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In my workshop I have a device that requires 220V 3 phase power, with a requirement of up to 1.5kVA. In North America, my wall outlet provides ~120V/15A single phases.

(EDIT - my device can take +/- 10% voltage, so anywhere from 220V to 240V 3 phase is fine.)

Doing some research, I found devices like these, called 'Variable Frequency Drives' that seem to take this type of single phase input and give the 3 phase output desired:

https://www.mcmaster.com/variable-frequency-drives

I am a noob at electronics, and I just want to confirm if I could buy one of these VFDs to solve my problem as described. I guess I would get the 2 HP version to match approximately 1.5kVA.

Thank you for any help, and open to other suggestions if this won't work.

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    \$\begingroup\$ What is that "device"? \$\endgroup\$ – Eugene Sh. May 2 at 21:07
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    \$\begingroup\$ While you will be able to find a drive that produces the 220V 3 phase, you won't be able to get 1.5kW from a single 15A circuit, you'll need either a higher current circuit, or a 240V circuit to power it from. Most likely your device won't actually need that full output, and with a soft start from the drive you'd be able to get away with it. \$\endgroup\$ – Phil G May 2 at 21:12
  • \$\begingroup\$ @PhilG the McMaster devices say they output 230V 3 phase (which is fine for us), I guess I made a typo. How much lower power would it be? Inefficiency from the conversion? \$\endgroup\$ – JDS May 2 at 21:15
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    \$\begingroup\$ A bit non-standard, but sure, they exist. \$\endgroup\$ – winny May 2 at 21:21
  • \$\begingroup\$ I'm just wondering what potential problems could arise. It's an investment on the order of $500-$1000 so I want to be more informed before I pull the trigger. But from what I've read it will solve my problem \$\endgroup\$ – JDS May 2 at 21:24
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There are VFDs that will accept 115V single phase input and give you a 230V 3 phase output. They use what is called a "voltage doubler" front-end rectifier, meaning they rectify the 115VAC to approx. 165VDC, then put it through a circuit that doubles the DC to 330VDC, then the inverter section uses PWM to recreates an output that MOTORS react to as if it is 230VAC 3 phase. The key point however is MOTORS; this can ONLY be used for 3 phase AC induction motors, you cannot use the output as a general 3 phase power supply source. it is the inductive nature of the motor that allows the PWM to become a pseudo-sine wave. Without the motor, it's just pulsating DC that changes direction.

Then there is the size issue. On a 15A 115V circuit, you can actually only load it to 80% of that continuously, so 12A. The largest 115V input VFD is for a 1-1/2HP motor, but the INPUT CURRENT on the 115VAC side is actually 20A; too much for a standard 15A circuit and actually, too much for even a 20A circuit (80% rule means a 20A circuit is only good for 16A continuous). For that reason, MOST of the companies that sell a 115V input VFD limit it to 1HP, and even those require a 20A circuit (the NEC allows you to use a 20A breaker for a 15A outlet if you use 12ga wire).

Bottom line, if you have only a 15A 115V outlet, you cannot (legally) connect a device to it that requires 1.5kVA continuously, that is too much for that circuit regardless of what you put on it.

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  • \$\begingroup\$ Thanks for your response. What I am trying to power is a controller box that runs AC servomotors, so would that quality for the first criteria you listed? Then secondly, I understand I won't get the full 1.5kVA, and I am OK with this. More than anything I just need the thing to turn on. Could you look at this product link and tell me if it could work? mcmaster.com/7786K43 \$\endgroup\$ – JDS May 2 at 22:41
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    \$\begingroup\$ yes at 1HP (650VA) or less there should be no problems if you use a suitable 1HP VFD \$\endgroup\$ – Jasen May 2 at 23:30
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    \$\begingroup\$ Servo motors are typically powered by a version of a VFD, called a Servo Amplifier. Like a VFD, it converts the AC to DC then back to AC. The rectifier of the servo amp will not like the PWM output of a VFD as an input, in fact it may damage the servo amp. many servo amps are OK with being fed with single phase input instead of 3 phase, because all it is doing is creating DC from AC. You just have to over size them by 2x, or reduce the load on the output to about 1/2 of what it is rated for. So all you need is a simple transformer to step the 120V to 240V single phase for the servo. \$\endgroup\$ – JRaef May 3 at 0:07
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    \$\begingroup\$ Check with your servo amplifier supplier if that is OK. As I said, most will allow it with de-rating. \$\endgroup\$ – JRaef May 3 at 0:07
  • \$\begingroup\$ Hey @J. Raefield thanks so much for your response. I'm just gonna link the controller I need to get working - what do you think is my best bet? XRC 2001 robot controller: manualslib.com/manual/1167213/Motoman-Xrc-2001.html#manual \$\endgroup\$ – JDS May 3 at 1:36
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Knowing the cost of doubling line voltages for 3 phase from 120 to 240V, I think it would be better to install a 2nd line to get 120+120=240V service wire to hard wire the VFD and the variety of choices is better, at a much lower cost.

Selection

my pick

enter image description here

$275

The come with a fancy set of interfaces that don't have to be used but can add value to some operations.

enter image description here

There is also a variable torque version can drive up to 3Hp for the same size/cost unit as this 2Hp constant torque version.

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  • \$\begingroup\$ Hey thanks so much for your answer, will definitely check it out. Could you quickly take a look at my comment on the other answer about running the XRC 2001 robot controller? I should have mentioned in the OP. Cheers \$\endgroup\$ – JDS May 3 at 1:44
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    \$\begingroup\$ Well you dont really need any VFD functions and I dont know anything about the robot. \$\endgroup\$ – Sunnyskyguy EE75 May 3 at 2:52
  • \$\begingroup\$ The controller requires 3 phase power and has transformers on the bottom for 3 settings with jumper wires: 575V, 480V, 220V. All I have is wall outlet in North America. So I'm thinking I need to get one of these 3 phase equivalent powers being outputted somehow. Hope that makes sense :) \$\endgroup\$ – JDS May 3 at 3:05
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    \$\begingroup\$ But I don't know about arc welding with a VFD source \$\endgroup\$ – Sunnyskyguy EE75 May 3 at 3:06
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    \$\begingroup\$ Then this is possibly overkill \$\endgroup\$ – Sunnyskyguy EE75 May 3 at 4:35
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With the luxury of not attempting to answer the question while it was so incomplete and misleading, I would say that you should not use a VFD. Using a VFD to power something that is essentially another VFD is asking for trouble.

I recommend that you consider:

  1. Determine if the servo drive will accept single phase input.

  2. If it will, see if you can get a 240 V outlet installed.

  3. If installing a new line for 240 V is not attractive, investigate the methods for using two existing 120 V circuits.

  4. Consider using a 120:240 V step-up transformer.

  5. If the servo drive will not accept single phase, there is probably a way that is can be hacked to make it work. However that will probably require a level of assistance that you can not get here.

  6. If you absolutely need 3-phase:

  7. There are both electronic and rotary phase converters on the market.

  8. There are hobby groups for metal working and perhaps other areas that have online plans for making phase converters.

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