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a. Is it possible to run a 230v three phase motor with a 115v input VFD? Where does the other 115 volts come from in this case?

b. How would I size the VDF for this case. I know my VFD will need to rated higher than the the FLA of my motor but by how much?

Thanks

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  • \$\begingroup\$ The on-topic and answerable part of your question appears to boil down to how do we get bigger voltages from smaller ones. \$\endgroup\$ – Andy aka Feb 17 '18 at 19:13
  • \$\begingroup\$ 3 phase VFDs which are specified to permit single phase input will have derating factors in the manual. It's not clear where you are to have a single phase 115v restriction, but do note that most US residences have something in the range of 220-240v single phase available at the panel for electric ranges, clothes dryers, and the occasional single-phase woodworking saw, so you can likely have an outlet installed to feed an appropriate VFD electronically synthesizing for your 3-phase equipment. But the details of doing so would not be on topic here. \$\endgroup\$ – Chris Stratton Feb 17 '18 at 19:30
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possible yes. It won't make 230V you'll be limited to one quarter power.

you need to know how much mechanical power you need.

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  • \$\begingroup\$ Please clean up your grammar and punctuation. This was flagged as a LQ answer for those reasons, even if the answer is correct. \$\endgroup\$ – Sparky256 Feb 17 '18 at 23:06
  • \$\begingroup\$ actually I think the other answer is better. I didn't understan the TLS "FLA" in the question. \$\endgroup\$ – Jasen Feb 18 '18 at 9:18
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There are VFDs on the market that accept 120 volts, single-phase as input power and produce 3-phase, 240 volts as maximum output power. They presumably have an internal voltage boost circuit. There is plenty of online information describing voltage boost circuits.

If you can get 240 volt, single-phase, note that virtually all VFDs convert the AC input to a fixed DC voltage. Therefore using single phase input for a VFD that is designed for three-phase input is usually a matter of determining how much the rectifier needs to be derated when only two thirds of the rectifier is in use. Also the DC bus filter capacitors need to be evaluated. Many manufacturers publish the rating for single-phase input at the normal input voltage. Some who do not will provide the information upon request. Others have design details that prevent single-phase input.

You can make an estimate of the derating factor based on assuming the current per input phase does not need to be reduced. That would make the derating factor 1/ square root of 3 = 0.58.

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  • \$\begingroup\$ Yes, the VFDs that are sold to accept 115V single phase input and provide 230V 3 phase output do indeed have a simple "voltage doubler" circuit on the front-end rectifier. So it rectifies the 115VAC to roughly 162VDC, then uses caps and diodes to boost the DC to 330VDC for the VFD's bus, which then inverts it back into 230VAC for the motor. The effective limit of those designs is a 1HP 230V 3 phase motor. Beyond that, the component cost of the voltage doubler circuit far exceeds the cost of a transformer on the line side. \$\endgroup\$ – J. Raefield Feb 24 '18 at 1:16
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While it is POSSIBLE to use a COTS 230V VFD capable of accepting single phase input and fabricating your OWN voltage doubler system ahead of it from scratch, knowing exactly how to interface that with the VFD you chose and make sure you connect ahead of the pre-charge circuit makes it something I never recommend. Unless you buy one already built to do this, it's ALWAYS simpler and cheaper to just buy a 115-230V transformer and wire it ahead of the VFD.

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