i would like 230VAC 1ph, to drive 380VAC 3ph simonet motor, with vfd - Page 2
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  1. #21
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    I thought my question would be simple for someone with lathes and vfd experience, but maybe it was not clear enough or the thread is considered too old. I will try again to ask my question clearly, in hope of some advice.
    The lathe motor, which is probably more than 70 years old, is at the moment wired most probably at a Dahlander configuration. For sure it is a two speed motor, 3 phase, 380 Volt. As i understand it is connected to star. By my research to find out how i would be able to have it running from my available mains power supply, which is 230Vac, i have come to a point to choose to go with rewiring, accompanied by a vfd. By speaking with the rewiring technician, he explains to me that with a rewiring, it will be possible to have the motor in a delta configuration, where power input can be 3x 220Vac in order to have it successfully running with a variable frequency drive. By simply changing the metal connecting plates, i will be having the motor at a star configuration, where i will be able to run it from a 380Vac 3phase supply if ever needed. The technician also informs me that no torque will be lost by the modification, it may even be added some. I asked him to simply rewind the motor to the high speed, as i 've been suggested, but he has the impression that by doing so, i might loose some torque in the lower end of the working speeds. So the case is frozen till i become a bit more sure about how the rewind configuration, would be better to be. Could any experienced machinist suggest if i should have it rewind to the low speed(1400rpm) or the high speed(2740rpm)? Or maybe it would be desirable to get into more trouble and have it with a two speed again?
    any help appreciated

  2. #22
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    My recommendation is reconnect for delta, highspeed by simply pulling all 12 wires out of the motor. No expensive rewound required.

    The problem with delta low speed connection, is you would still need a 480volt vfd in order to get nameplate torque at 3600 rpm. (Or 380v at 2800rpm) otherwise you are stuck with half the hp available.

    Rewinding the motor for single speed could deliver you maybe 20% more torque, i can explain later.


    Some vfds (mostly due to bad configuration) have trouble delivering smooth torque below 3 to 10hz.

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    thanks for the reply johansen,
    I asked the technician if it would be possible to simply pull out the 12 wires of the motor in order to do a simple modification, but he replied that the wires are full of varnish that has turned to rock. So no other way around.
    So i asked him to rewind it for the highspeed configuration. It will be ready next week. I hope everything will turn good. Can't wait to receive
    Afterwards i think i ll go for a Santerno Sinus N vfd, rated for 1,1KW to drive the motor. The motor is indicating an 1,1hp for the highspeed, so i guess the 1,1KW will be good, unless the hp will increase with the rewinding.
    I' ll give it a try with the allen bradley unit again, but i don't think i ll be lucky with it.

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    1.jpg2.jpg3.jpg

    So, i received the motor rewinded for high speed, approximately 2800rpm. I tried again to have it run with the AB vfd, but no luck. So i m going to buy one, probably of the santerno sinus n series.
    My issue here is which power rate to choose. Talking with the guy that did thee rewind and customer support from santerno and ABB, i remain confused.
    The rewinder says that now he measures the motor at 2,4 Amps when running. He also suggests that the motor is now 2hp. And suggests to run it from a 2,2kw vfd.
    The vfd companies customer service suggests that if the motor is 2,4 Amper, then multiplying it with 380 Volts we get a power of 912Watt (and dividing by 750 we get an aproximate horsepower of 1,2hp.)
    So they suggest that if i go with a 1.1kw vfd i will be fine.
    I understand a difference where the rewinder tries to include a maximum motor power under torque while the vfd service personel don't. Another factor that the rewinder suggested is that when running the motor from 380v i will have 2.4 amper but when i run it from 3x220volt, i will have bigger amperage, which sounds logical.
    Another factor that i consider is the ratings on the motors label, where for 2750 rpm, it is indicated an amperage of 1.8 and a horsepower of 1,1. In this case by multiplying 380volt to 1.8Amper i have 684 watt. 1,1 horsepower is around 825watt. I guess that the difference from 684 watt to 825 watt are either the motor's inefficiency or that the nominal 1,1 hp would suggest the hp of the motor under force. So now that the measurement is 2,4 Amper, 912w a similar inefficiency would lead to about 1100watt.
    These is as far as my understanding can go. Practically, my vfd choices are between units of 1,1kw, 1,5kw, 2,2kw.
    With my understanding, i would say that the 1,1kw would be just enough, and i would go with the 1,5kw just to be sure. I am wondering if there would be any reason to go for the 2,2kw unit or if it would more than enough.
    Any suggestions?

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    You forgot to multiply the amps by 1.73 for a 3 phase motor and account for efficiency and power factor. assuming both of them are 80%:

    for your old motor:
    1.8*380*1.73*.8pf*.8efficiency = 757 watts which is about 1 hp at the shaft.

    your new motor is a 380/220 star delta winding correct? if so then it will be 4.1 amps at 220 instead of 2.4 amps at 380.

    even a 1kw 220volt vfd would drive the motor, but you wouldn't get 2 hp out of it. (do you need it?)
    also, if you only have single phase available usually you should derate the vfd, they last longer.

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    The new motor winding can be set externally to 380volt star or 220 delta by altering the plates position.

    I dont know if i will need the full 2hp of the motor, but it is not a really big price difference between the three units i am looking, starting from 110 euros for the 1,1kw unit and ending to 170euros for the 2,2kw one. If the bigger one will last longer and will be able to provide better characteristics i will pay this difference. The only reason not to do it would be if there would be no benefit out of it.

    I still wonder if the 2,2 kw unit would make any differnce from the 1,5kw one. As far as i understand i will not go with the 1,1 one

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    Default the motor is finally working

    It's been a while now, but since i finally got my built to work, i thought of it as proper to report back here and have the thread as solved.

    So, i went with the Santerno Sinus N 0003 choice, which has a motor rating for 1,8 Kw motors.
    I am able to complete some types of basic jobs with the lathe now. I deal with problems when trying to drill holes to stock pieces, with drill held in the tailstock chuck and the piece clamped in the headstock. When a comperitavely larger diameter drill is held in place, eg 6mm and above (not really big), it is like the resistance created in place is big enough to lower the speed of the motor down, usually resulting the transmission belt to go off place. The problem, for more or less, may lay at the transmission belt material, which is animal leather, handmade by miself, not providing sufficient grid on the metalic transmission wheels. It may be for some part as well though, at the isufficient motor torque. I guess i will have to place a better belt in first, and then trying to figure out the rest possibilities. The same problem happens when i try to cut a piece with a cut off tool. I bought a couple of HSS cutting tools. A 2mm and a 3mm. No luck with neither.

    10.jpg

    I did some work making a box in order to fit the vfd unit in, as suggested by the manufacturer. This is a DIY box made out of an old PC unit and you can see it at the top-right side of the photo. The white things in the front are cooker hood filters. On the top and the bottom of the box, two more of these are placed. A plastic screen is placed at the center of the front lid, so i am able to have a preview of the vfd's screen. A temperature meter has also been added on the front door, in order to have a preview of the temperature inside there.
    The vfd-->lathe motor are controlled through the control panel i made, visible at the lower-left side of the picture. The buttons there include an on-off master switch, a three position rotary switch which begins forward the motor and can also start it going in reverse direction, a knob for frequency alteration and an emergency stop switch. (I have to tag the controls someday).

    So, i consider this thread that i opened a while ago as solved now, since i now have the motor working, although i am not quite capable of reporting the limits of this combination clearly.

    Next steps will be repairing a play there is at the crosslide and putting a proper belt in place and from then on the research and progress will be continued.

    A thank you to the input of all of you that helped me with your comments on this.


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