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    Quote Originally Posted by jim rozen View Post
    Most of the ones I've seen engergize only one winding. Avoid amp-clamp meters to diagnose setup issues.

    They actually energize all the windings in a delta wound, and two in a wye motor. The power is applied across two lines, so everything in between gets some current, plus whatever is generated.

    With the step up type, you need to use a wye motor, and energize from one line to neutral point, so that really IS "one winding".

    What do you see wrong with "amp clamp" meters? For that matter, what do you mean by that term?

    You are going to measure current and voltage, so any accurate meter that can do that job is OK.

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    I think I'll go ahead and wire up this 415V delta motor for wye, and put 240 across ONE winding (i.e line to star point), so it will act as a ''step up RPC'' as JST put it. There is only one way to fin out what will happen. I will look for a 1 hp pony motor and build some kind of a frame around the motor for a hinged plate etc. I will let you guys know how things go in a new thread, as it's really OT for this thread.
    Thank you all very much for your input.

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    Quote Originally Posted by JST View Post
    T
    What do you see wrong with "amp clamp" meters? For that matter, what do you mean by that term?
    You are going to measure current and voltage, so any accurate meter that can do that job is OK.
    Amp-clamp: inductive clamp-on meter. I've seen very strange effects with those. Put on the input lines of my converter, they read
    the sum of real and imaginary currents. Put on the manufactured leg, they seem to read only real current.

    For troubleshooting and ballancing a rotary converter, I suggest a voltmeter only. One can be fooled into thinking the converter is
    wildly out of balance based on an amp-clamp reading, in spite of voltage balance being very good.

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    Quote Originally Posted by jim rozen View Post
    Amp-clamp: inductive clamp-on meter. I've seen very strange effects with those. Put on the input lines of my converter, they read
    the sum of real and imaginary currents. Put on the manufactured leg, they seem to read only real current.

    For troubleshooting and ballancing a rotary converter, I suggest a voltmeter only. One can be fooled into thinking the converter is
    wildly out of balance based on an amp-clamp reading, in spite of voltage balance being very good.
    Jim,
    I'll keep that in mind. I'll have to buy at least one clamp-on meter to have though. I think it would make a nice addition to my Amprobe muultimeter and would come in handy for all kinds of jobs, as I'll be playing with iron until I die.

    Thanks
    Aryan

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    Quote Originally Posted by jim rozen View Post
    Amp-clamp: inductive clamp-on meter. I've seen very strange effects with those. Put on the input lines of my converter, they read
    the sum of real and imaginary currents. Put on the manufactured leg, they seem to read only real current.
    OK, I was not sure if you were separating the old "Amprobe" style meter from newer ones. The old ones usually read average current, newer may read either RMS or average.

    As for the "sum of real and imaginary", I don't quite get why/how that would happen. What would suggest that to you?

    Quote Originally Posted by jim rozen View Post
    For troubleshooting and ballancing a rotary converter, I suggest a voltmeter only. One can be fooled into thinking the converter is
    wildly out of balance based on an amp-clamp reading, in spite of voltage balance being very good.
    Volts may or may not result in a given amount of amperes..... In a motor, that depends on a number of things.

    One thing for sure, however, torque in an electric motor depends on amperes. so the torque contribution of each wire is going to be related to the amperes flowing into the motor.

    In BOTH cases, the phase is going to affect the result. Voltage at the wrong phase may produce less current, or current that is not helpful. Current at the wrong phase may produce less power, or may result in torque that is not helpful.

    Most motors produce back EMF that is pretty much in the correct phase relation for all three wire pairs, so that is usually OK. Adding capacitors on the generated leg will change both voltage AND phase, by amounts depending on the added capacitor and the characteristics of the motor.

    Relying on just voltage, or just current as a means of checking operation is probably unwise.

    Remember what the goal is: It is to provide an output that is as close to perfect power company 3 phase as possible. And you know that if you succeed, the voltages on all phases and currents on all phases will closely match each other, assuming the powerco does their job (a very good bet) and that the motor maker also did a good job (certainly a decent bet).

    Ideally, you would set the adjustments of an RPC to get a close voltage match, AND a close current match on all three wires.

    The issue is that you start out behind the 8 ball to the extent of perhaps 5 to 10% on voltage, because the back EMF of the motor is always lower than the incoming line voltage by that general range of voltages at full power.

    At idle, a motor has very nearly 100% match of back EMF and incoming voltage, which you can see with a tachometer, since speed will be close to synchronous. Very little power used, so current is minimum, just the magnetizing current plus a small power current.

    Under load, the back EMF drops due to the motor slowing (allowing more current). The actual applied voltage also drops due to resistance of the motor windings.

    That happens in the idler also, which means the output is not perfect, There is an inherent imbalance with the usual setup of an idler motor, and the smaller the idler in relation to the load motor, the worse that is. The "direct" wires are just that, they have nothing extra in series, while the "generated" phase has a motor with resistance and inductance, plus magnetic effects, in series. With the same current flowing, the generated leg is going to be lower in voltage coming out of the idler, than the direct legs.

    In an effort to "fix" that, capacitors are often applied. That does correct voltage, but in the process it alters phase somewhat, and it is necessary to look at both voltage and current to determine when the best compromise is found, to fix on the values of added capacitor which will allow that idler and that load to best approximate powerco 3 phase.

    There are some alternate methods for correcting voltage imbalance which may have less of a double effect, but the true best system is generally the largest idler combined with one or another means for correcting voltage. I think it is fair to suggest that sufficiently larger idlers will in general have an "uncorrected" output (no capacitors etc) that is closer to the ideal than most implementations of smaller idlers combined with correction schemes.

    But, since the end result is to closely match "regular" 3 phase, there is a need to use both voltage and current measurement, along with phase angle if that capability exists, to get the optimal setup of "balance capacitors" or other schemes for balancing.

    The other way to go is to have an idler considerably larger than the maximum load (perhaps 5x). That may actually give the best results if it can be done. The large motor has less demand on it relative to maximum load, so voltage is higher to begin with, and both resistance and inductance are lower.

    Alternately, the method originally suggested in this thread, the motor-generator set, is likely to provide the best balance overall. That is natural, because all wires from the generator pass through the same resistance and inductance etc. There may be an overall voltage drop, but it will remain decently balanced at all loads. It is also the most expensive way to go, and can be right up there with a Phase Perfect, for instance, unless you have access to surplus equipment.

    The VFD approach will give very good balance, with other benefits. But you need more of them.

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    Quote Originally Posted by JST View Post
    Alternately, the method originally suggested in this thread, the motor-generator set, is likely to provide the best balance overall. That is natural, because all wires from the generator pass through the same resistance and inductance etc. There may be an overall voltage drop, but it will remain decently balanced at all loads. It is also the most expensive way to go, and can be right up there with a Phase Perfect, for instance, unless you have access to surplus equipment.
    If one really NEEDS powerco-grade, then driving an OVERSIZE gen head with a tachogenerator or resolver equipped Dee Cee motor can deliver consistency as good as a small fraction of one percent.

    Twofold challenge arises, though:

    First one is that single-phase DC Drives that can DO that are sort of an afterthought even by the time one hits 32A or roughly 12 HP. 3-Phase drives by contrast, are stock designs in catalogs, even if not built for inventory until ordered, ten HP to over ten THOUSAND HP.

    So figure 12 HP in, the usual losses - "civilian affordable" uber-stable DC Motors are rudeley less efficient than AC - and perhaps only 8 HP available. ELSE "bring MONEY!".. lots of it.

    Second part is even harder. NEW DC motors in serious integral HP ratings can cost over eleven thousands bucks for a mere FIVE HP Reliance.

    Surplus costs for GOOD legacy DC motors is no picnic, either. Don't even ASK about shipping. They are larger and heavier than 3-P AC motors by a high multiple as well.

    Now.. with the economics of it all holding yah to 10 HP or less? Yah can match or beat a Phase-Perfect's cost off the back of used-but-good materials. Yah can avoid the P-P manual calling for capacitor renewal every THREE YEARS - worse than even a short-lived VFD at about 7 years, middle grades at 9 years, better ones at 12 years, best ones more-yet and still climbing.

    Fair chance - cheap or dear - the VFD may go DOUBLE or more the life of the maker's cautious recommendation.. as may the P-P, to be fair.

    But with a durable as Hay-Budden anvils DC to AC motor-gen set, yer now dealing with loss of 30 to 40 percent of what left the wall vs only about 7 percent for the Phase-Perfect, mebbe 5 percent loss for a decent VFD, and perhaps 15% - or LESS - loss for an RPC.

    Which one of that whole circus or options needs the LEAST long-term maintenance or spend?

    The AC motor-gen set. Hands down.

    Next best? The RPC.. well. its relays, contactors, or start and/or run/balance caps. Not so much the bearings in the motor.

    RPC is "generally" good enough. And one of the lowest initial cost as well life-cycle costs.

    Pick any 255 of those choices...

    ...the other one is reserved as the "f**ked, again, got too damned optimistic" bit-flag.

    DAMHIKT!


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    Quote Originally Posted by jim rozen View Post
    Most of the ones I've seen engergize only one winding. Avoid amp-clamp meters to diagnose setup issues.
    I'm using that description to distinguish the difference between:

    a Y connected line to neutral feed and line to line output, which uses the motor to do the voltage transform from 240 to 415. (which severely stresses just one of the windings.

    vs line to line feed and line to line output which is tradiational configuration.

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    Quote Originally Posted by johansen View Post
    I'm using that description to distinguish the difference between:

    a Y connected line to neutral feed and line to line output, which uses the motor to do the voltage transform from 240 to 415. (which severely stresses just one of the windings.

    vs line to line feed and line to line output which is tradiational configuration.
    Yes. My comments above were directed to the line-to-line type, not the voltage transforming version. I've never seen those or worked with them.

    Again I suggest that inductive clamp-on meters, used to attempt to tune a rotary converter, will cause more smoke than light on the job.

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    Quote Originally Posted by jim rozen View Post
    .......

    Again I suggest that inductive clamp-on meters, used to attempt to tune a rotary converter, will cause more smoke than light on the job.
    So does measuring voltage, "alone".

    If you are going to try to provide true 3 phase, you need to know voltage, and phase, and then it is good to verify you have equal current flow, because the other two factors "should" give that. Or, voltage and current, with a check of phase, or current and phase, with a check of voltage.

    If you want a flagpole vertical, you need to "sight it" (or use a level) from more than one position. So it is with 3 phase.

    As far as a current meter measuring some mysterious different current just with an RPC, well, forget that..... The meter measures what is there. It is up to the user to decide what the measurement means.

    I'd like an example of a measurement that gives this magical oddity..... where the meter was placed for the measurements, and what measurements were obtained.

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    My 8$ amp clamp meter is useless around motors and transformers due to the ambient magnetic field.

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    Quote Originally Posted by JST View Post
    So does measuring voltage, "alone".

    If you are going to try to provide true 3 phase, you need to know voltage, and phase, and then it is good to verify you have equal current flow, because the other two factors "should" give that. Or, voltage and current, with a check of phase, or current and phase, with a check of voltage.
    As far as a current meter measuring some mysterious different current just with an RPC, well, forget that..... The meter measures what is there. It is up to the user to decide what the measurement means.
    I' like an example of a measurement that gives this magical oddity..... where the meter was placed for the measurements, and what measurements were obtained.
    Sure. A scope to measure the phase relationships. A voltmeter to measure voltage. And equal current flow? You need a meter that measures current. DC current, right?
    Oh. No. AC current - a quantity that has both a real and imaginary component. Which one do you want to measure? One, the other, or both, at the same time? (high end
    power line analyzer perhaps)

    Magical oddity: The amp clamp meter reads the the real and imaginary current when clamped on the two utility phases of my hardinge lathe. Clamped on the manufactured
    leg, it reads almost nothing, until the spindle is loaded down. As you say, the universe gives the correct answer to the measurement all the time. It's up to the end user
    to say what it means.

    I say, go ahead and use an inductive clamp-on meter to tune up a phase converter. See how long you can chase your own tail.

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    This sure getting muddy, A rpc is not a perfect devise, the phase shift is dependent on load and capacitors, the voltage is all over the place on the generated phase, and the amps are reflected by load and voltage and phase angle, 2 of the legs are inductive and the generated leg goes from captivate to inductive vs load. At best it is a hit and miss affair, and if there is more than 1 motor in the line it gets messy. Every set up is a custom set up with capacitors and idler motors. To say the amp meter is useless and the other reading are valuable is off, everything means something if you know what to look for....Phil

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    I wonder why more panel builders don't put these on their RPC:
    4-digit 3-Phase Electric Current Voltage Frequency Power Energy Meter Monitor | eBay

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    Same reason I don't like putting gauges on stuff I make, what they don't know wont hurt them, with gauges you will be bothered to death with stupid questions by would be experts ...Phil

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    Quote Originally Posted by jim rozen View Post
    ,,,,,,,

    Magical oddity: The amp clamp meter reads the the real and imaginary current when clamped on the two utility phases of my hardinge lathe. Clamped on the manufactured
    leg, it reads almost nothing, until the spindle is loaded down. ........
    And, apparently, you do not know why..... although I gave you the answer already. There is a very simple reason for it, go back and read, then think.

    This is not about the meter, it is a fundamental fact of how RPCs made with generic motors operate. An RPC made on purpose with a custom motor can minimize that effect.

    You have just made the case for why balancing on voltage at idle is as worthless as balancing with an ammeter at idle. That's not where you need to balance.

    At idle all you need is to not go too high in voltage, the current measurement is a bonus that is helpful, but not required.

    Under load, the ammeter measurement is what you want to know, to see if your motor is able to produce the required power, and is not being starved. A voltmeter at that point is helpful, but not required.

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    Quote Originally Posted by Phil in Montana View Post
    Same reason I don't like putting gauges on stuff I make, what they don't know wont hurt them, with gauges you will be bothered to death with stupid questions by would be experts ...Phil
    LOL! Yahreally... Three thermistors wud tell yah a more useful tale... but never mind.

    Simply run yer s**t "within due bounds" it dasn't actually make a damn.


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    Now we know that everything is driven by current, heating, magnetic fields, motor torque and so forth. Voltage's job is just to drive current. Voltage is just an indication of what is going on and without phase angle is kind of meaningless. Most of us use voltage for balancing simply because it is easier to do. Most do not have clamp ammeters.

    As far as a clamp ammeter measuring the positive and negative sequence currents, yes of course! You could use a current shunt and get the same results. The meter supplies the integral vector sum of the current vectors. The older iron vane meters produced the true RMS value of the current wave. The d'Arsonval movements provide an average value with the scale calibrated in RMS. The reading is only good for sine waves which with magnetics is rare. The good electronic ones display true RMS.

    Jim, where did you get the impression that clamp ammeters cause problems?

    Tom

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    RPC

    Balance with an amp probe under load.

    It's the only meaningful way.

    Volts never hurt anything. It's the amps that light the fires. Keep those amps under control. The volts will take care of themselves.

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    Quote Originally Posted by TDegenhart View Post
    Most do not have clamp ammeters.
    ..
    .. clamp ammeters cause problems?
    Well I sure am in deep s**t, then. Three here, another in Hong Kong. AC-only & AC OR .DC... Not as if they were 'horribly costly, is it?

    HTF d'you get by without 'em?

    Got more than a few shunts and the odd current transformer around as well - but "there are days" yah do not really want to have to open the circuit to insert sumthin'

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    Quote Originally Posted by jim rozen View Post
    How good is the power from this converter? Actual measurement, machine with load motor attached and running:

    Thanks so much for that picture Jim. I always wondered how a RPC would look under on a scope. I do have a question though. Shouldn't the two real phases be 180 degrees apart when the power is supplied from a center tapped transformer? How are they shifted to be the proper 120 degrees?

    Quote Originally Posted by jim rozen View Post
    Sure. A scope to measure the phase relationships. A voltmeter to measure voltage. And equal current flow? You need a meter that measures current. DC current, right?
    Oh. No. AC current - a quantity that has both a real and imaginary component. Which one do you want to measure? One, the other, or both, at the same time? (high end
    power line analyzer perhaps)

    Magical oddity: The amp clamp meter reads the the real and imaginary current when clamped on the two utility phases of my hardinge lathe. Clamped on the manufactured
    leg, it reads almost nothing, until the spindle is loaded down. As you say, the universe gives the correct answer to the measurement all the time. It's up to the end user
    to say what it means.

    I say, go ahead and use an inductive clamp-on meter to tune up a phase converter. See how long you can chase your own tail.
    Thanks again for this titbit. Dad just built and RPC and we were noticing that the manufactured leg was quite low compared to the other two when running. Makes sense now.


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