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  1. #21
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    He's BACK.....

    Dude: The OP apparently OWNS the 3 HP. If he can go get a 5 HP, that may improve matters..... MAYBE.

    There is a small matter that you may have missed. The OP has a 40A circuit. The 5 HP is not going to pull LESS amperage than the 3 HP. The only hope there is that the extra HP will accelerate the RPC fast enough to get below 40A before the breaker opens. Of course it will pull MORE current to do that.

    Changing the pulley is easy and relatively cheap, especially if we knew what he has for a ratio now..... And with his limited power, may be the best idea At least that will pull LESS current than what he has now.

    If the full speed friction and windage losses are 4 HP, which is "kinda reasonable" with that being about 10% of the 75HP.... even the 5 HP is going to work hard. FLA on the 5 HP is around 28A, and start current 150A or so. It may not get the acceleration to be fast enough without pulling even MORE current, and opening the breaker faster.

    It's a pretty thin justification for obtaining the 5 HP unless I missed where he said he had one already. If he does, may as well try it, of course, but the shaft size may be different, so another pulley may still be needed.......

    I assume he can start the 3 HP by itself OK. If it pulls 40+ A by itself, there is another problem.

    EVERYONE HERE already knows that the real problem is either a power problem, or a motor wiring problem. He's basically trying to pull his 40' yacht and trailer with an old VW bug.... If he had decent power, the RPC would probably start as-designed just as we see it. It's POSSIBLE that the motor has been connected with a coil backward or some such issue that would prevent a start. That needs checked if there is any chance a wiring issue could have occurred.

    The OP (IIRC) has a nominal 400A service, but it is broken up into 2 separate 200A subpanels, and even there he has only 100A for this RPC. He may never USE more power IF he can get the thing started, but there is the problem of starting current, which is huge.

    AND IIRC, the power company has him on a 15 kVA transformer (is that the OP that said it in a different thread?) I believe if that was him, the powerco was going to upgrade him, but.... Did they? and if so, what TO?

    NOTHING is going to help if the power is being pulled down to 170VAC by the load..... ANOTHER pice of info that I don;t recall seeing anywhere.... what the volts are as he is trying to start the thing.

    >>>>>>>>>>>>>>>>>>>>>>>>
    Frankly, he may be better off, if he cannot do anything about the electric service, to push that tanker-anchor into a corner and get another RPC, or at least another motor to use as one which is better suited to the power he has.
    <<<<<<<<<<<<<<<<<<<<<<<<<<<


    Oh, yeah... the rope start thing.... All a rope start does is to get the motor rolling over . It "biases" the motor so it can get going. If you were thinking it was intended to get the motor up to 80% of full speed, or anything like that, you got another think or two coming....

    And, he would STILL need to have the basic ampacity to supply start current (as much as 700A !!!!) to the motor for as long as it takes to get up to speed. He does NOT seem to have that, so it's a moot point.

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    Quote Originally Posted by JST View Post
    Trimming, once again, to any new content of value...
    it's a moot point.
    Yes, actually, it is.

    Ryan is a 'country boy'. He has succeeded at far tougher challenges than this one. I took the time to check.

    He will sort this one also.

    And/or get similarly capable local help to make damned sure of it.

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    Couple of points.

    The motor is a twelve lead designed for normal wye delta start.
    But is currently wired for DOL start, 230V, along with a healthy cap bank. Motor and cap leads terminated on multitap 3 pole block.

    I take the cap bank to be the large section for phase shift. 800MFD
    The smaller bank to be PFC, for the low idle value 13.6A it lists. 400MFD

    Idler Specs NEC values 75HP 230V 192A FLC 55KVA, Listed as 713A starting current on the RPC label.

    Utility Power supply 230V 1Φ, 62A FLC 15KVA

    2P 100A 240V Breaker for starting means.

    Original Thread -Advice needed on wiring up 80 HP RPC to 400amp service

    My take is there is a few combined issues. Utility supply of 62A FLA. Then the trip current curve of the 100A 2P breaker, shown below. Then is the issue of the supply voltage dropping like a stone under the startup load, acting as a built in reduced voltage starting, prolonging the start times, which then affects the breaker trip curves timing ratings.

    A Sq D QO 2P Breaker trip curve for reference. We don't know what brand he is using, but I would suspect the bi-metal element being out of calibration from his repeated attempts to use it as a starter for a DOL 75HP motor.
    100a-qo-curve.jpg
    7x rated 100A = 700A = 0.6sec trip time
    4.25x rated 100A = 425A = 2.0sec trip time
    3.25x rated 100A = 325A = 6.0sec trip time

    My feeling is if he had some means to reduce the starting voltage, to get from 713A starting surge to below the 325A shown above, that would increase his starting time from 0.6 sec to 6.0 sec, which would allow for the stone dropping voltage to recover before the breaker tripped out.

    A larger breaker is not likely in his future with a standard loadcenter panel, or without a service rework.

    The other thing I see adding to the start problem is the cap bank permanently connected. It surely adds additional current inrush to the motor currents.

    I have done some 3Φ motor testing in the past to record some starting/running currents of 9 lead 10HP 460/230V Y/YY wound units, that were unloaded.

    Testing was done from rest with reduced voltage with 1/2 voltage applied to a YY connection, the current was reduced by a factor of 2.4, starting time was slightly extended but normal, about 1 sec

    A standard Y connection (460V), fed with 240V, so that would be a Y start, YY run on 230V, reduced the current buy a factor of 5. Starting time was extended to about 1/2 sec, but normal.

    The best current reduction was obtained with 1/4 applied voltage on start. With a Y connection (460V) and YY (230V)run connection. 110V 3Φ was used as the source. Current was reduced by a factor of 9. It took about 2 sec starting time but was smooth.

    Most of the builders I looked at, that provide these large units use a Y/Delta or Y/YY starting setup on all of the larger units I looked at. In the case of a 75HP unit that would require a Size 4 Nema starter for the Y/Delta Mode.

    If this were my conundrum to play with, and the start circuit is 1Φ, using a pony motor. I would consider using a 1Φ autotransformer in one leg for reduction taps, and using a contactor to shunt it out once at speed.

    The OP got a quote from the vendor for such a setup with a new cap bank, but decided it was a little to spendy for him.

    Even if he manages to get it started on a 100A 2P breaker that wont leave much headroom for attaching any loads to it. Especially his 73A 3Φ load.

    SAF Ω

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    Quote Originally Posted by SAF View Post
    If this were my conundrum to play with, and the start circuit is 1Φ, using a pony motor. I would consider using a 1Φ autotransformer in one leg for reduction taps, and using a contactor to shunt it out once at speed.
    A bit of jackleg ingineering, something common that could handle the current might be ID'ed that could be connected-as an autotransformer to do that.
    The OP got a quote from the vendor for such a setup with a new cap bank, but decided it was a little to spendy for him.
    Add one more contactor to the list of goods he is already short of, and DIY might still not be cheaper. It surely would not have the OEM's experience and blessing coming in the hall along with it. That does have real-world value, what with Inspectors, Fire Marshalls, Insurance folks, and the basic "Prudent Man" test as to personal safety of owner and staff, even if none of those other Agencies ever existed.
    Even if he manages to get it started on a 100A 2P breaker that wont leave much headroom for attaching any loads to it. Especially his 73A 3Φ load.
    I don't see much in the way of "quitting" on the menu, so that may be the point where it hits the wall unless he's at least had a serious mains power upgrade to get around that 15 kVA pole-pig AND can source a panel that supports a larger breaker.

    Using the main breaker of a service-entrance grade panel for this task alone as sole load the easiest and cheapest if 'legal'. I'm not current on that part.

    Back to the real-word load and how many hours of how many days it has to be operated in any given week or calendar quarter. Doubt it is anywhere near even one full shift a day, all week, let alone three, and all-month.

    And that "Beansdiesel" is not just a PM-handle - Diesels actually ARE are he, plain or exotic.

    For part-time use, refurb of a medium 3-Phase Diesel gen set could solve the whole problem in a manner he is already better equipped to support than the average bear. If trailer-mounted, such critters can be all-around useful for lots of other things, too.

    RPC no longer required at all.

    Except for keeping an old GE Telecron wall-clock dead-accurate - and who still even needs THAT? - they are as good as utility mains.

    Just sayin'

    "I got mine." Flip a switch, my smaller MEP-803A becomes a 3-phase source, minimal hassle, 15 kVA peak, 12 kVA sustained. The 10 kVA continuous MIL-spec rating was at 8,000 feet above sea-level, after all, not my mere 350 feet-minus.

  6. #25
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    When he gets back, let's see a voltmeter reading of the line when the pony is turning it, and then when he hits the power for the idler itself. That will pretty much tell the story.

    If he has been upgraded to a 25 kVA that may not be enough. 50 kVA would be a bit over 200A actual service capability, getting to be credible.

    With 15 kVA, at a 5% impedance, about 12V drop at 62A. At 620A, that would be more in the 120V drop category, and nothing is going to work that way. Been there, seen it. Now that I have done this estimate, I see what the issue iis with the motor slowing when power is applied. Depending on what rpm he gets to, he may still have a drop of 50 to 100 V out of 230 when he hits the switch (breaker). No wonder it slows down.


    With 50 kVA, about 12V at 200A. so more like 35V drop at 600A, or 15%. That has a chance of working straight up if the breaker is upgraded. If he was only boosted to 25 kVA, then it's not as nice, I'd expect the drop to be in the 70 volt area, and that is somewhat more of a problem.

    Converting to a wye delta is possible, but seems like a good bit of work, and the OP may not be up for that. It might get the 100A breaker to hold, but whether it will work on 15 kVA seems doubtful. About 58% of normal start current.

    He does have a pony start operating, although not working right nor starting the motor. A pony start is very likely to be the lowest current approach he can do. But right now his pulley ratio is overloading the 3 HP motor. If he changes that to something that the 3 HP can actually do, then he very possibly may get it to run.

    The pony start is a form of reduced-voltage start. With the motor already spinning, the voltage is reduced by back EMF as soon as the initial short magnetizing surge is over. So if the motor is brought up to 50% speed, the effective voltage reduction is about 50%. If brought to 60%, the reduction in effective voltage is 60%, meaning the effective voltage is 40% of line voltage, and current will be a bit less than 40% of normal start current.

    With voltage reduced, current is reduced as well. So long as the RPC has no load, it should "go" at that point, and very possibly will not pop the breaker, since most of the high current part of the start is avoided. The motor essentially gets a "head start".

    Dunno if the 100A will hold it, but seems possible if he can get the pony to run it up reasonably close to 1725 RPM. Whether it will hold with the lathe in operation is another story that depends entirely on the machining power required.


    SAF:

    What di you think of that spec of 13.6A idle current for the RPC? If so, that is the losses, and I would tend to believe in 5% mechanical losses and iron losses as at least credible (about 4 HP out of 75).

    Without any correction, I would expect a motor with 190A FLA to pull around 60A at idle, most of which is reactive current. Then the power factor caps need to compensate out 12 kVA of reactive current, and the caps which you think (and I agree) are the PFC caps appear to be 8 or 9 kVA worth... Reasonably possible, I'm just guesstimating at the idle reactive current..

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    Quote Originally Posted by JST View Post
    When he gets back,
    Good post. No argument. One suggestion.

    First thing back should probably start with confirming (or not) that he has been given the upgrade from 15 kVA, or a planned install date, and if so to WHAT?

    Can't really 'get there from here' if not, no matter how well planned or executed, load-side.

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    Beansdiesel,

    Why such a large RPC? What are you running that requires 100 amps of three phase power? Would a smaller RPC be appropriate?

    Vlad

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    Quote Originally Posted by Vladymere gr View Post
    Beansdiesel,

    Why such a large RPC? What are you running that requires 100 amps of three phase power? Would a smaller RPC be appropriate?

    Vlad
    Covered in an earlier PM thread. JST linked to that already.

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    Quote Originally Posted by JST View Post

    SAF:

    What do you think of that spec of 13.6A idle current for the RPC? If so, that is the losses, and I would tend to believe in 5% mechanical losses and iron losses as at least credible (about 4 HP out of 75).

    Without any correction, I would expect a motor with 190A FLA to pull around 60A at idle, most of which is reactive current. Then the power factor caps need to compensate out 12 kVA of reactive current, and the caps which you think (and I agree) are the PFC caps appear to be 8 or 9 kVA worth... Reasonably possible, I'm just guesstimating at the idle reactive current..

    "Originally Posted by beansdiesel

    I got the quote back, having the SS and a better cap setup with a new wall mounted box sounds nice and all, but I don't want to spend that much.

    The transformer is a 15kva and we are the only one on it.

    Him saying the Cap setup wasn't good enough for CNC has me worried about it. Is there a way to just add more caps or change them out to better ones?"
    Reviewing the Starting, Idling, Reactive Current and Cap Setup

    In my area the line voltage usually runs on the higher side, so I would expect to see the idle/reactive current be much higher than the 13.6A listed, as the iron becomes magnetized stronger. Can be as much as 1/2 FLC on an uncorrected motor. Then given the earlier fact, that the unit was shipped in 2011, That tells me, that the motor is an EPACT energy efficient model with the much higher inrush starting current. Higher efficiency at the cost of increased start current.

    The idle current with correction on the current model of this size is listed at 25A @ 96PF found here:
    Remco Electrical Manufacturing | Phase Converters

    So even the builder has upped the idle current spec by a factor of almost 2. In some field conditions that could be higher. Given your suggested value of 9KVA worth of PF correction that is approaching the 15KVA value of the service in question.

    After reviewing the photos in the original post, there appears to be NO power factor correction connected!! L1 & L2 are the line terminals and L3 the generated terminal. Viewing the reworked capacitor terminations it appears that what used to be the PF bank has been re-purposed as part of the phase shifting bank. Leaving the RPC uncorrected. This I believe would leave the unit drawing around or above the 12KVA figure given above, again close to the FLA capacity of the service.

    It appears that some additional #12 AWG conductors, GRN & YEL, were added to parallel the runs to the bank rows and that the OEM, BLK conductors were also paralleled to make up the other half of the paralleled set. All cap bank leads are connected to T2 & T3. So it appears that the modification to give better CNC capability to the unit as suggested by the OEM, has left the unit with no power factor correction and drawing some serious reactive current during idling.

    There is some serious oxidation on the components in that enclosure. The aluminum terminals, the steel cap cans, and the tin plated cap tab terminals. Looks to be due to condensation from an unheated environment and no ventilation in the enclosure. Those spade terminals I consider only good for about 10A max and 7A if used under continuous load. With them so oxidized I would consider them very unreliable as did the OEM. For the kind of service here I would be putting separate leads on each cap. Appears that that has been already partially done by paralleling due to field failure, but not completely.

    If I were going to replace them as an upgrade I would be looking for units with stud terminals, for a more robust and reliable connection, for this type of service. Especially since they are attached inside an enclosure affixed to a vibrating motor.

    As a side note on those oxidized cap cans. Notice how the top sections are less oxidized? I would surmise that the top of the cans were heated due to the connection resistance, driving off any accumulated condensation sooner than the rest of the can.

    For a different method of a start test, I would reconnect the small bank as the PFC use and disconnect the phase shifting bank. That would reduce inrush and maybe allow it to get started on the limited means available and get some actual current readings to base any further alterations on♦

    SAF Ω


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    Quote Originally Posted by SAF View Post
    I would suspect the bi-metal element being out of calibration from his repeated attempts to use it as a starter for a DOL 75HP motor.
    He keeps saying "Trips the breaker, trips the breaker ..." I swear, those things won't live if you treat them like that. Not that I have any experience burning up breakers or anything but ....

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    Post a video when you get it running.

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    Quote Originally Posted by Shawn Ghormley View Post
    Post a video when you get it running.
    Don't know much about you, Shawn. But I shall hazard a guess.

    You are one seriously PATIENT individual, are you not?

    ...or is it just an optimist?


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    SAF:

    Good eye... I totally missed that about the repurposing, but as soon as I read your comment and looked, it was perfectly obvious.

    The other reason for the tops being less corroded may be due to the caps warming up in use, and the heat rising to the top, so that the top had less condensation.

    In my experience, the spade connectors, if tight and properly assembled to begin with, not disturbed and not overloaded, tend to produce a good connection over time until they get really corroded.

    But that varies. if overloaded so they heat up, they relax and are terrible. Same if some person has trouble getting them installed and decides to "relieve the pressure". or gets them cocked putting on, so the female half is stretched open, And then there are 0.020 and 0,032 versions of them. The wrong connector thickness combo will be loose, or so tight that the female half is distorted when put on and soon becomes loose.

    The bad rep is probably as much or more from screwups assembling as it is from real problems. At a former employer we used millions of them, and had very little trouble.

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    Quote Originally Posted by JST View Post
    SAF:

    Good eye... I totally missed that about the repurposing, but as soon as I read your comment and looked, it was perfectly obvious.

    The other reason for the tops being less corroded may be due to the caps warming up in use, and the heat rising to the top, so that the top had less condensation.

    In my experience, the spade connectors, if tight and properly assembled to begin with, not disturbed and not overloaded, tend to produce a good connection over time until they get really corroded.

    But that varies. if overloaded so they heat up, they relax and are terrible. Same if some person has trouble getting them installed and decides to "relieve the pressure". or gets them cocked putting on, so the female half is stretched open, And then there are 0.020 and 0,032 versions of them. The wrong connector thickness combo will be loose, or so tight that the female half is distorted when put on and soon becomes loose.

    The bad rep is probably as much or more from screwups assembling as it is from real problems. At a former employer we used millions of them, and had very little trouble.
    I have had miserable experiences with them. Some of the locomotive equipment has them and after a few years in a Diesel engine compartment, they are so dirty that the only place where they can make a good connection is the tiny protected surface where the connector kept dirt off the spade. If anyone moves them or vibration shifts them slightly, the connection is gone. Then you have to clean off all the dirt and oxidation to make a new connection. I hate them.

    Bill

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    Yeah... that is under the "not disturbed" clause.

    I should have added that they are never as good the SECOND time you push them on.... even if you do it perfectly.

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    With quality connectors and the approved tooling, and a use case that requires little service, there a beautiful thing.

    For high current, severe duty, corrosive environment using cheap PVC knockoff connectors with generic tooling, there about the worst you could pick. Especially on things that will require service in its life.

    The ones in the photo a a prime example. Cheap PVC connectors, generic dimple tooling, and a tough environmental application. They have been replaced / augmented once already.

    I have a surplus supply of high quality, temperd, F crimp style silver plated connectors with the proper $400 crimper. And I would not be using them in this application.

    There great for control applications and low heat and current, but in this application not a preferred choice.

    The OEM even commented to that effect in his response to the OP.

    On a 10HP or less intermittent use RPC, I could see it, but a 75HP unit built for agricultural use out in the field, I see it as a poor choice. Your mileage may vary.

    SAF


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