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  1. #41
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    Editing out the slander and drivel... again...

    It did what I said it would do, not what you said it was 'supposed to do'.
    Put that in your Funk and Wagnells.


    BUT... An induction motor with no power applied will NOT produce any appreciable voltage out.....
    Pony motor supplied 'power'. Kinetic energy. Motor-as-generator did the rest.

    And it will produce VOLTAGE just fine without the caps.
    Measurement is done with high-impedance meters or 'scope, after all. Near-as-dammit open-circuit.

    What it will NOT produce on remanence alone is appreciably useful CURRENT or 'ergs', nor for any appreciable span of service, time-wise. The residuals decay if not replenished.

    Likewise, attempting 'near-as-dammit' open-circuit measuring of current is not one of the more useful ways to waste time on a task of this sort, whether you have the theoretical maths handy for it or not.

    IF one NEEDS to make a reasonably passable field-expedient generator-head out of a motor, one adds coils or permanent magnets as well as caps to up the efficiency and predictability. ELSE NOT.

    What has to be dealt with here is not on that route or plan. What it DOES ACTUALLY DO, is.

    That DID need the predicted attempt at matching phase before hard cut-in even became enough less 'hard' to show promise that practical use could become possible.

    QED

    Nothing new about that by a hundred years and more.

    Disconnecting 'many' fragile terminations to corroded caps to prove you are STILL not-quite 'with it' is of no benefit to anyone, not even to your own argument. Voltage will still appear as pony ramps up idler. Phase of it will still be related to physical bars in the Armature, not random chance. If it becomes easier to spin, drama returns when the caps are hard-dropped back onto the lines. They do a damned good imitation of dead-shorts in that mode.

    BTW: If Power Factor is to be improved, I'd trust 'Ed' to show the way.

    He's proven he has the knowledge. He is on site and on the case.

    He doesn't have any 'baggage' so far that requires side-trips for ad-hominem attacks nor a succession of rationalizations.

    I hope and trust that he never will. I take less-than-zero pleasure in seeing you trap-out into theoretical corners contrary to field observations, either.

    'nuf said.

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  3. #42
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    Sorry, Thermite, you may get some small voltage out of it, bit you will not get 240V out of it with the small remanent magnetism. You can talk about it all you like, it ain't happening. If he said he got 20 volts, I'd say that was much higher than I ever saw, but at least somewhat "possible". I would honestly say a few volts is close to the limit of what I have seen when messing with induction generators. And I had to "flash" the windings with DC (to establish a remanent field) to even get that.

    I can walk down to the lab now, and spin any of a half dozen motors I have on hand. and if I can get anything like rated line volts out of one of them just from spinning it at near rated rpm, I'll send the flipping thing to you FedEx clear to china at my expense. Overnite rates. I'm not too worried about having to do that.

    Believe me, I would LIKE it to be true, but nope, it ain't. I've worked with the induction generator deal before, and made it work, but never just straight up like that, no load, no capacitors. You need to move a conductor through a magnetic field to get the voltage, and there ain't much field with remanent magnetism. You'd have to spin it VERY fast

    Now, if there WERE this mythical voltage, "at high impedance", that would STILL not be a factor in the current. low power, no phasing issue, no loading.

    But, it is up to YOU ro explain where this voltage is coming from, that is apparently able to produce 240 V WHEN LOADED BY THOSE CAPACITORS that are not yet disconnected.. They are 100 uF per can, so there must be a fair bit of current flowing if there is 240V across them.....

    Perfectly possible if the thing "built-up" as an induction generator,,,, And that would explain the way-too-big load on his pony motor.

    If the thing has , as I suspect, "built up" on the basis of the capacitive load, then there is a substantial field from the exciting current, and that COULD have an effect. There could be full magnetizing current flowing (would have to be to get full voltage) "Theory"? Sure... Theory is not some wild idea, it is, in electrical matters, a tool for understanding what is going on. If you know how, and why it works, then you are way ahead in figuring out why it is NOT working.

    Rather than all be yammering about slander and drivel etc, let's have the OP DISCONNECT ALL those capacitors and give it a try then. They are not needed with a pony start, unless there is balancing to be done, but that presupposes getting it to go as a pre-requisite. Balancing can be worried about later.

    First thing is to get it spinning at near full rpm. Right now that is not happening, and the information we have suggests an electrical reason for that. Either power issues, more load than expected, or both.

    If he can get it spinning decently, which should NOT overload a 3 HP pony motor to the degree he is describing, AND if we can get a damn reading on his incoming power voltage so we know how badly he is overloading things, maybe there will be an answer come out of this crap.

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    I suggested back in post #23 that the permanently connected cap bank was going to be an issue with across the line starts on a weak supply system.

    Building an automated starter with a synchroscope controller for a across the line, pony start, seems more difficult than building a reduced voltage starter to me. I mentioned back in the first thread of this 75HP RPC, that the controls were missing in action, so we started down the pony road as a substitute. Its been interesting to follow...

    As to the residual magnetism remaining in the core iron it occurs in machines below 5HP as well, just usually isn't large or severe enough to even notice. Caps or no caps.

    I have a 1950's 5KW wound rotor generator that operates from this principal. There's not a single cap in the the thing, not even a voltage regulator. The only component in it other than the winding's and brushes is a rectifier. Originally equipped with a selenium unit, now equipped with a silicon version.

    The residual magnetism remains in the iron for decades without use. The magnetically induced energy is rectified and fed back into the stator. Amplification occurs and the thing is up to full voltage before you can lay the starting rope down. Self regulating as well.

    You can leave it sit unused for decades and it always works. Bone simple and reliable. A fine piece of engineering in it's day.

    Back to the issue at hand. If the 75HP RPC was started from the line with some version of reduced voltage starting there would be no generated voltage that is out of phase with the line voltage. It is the pony start with the across the line start that is the issue here.

    SAF Ω

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    I can't fault your input. Now or hardly ever. But this one might justify the 'sub-optimal' compromise.

    Quote Originally Posted by SAF View Post
    Building an automated starter with a synchroscope controller for a across the line, pony start, seems more difficult than building a reduced voltage starter to me.
    For a long time, it was 'more difficult'.

    With cheap sensors and cheap dirty-beach sand available NOW, it can be far cheaper than switchgear and some form of limiting device(s) required to physically implement the reduced power prenuptials.

    That is so even if it is in support of a "BFBI" approach, rather than an elegant, less dramatic, even perhaps a far more efficient approach.

    The phase detection is easier now. Ditto RPM. So are stable timers, and producing a useful control signal.

    I'm expecting 'Ed' to come back with something along that line in the proverbial 'black box', plus a whopping-great oversized set of contactors readily available, surplus market. Proper fused disconnects are also common, surplus market.

    The largest of the Mercury-Displacement contactors I keep a stash of would do. I don't like exposed arcs nor wearing parts. An RPC of this size isn't ever going to be asked to fly an outside loop in a Fleet "Mailwing" biplane and risk going bat-f**k when gravity comes at it from changing directions anyway.



    The CB having been abused to within an inch of its life - or beyond - should be replaced as well.

    The residual magnetism remains in the iron for decades without use. The magnetically induced energy is rectified and fed back into the stator. Amplification occurs and the thing is up to full voltage before you can lay the starting rope down. Self regulating as well.

    You can leave it sit unused for decades and it always works. Bone simple and reliable. A fine piece of engineering in it's day.
    A portion of said Engineering as simple as using 'ordinary' Iron or steel, not a costlier lower-remanence alloy.

    And I said 'low' not 'no', even so.

    Economics dictates similar savings in large motors.

    What the makers select is 'good enough' and no more than that, so remanence we have had and shall continue to have.

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    Looks like we've gone full circle now. Back to post #5 in thread #1 of this RPC. Only this time it's been proven as a given and not speculation.

    With a right serious-sized 80 HP of idler pony-ing up, I would also want that ponying process to be simultaneously 'leaking' mains current into the idler windings so it aligned itself pretty closely, phase-wise, with the supply by the time you were ready to slam full-power to it. Sort of a cross between pony and soft-start. Or at least phase-match indicator lamps as used for syncing gen sets.

    Could otherwise get noisy at the breaker if the full power and the motating 80-hoss idler - hardly a baby kitten - happen to be the better part of a half-wave in phase disagreement when you make that cutover.
    So how would you use those mercury contactors to leak some line current into that idler during pony up to speed?

    I think that is what beansdiesel and Ed want's to know at this point....

    SAF Ω

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    Quote Originally Posted by SAF View Post
    Looks like we've gone full circle now. Back to post #5 in thread #1 of this RPC. Only this time it's been proven as a given and not speculation.



    So how would you use those mercury contactors to leak some line current into that idler during pony up to speed?

    I think that is what beansdiesel and Ed want's to know at this point....

    SAF Ω
    A couple of replacement electric range cooker elements. Two 3PST Mercury Displacement relays. One to not cut power in right away, second to shunt the resistance.

    'bout $35 each contactor, NOS, and around ten bucks, times two for the cooker elements. Those don't need a heat-sink, as heat is wot they were built to do.

    Yes, $400 or so worth of high-current Copper and Iron inductors would be more 'elegant' than stove coils. Prettier, too.

    But this rig doesn't even use a timer.

    Galco sell a center-off toggle switch KB-Penta spec for 'not quite instant' reversing to protect their 1Q DC drives. Has an ignorant zig-zag 'gate' at centre so going from one side to the other encounters a modest mechanically-induced delay.

    And it is enough of a delay for MY use.

    Ryan needs more than that. Multiple paralleled stove elements, too. My largest is a 'home canning' element, and that is only 9 kW.

    The resistive approach may or may not be suited to his needs, but is for-damned-sure cheaper than heavy inductors at present-day prices per-ton of copper.

    Capacitors, BTW, are ephemeral. Iron and Copper endure. I like to avoid caps if I can.

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    I think I would opt for a 4 winding transformer, wired as an auto transformer to provide the reduced voltage. Only one would be necessary. Then shunted out once up to speed.

    These come potted in a can ready for mounting, and less of a fire hazard than resistive elements.

    SAF

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    Quote Originally Posted by SAF View Post
    I think I would opt for a 4 winding transformer, wired as an auto transformer to provide the reduced voltage. Only one would be necessary. Then shunted out once up to speed.

    These come potted in a can ready for mounting, and less of a fire hazard than resistive elements.

    SAF
    Don't fall into a JST-style 'elegance' or 'perfection' trap.

    Custom transformers, or even adapted standard ones, are expensive, even for 3 HP and 5 HP motors. Even a 500 VA dry-type costs way more than a stove element and a bit of perfed metal or heavy screen wire. Stove element can STAND heat, but isn't actually in the 'ON' state long enough to have to do much of it.

    Either critter is only in-circuit briefly, one or few 'starts' a day, but its costs must still be amortized just as much as if it were a continuous-duty contributor.

    Keep it cheap.

    Recall the current rating, hence mass and shipping costs as well as acquisition cost for the currents involved HERE.

    Then go and buy a cheap resistance. Incandescent lamps for smaller motors.

    And something ELSE more useful yet on the savings.



    Oh.. BTW.. you do NOT want that reduced-power syncing 'helper' active at Time-Zero.

    It will but try to lock the rotor, pretend to be an armchair-recliner massage vibrator, and fight the pony motor.

    Kick it in once right up into the speed-range between nameplate slip RPM and nominal synchronous RPM for that pole-count.

    You like inductors? Grab a cheap Chinese Variac, put a clock-spring or drop-weight onto the shaft, and you can 'rapid ramp' the boost in.

    Mine are rated 20 A @ 240 VAC... handy for LOTS of stuff..

    Some folk make chips.. others make tests...


  12. #49
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    Quote Originally Posted by SAF View Post
    ....

    As to the residual magnetism remaining in the core iron it occurs in machines below 5HP as well, just usually isn't large or severe enough to even notice. Caps or no caps.

    I have a 1950's 5KW wound rotor generator that operates from this principal. There's not a single cap in the the thing, not even a voltage regulator. The only component in it other than the winding's and brushes is a rectifier. Originally equipped with a selenium unit, now equipped with a silicon version.

    The residual magnetism remains in the iron for decades without use. The magnetically induced energy is rectified and fed back into the stator. Amplification occurs and the thing is up to full voltage before you can lay the starting rope down. Self regulating as well.

    You can leave it sit unused for decades and it always works. Bone simple and reliable. A fine piece of engineering in it's day.
    ....

    Yep NO quarrel with that. Guarantee residual magnetism. ABSOLUTELY.

    If you are NOT old enough to remember having to "flash" automotive generators when they had no output, that won't be clear to you unless you understand how a generator works.

    But THAT works. Just a few volts of output rectified into the field, that generates more, and you are up to full output in no time. Old folks call thet the generator "building up". It's a feedback deal.

    BUT, that is a genset. NOT an induction motor. To get FULL output at nominal RPM, YOU HAVE TO HAVE FULL FIELD... It's just how the physics works, folks. It works just as well below 5HP and ABOVE 5 HP, the physics does not change. (and I suspect if I had done the RPC with 15 HP, he'd have made THAT the limit, and not 5 HP)

    Ol Thermite may want that not to be so, but unfortunately for his theory, it is that way. No field, no output. They knew that over a hundred years ago, and it is still true

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    Quote Originally Posted by JST View Post
    Ol Thermite may want that not to be so, but unfortunately for his theory, it is that way. No field, no output. They knew that over a hundred years ago, and it is still true
    LOL! Guess you have forgotten that putting 'lectricity at it was meant to run round in circles on wires for the purpose of producing a magnetic field. Ampere-turns, left and right hand rules, Joules and Ergs... all that s**t and its math that matters when scratch building a new design.

    Thing is we ain't. Inventing the wheel.

    Factory-made goods will not have changed much from as-built when you walk up to a device some other Pilgrim already has built. Have to just eat what was put on your plate.

    If there's enough remanence, there already IS a magnetic field....

    Dunno just WHAT your position might be on Permanent Magnet goods. Fair certain we dare not ask.

    *yawn*

    Why not just wait and see, old bean?

    Wait 'til he has it runnin' and makin' chips.

    THEN tell him it ain't possible.

    Less delay to his work or income that way...


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    I'd like, and the forum owner would like, for this area to have good info, that has some sort of basis in engineering, and perhaps "science". In other words, for there to be info from those who know how things work , and can do it.

    I'm going to have to put my "forum hat" on and start deleting the irrelevant and junk-science postings. No matter WHO posted them.

    You could make that job a lot easier if you would post useful things instead of things with 3% useful content.


    Quote Originally Posted by Monarchist View Post
    LOL! Guess you have forgotten that putting 'lectricity at it was meant to run round in circles on wires for the purpose of producing a magnetic field. Ampere-turns, left and right hand rules, Joules and Ergs... all that s**t and its math that matters when scratch building a new design.
    .....
    A few important points that may have escaped you.....

    1) He has not been able to spin up that IDLER with a 3 HP motor and a 40A breaker.

    2) and that is WITH NO electricity to or load on the IDLER. And so none of that "electricity" you were just touting is (or should be) flowing in the IDLER...... UNLESS of course it is doing what I suggested, and generating.. if, as I suspect, it is generating, then there could be 40A flowing in the capacitors that apparently have not been disconnected yet. (But they should be) .

    That's a goodly load... when the losses are considered. Could explain why his motor can't spin it up without blowing a 40A breaker trying.... Also handily explains his 240V output.... which remanent magnetism does NOT explain.

    3) Of course there is a remanent field. Not very strong compared the field created by the 60 or more amps that a 190A motor might be expected to pull on idle, though.... less a few HP of probable losses that's still a strong field.
    And it takes all of the 50 or 60A current to produce a field that produces back EMF slightly lower than the line volts. Remanent magnetism is not going to come close, unless you spin it a LOT faster. The volts are STILL about how many magnetic "lines of force" you cut per second... Field strength produces generator volts, shaft torque produces power. Always has, always will.


    You may want to delve into the way motors work so that you can contribute something useful here. And I mean that in a kindly way... just listen to Uncle JST and take it easy.


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