I need 3Phase AC source, I only have access to 2Phase AC - Page 1
Forum section: electronics / projects

author: lugaw
author_rank: Regular Contributor
timestamp: February 14, 2023, 01:43:36 pm
content: Can I use a single phase inverter VFD (variable frequency drive) as a power source to test my AC Servo system?

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 14, 2023, 02:55:49 pm
content: Not sure exactly what's an "AC Servo" motor, but if it's the same thing as a "Selsyn", it's basically just a synchronous motor with a wound rotor and will work just fine on a VFD. However, I don't think there would be any use adjusting the frequency unlike normal motors.

author: Technical Ted
author_rank: Contributor
timestamp: February 14, 2023, 03:00:35 pm
content: I don't know if your servo drive would like a PWM source or not... a rotary phase converter would give you the best true 3 phase source, but these don't come cheap.TedAB2RY

author: lugaw
author_rank: Regular Contributor
timestamp: February 14, 2023, 03:25:19 pm
content: A AC servo system. AC servo motor and a controller. Like these systems:https://www.keyence.com/products/controls/motor/sv2/models/I am planning to set it to just 60Hz.

author: lugaw
author_rank: Regular Contributor
timestamp: February 14, 2023, 03:26:04 pm
content: Quote from: Technical Ted on February 14, 2023, 03:00:35 pmAh so I wont be getting sinewave out of a VFD?

author: jmelson
author_rank: Super Contributor
timestamp: February 14, 2023, 04:14:05 pm
content: Quote from: lugaw on February 14, 2023, 03:26:04 pmNope! It gives a ~400 V "square" wave with varying duty cycle, the inductance of a motor turns it into a roughly sine wave current. Do NOT attempt to run any electronics off a VFD, it will almost certainly cause damage. Some motor drives intended for 3-phase input will run fine on single-phase. Almost all will run fine at reduced output power unless the drive has a phase loss detector, which is rare on the smaller units.Jon

author: lugaw
author_rank: Regular Contributor
timestamp: February 14, 2023, 04:32:54 pm
content: Quote from: jmelson on February 14, 2023, 04:14:05 pmThanks for the advice, good thing I didn't try it out. I am reading a lot on the internet about the topic right now. Seems it's better to stay away from 3 phase for now.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 14, 2023, 06:52:39 pm
content: A VFD is better called "motor controller" than "inverter". "Inverter" gives a wrong idea of the thing being general purpose. It isn't, it is highly specialized device for driving motors. There are two main types of 3-phase AC motors, synchronous and induction. Only some of the VFDs are able to control both, so choose wisely.Other points:You don't have 2-phase AC. 2-phase AC supply does not exist anywhere AFAIK, for at least a century. Instead, you have a so-calledsplit phasesystem which is just a variation of single phase. Phase difference between the "phases" is 180deg.VFDs also decouple the number of supply phases from the number of motor phases. A VFD (usually) drives a 3-phase motor, but most VFDs can be supplied from a single phase supply, just possibly with reduced maximum power or speed. Internally, the VFD just turns the input into DC. From 3-phase supply, one can get higher DC voltage and more power, but otherwise there is no difference.

author: langwadt
author_rank: Super Contributor
timestamp: February 14, 2023, 07:09:35 pm
content: Quote from: Siwastaja on February 14, 2023, 06:52:39 pmas I understand it, in some places you get two out of three phases, that's 120V/208V instead of 120V/240VQuote from: Siwastaja on February 14, 2023, 06:52:39 pmyep often just a de-rating because only a single rectifier has to do all the work and the bypass caps have to deal with much more ripple

author: ajb
author_rank: Super Contributor
timestamp: February 15, 2023, 01:04:32 am
content: Quote from: lugaw on February 14, 2023, 03:25:19 pmThose drives--or at least the specific model I clicked on at random--show that they support 3-phase or single phase AC or even DC input. Which makes sense, because, like a VFD, it will be rectifying the input to create an internal DC bus which is then modulated to create whatever AC waveform the accompanying servo motor requires.Have you confirmed that the specific model you're planning to use does NOT support single phase input?

author: james_s
author_rank: Super Contributor
timestamp: February 15, 2023, 01:17:14 am
content: Quote from: langwadt on February 14, 2023, 07:09:35 pmYou see that in apartment complexes here. The building has a 3 phase feed, and each unit gets two phases to a standard split phase panel.As for rotary converters, they don't have to be expensive, you can build one easily out of a surplus 3 phase motor and some capacitors.

author: lugaw
author_rank: Regular Contributor
timestamp: February 15, 2023, 02:37:38 am
content: Quote from: ajb on February 15, 2023, 01:04:32 amI wanted to drive a 1Kw and above servo. Their servo driver do work single phase from 50W to 750W.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 15, 2023, 04:43:02 am
content: The 3 phase drives also accept DC. Just make a single phase rectifier, just use a bridge rectifier module (quite cheap, a quick search finds 100A units going for less than $10) and add some additional capacitance to compensate for the increased ripple.

author: james_s
author_rank: Super Contributor
timestamp: February 15, 2023, 04:44:25 am
content: There are many VFDs that will accept single phase AC input right out of the box.