Rotary phase converter won't start Monarch 12C
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    Default Rotary phase converter won't start Monarch 12C

    I bought home a 12"monarch lathe with 3hp motor but it does to seem to want to start on my RPC which happily starts my 7.5hp Parkson mill the coolant pump starts fine but as soon as you hit the start button it pulls a lot of current and drags the RPC down.
    I could use some bright ideas at this stage really wanted to get it up and running by the weekend

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    Is the 3hp 440 3 phase? Is the wiring correct on it? Will the 3hp sping without electric to it?

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    Try starting the Parkson mill, then try the lathe. What you would be doing is using the Parkson as an additional RPC. And yes make sure the wiring is correct.

    Tom

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    What size is the RPC?

    If it starts a 7.5 HP mill, it would seem as if it is a 10 HP, which should have no trouble with a 3HP motor.

    The most likely problem is a wiring issue, one phase not actually getting connected. Could be a loose wire, switch problem, etc.

    If that is for-sure OK, then look elsewhere.

    If the monarch has no clutch, and the motor has to spin up the entire drive train and a heavy workpiece, that is more of a load, but an RPC able to start 7.5 HP ought to handle a 3HP even so.

    What if you take off the belt from the motor to the gearbox.... does the motor start by itself? If not, go check wiring again.

    Does it act differently in different speed ranges?

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    Quote Originally Posted by Krankieone View Post
    I bought home a 12"monarch lathe with 3hp motor but it does to seem to want to start on my RPC which happily starts my 7.5hp Parkson mill the coolant pump starts fine but as soon as you hit the start button it pulls a lot of current and drags the RPC down.
    I could use some bright ideas at this stage really wanted to get it up and running by the weekend
    Been mentioned, but it IS the most likely - it was previously set up for more than 220/230/240 VAC.

    Dunno what that is in Aus w/o looking up your grid practice, but Canada ISTR it is 5XX, not even just 440/460/480?

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    Thank you for the replies

    In Australia we have 240 single phase or 415v 3phase and I have a 15hp idler which on the RPC. Currently I have only 1 outlet on the converter so until the one I ordered arrives I can't try starting the mill first but it is a good idea.


    I will check the the wiring it is possible something has come loose in transit.

    I

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    Missed that you are in Aus.....

    So you have single phase input, with 240V line to neutral. Are you outputting the 415V L-L from the RPC?

    If so, the input to the idler will have to supply two phases of output from one single phase of input, which pretty much makes the RPC about half as effective as it would be in the US with 240V input and 240V L-L 3 phase output.

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    The idler is currently wired in Wye (star) configuration with neutral to the centre point and 3 live legs at 415v. If I can't find anything wrong with the wiring I may rewire the idler in delta to see if that helps

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    Hi Krankieone,
    Would you post a picture of the 15 hp Idler motor rating plate and are you using a transformer.

    Jim

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    Quote Originally Posted by Krankieone View Post
    The idler is currently wired in Wye (star) configuration with neutral to the centre point and 3 live legs at 415v. If I can't find anything wrong with the wiring I may rewire the idler in delta to see if that helps
    ?? You are running an RPC Idler off a 3-Phase input side to tap it off as Delta?

    "Wye" would one need the idler?


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    Quote Originally Posted by thermite View Post
    ?? You are running an RPC Idler off a 3-Phase input side to tap it off as Delta?

    "Wye" would one need the idler?



    He apparently has ONE 240V line to neutral input. The RPC has to run on that, and supply TWO more 240V line to neutral outputs (415V L-L). That is more of a load on the RPC than we have here, because we have two incoming lines at 240 L-L, and need to supply ONLY ONE output..

    I have experimented with that, and it works his way, but is a lot more of a load, and consequently the normal rules we would use to size the idler do not apply, you have to cut in half again, so that you need an idler of at least 2x the largest load, and probably more like 2.5 or even 3x for hard to start loads. We would normally say 1.5 x the biggest load, and 2x only for the hardest to start loads

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    JST,I'm a little confused by your explanation. There's still a 240 volt ac supply between the two terminals of the supply. If I'm a converter looking back at the supply, how do I know that one of the lines with 240 volts between them happens to be a neutral? I'm floating free from the source, which happens to have one side of a 240v transformer output at a particular potential(neutral), but how can the converter tell that?

    My thought experiment. I take my gas generator, connect the 240 volt output to a rotary converter, with the whole system floating free from any grounding reference. That should work, right? So then I ground one side of the output, with the rest of the system still floating free. How would the converter know?

    I'm sure I'm missing something here, as my experience with rotary phase converters is an un-measurable fraction compared to yours.

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    Does your converter use a transformer to produce a 415V output that then goes to the idler?

    That would change the way it has to work, and make it easier on the idler, at the cost of adding a transformer that has to handle the full output power, drawing it all from the 240V line-to neutral input. The result would be much more like what we can use for a converter, only at 415V instead of the 240V we use.. You would use a 415V idler which would then produce just one generated leg.

    But, since the entire input comes through a transformer as well as the idler, that can produce more voltage drop and a hard-to-start load possibly might not start.

    The grounding of the neutral is not relevant either way, it just happens to be what you are supplied. You are correct that a transformer will isolate the input ground. Presumably your output is either floating, or else "corner grounded" (which we would have to do, but you may not need to).

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    I'm not useing a transformer at this stage as the cheepest I've found is just under $1000 for a 10 kva
    And I'd rather spend that money on tools.

    The mill motor is wired in delta and from my quick look this morning after I got home from a 12hour night shift the lathe appears to be too. The lathe has been re wired at some stage and is not too easy to follow as the new contactors have been shoehorned into the enclosure and the wiring jammed in afterwards.

    Iwill look again after I have slept tomorrow and hopefully have more patience and a sharper mind.

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    Hi Krankieone,

    You asked for some "bright ideas". If you could post a picture of the rating plate of your 15hp Idler,I will be able to tell you why your RPC is not running your 3hp Lathe motor.

    Jim

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    If the idler motor is 15hp as stated, it will be 415 volt Delta connected for continuous Duty, that means the 3 coils in the windings will be wound for 415v. So transformer will be required.
    And it does not get any simpler than that!

    Jim

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    Quote Originally Posted by Jim Kennedy View Post
    If the idler motor is 15hp as stated, it will be 415 volt Delta connected for continuous Duty, that means the 3 coils in the windings will be wound for 415v. So transformer will be required.
    And it does not get any simpler than that!

    Jim
    Apologies, Jim.

    JST has the world turned upside down. Again.

    I was accordingly much too hasty in ass u me 'ing as he has done that all there is under-roof is single phase. We don't know that yet.

    Given y'all might not be keen on two winters in a row, I strongly suggest you take over support to sort this by PM or direct email with the OP and drag Australia back into the Southern Hemisphere!

    The electrical side of that cannot really be all that complicated unless one lets it be made so.

    Cheers!

    Bill
    Last edited by thermite; 11-04-2018 at 12:33 AM.

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    If no transformer, and input is 240V L-N, as should be standard, then the idler has to be a wye, with the neutral brought out, if output is 415V.

    Aus and British 240V is derived from 415V 3 phase, being one line of it, similar to US 277V that comes off 480V.

    So an idler run wye, connected with one line and neutral point to the source, would produce 2 generated legs, with the output being 3 wires with 240V L-N, and 415V L-L. One is a "pass-thru", two are generated.

    It will be weaker than one which has only to generate a single output, but it does work.

    It would be entirely different if the output were 240V.

    Are we CERTAIN that the output of the RPC is actually a measured 415V L-L? Things might appear to work if the 415V motors were. being fed 240V, but it would be rather weak.

    I am presuming these machines were used, and had been run for years/decades on local 3 phase 415V. If so, then the motors are proper for local power.

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    OK,,, Questions for the OP

    1) What is the measured line-to-line voltage coming out of the RPC with no load?

    2) What are the motors rated for..... voltage, frequency, amps?

    3) What does the RPC produce as Line-to-Line voltage when it is failing to start the Monarch?

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    Don't confuse the issue, please. Let it be three simple questions....

    That other stuff is good to know IF the results to simple questions are not what they should be. Remember, TWO motors are alleged to work.... so we need to know what they are rated for, and what the other is rated for. Just now, I do not CARE how the input is, although I do know what it should be and seems to be. What I care about is what comes out of this mythical converter, vs what the motors want. If we have a mismatch there, we can start cutting up the corpse.

    I repeat:

    Questions for the OP

    1) What is the measured line-to-line voltage coming out of the RPC with NO load?

    2) What are the motors rated for..... voltage, frequency, amps?

    3) What does the RPC produce as Line-to-Line voltage when it is failing to start the Monarch?


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