550 Volts for a 380 Volt lathe
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  1. #1
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    Default 550 Volts for a 380 Volt lathe

    Hello,

    I built an RPC with a 10hp motor, and it works great. Unfortunately I have a French Cazeneuve lathe circa late 70s an HB575 that wants 380V.

    I used a 15kva transformer and wired it low voltage Delta and high voltage Star which has a neutral. Even on the lowest voltage setting I'm getting 504v between line 1/2, 540v between the next two 2/3 and 550v on the third pair 1/3.

    Will this destroy my 380v motor? It is not very sophisticated except a bunch of contractors in the electrical bay, no real boards or anything.

    504v is 33% over and 550v is 44% over the designed 380v. Is that crazy?

    I was thinking worst case the motor shorts and I have to have it rewound to match my voltage perhaps?

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    Take a picture of the data plate on the transformer. Something isn't right.

    You don't want to run that motor at anything other than what it's wired for, unless the data plate indicates it can be rewired for 550.

    Sent from my SM-G973W using Tapatalk

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    Here you go:
    Attached Thumbnails Attached Thumbnails img_0282.jpg  

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    I hooked up the output of the RPC to H1 H2 H3 tapped specifically to "LV Tap 1 240". I see the image is not very high res, but the "HV" says 480/277 and the "LV" is 208v on tap 1, tap 2 is 198v and tap 3 is 188v.


    I then took the high voltage L1/2/3 from the X1 X2 X3


    When I measure from "H0" to line H1, H2 or H3 it is consistently about 321v.

    When I look at the current being drawn on each of the RPC's L1/L2/L2 is about 5.6-6.0 amps each. And the RPC neutral to L1 is 119v, L2 119v, and L3 is 220v. This is of course what is going into the transformer at H1/H2/H3.

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    Quote Originally Posted by Tipsy View Post

    Will this destroy my 380v motor? It is not very sophisticated except a bunch of contractors in the electrical bay, no real boards or anything.

    504v is 33% over and 550v is 44% over the designed 380v. Is that crazy?
    No, I would say that it is a desperate act. You will probably ruin the wire coils in your contactors first and then they will disconnect and save the motor.

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    Wait a sec here.....

    380 50Hz is the same thing as 440/460 60 Hz.

    10% higher may be OK. 550V is too much.

    You need to get that lower somehow.

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    Wow, no kidding, I didn't realize the Hz would have an effect on the RMS, but I guess it make sense.

    I'm going to try poking the tester into a few other accessible coils on the transformer and see if I find any with better voltages, then maybe try to solder a tap onto them

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    So I decided to find a coil that had the voltage that I needed, I took a tiny pin and stuck multiple coils with a tester (very carefully) until I found 380v. It was an inner coil of course, on the bottom. The outer coils are the high side and I would need additional coils not fewer to get lower volts---so that is not possible.

    I carefully pried out the lower four coils on one of the inner windings where I could get 390 volts testing between the same point on two separate banks, I stripped a section, used a copper screw splice type mechanical connector and connected the LV side connections to this same coil on all three banks. I painted liquid tape all over the stretched and displaced coils. The wires were aluminum squares 3/16", individually wrapped with insulator and the whole transformer solidified with resin. It took the better part of an afternoon for those who may try this in the future.

    The lathe runs and all is well.

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    Quote Originally Posted by Tipsy View Post
    Wow, no kidding, I didn't realize the Hz would have an effect on the RMS, but I guess it make sense.

    .....
    Motors respond to the volts/Hz.... 380/50 = 7.6 440/60 = 7.6 so both volt-Hz combinations work similarly with the motor, except that the 60 Hz makes the motor run faster.


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