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Phase Converter - Frequently Asked Questions

General Information on 3-Phase Converters

How efficient are phase converters?

Extremely efficient. Losses are generally less than 15% and usually under 10%. One must remember, however, that only one third of the total energy consumed by the load actually passes through the converter. Therefore, the total loss of the converter system is 15% of 33% or about 5% of all the energy consumed. That translates to 95% overall efficiency.

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Do I lose power or capacity when I run my equipment on a phase converter?

For rotary phase converters, the answer is a resounding "No!" Provided the converter is large enough, a rotary phase converter will develop the entire nameplate horsepower of the motor. You will have no power or capacity loss at all on a rotary phase converter.

The same cannot be said for static converters, which generally do not allow motors to develop full horsepower. Static converters are unable to balance a current into three different legs. Once a static converter starts the motor, it switches off the line and the motor actually "single-phases" one winding carries most of the load. Once that winding reaches its full capacity, that's all the load the motor can carry without tripping off or burning up. This usually occurs at between 60-80% of the nameplate horsepower. This is why static converters are only recommended for small-horsepower, single-motor applications.

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How much power do phase converters draw?

As with service sizing (see next question), the power drawn by a phase converter depends on how much load is connected. Converters are actually transformers, passing through whatever current is called for by the load. If the load calls for 100 amps per phase, that's what the converter must deliver - and will deliver, if it has been sized properly.

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What size service do I need to run a phase converter?

As with power draw (see prior question), service sizing depends on the amount of the total connected load. The best way to size the incoming single-phase service is to add the full-load running amps of all the 3-phase loads that will operate simultaneously. The National Electric Code requires the service to be at least 250% of the total 3-phase load amps.

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Do utility companies approve of phase converters?

Yes. In fact, many even recommend them. Unless you are planning to operate large motors in a residential area, you generally will not need to consult your utility prior to installing a converter.

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Will running a phase converter affect my utility bill?

In most cases, a phase converter will have little or no effect on your bill. This is because the load will take exactly the same number of kilowatt-hours of electricity regardless of whether it is being registered on a three-phase or single-phase meter. Any change in your power bill will be caused not by the converter, but by the rate structure that the utility applies to single-phase power vs three-phase power.

In other words, if you are currently running single-phase power, you will see no difference in your bill running a phase converter. However, if you are currently running three-phase power (or are considering installing utility three-phase power), switching to single-phase with a phase converter could result in lower utility bills. For one, you'll be able to take advantage of the single-phase rate structure, which can often be lower than the three-phase rate. In addition, most three-phase rates include a demand charge, something rarely included in single-phase rates.

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How does the cost of a phase converter compare to that of replacing three-phase motors with single-phase ones?

In small horsepower ratings (under 3 HP), it may actually be economical to replace the motors. When the motor size is larger than 5 HP, however, single-phase motors are extremely difficult to find and expensive. Single-phase motors are also far more maintenance-prone and much less efficient than three-phase motors.

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How noisy are phase converters?

Listen to our sound-level data and find out. Phasemaster^® converters have been designed to run quietly and without vibrations. The sound level is the same or less than a motor of the same horsepower as the load. Normally the sound level will measure 72 decibels or less at no load and will decrease when load is applied.

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A phase converter is just like an M-G set, right?

No, phase converters are nothing like motor-generator sets. A phase converter is a single-frame device with three windings that starts from a single-phase line. Induction enables the spinning rotor to replicate the applied single-phase voltage into the other two windings. The result is true three-phase output, with each line shifted by 120^o.

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Operating and Installing Phase Converters

Can I run a phase converter all time, even when there is no load connected?

Absolutely. Phasemaster converters are designed to operate continuously without overheating, whether or not a load is connected. You may notice that a converter running without the load will operate at a slightly higher temperature; it will cool down as soon as a load is applied.

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How many motors can operate on a single converter?

Rotary phase converters can operate many motors simultaneously provided the loads don't need to start together. Rotary phase converters carry two ratings, the maximum starting horsepower and the maximum running horsepower. Any combination of motors that fits within these ratings will normally operate successfully. Phase converters are thus ideal for running many different machines in a single shop.

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Where are phase converters normally installed? Can they be installed outdoors?

Phase converters are most often installed next to the incoming single-phase service panel. They may also be placed near the load equipment. For outdoor use, converters should be kept in a sheltered area or in an enclosure. Kay Industries offers an outdoor fiberglass enclosure and also manufactures a totally enclosed converter suitable for the most severe environments.

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What controls are necessary ahead of a converter?

A two or three-pole safety switch is all that is required to provide on-off control for attended loads run by a phase converter. Economical operation of unattended loads, such as elevators or pumps, require magnetic controls that turn the phase converter on and off as required by the load.

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Can converter output be wired into a three-phase panel?

Yes. Just be sure to keep track of the phasing so that the manufactured phase from the converter is not used in the control circuit of the loads connected to the panel.

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What type of maintenance do phase converters require? What can go wrong?

In truth, phase converters are reliable machines and require very little maintenance. Converters should be regularly inspected to see that their ventilating slots are open and unobstructed. Converters that contain automatic controls should have their contacts inspected at scheduled intervals. Bearings are factory sealed and require only a periodic shot of grease to give many years of trouble-free service.

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Do phase converters require any adjustments during operation?

If your phase converter is properly sized, the voltages and currents should balance without further adjustment.

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Applications

Can I operate a motor with a variable speed (variable frequency) drive (VFD)?

Absolutely. And don't believe anyone who says otherwise. Just be sure to make it clear that you will be powering a VFD because it may change the size recommendation.

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Why can't I run a heating load on a static converter?

Because a static converter is not really a phase converter. Unlike a rotary phase converter, static converters cannot split a single-phase supply into three separate real voltages and currents. Rather, static converters use capacitors to produce a phase-shifted voltage that can start a three-phase motor from single-phase. That phase-shifted output voltage can start and run a motor, but it cannot produce a current through a resistance heater.

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I have 240V single-phase but I need 480V three-phase. How can I get it?

This application requires a single-phase step-up transformer ahead of the converter. Operating the converter at 480V will produce the necessary 480V, 3-phase output.

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Will a phase converter operate a welder? How about a welder and a motor?

Yes, to both questions! And we invite you to learn more about other specific applications that phase converters can serve.

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