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3 Phase Converter Schematic. (Miller system)

Discussion in 'RE Projects' started by tcmtech, Nov 27, 2009.

  1. customMotion

    customMotion New Member

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    i appreciate the info, i will abandon the idea of mismatched caps. i have already cleaned up enough confetti. i was looking for a shortcut as usual but instead i will delve into the internet as i need more info.
     
  2. customMotion

    customMotion New Member

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    i don't know whether or not it is acceptable to share sources here, if not please chastise and delete.
    anyway, here is an excellent source for run capacitors and many other items for phase converters.
    i have been buying welding cable and other hardware from them for years. i wish i had thought of them at the start of this project.
    http://www.ebay.com/itm/261104087753
     
  3. Diver300

    Diver300 Well-Known Member

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    I've got a three-phase motor that I've got to run using the circuit and capacitors as recommended by Tcmtech. It's a 380 / 220 V motor, 3 kW.

    So far, I've switched the starting capacitor manually.

    Any suggestions where I could get a suitable voltage sensitive relay? Would a time delay relay be easier to obtain, as this is a hydraulic lift that gets to speeds in fractions of a second?
     
  4. dave

    Dave New Member

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  5. cowboybob

    cowboybob Well-Known Member Most Helpful Member

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    I would say yes.

    Perhaps something like this. 220VAC supply, 220VAC, 10A capacity control relay and adjustable delay OFF. I'm not sure, however, how you select the timing range, i.e., the "0 to ≈10 S" option, given your "fractions of a second" timing requirements..

    There are others, of course.
     
  6. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Yes, in a fixed load application time delay relay would work but most of those cost as much as a voltage sensing relay.
     
  7. Diver300

    Diver300 Well-Known Member

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    Have you got any specific suggestions for a voltage sensing relay?
     
  8. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Not really. I typically shot for ones with drop-out voltages a bit below the line voltage. The reality is the vast majority of VSR are easily disassembled and adjusted to raise or lower their drop-out voltage point if the range they have is showing issues with either dropping out too soon or not at all.

    The alternate name for them are HVAC Potential relays and they cost around $25 - $30 new or about half that on online auctions now if you know where to look. The older style 3 terminal (spade or screw) are the ones I prefer.
     
  9. tink111

    tink111 New Member

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    I built this based on your system. I am having a problem with it coming up to speed. It starts but turns slowly. Any ideas?
    Thanks
     

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  10. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Are your K2 and or K3 relays switching the start capacitor out too soon? The start capacitor needs to stay in the circuit until the motor is nearly up to speed and to do that the start relay/contactor has to be a special type that does not pull in until a specific voltage is reached.

    BTW, your way you have it wired as your circuit shows is very questionable in a number of ways. :(
     
  11. tink111

    tink111 New Member

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    Tomorrow I am going to wire the motor just like your diagram without the potential relay. If the motor runs that will verify that there is no problem with the motor or capacitance issues. I also have a 7.5 HP motor that is a Wye configuration.

    I bypassed the potential relay by tying the coil of k2 to neutral. So the start caps are in the circuit until I press the stop button. The motor speed is about 40 rpm.
    What do you suggest?
     
  12. Diver300

    Diver300 Well-Known Member

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    What are the voltages and phase relationships of L1 and L2?

    Tcmtech's circuit has only two input wires. Using the notation on your diagram, he has the start capacitor between L1 and PH2 when it is connected and the potential relay measures the voltage between the same two points. On yours circuit, the start capacitor is between L1 and PH2 when it is connected, but the potential relay measures the voltage between L1 and N.

    Also it seems odd to have the run capacitor, C1, disconnected for startup. It would be better to have it directly between PH2 and PH1
     
  13. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Don't deviate from the design by adding things not shown or using the wrong type of parts in the wrong places.

    I'm assuming, given the capacitor values, its a standard 10 HP 230 VAC 50 - 60 HZ induction motor and that the capacitors are the correct type (motor start and run or power factor correction, not DC electrolytics) and working as well?
     

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