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  1. #61
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    Quote Originally Posted by cg285 View Post
    after spending most of the day accessing the motor i find it's a 9 wire which i understand is already wye and can't be changed? i ohm'd out the windings and they appear ok. to ground i have approx 0.7xx meg which i think should be ok - probably should have had the meter on a smaller scale. i did find one wire nut i had to cut off (overheated/corroded) MAYBE i could get lucky with that.

    healing from my second elbow surgery in the last 5 months may the pricks that use a roll of black tape on every wire nut break both elbows.
    check this out

    9 wire motor wiring - Bing

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    Quote Originally Posted by thermite View Post
    T

    Not even CLOSE to a "new challenge". His rig WAS WORKING. It doesn't need much.
    It was working on a regular three phase line. Running on a converter is a whole different problem. First he has to see if the required current is even available.

    Then, instead of shotgun increasing everything, he needs to determine the components to change.

    Bill

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    Quote Originally Posted by 9100 View Post
    It was working on a regular three phase line. Running on a converter is a whole different problem. First he has to see if the required current is even available.

    Then, instead of shotgun increasing everything, he needs to determine the components to change.

    Bill
    He STARTED by posted his current, standby and starting inrush, has Ohm'ed the motor, posted that, etc. etc. Listed Amperage "no work on the table" is a close match to the FLA of a 10 HP motor under MY roof.

    That fool grinder must have more monkey-motion power parasitism than it needs to do work that IS on the table?

    I don't know what else you "take readings so we can stretch this out longer" proponents expect him to do?

    "Pony" the load with a gas turbine? Diesel? Colpitts cartridges? Repurposed Allison inertial starter off a 1939 P-40? Or the ENTIRE Allison? Or only a Pierce fire-truck engine?



    Move to a facility that HAS good 3-Phase?

    Or just sell the grinder to someone who HAS gobs of utility-mains 3-Phase, then hire-back the work off it?

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    Quote Originally Posted by thermite View Post
    Threw away three VFD's, two brand-new, never wired up, the third a decent-grade Schneider Altivar 71 ten hoss.

    Spent about $1600 on a used P-P, then $4,000 on a NEW one. As with VFD wanting new capacitors every 7 to 12 years? P-P want new caps at THREE year intervals! RTFM.

    The RPC, all new parts? 10 HP Weg motor, one of Jim's Phase-Craft controllers?

    About $700. Caps will probably outlive me if not also impeachment as a national sport.

    Cheapest VFD I'd allow under-roof starts at $1,600 or so. It would operate exactly ONE machine-tool.

    The RPC and Phase-Perfect go to a load center and whole buncha CB's and Hubbell twist-lock wall outlets. By way of a "pure Sine wave" filter in the case of the P-P, then a Delta-Wye transformer for both. No corner-grounding or high-leg Delta for me!

    All my motors are OLD. They weren't BUILT for "inverter duty" any more than I was!

    Always liked GIRLS, y'see!

    I hope you consulted with the P-P people before mixing that RPC with their their unit in a load center. I would hate to see that 4K unit go tits up on you!

    Quote Originally Posted by thermite View Post
    Take note that one of the older and larger commerial makers of RPC publish a table that takes hard starting under load into account as to RPC sizing.

    Add idler. Upsize the feed. Go make parts. No meter required.

    Not even CLOSE to a "new challenge". His rig WAS WORKING. It doesn't need much.

    Yeah, you could keep adding additional idlers and capacitors until you found a good match. Remember that idlers use current and the more current the more KW used. Take a look at American Rotary website and see that they recommend a 25hp rotary for a hard starting 10hp load, that's a rotary capable of starting a 25hp load.


    VFDs' have.a place, I just don't believe that the OPs' situation is a correct application for a VFD. IMHO I think you would need to size the VFD to at least 3 times the size of the motor. VFDs' themselves have a limited amount of capacity vs time that they are capable of providing without over loading, whether it's limiting the voltage and/or current.

    In all the scenarios mentioned, there seems to be a significant amount of money involved to get this motor up and running. Since cg285 already has the Rotary, I would call the people who make/sell the soft starters and explain to them what he has and his problem. Have them make a recommendation and if they would guarantee that their solution would work. This approach adds the least amount of additional monies needed for a solution. I think soft starters around in the $400 range.

    Of course you could just buy a 10hp 220v WEG single phase compressor duty motor with a magnetic starter for about $1K delivered on Amazon. Probably could find it cheaper elsewhere.

    3 phase motors are about 90% efficient while single phase motors are only about 80% efficient so it cost a little more to run the same hp on single phase power. Depending on how many hours you are running the motor it could add up, however if it were only a few hours a month, probably no big deal. Only the OP can determine how much to spend on getting this working vs ROI.

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    Quote Originally Posted by tmt View Post
    I hope you consulted with the P-P people before mixing that RPC with their their unit in a load center. I would hate to see that 4K unit go tits up on you!
    I'm retired. Doubt they could have afforded my rates even 25 years ago, so no. They can get their own cawfee.

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    9 lead motor wired as wye. fixed bad connection but no change in @draw. when i can find a helper i'll meas voltage

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    There is absolutley no reason to oversize a VFD by 3X. Or at all, even.

    If a VFD is rated for 30 amps, that is a continuous rating. Every minute of every month of ever year.

    If you have a 30 amp VFD that times out or overheats, you have a piece of junk VFD that is masquerading as something it's not.

    That's the whole point of VFD technology...you are varying the frequency, which means you can toss out all the old ideas of 'overload during start'. A start uses no more amps than a run. The only time that would not be the case is if you asked the VFD to do something unreasonable - for example, asking it to start the motor/load in .0005 seconds. All equipment will fail to do the job if you abuse or misapply it.

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    Old school soft start was time delay relay and a big resistor.
    Nice and easy to the working guys side on mechanical hit. Not sure the power side but amp meters where down.
    Now we have electronics.... comments?
    Bob

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    Old school methods are very crude and sometimes effective. New methods are far less crude and far more effective. That's called progress. I know, the world is going down the drain...but sometimes progress actually happens.

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    Quote Originally Posted by thermite View Post
    He STARTED by posted his current, standby and starting inrush, has Ohm'ed the motor, posted that, etc. etc. Listed Amperage "no work on the table" is a close match to the FLA of a 10 HP motor under MY roof.
    HE DIDN'T POST THE VOLTAGE AND PHASE ANGLE OF THE GENERATED PHASE WHEN TRYING TO START!!!!!

    Without that, the rest is pointless. What does it take to get a simple point across? That leg is probably being dragged down so low that the motor is essentially trying to start on single phase current. Why is something so obvious so hard to understand?

    As to a current limited VFD, since it maintains phase integrity when loaded, there is a chance that it will develop enough torque to start moving with a high static friction load, but I wouldn't count on it. It is likely to need a lot more to get moving, which means a larger VFD.

    Bill

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    Quote Originally Posted by GregSY View Post
    My personal experience with VFDs - modern, non-Chinese VFDs - is they are dead reliable and trouble free.

    In my case, I bought a three phase input VFD and connected it for single phase input power. As JST notes above, this works if you operate in a derated mode. Why did I do this? Well....I talked to the factory expert and he said that was best for what I wanted....best being slightly less money. If I didn't have access to the factory engineer I would just buy the purpose-built single phase input VFD.

    It's compact, quiet, allows 'soft' and regulated starts and stops and the motor has all three phases doing full work. Plus I can vary RPM if I want. I can also reverse rotation. Nothing else touches that.

    Quote Originally Posted by GregSY View Post
    There is absolutley no reason to oversize a VFD by 3X. Or at all, even.

    If a VFD is rated for 30 amps, that is a continuous rating. Every minute of every month of ever year.

    If you have a 30 amp VFD that times out or overheats, you have a piece of junk VFD that is masquerading as something it's not.

    That's the whole point of VFD technology...you are varying the frequency, which means you can toss out all the old ideas of 'overload during start'. A start uses no more amps than a run. The only time that would not be the case is if you asked the VFD to do something unreasonable - for example, asking it to start the motor/load in .0005 seconds. All equipment will fail to do the job if you abuse or misapply it.
    I am not trying to stir the pot or anything like that, just making a suggestion. Perhaps I should have said to contact a VFD product engineer with his scenario and ask for a recommendation. In the first Quote noted, you said you de-rated the VFD you purchased, however in the second noted Quote of yours, you indicated that a good VFD will run 24/7/365 at the rated output, so why did you go the de-rated route? My guess yours is probably rated the size closing in on twice the motor ratings.

    It's not that the output can't handle it, it's because the input won't handle it. An VFD needs a good DC supply source in order for it to work properly. The DC power supply portion is designed for a 3 phase AC input It needs 3 diodes (one for each line) and there are inductors, capacitors and other things to make up the DC power section. Anyway by supplying a single phase power to the diodes in order to get the same amount of current supplied to the DC supply, you have to supply the each of the two lines diodes with 150% more current and at that rate they will not last long. Also the ripple voltage is much smoother for 3 phase over single phase. So who cares, well the inductors and capacitors care a lot. The more ripple current through a capacitor the shorter their life expectancy. This is a really simplified picture of the DC supply, since most all VFDs use a switching power supply which are carefully thought out and designed for 3 phase input and most everything in its design will not continue to function very long if the components are over loaded . This is why most recommendations are to de-rate the output rating for the VFD.

    There are examples that require a higher ratio than just 2 to 1. I use VFDs on my irrigation wells each is a 7 1/2hp Grundfos submersible pump. I use a Schneider Altivar on one and Yaskawa on another. Grundfos requires that when using their submersible pumps that you must ramp up to 30hz in a specified time. It's not because of the electrical need of the Motor, but because the motor and pump bearings need that speed in order to be properly lubricated. I contacted product engineers from both companies when sizing my VFDs. On the Altivar, it is a 10hp single to 3 phase designed VFD. Physically it is same size as the Yaskawa yet it is several pounds heavier. Its amp output is rated at 33 amps for a 22 amp motor. Yaskawa which isthe world's largest manufacturer of AC drives and motion control products is just a straight 3 phase VFD but the output is rated at 55 amps. Since I didn't get into the design of each one I can only assume with the Schneider Altivar DC input is designed around single phase input with only single phase line inputs and larger heavier inductor. They were both basically the same price. I like the Yaskawa a little better than the Altivar since it reads both my flow meter and pressure transducers directly, while the Schneider would have required some additional add-ons. Both required more than the rated horsepower of the motors due to acceleration required. I am not aware of any VFD that goes from 0 to 60hz instantly, they all ramp up to that speed so as not to overload the system components.

    I can only guess that cg285 requirements are greater than mine.

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    What I said is very clear - I used a three phase input VFD that is derated to allow for the fact that it is being inputted single phase power. I have forgotten the exact numbers but it's something like a 32 amp drive derated to 16 amps.

    The derating is solely for that purpose - not because the drive cannot output its rated amps under nameplated conditions. When I supply a 3 phase input drive with single phase power, it's not gonna be reasonable to expect it to perform the same. The drive is not a magic box.

    Notice - I said the OP needs to buy a drive rated for 30 amps OUTPUT based on 240V single phase input. His choice would be to buy a three phase input drive (of around 60 amps) or a purpose-built single phase input drive. Either way, it needs to be good for 30 amps OUTPUT by the manufacturer. That's why you look at output...that's where the rubber meets the road.

    So I'll say it again - a 30 amp output drive will do that all day long, for many years. If you buy a 30 amp output drive and deviate from its nameplate rating by running it on a different power supply, things will change.

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    Quote Originally Posted by 9100 View Post
    HE DIDN'T POST THE VOLTAGE AND PHASE ANGLE OF THE GENERATED PHASE WHEN TRYING TO START!!!!!
    Why would he?

    Got him a Florida lawster as is plannng a legal challenge to the "Laws" of physics? He'd want to be inside the Capitol beltway for that to fly.

    He is not trying to "INVENT" the electric power industry.

    He is only trying to UTILIZE one tiny 10 HP ration of it.

    "BFBI". He needs a bigger hammer. Or a lower-load platen grinder.
    or.. by this point? Maybe a new line of work.. as a talk show host?


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    Quote Originally Posted by thermite View Post
    Why would he?

    Got him a Florida lawster as is plannng a legal challenge to the "Laws" of physics? He'd want to be inside the Capitol beltway for that to fly.

    He is not trying to "INVENT" the electric power industry.

    He is only trying to UTILIZE one tiny 10 HP ration of it.

    "BFBI". He needs a bigger hammer. Or a lower-load platen grinder.
    or.. by this point? Maybe a new line of work.. as a talk show host?

    How many thousand posts are there here of people balancing RPCs by reading the voltages? With that starting load, the voltages are almost sure to be way off and in effect the phase converter is not phase converting. The generated leg is probably getting a weak current, way more phase shifted than the 60 degrees needed. If it is getting enough current from the line (another reading), adjusting the starting parameters should cure the problem. Instead of addressing the actual issue, we have all this sturm und drang, everyone guessing about something where they have no real data and wanting to discard the already invested in system without looking at fixing it.

    Bill

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    Back in my earlier days in the shop where I worked in 1978, we were putting together a double end trepanner that had a 200 HP motor-generator set. Remember those? Owner was too cheap to go with SCR drives!!! That provided enough DC current to power a 150 HP constant HP DC motor. The shop was almost maxed out on power coming into the building. I don't remember the KVA rating of the power coming into the shop, but when you have six plus trepanners and other machines running with all of the coolant pumps running, it was close to maxing out power. Well, this 200 HP M-G set would not start without tripping the breaker. So what we did would start turning the motor shaft by hand, be surprise how easy it was to get it turning about 30-50 RPM by hand. Then we would hit the start button and off it would go up to about half speed and we would kill the motor relay, then hit start again, this would get it turning almost full speed. Again, kill the relay, hit start again, this time it reached full RPM of about 1200. We keep the M-G set running all day long until we were finished for the day, then shut it off. We could only do this before all of the other machines were on line. Kind of a soft-hard start in a way.

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    In two places I ha some dealings with, Peabody #10 mine, near Springfield, IL and Rock Island Arsenal, they had both MGs and solid state supplies, for powering the trains in the mine and big plating tanks. Both people much preferred MGs. They had to do scheduled maintenance, but they had much less trouble with breakdowns. The train system in the mine was divided into two sections, one solid state and the other MGs. If they tied them together, spikes from the MG contactors promptly blew up the SCRs. When you open a contactor on a half megawatt MG running on 4160 three phase, you are not going to protect your semiconductors with a Radio Shack surge protector.

    Bill

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    Maybe get back to the basics of this issue?

    The OP has a machine that is known to draw a lot of current on start-up. We, or at least "I", do not know if the machine "starting under load" simply means that it has a part on it, or if it not only has a part, but has to start when actually grinding, meaning it has to start when part way through a cutting pass.. To me those are two different scenarios.

    Having to start with a part on-board sounds as if it is mainly an inertia issue, with the probability of some "stick-slip" action when starting. That means that a form of soft-start WOULD work, because the actual "power" needed is not necessarily large. Lower power would mean a slower start, but as long as the torque is more than the "sticking" can resist, it will start and accelerate.

    In that case, the idea of a standard soft-start might work, but it is likely that some methods would not be good because they are set up for a soft but fairly fast start.

    The VFD is very flexible in the times and other details of it's working. A VFD can be set up for a wide range of acceleration times, and will not overheat if the time is long, the way many other soft-start systems may. For other systems, resistors, reactors, transformers, or some solid-state, they may overheat simply because they are made under the assumption that they will not be "on" more than a fairly short time.

    With a high inertia load, you get a heavy electrical load for an extended time. You really need to have the best "torque per ampere" you can get.

    The VFD should provide that. The whole derating deal is to take care of two parts in the VFD. One is the input bridge rectifier, and the other is the "bus capacitor". VFDs are a highly competitive market, and customers buying a lot of them will change vendors for surprisingly small amounts of money per VFD. So, the "power modules" are made to the minimum cost to do the job, including rectifiers rated for the expected 3 phase input. Bus capacitors are chosen that are no larger than required.

    Single phase has higher input current, and also higher demands on the bus capacitor. The de-rating of the output is to limit the stresses on the rectifiers and capacitor to an amount that is not going to cause a premature failure problem when run for weeks at full power.

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    The VFD also has a cooling fan. Much a like my fairly new Miller MIG welder, the fan only comes on when the unit reaches a certain temp. Well, it comes on anytime you power up but goes off after the run-up cycle.

    Anyway, the fan is there to cool, primarily, but it's also a good indicator of how hard you are working. A lot of times, I'll run the lathe for half an hour and never hear the fan come on.

    And....if you are 'high tech' you can also take information out of the VFD that pretty much tells you how many amps you are/were pulling, etc. You probably can damage the VFD through over-heating but you'll have to try pretty hard to do it.

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    Quote Originally Posted by JST View Post
    Maybe get back to the basics of this issue?

    The OP has a machine that is known to draw a lot of current on start-up. We, or at least "I", do not know if the machine "starting under load" simply means that it has a part on it, or if it not only has a part, but has to start when actually grinding, meaning it has to start when part way through a cutting pass.. To me those are two different scenarios.

    Having to start with a part on-board sounds as if it is mainly an inertia issue, with the probability of some "stick-slip" action when starting. That means that a form of soft-start WOULD work, because the actual "power" needed is not necessarily large. Lower power would mean a slower start, but as long as the torque is more than the "sticking" can resist, it will start and accelerate.

    In that case, the idea of a standard soft-start might work, but it is likely that some methods would not be good because they are set up for a soft but fairly fast start.
    More example of the frustration of dealing with an issue at a distance. I learned never to take a customer's word and especially never, never, never take a salesman's word for anything. Go there and measure it yourself, but we can't here. As you say, much of it hinges on the breakaway torque and we just keep endlessly arguing about an unknown.

    Personally, I'm about ready to get out of the debate. I have a Heald internal grinder to put a couple of VFDs on, for money.

    Bill

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    Quote Originally Posted by 9100 View Post
    ........ I learned never to take a customer's word and especially never, never, never take a salesman's word for anything. Go there and measure it yourself......

    Bill
    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"...


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