The nameplate amps are not the amps you need
A 5 hp motor with a nameplate reading 230 V, 15.2 A, power factor 0.82 is drawing 6.06 kVA and 4,965 W. That real power has to come in from somewhere, and on a single-phase service it comes in through two conductors at 240 V instead of three at 230 V. Even with a perfect converter at unity power factor that would be 4,965 divided by 240, or 20.7 A. Neither route is perfect.
Through a drive at 97 percent efficiency the input is 5,119 W, and at an input power factor of 0.65 that is 32.8 A on the single-phase line. Through a rotary converter at 92 percent efficiency and 0.9 line power factor it is 25.0 A plus 4 A of idler, which is 29.0 A. Either way it is about twice the nameplate figure, and that is the number the service has to carry.
The doubling is not a law, though, and it is worth knowing where it comes from. It falls out of the three-phase motor voltage and the single-phase supply voltage being close to each other, which is the ordinary shop pairing of a 230 V motor on a 240 V service. Put a 460 V motor on the same 240 V service and the multiplier runs 3.6 to 4.3 times, and a 575 V motor 4.4 to 5.4 times, because the same power now has to arrive at half the voltage or less. That is the point at which the conversation stops being about a converter and starts being about a transformer. The page prints the multiplier for whatever voltages you enter rather than repeating the factor of two.
The drive derating is the trap
Most general purpose drives have a three-phase input. Fed from single-phase they still work, but the input rectifier and the DC bus capacitors see a much harsher ripple current, so the manufacturer publishes a derating: the drive can only deliver some fraction of its rated output current. At 0.5, a motor needing 16.7 A of drive output requires a drive rated for 33.4 A continuous — which is a drive sold for a motor roughly twice the size.
That fraction is not a constant and it is not something to guess. Some manufacturers publish 0.5, some publish a different figure per model, some build drives specifically for single-phase input which need no derating at all, and some void the warranty on single-phase input entirely. The field defaults to 0.5 as a placeholder and the number that belongs there is the one in your drive manual.
Which one draws less is not settled
At the defaults the converter wins by 3.8 A, and that gap is fragile. It is decided almost entirely by two power factor figures. Fit an input reactor or buy a drive with an active front end and the drive input power factor climbs from 0.65 toward 0.95, taking its single-phase current to about 22 A and putting it comfortably ahead. Load the converter lightly and its idler current, which never goes away, becomes a bigger share of the total.
So the page prints which is lower for the numbers you put in and says so explicitly, rather than declaring a winner. Anybody claiming one route always draws less current than the other has not varied the power factors.
They are not the same product
The comparison above is only about amps, and amps is rarely why people choose. A drive gives one machine variable speed and a soft start, and its inrush on the single-phase side is small because the bus capacitors charge through a limiting arrangement rather than the motor pulling locked-rotor current. But the drive output feeds one motor. Machines with a control transformer, a coolant pump, a work light or a contactor coil hanging off the three-phase supply usually cannot be fed from a drive output at all without rewiring the machine.
A converter produces a three-phase bus that a whole shop can share and leaves every machine untouched, including its controls. The costs are an idler spinning all day, an idler start that is itself a substantial single-phase inrush event, and no speed control anywhere.
What is missing here
Everything about the installation. This page does not size the single-phase service, the branch circuit, the disconnect or the overcurrent device, and it does not know whether the service you have can carry 30 amps more than it does today. The currents above are running currents; starting events on both routes are separate numbers from the equipment data. The converter output leg arrangement and what it does to single-phase accessories inside a machine tool is the detail that most often turns a converter installation into a project, and it is worth settling before anything is bought.
Questions people ask
How many single-phase amps does a 5 hp three-phase motor need?
Roughly double the three-phase nameplate figure. At the defaults, a 15.2 A nameplate becomes 32.8 A through a drive at 0.65 input power factor or 29.0 A through a rotary converter with a 4 A idler, both at 240 V single-phase. The exact figure moves with the efficiency and the power factor of whichever converter you use, so put your own in.
Why does a VFD need derating on single-phase input?
Because a three-phase input rectifier fed from two wires sees a much harsher ripple current in the DC bus capacitors, and the manufacturer limits the continuous output to keep that inside what the parts can take. The fraction comes from the drive manual — it varies by model, some drives are built for single-phase input and need no derating, and some manufacturers do not permit it at all.
Is a rotary phase converter cheaper to run than a VFD?
It depends entirely on the input power factor of the drive, which is why the page computes it rather than asserting it. At the defaults the converter draws 3.8 A less, but fitting an input reactor to the drive reverses that comfortably. A converter also runs its idler all day whether a machine is cutting or not, which a drive does not.
How big an idler does a rotary converter need?
The manufacturer sizing sheet decides, and the multiple depends on how hard the load starts. The field defaults to 1.5 times the largest motor as a placeholder. A lathe coasting up under no load and a compressor starting against pressure are not the same problem, and the sizing sheet for the converter you are buying is the authority rather than any general rule.
Can I run a whole shop from one VFD?
Generally no. A drive output feeds the motor it is set up for, at a frequency it is controlling, and putting several machines on it does not work. Machines with control transformers, coolant pumps or contactor coils fed from the three-phase supply usually cannot be run from a drive output without rewiring the machine. A converter feeds a shared bus, which is the reason people still buy them.