7.5 HP 3 phase rotary pass converter
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  1. #1
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    Default 7.5 HP 3 phase rotary pass converter

    A which search did not show much so we will just start new.

    We have a 16 inch Lodge and Shipley model A with 7.5 hp motor and it came with static phase converter.

    Works...not well.

    Cold days we are limited in rpm due to oil drag in the gearbox.

    Been looking for VFD but anything not Chinese is quite costly.

    Can get a 3 phase 7.5 motor and was thinking about a "poor man's" rotary where one uses the static as a starter for the rotary.

    Basically connecting both motors in parallel.

    Not sure if this is hairbrained idea or possible so asking here.

    Other machines have VFD and car lift is on a rotary but it is only 5 hp.

    Also thought of using the 5 hp rotary but not sure if it would tolerate the intermittent.



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    If the lathe has a 7.5hp motor, you need a 15hp idler, might as well get a 20hp if you want to run multiple machines. I've seen the static/rotary done, with 2 idlers, minimal use on my part so other than saying it worked there is not much else for me to add.

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    Quote Originally Posted by Tony Quiring View Post
    We have a 16 inch Lodge and Shipley model A with 7.5 hp motor and it came with static...
    .. motor-killer..

    The ONLY good news about a static not-converter is that they can easily be made into a starter//control for a ROTARY Phase Converter. Sometimes with a bit of parts or termination re-arrangement, sometimes as-had, no changes. If a major-maker item, there will be info published on that.

    So yes. You can do this.

    3 phase 7.5 motor ....
    Presuming the Large & Shapely has a clutch, even @ Zero Load, it is asking a lot to start a 7.5 HP load-motor with anything less than a 10 HP idler.

    Even IF.. your working loading is light enough it might RUN the L&S just fine.

    That said, all it takes to ADD a "supplementary" idler to an existing RPC, minimalist approach, is one 3-Pole "contactor" per-each add-on idler.

    Suggest you proceed with the 7.5 HP.

    If it struggles, fire it up first, NO load.
    Load it with any other 3-Phase motor of same or lesser HP. More than one if yah have such.
    Your "5 HP RPC" could be a player as well. It is not rocket-science to parallel them. Major-makers will OFTEN deliver a 100 HP RPC as a pair of 50's.

    Now you have a de-facto 7.5 HP + <other> + <other> "summed idler HP" RPC. A 12.5 HP if the only players are the 7.5 HP and the 5 HP.

    THEN try starting the L&S.

    If that works well- and it is a VERY safe bet it will do - THEN dedicate the 5 HP into the mix, and/or seek a second used motor to dedicate to the tasking. My smallest is only a 3 HP. I have some 1.5 HP or 1.75 HP loads, so why run more?

    Use of two or more (I have FOUR) selectable idlers allows:

    - stagger-starting for lesser load on the power service,

    - selecting only what you need at any given hour or day for lesser waste,

    - selecting more appropriate balance/run capacitor tuning.

    Starting the RPC idler ITSELF starts to get hairy above 10 HP on the service the average smallholder has available in any case. Bigger is harder yet!

    I can max @ 28 Idler HP, but.... the MAX starting load is only 10 HP. I only need the ONE (Phase-Craft) 10 HP starter/control. It can start any LESSER idler just fine, too. The rest is just a box of selector toggle-switches, a contactor per-each, the run caps are mounted right ON "motor side" of each idler so it brings its own "balance" into the mix automagically when active, ELSE NOT.

    Stagger-start is MUCH easier as well as cheap-enough.

    4 idlers-worth.

    Two should do most folk.

    I just happen to do more experimenting than chip-making, and have the odd need for uber-uber generated-leg stability more than I need but HALF that total power, otherwise.


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    It's most of the same stuff in the box, aside from no run caps ("balance" caps).

    Yes it works fine. Any method to start the idler will work.

    If you look on the Phase-a-Matic site, some searching in the "application notes" will turn up their system which seems to include a switch between the box's wild leg terminal and the wild leg (manufactured leg) of the idler. So you start the idler normally, then open that switch. Apparently, if you do not open it, bad things happen.

    No clue if others need that, may depend on what is in their specific box.

    The "static" has to be rated to start the size of motor you use as an idler.

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    The lathe does have a reversing clutch so it is always started unloaded.

    The starter pops in cold days with higher speeds,

    There are starters where the motor is so we could easily build a control to bring second idler inline as needed.

    This lathe is not used often as we have a smaller one for common stuff but this one is the "real lathe" that is so much better to operate.

    This may increase its use maybe.

    Thanks for the input.

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    Quote Originally Posted by Tony Quiring View Post
    The lathe does have a reversing clutch so it is always started unloaded.
    A "pilot motor" to use the old term, or "idler", because it's shaft needs to NOT be doing any "work", (some are cut-off and covered or were never there) is a bit of a weird duck.

    As an RPC, it begins life looking for all the world like any other 3-Phase motor with a MASSIVELY greater starting "inrush" current than it would need once running.. and generating "CEMF".

    Double-trouble is that we have to start them off single phase.. with TWO phases absent. Enter the start cap or "pony" motor.

    Then.. we get it up off its at-rest knees.. and run it as a special case of rotary transformer ... or watcha might call an auto-generator!



    The bugger is STEALING the CEMF to push the relative phases around, coupling the CEMF from what it DOES have out of the wall - into the missing phase to derive the "generated" leg.

    Enter the UNloaded L&S final-drive motor, de-clutched.

    The windings and Iron in the at-rest condition STILL want a huge slug of current to get moving.

    But we don't have as MUCH of the powerco grid back of the RPC as we would have off raw utility mains. The RPC is a limiter as well as an enabler.

    A really demanding start can actually flip the RPC idler into instantly reversing its direction of rotation, so much energy is involved.

    (At least) one of the commercial RPC makers has (or DID have) a chart on their website that categorized loads by how hard they were likely to be to start and how much to oversize their RPC HP rating vs the load HP rating.

    Our common 1.5 times so often used on PM is only the beginning.

    Some types of loads need a far higher multiple for it to work.


    The starter pops in cold days with higher speeds,
    A "static" phase converter does no "conversion". It simply uses capacitors to trick a 3 Phase load motor into a "third-ass", not even "half-ass" version of its own RPC whilst also trying to move the shaft load. Can't DO both with caps alone.

    It is running on ONE rock-solid phase by robbing from the upstream input source to put enough energy via caacitance into where the TWO, not ONE, missing phases should have been.

    So the motor does not QUITE fall off its perch to sit locked-rotor and just hum.

    That works OK up to around 31 percent of rated load. The theoretical 33% left when the other 66% were never THERE to begin with, plus modest loss.

    Then it falls off it's perch into the petrified birdshit in the bottom of the birdcage with uneven heating and progressively rougher operation - until a protective device interrupts the torture. Or it eventually fails a cap and kills the load motor. DAMHIKT. Cazeneuve. Previous owner. "Big Name" static converter. BFD. Never liked Euro-wimp motors in the first place!

    The RPC has it limits as well, But up around 91 percent of load-motor nameplate. never quite 100% because even if the Voltage on the "generated" leg has been pumped-up with extra capacitance, it remains a "generated" leg - dependent on petty theft from its siblings for its tucker.

    It can never be as "stiff" under load as native 3-Phase with all legs being fed whole food, equally, and directly.

    Steelman-Haas reconfiguration, Peter was proud to point out could push the modified "SELF" converting load-motor ABOVE 100% of unmodified nameplate HP.

    True enough as far as it went. Done with re-arranged WINDINGS, not "just" caps, the effect is as if three single-phase motors of one-third the total rating, each, were crammed into the same housing, just staggered equally around the same shaft.

    Not so widely mentioned was that the price was paid in heavier power draw than a proper 3-Phase source fed UNmodified 3-Phase motor needed for the same output HP.

    That rig trades efficiency for convenience and space-saving IOW.

    TANSTAAFL

    But an RPC at least gets an AFFORDABLE lunch, and at low/no age-degradation nor maintenance hassle!

    Best we can expect. Nearly always good enough.

    Why fight that when it is gonna cost yah more money, not less money?

    My 10 HP Phase-Perfect? Around four thousand bucks, bought brand new.

    And the MAKER sez - right in the manual - to give it new caps at three-year intervals!

    WTF? Average VFD needs new caps only at about SEVEN years out, and the "great ones" will do 12 years and "might" double that.

    The RPC? Caps could be good for 20 years. It can range to 28 max idler HP, but a P-P has easily double its nameplate for starting loads, so not all that different, "real world".

    And I only have 30 or 40% of the cost of the Phase-Perfect in it, even WITH the complex four-idler rig. Folks do 10 or 15 HP all the time with used idlers for under $400. Ten percent of theP-P cost. Sometimes LESS. Freight is the big variable.

    All idler motors here wer bought NEW or "NOS", average about $200-or btter in freight, too, BTW. And all but the one Brazilian Weg are monster-heavy Reliance "Duty Master" uber-durables, too. Triple the mass of the Weg, even at lesser HP.


    RPC?

    "Best we can expect. Nearly always good enough."


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    Yup, we know the SPC is basically a motor starter to get the motor turning by using one leg like a start winding.

    For the most part it does work.

    We were able to peel off about 0.375 chips at 8 inch diameter just fine.

    It is when we need higher speeds the oil sloshing creates enough drag to overload the starter.

    It may be simple as incorrect heaters, but we have not investigated that yet.

    We can get a NOS 7.5 HP motor for song so looking at better options.

    Our work is primary hobby and repairs so not a production unit, but would like to make it better


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    if all that you have is 1 Phase power, why not just switch to a 7.5HP single phase motor? much easier.

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    Quote Originally Posted by Tony Quiring View Post
    Yup, we know the SPC is basically a motor starter to get the motor turning by using one leg like a start winding.

    For the most part it does work.

    We were able to peel off about 0.375 chips at 8 inch diameter just fine.

    It is when we need higher speeds the oil sloshing creates enough drag to overload the starter.

    It may be simple as incorrect heaters, but we have not investigated that yet.

    We can get a NOS 7.5 HP motor for song so looking at better options.

    Our work is primary hobby and repairs so not a production unit, but would like to make it better


    Sent from my SAMSUNG-SM-G930A using Tapatalk
    If the L&S even starts OK with the silly static, near certain you'll be golden with the 7.5 plus the 5 for starting AND peeling chip. You can probably drop the 7.5 off the line once started and run any lighter work off the 5 alone.

    RPC is going to give you nearly triple the heavy-load end power of the static.

    Then you won't be limited to those half-depth .375 passes. "Large & Shapely" is not a joke, even on your smaller-motor optioned one. 20 horse is where the "hard stuff" was run.

    The came into this world as first-tier pee-bringers, Big Bang and just before.

    Billy Lodge had no other option.

    Other makers had already grabbed the market for the EASY s**t

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    Tony... this might be a dumb idea, but...

    "Cold days we are limited in rpm due to oil drag in the gearbox."

    Madera, California 'cold'??


    How 'bout slappin' on A magnetic engine-block heater on a timer? That's what I do to make the tractor hydraulics work when it's -30f outside... or just mount a resistor down in the oil... or a resistive oil-heating dipstick...


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