3 Phase Converter Help!
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    Default 3 Phase Converter Help!

    So after purchasing my lathe I needed to get a phase converter. So I purchased the Control through North American Phase Converters out of New Berlin Wisconsin. The Motor I have is a WEG brand 7.5 HP with 12 wire leads. Which I have later found out may or may not be aWye start zero run motor? I have everything wired up but the on the 3rd generated leg is way too low. From L1 to L2 242 volts. L1 to L3 239 Volts and L2 to L3 is 127 Volts. DO I have a bad run capaciter? Is there something wrong with the motor? How do you tell if it's up to speed?

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    Default Pics

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    Talk to the person you bought it from.

    That is a delta wound motor, it should not be a problem.

    there appear to be some differences thermally between Y and delta motors when used as a rotary phase converter, I'm not sure there are electrical differences between the two connections, they should both work equally well. (the delta motor concentrates more current and heat in one winding, where a Y connected motor splits it equally between two windings)

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    Quote Originally Posted by SufernTlmkr View Post
    So after purchasing my lathe I needed to get a phase converter. So I purchased the Control through North American Phase Converters out of New Berlin Wisconsin. The Motor I have is a WEG brand 7.5 HP with 12 wire leads. Which I have later found out may or may not be aWye start zero run motor? I have everything wired up but the on the 3rd generated leg is way too low. From L1 to L2 242 volts. L1 to L3 239 Volts and L2 to L3 is 127 Volts. DO I have a bad run capaciter? Is there something wrong with the motor? How do you tell if it's up to speed?
    That is an odd reading, because the listed voltages do not just suggest a wrong voltage, they also suggest a wrong phase angle.

    If you are sure of your reading, I think I would disconnect all the run capacitors to the generated leg (noting the connections first), and check again.

    If the voltages come out better, as they should, then the "balance" capacitors may be unsuitable values. I doubt that, since it would draw a lot of current, and it might take rather a large capacitor to do it.

    If the voltages come out the same as with everything connected, then double-check the way the motor is connected internally as to its windings. It seems suspicious that the one phase voltage is close to half what is expected. If they are wrong, that also should be pulling extra current, but maybe not as much extra.

    You mentioned the motor speed, do you have reason to suspect that it is wrong?

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    When all else fails, contact North American customer service, ask them the questions and perhaps the motor wiring diagram. They should be able to help you.

    Tom

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    The first thing I did was call North American Phase Converter. They are puzzled. They are suppose to call back today,. But they seem to be going down the 12 lead motor Wye start zero run road. At least questuioning if that motor will work properly. They asked the question if the motor is getting up to speed. Makes sense if it's not it would be low on the generated leg. But how do you check that? Nobody seems to know of a way to do it.

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    Make sure that you have the motor leads connected properly, and ensure that you do not have T6 and T9 transposed.

    12-lead-.jpg

    For measuring motor speed a optical tachometer can be used.
    Digital Photo Sensor Tachometer

    It would also be helpful if you measured the current draw on each of the supply legs.

    SAF Ω

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    Quote Originally Posted by JST View Post
    That is an odd reading, because the listed voltages do not just suggest a wrong voltage, they also suggest a wrong phase angle.

    If you are sure of your reading, I think I would disconnect all the run capacitors to the generated leg (noting the connections first), and check again.

    If the voltages come out better, as they should, then the "balance" capacitors may be unsuitable values. I doubt that, since it would draw a lot of current, and it might take rather a large capacitor to do it.

    If the voltages come out the same as with everything connected, then double-check the way the motor is connected internally as to its windings. It seems suspicious that the one phase voltage is close to half what is expected. If they are wrong, that also should be pulling extra current, but maybe not as much extra.

    You mentioned the motor speed, do you have reason to suspect that it is wrong?
    Well I think I did this. The 3rd generated leg is L3 in the pic which seems to have blue wires running to it so I disconnected all three blue wires to the caps on the right. Voltage reading L1 to L2 242 L1 to L3 101 and L2 to L3 99. Different. I did also check T6 and T9 are not transposed they are grouped correctly.

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    Quote Originally Posted by SAF View Post
    Make sure that you have the motor leads connected properly, and ensure that you do not have T6 and T9 transposed.

    12-lead-.jpg

    For measuring motor speed a optical tachometer can be used.
    Digital Photo Sensor Tachometer

    It would also be helpful if you measured the current draw on each of the supply legs.

    SAF Ω
    Thanks for the tip on the tachometer reader. Just got one and checked it. Rated to run 1775 rpm when I checked it it was running 1799 RPM.

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    That's fine, they run at almost synchronous when not loaded, and running very close to 1800 for a 4 pole motor is expected.

    Now for the odd voltages.

    1) if you are measuring with a digital meter, you can read "induced" voltages, even when the wire you are measuring is not actually connected to a voltage. This is because the voltmeter has a very high impedance and draws only a tiny current, so you may measure "capacitively induced" voltages.. Oddly, the voltage is often about half the expected.

    So check all connections. Check for a good connection, but also check for a "correct" connection... that the wires are connected where they should be.

    2) If the motor is not connected right, there are various ways in which you can get bad voltages. BUT, the voltages you get are not even adding up right.... if there was NO generated voltage, one would expect half the 242, or about 121V.... you get two voltages that do not even add up to that. The suggestion is that your voltages are not "real" and there is a bad connection somewhere.

    This situation is what a "wiggy" voltage tester is made for... it won't register a voltage unless there is some actual power behind it. I doubt you have one, so....

    3) If you can, and are willing/able to do a less than perfectly safe test, wire up a couple of identical low power 120V old type light bulbs in series, and use the 2 wires running to the seriesed bulbs as the test probes. If the 100V readings are "real", then the bulbs should light up somewhat, they won't be very bright. I say series, because that would be OK even if across 240V, they would just be brighter.

    If the bulbs do not light at all, the wire you are measuring is not connected effectively.

    If you prefer not to do that type test, then do a very thorough check of your wiring, for correctness, and for good connections.

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    No i am good with electrical as it is and not willing to try that. I've already checked connections several times and they are good. I appreciate the help. But are you leaning something wrong with the motor or more the control panel? Sounds like motor related is a higher possibility.

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    Update. At the request of North american Phase Converter I took the motor in to a vendor they suggested and had it tested. THE motor was connected to 3 phase power and Voltage checked on all 3 legs was the same. They suggested that it was a bad capaciter. Waiting to hear back from N.A.P.C.

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    Just to be sure.....

    How were you measuring the voltages? From what to what did you put the meter leads for each measurement when you got the low voltages?

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    When I checked it it was from T1 to T2 242V, T1 to T3 239V, and T2 to T3 (manufactured leg) 127V. Sorry for any confusion in earlier post I labeled them L not T. THE Incoming Line Voltage is Labeled L! and L2 and the 3 phase connections are laveled T1,2,and3.

    I took the motor to a vendor N.A.P.C. suggsted to be checked. I don't know what all they checked or how but at the leaset I know they connected it to 3 phase power and said all the voltages were the same and it appeared to them nothing was wrong with the motor.

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    Are these voltages measured with or without the motor connected? The run caps are most certainly affecting the generated leg voltage which I would expect to change significantly under load. A motor is a variable inductance load, appearing to decrease as load increases (simple explanation) thus the generated leg phase relationship seems to change with load. Note that referencing to the neutral will give lots of interesting though generally not relevant numbers and all bets are off if a neutral is connected to the load with numerous problems resulting.

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    Quote Originally Posted by SufernTlmkr View Post
    When I checked it it was from T1 to T2 242V, T1 to T3 239V, and T2 to T3 (manufactured leg) 127V...... .
    If T3 is the manufactured leg, then there are two voltages that do not seem to go together.

    T1 to T3 at 239V and T2 to T3 at 127 are both measurements of the generated leg. But the phase triangle is very odd indeed if they are correct. I am trying to make sense of them as if they are correct, and most of the ways I see possible involve higher currents than should exist..... Unless there is a wiring problem, OR a measurement issue

    Yes there is some phase change with load, but with any load that is "reasonable" the change is fairly small, because the voltage drop on the inductance is small. Most of the drop across a motor winding is from back EMF, which is how a motor can draw more current under load.

    The phase relation is set mostly by the mechanical relation of the windings.

    A large change in generated voltage vs just one input leg is somewhat difficult to create. It suggests that there is a wiring fault that is not yet found.

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    sounds like some of the capacitors or a contactor isn't connected at all. check your wires in the box to make sure they are tight.

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    Even if a capacitor was dead or not connected at all, I don't think you'd see THAT much voltage swing. Up to say 30-40v, sure. But over 100V difference (120v to 240v)? I would think very unlikely. Having built and tuned a few RPC's, that voltage difference can't seem to be caused solely by capacitors or lack thereof. I've heard of wires being mis-labeled from the manufacturer in some cases. Have the windings vs respective wire lead #'s been verified?

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    That's a possibility.

    OP has not been back in a month..... either he solved it, gave up, decided we were no help, or it electrocuted him. Dunno which, hope not the latter.

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