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3 phase to 1 phase

Discussion in 'Electrical Engineering' started by [email protected], Jul 11, 2013.

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  1. Guest

    I found a Hunter DSP 9000 wheel balancer I would like to have for my home shop. The problem is it is 230 volt three phase. I only have single phase available to me.

    Can anyone tell me if a static converter would work for this application or what is the cheapest esiest way to make something like this work?

    I appreciate it!
  2. Tom Biasi

    Tom Biasi Guest

    You can use a single phase to 3 phase converter but they may be more
    than you want to spend. I would check with the manufacturer and see if
    they had that unit with a single phase motor and could you buy the motor.
  3. Glen Walpert

    Glen Walpert Guest

    Static converters work for all but hard to start motors such as 3450 RPM
    or higher speed motors, motors with direct coupled high inertia loads, or
    motor designs with inherently low starting torque. Most 1725 RPM 3 phase
    motors will start easily with an appropriately rated static converter,
    but the wheel spin motor on a balancer might be an exception as the ones
    I have seen start fairly slowly due to the wheel inertia. Since these
    motors are fairly small a single phase input Variable Frequency Drive
    might be a better alternative, but this requires rewiring the motor
    contactor to the VFD RUN control terminals and direct wiring the VFD to
    the motor. Either way you will need to be sure the single phase loads in
    the machine are powered from your single phase line, with only the motor
    connected to the derived phase of a static converter or the output of the

    A quick check on eBay turned up a couple of single phase Hunter DSP
    9000's for around $800, which might be more economical than getting a
    converter for the 3 phase machine unless you are getting a really good
    deal on it.

    A rotary converter would also work, but with additional size and expense.
  4. Rich.

    Rich. Guest

    The cheapest way is to replace the 3 phase motor with an equivalent single
    phase one.
  5. operator jay

    operator jay Guest

    VFDs were mentioned, and yes in general that can be done. Normally, one
    sizes the VFD at double the rating of the load if using it in this fashion
    (single phase in, and three phase load on the VFD output). E.g., if the
    load is rated 10A, 230V, 3 phase, then the VFD should be rated 20A, 230V.
    The VFD will pull in a lot more than 10A on each of the two energized input
    phases, in order to deliver 10A out on each of the three energized output
    phases, and therefore needs to be rated higher than 10A to handle that
    higher input current.

    The VFD input current distortion will be very high. If this load is a fair
    portion of your total load then this can become problematic.

    VFD output voltages are kind of tough on motor insulation. The VFD output
    is a PWM waveform with pulses that have a very fast rise time, which travel
    down the wire and reflect, leaving the motor insulation subject to voltage
    transients up to about 3x the nominal motor voltage. Over time this can
    break down the winding insulation and cause the motor to fail. Where I am,
    it is madatory that a motor that is connected to a VFD be rated and labeled
    as 'inverter duty rated' (NEMA MG part 31) for this reason. I do not know
    whether that is the case where you are. I have heard it said that motors
    with Class F insulation and SF 1.15 are generally able to handle being
    powered by VFDs fairly well. But, caveat emptor.

  6. Guest

    The balancer is 300 dollars. I would prefer a single phase unit, however I live in a small area in Kentucky and not alot nearby. And of course shipping on such an item would be very expensive if purchased online.
    I called the manufacturer and he said he would get me a price of the componets needed to convert it but that it would probably be more thna I would want to spend. It would require a single phase motor, a new board, as well asof course the plug.

    I have read conflicting things on using a converter on a balancer. Some sayonly the motor should be 3 phase and everything else within the unit should be single. Others have said everythign within is three phase. I have readthat you cant use a vfd or static converter. I read rotary converters havevery unplanced voltages on each of the legs so I wonder if this would affect the accuracy of the balancer.

    Kind of frustrating...
  7. Glen Walpert

    Glen Walpert Guest

    Without having either the balancer or it's schematic available the
    questions you posed are unanswerable. You need to provide more
    information to get anything other than suggestions of things you can look
    into as already provided.

    It is highly unlikely that the balancer computer/controler runs on 3
    phase power. Most likely it will be powered from only 2 of the 3 input
    leads, possibly through a single phase 230/120 control transformer. You
    need to find or create (from inspection of the machine) a schematic for
    power input to the machine controls including the rating of any
    transformers, fuses or circuit breakers.

    The motor nameplate will have the information required for specific motor
    power recommendations. Essentially all info on the label is required,
    including any design designation, insulation class, service factor,
    voltage, full load current, or pretty much anything else on the label
    could be significant.

    Existing motor control means (contactor? - rating, overload element size,
    source of control power, auxiliary contacts used/available) will also
    influence your options.

    All of your options could easily be botched, but one or more are
    certainly viable if done correctly.
  8. Glen Walpert

    Glen Walpert Guest

    Rotary converters based on standard induction motors should include
    capacitors between the single phase line connected motor terminals and
    the derived phase motor terminals, also sometimes a power factor
    correction cap across the single phase line. One design I have seen
    posted on the rec.crafts.metalworking newsgroup used a 5 HP motor with 60
    uF and 50 uF capacitors to the derived phase, with an additional ~300 uF
    motor start capacitor temporarily connected across the 60 uF run cap for
    starting. and a 50 uF power factor cap across the line. Current and
    voltage balance will never be perfect with a rotary converter based on an
    induction motor with capacitors, but it is good enough to power 3-phase
    motors in a home shop where the motors are not generally run continuously
    at full power.

    There are a number of variations on the rotary converter in use including
    use of fixed capacitors large enough to start the load without a starting
    capacitor, and the rope-start converter where a rope wrapped around the
    motor shaft is used instead of the starting capacitor. The rope-start
    version will even run and power a smaller load with poorly balanced power
    without any capacitors at all; the single phase line provides enough
    reactive power to keep a lightly loaded 3 phase induction motor running
    once it has been started.

    Better rotary converters use a special multi-tapped single phase
    transformer with a non-standard induction motor winding to produce very
    well balanced 3-phase power using no capacitors. This design was once
    widely used in electric locomotives, and is described in detail in
    "Principles of Alternating-Current Machinery" by Lawrence and Richard,
    4th ed 1953 (the classic book on the subject). I don't know if these are
    still made but I have seen them show up at auctions occasionally.

    The static converter is a box of capacitors only, using your motor(s) for
    the other half of the converter, suitable for powering motor loads only
    and typically even more imbalanced that a homemade rotary converter - but
    also cheaper to build yourself and often well suited for the home shop.

    The VFD is also designed for driving motor loads only, and some care must
    be exercised when using them with standard (not inverter rated) motors,
    however if mounted very close to a 240 volt motor (short wire from
    inverter to motor) or if the optional output filter is purchased with the
    VFD (or better yet use the output filter and a very short cable for
    minimum chance of EMI problems, possibly also use the optional VFD input
    filter if sharing a power feed with sensitive loads), and the motor is
    never run at reduced speeds except during ramp up to 60 Hz on start and
    ramp down on stop, and good wiring practices are followed to keep VFD
    noise out of the control system, then the VFD will provide the motor with
    well balanced 3 phase power and operation as good as with a utility 3-
    phase feed can be expected.
  9. Don Kelly

    Don Kelly Guest

    Can you find a surplus 3 phase motor of a larger HP size. drive it with
    a smaller single phase motor (the idea is simply to run it near
    synchronous speed) and supply single phase to two of the phases- and
    connect all 3 phases to the balancer. This is an old farmer's trick in
    rural areas where only single phase is available.
  10. Don Kelly

    Don Kelly Guest

    Essentially it will work- even without the capacitors -in which case an
    external drive is needed to get it up to near synchronous speed. Surplus
    induction motors are more readily available than synchronous machines.
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