about conversion of 1 phase to 3 phase

Discussion in 'General Electronics Chat' started by cheque, Aug 6, 2008.

  1. cheque

    Thread Starter New Member

    Aug 6, 2008
    one person ask this question for me,,,,,,
    the question is ,,,,,,,,,,,,,,,,,
    "conversion of 1 phase to 3 phase possible or not in motor"...................
    if it is possible means,any instrument to used for conversion.give me circuit . please give circuit it is very very important.........
  2. theamber

    AAC Fanatic!

    Jun 13, 2008
    If you want to operate a motor that was designed to be operated from a 3 phase supply, yes you can do it. The Motor will not run very well balanced so it will reduce motor life.
    The phase converters I have known are rotary machines that transforms 3 phase electrical power from a single phase source.
    I dont know of any circuits but once I saw someone selling on ebay a circuit information on how to do that.
    Here I found a page that has some.
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    The "phase converter" is used for producing three phase current from a single phase source. "Rotary phase converters" are basically motor-powered generators. "Static phase converters" make the conversion with solid-state power electronics. The phase converter must be rated at least as high as the motor.

    Attempting to simply hook up a 3-phase motor directly to a single phase source will quickly destroy the motor.
  4. jpanhalt


    Jan 18, 2008
    That is true, but the motor and the generator may be the same device. Here is one reference on the web by Hanrahan that is often cited. There are also many systems that use a single capacitor. Just search on the internet.

    Basically, one needs an idler 3-phase motor, which is started on single-phase and generates the other two legs. The idler can be started by hand (or foot), but more often it is started with a capacitor. Attached are some pictures of a phase converter I used in my shop for 25 years. The converter is a conventional 5 HP 3-phase motor. The output ran a 2 HP mill and 2 HP lathe. The converter motor is usually the same or larger than the largest motor you want to start. However, the sum of the motors can be bigger , as each motor in a daisy chain (parallel) helps to run the others. To be conservative, however, I would still pick my converter motor to be larger than any other motor. It is also said that the older, "big iron" 3-phase motors make better converters than the newer, lighter frame motors do. In my case, I got a really good deal on a new, 5HP Baldor, which has worked fine.

    The Hanrahan design uses several capacitors and may be considered a bit more refined. My converter uses a single capacitor and has worked fine. As mentioned, it has been used for 25 years, and the driven motors had no problems in that time. Unfortunately it is in storage and was built so long ago that I can't find the wiring diagram for it.

    A second item to consider is whether to make disconnection of the capacitor start for the idler motor manual or automatic. I chose automatic. In the photos, you will see the voltage controlled relay (like what is used in A/C units) in the corner of the box, which drops out the capacitor once the generated legs get up to voltage. Some people just manually hold a start switch on until the idler comes up to speed.

    Last edited: Aug 6, 2008
  5. Toughtool


    Aug 11, 2008
    Here is a schematic of a basic rotary phase converter, and the schematic of my RPC with control contactors (relays). Also a link to,
    a forum which has a lot of information about building a rotary phase converter. I posted a project about a year ago, using three current transformers and a 2 Volt AC digital voltmeter to measure the three AC motor currents. Nice for balancing and trouble shooting
    See at:

    BTW, a three phase motor will run single phase, with about 80% of rated HP and will not burn up if so loaded appropriately. It just won't start by it self. My idler motor (unloaded) uses a start capacitor. Some people use a rope.This will produce a 3 phase output of (approximately) 240/240/240 with the motor producing a manufactured leg (B) and two manufactured phases (AB and CB), with or without the run capacitors. Please notice the Neutral is not used. However a (Green) safety "Grounding Wire" must be used and connected to the motor frame. The run capacitors C1 and C2 are voltage and current balancing capacitors, (65mf and 55mf for my 2HP shown here) and should be rated at 370 Volts AC (oil filled run type). Balancing is recommended if you use a small motor (i.e. 1.5 to 3 times the size of the load motor). Joe

    P.S. On my circuit, you will have to hold the start button in until the motor starts, then release. About 1 second is enough.
    Last edited: Aug 11, 2008