD-A-PHASE had to be "all things to all people".

    The autotransformer also provides a soft-start in some cases as low as 2.5 FLA. With a 10 hp 3 phase motor ADD-A-PHASE tests showed that at 85% of the FLA on the motor nameplate the ADD-A-PHASE provided full 10 hp.

    Don't believe me, read the links previously provided. I've built and still use a number of them and I have experienced exactly what I stated above.

    Joe

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    Quote Originally Posted by Joe H View Post
    Thermite,

    You bring up some interesting points:

    These converters, up to 125 hp, have been commercially available and used since the 1950's, originally developed for oil pumps in S. Il. where 3 phase power was lacking.

    Type S - ADD-A-PHASE - Static Phase Converters - Ronk Electrical

    The previously posted operating instructions, or better yet click on the user manual in the link I provided above for the Add-a-Phase showing it is essentially a static with a run cap plus an auto transformer to increase the voltage to the run cap. The voltage to the run cap provides the required power factor so that the device will operate a motor at rated HP.

    A tapped auto transformer is not required if you set it up for your specific motor, A dry power transformer can be used and wired as an auto transformer. The KVA is far less than you suspect since you are only transforming one leg of single phase power in the case of a 1800 rpm motor about 120v. The commercial ADD-A-PHASE had to be "all things to all people".

    The autotransformer also provides a soft-start in some cases as low as 2.5 FLA. With a 10 hp 3 phase motor ADD-A-PHASE tests showed that at 85% of the FLA on the motor nameplate the ADD-A-PHASE provided full 10 hp.

    Don't believe me, read the links previously provided. I've built and still use a number of them and I have experienced exactly what I stated above.

    Joe
    The only part I "don't believe" is how otherwise "aware' posters keep losing sight of the KNOWN merits and demerits and whoring a "niche" kludge that is still a kludge, even within a niche.

    See Post 22.

    That's reality.

    As to a Ronk Add-A-Phase static converter magically driving a 10 HP motor to full torque and full HP off 85% of nameplate current?

    I think "haven't a klew what you were looking at" or "inordinately gullible as to commercial puffery" is less impolite than:

    "That's obviously horsehit",

    ...what with 40 staff at Ronk beavering away for over 60 years while denied a magical fortune by electrical goods makers who spend more on staff coffee in a year than Ronk's turnover the whole 60-plus years.

    Same "big money" conspiracy as kept us having motorcars as could run a hundred miles to the gallon off tapwater, yah?

    So I'm flexible on that "manners" part when claims of "magical" are afoot.


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    Thought occurs to me that forcing current into the third leg at a 90 degree phase shift with a capacitor in series with a voltage source which is in phase with the other coil's supply... Is not what the motor wants.

    Induction motors draw lagging power factor on the order of 80%

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    Quote Originally Posted by thermite View Post
    The only part I "don't believe" is how otherwise "aware' posters keep losing sight of the KNOWN merits and demerits and whoring a "niche" kludge that is still a kludge, even within a niche.

    See Post 22.

    That's reality.

    As to a Ronk Add-A-Phase static converter magically driving a 10 HP motor to full torque and full HP off 85% of nameplate current?

    I think "haven't a klew what you were looking at" or "inordinately gullible as to commercial puffery" is less impolite than:

    "That's obviously horsehit",

    ...what with 40 staff at Ronk beavering away for over 60 years while denied a magical fortune by electrical goods makers who spend more on staff coffee in a year than Ronk's turnover the whole 60-plus years.

    Same "big money" conspiracy as kept us having motorcars as could run a hundred miles to the gallon off tapwater, yah?

    So I'm flexible on that "manners" part when claims of "magical" are afoot.

    Thermite,

    Jarrette came to the Board with a specific request, all you have done is belittle all those with the first hand knowledge of possible ways to solve his problem. No further comments from me regarding your auto-transformer posts. You have shown how knowledgeable you are on the subject.

    Joe

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    Quote Originally Posted by Joe H View Post
    Thermite,

    Jarrette came to the Board with a specific request, all you have done is belittle all those with the first hand knowledge of possible ways to solve his problem. No further comments from me regarding your auto-transformer posts. You have shown how knowledgeable you are on the subject.

    Joe
    "See post 22". It wasn't MY POST, BTW.

    No one who actually HAS "the knowledge to solve his problem" has found the least argument from me or anyone else who shares the relevant experience.

    The gaps in your own understanding, your Ronk bias - or BOTH - are on offer to help him increase his costs, waste his time, and have to start-over?

    Up to y'all how contrarian a path your respective budgets will support as to trying to get a SCUBA tank-filling 15 HP compressor motor playing nice off ANY form of static converter at anything close to the economy and effectiveness of a rotary, however imperfect.

    But go ahead. Just go for it. Ronk will appreciate the income.

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    Quote Originally Posted by thermite View Post
    ......
    As to a Ronk Add-A-Phase static converter magically driving a 10 HP motor to full torque and full HP off 85% of nameplate current?

    I think "haven't a klew what you were looking at" or "inordinately gullible as to commercial puffery" is less impolite than:

    "That's obviously horsehit",

    .........

    The horsehockey ain't where you think it is.....

    That 85% is perfectly possible. What you have is an effect of improving the power factor of the motor. Motors at full load can get to 0.6 to 0.7 PF without trouble. That leaves a considerable range for improvement.

    Stepping aside slightly, a "PFC" motor (which is an induction type not too different from a standard induction motor), can have its start/run capacitor selected by trying several and choosing the one that provides the least input current under load. They can approach a PF of 1.0 under load, with the right capacitor.

    The motor with the add-a-phase or similar can also get nicely up in PF, and that is where that 85% of normal current comes into the picture. I'd not expect a PF of 1.0, but it can be better than 0.7.

    You are of course correct that the "in-phase" current, the current corresponding to power, has to be there. The trick is that the out-of-phase current is reduced, which reduces the total current input.


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