3 phase soft start application - Page 5
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  1. #81
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    Quote Originally Posted by JST View Post
    Right... because they are (almost) always WRONG.... If they understood the problem, they would be able to fix it. Both because they know what it is, and because if they could understand it, they would have to be savvy enough to probably fix it.

    Reminds me of working at a HIFI repair shop way back in the last century when I was in school (and stuff was worth fixing). Every second customer would come in and, no matter what the problem or symptom was, they would say "it sounds like it's shorted out". I never have figured out what a "short" sounds like, because most all of them were in no way "shorted" and for certain not "shorted out"...
    LOL! Uncle by marriage of a close friend was a prize-winner on that!

    Young puppy Dog chews through the power-cord of his new high-tech "Color!" TV. DOES "short out"... the breaker or fuse.. Miraculously, puppy even lives to whimper about it.

    Wife calls the "RCA" Tee Vee repair tech. They still had dominant-brand service trucks and did house-calls back in the day.

    Arsehole sez. "Just tell him it exploded!"
    Uniformed Tech rolls in, asks what seems to be wrong.

    She sez "Er.. ah .... it just sort of exploded!"

    Tech looks to plug the set back into the wall, see's all the raggedy ass teeth marks, clear up, down, and through to tinned-Copper,

    sez:

    "Exploded?"

    "The TV?"

    "Or the animal that made all these teeth-marks?"

    Wuddn' yah know it? Here we are. Human nature as it is, still better at dealing-up teeth-marks than solutions, many a day.

    Go figure.


  2. #82
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    well here's where i sit at the moment.

    my automotive scope shows no clear way to measure ac. push buttons on this machine are geared to automotive and i don't care to risk damaging it.

    i still don't have any practical information on a soft start but what i read is soft start is low torque compared to vfd.

    my motor is rated for a vfd but i have to consider ROI. at one time this tool was busy and while still needed the market is soft on auto machine work these days.

    i have a 5hp motor laying around. for a pulley, 2 belts and some fab work i think i will give that a try. similar machines still left on the market use 3hp motors.
    i'll report back. thanks

  3. #83
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    Quote Originally Posted by cg285 View Post
    well here's where i sit at the moment.

    my automotive scope shows no clear way to measure ac. push buttons on this machine are geared to automotive and i don't care to risk damaging it.

    i still don't have any practical information on a soft start but what i read is soft start is low torque compared to vfd.

    my motor is rated for a vfd but i have to consider ROI. at one time this tool was busy and while still needed the market is soft on auto machine work these days.

    i have a 5hp motor laying around. for a pulley, 2 belts and some fab work i think i will give that a try. similar machines still left on the market use 3hp motors.
    i'll report back. thanks
    Hybid approach might be to...

    - Leave the OEM rig as-is.

    - ADD the 5 HP with some mechanical advantage and a mechanical clutch to "ramp-up" the rig.

    - WHEN it is up off its knees and rolling, kick in the primary motor and drop the 5 HP off.

    The 'pony" motor to the rig, not the RPC idler, doesn't need to be 3-Phase.

    Nor even AC electric, actually... IC engine starter should kick ass.
    If not, the IC engine could. Not exactly a shortage of 'em, down Florida way, is there?

    "Hear tell yah fnally got yhat platen grinder running. Watcha got driving it?

    "Well ..we TRIED.... "

    YouTube

    "But needed more, so ...C280-16"

    YouTube


  4. #84
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    or, instead of a pony motor, maybe try a pull rope

  5. #85
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    Quote Originally Posted by Larry Dickman View Post
    or, instead of a pony motor, maybe try a pull rope
    ..with a TALL gravity tower... like they once used to launch gliders?


  6. #86
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    Quote Originally Posted by thermite View Post
    Hybid approach might be to...

    - Leave the OEM rig as-is.

    - ADD the 5 HP with some mechanical advantage and a mechanical clutch to "ramp-up" the rig.

    - WHEN it is up off its knees and rolling, kick in the primary motor and drop the 5 HP off.

    The 'pony" motor to the rig, not the RPC idler, doesn't need to be 3-Phase.

    Nor even AC electric, actually... IC engine starter should kick ass.
    If not, the IC engine could. Not exactly a shortage of 'em, down Florida way, is there?

    "Hear tell yah fnally got yhat platen grinder running. Watcha got driving it?

    "Well ..we TRIED.... "

    YouTube

    "But needed more, so ...C280-16"

    YouTube

    that won't work for me.

    my bride can't drive the tractor (or forklift or back a trailer) - tried all three once

  7. #87
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    Quote Originally Posted by cg285 View Post
    that won't work for me.

    my bride can't drive the tractor (or forklift or back a trailer) - tried all three once
    In the same go?

    Well it is NOT why I married her, but my Lady Love is a rather expert cross country / off-road driver.

    If only out of a stubborn "Take THAT, Earth!!!" attitude.

    Another 30 years in this house, she might even give it up outta boredom and start using the conventional driveway aprons (two...) to and from the street.

    Meanwhile fifty-plus tons of gravel onto point two-three acres? She can go wherever she pleases over it, all-weather, not get mired!

    And I don't have so much damned grass to cut in me dotage.

    What's not to like about that?



  8. #88
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    Quote Originally Posted by thermite View Post

    Well it is NOT why I married her, but my Lady Love is a rather expert cross country / off-road driver.
    mine said she was/could too but after 47 attempts to let the clutch out without stalling she did a 50 yard wheelie right into a pine tree. that ended that forever.

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    Quote Originally Posted by cg285 View Post
    mine said she was/could too but after 47 attempts to let the clutch out without stalling she did a 50 yard wheelie right into a pine tree. that ended that forever.
    Wimminfolk - G'Mum's generation - usta figure the only "complex machinery" they needed to have truck with selecting and controlling was the male of the species.

    Get THAT shot right, it was HIS job to go-fetch or carry her about. Safer and more comfortable to drive from the back seat without all those damned wheels, knobs, and levers in the way. Back when cars HAD useful-spacious back seats yah could get into and out of, anyway.

    Now? Males having gone 'bout half useless, and even LESS reliable? The "ladies" are driving racing cars, bulldozers, Boeings, and Peterbilts.

    Well they always COULD. They only had to WANT to do.

  10. #90
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    Quote Originally Posted by cg285 View Post
    i have a 5hp motor laying around. for a pulley, 2 belts and some fab work i think i will give that a try. similar machines still left on the market use 3hp motors.
    i'll report back. thanks
    Is the motor single phase? If it is three phase, it won't change the problem.

    Bill

  11. #91
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    Quote Originally Posted by 9100 View Post
    Is the motor single phase? If it is three phase, it won't change the problem.

    Bill
    3 phase. why is that? 20hp rpc should be over kill?

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    i did find a helper today and checked voltage at start up. you are correct. significant drop in voltage on the generated leg. 251 to 85.(barely noticeable on the others) is that fixable?

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    That level of drop is basically not very fixable with "balance" capacitors. It might be possible to improve the voltage to a reasonable level, but the capacitor value needed is likely to be wrong for every other running condition of the motor.

    The real need is probably for either a considerably bigger RPC, or a VFD, which will not be subject to the same issues.

    The essential problem is that the RPC cannot supply sufficient current to hold up the voltage. The required current causes too much voltage drop across the "source impedance" of the RPC.

    That may be due to just the size of RPC, since bigger ones have lower impedance. It may be partly due to the load motor being a type that takes a very high start current.

    The large drop may also be accompanied by some phase shift, but the shift is not the real issue, the voltage is. Less voltage drop would also mean less phase shift.

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    10hp motor, 20hp rpc. what would be a appropriate size converter?

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    and why wouldn't a smaller motor work?

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    A smaller motor WOULD work. As long as it runs the machine acceptably.

    There is no sure way to be sure any particular size converter will work with the information we out here in "internet land" seem to have. It is very dependent on the load on the motor at startup, the characteristics of the RPC, the motor's kva code, etc. Most of that we do not know.

    The data point we have is that the 20HP RPC (characteristics unknown) does not start the 10 HP load motor (starting load and motor specs unknown), and that the generated leg drops to 85 volts, although it starts OK on real 3 phase.

    The very wild ass guess here is that the motor would pull 6 or 7 x FLA on a line start, which is a fairly heavy start load, and that it does that for a significant time.

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    My guess is that his vector diagram looks about like the attached picture. Two sides of the triangle are guesses because he seems to have made readings referenced to neutral instead of leg to leg, which would pin it down. Again a guess, at the large starting load here, the idler would have to be huge to be meaningful. The solution, which I proposed about 90 posts ago, is to use a large starting capacitor, I suspect 1000 mfd or larger, which would be switched out when the motor is running.
    Attached Thumbnails Attached Thumbnails vector-diagram.jpg  

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    Maybe I missed your point... I was thinking you meant a balance cap, but you just said "starting" cap.


    Exactly what are you proposing here? It may have more promise than I thought.

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    Quote Originally Posted by cg285 View Post
    i did find a helper today and checked voltage at start up. you are correct. significant drop in voltage on the generated leg. 251 to 85.(barely noticeable on the others) is that fixable?
    It is "band-aid able".

    See 9100 on a LOAD motor "start" cap.

    Similar use as a "hard start capacitor" on a single-phase HVAC reciprocating refrigerant compressor's motor. Usta bee common as dirt.

    Not sure the ubiquitous "Copeland Scroll" still need that, but I run a York/Bristol recip that does need it and HAS such - provision for already built-in as it is.

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    Quote Originally Posted by thermite View Post
    It is "band-aid able".

    See 9100 on a LOAD motor "start" cap.

    Similar use as a "hard start capacitor" on a single-phase HVAC reciprocating refrigerant compressor's motor. Usta bee common as dirt.

    Not sure the ubiquitous "Copeland Scroll" still need that, but I run a York/Bristol recip that does need it and HAS such - provision for already built-in as it is.
    Now you have it. With a free wheeling motor, the sort of phase relationship I diagrammed will start the motor turning and once it does, the situation will keep improving until it gets up to speed. This case seems to have large starting friction, which keeps it from starting to turn, Forget the idler. At this point it is only along for the ride. View the operation as just starting a three phase motor off the line with a large starting capacitor. I said 1,000 mfd or more. Actually, my back of he envelope calculation is more like 2,000. You could have the idler in the circuit and switch the large capacitor in to start, but it would probably be simpler with less chance of frying something to simply have the idler running but not connected and start on the capacitor alone. Once it is moving, switch to the idler for running.

    Bill


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