Name of an induction motor using 2 phases and a capacitor - Page 1
Forum section: electronics / beginners

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 05:56:32 am
content: Hi,What is the name of an induction motor using 2 phases and a start capacitor

author: Xena E
author_rank: Frequent Contributor
timestamp: February 26, 2023, 07:18:21 am
content: If the motor is powered by a two phases of a three phase supply it is still just a single phase motor. If you mean the motor is constructed with two windings, and a single capacitor, and the capacitor is a large AC rated electrolytic that is switched out by a centrifugal switch when the motor approaches aproximately 75 % of design running speed, that is known as a 'capacitor start' (induction run), type.If the capacitor is a non electrolytic type and the start winding has NO centrifugal switch to remove it from circuit during normal running, then that is a 'capacitor start and run' type.

author: Xena E
author_rank: Frequent Contributor
timestamp: February 26, 2023, 07:31:38 am
content: I noted the OP already answered his own question in his other thread 😵‍💫

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2023, 07:43:20 am
content: The name is simply "single phase induction motor".But it seems you already know more about how it actually works, than most people - yes, it's actually two-phase, and the second phase is made by phase shifting the single available phase with a capacitor. If this second "phase" is disconnected after motor has started up, the capacitor is called "start capacitor". If the second phase remains connected, it is called "run capacitor".

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 01:02:09 pm
content: Quote from: Siwastaja on February 26, 2023, 07:43:20 amYes i know how it works, i'm just interested in the name. In my country we have 3 phase 3X220 Volt and single phase 110 volt. So a single phase motor 110 volt uses one phase and the neutral, with a start capacitor. The name of this motor is a "single phase motor". A 220 volt AC motor uses 2 phases and a start capacitor. Is the 220 volt AC motor called a "two phase motor"?

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 01:48:32 pm
content: Quote from: Xena E on February 26, 2023, 07:31:38 amRead carefully, that is not true. In my other thread i asked something else

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2023, 01:59:18 pm
content: Quote from: robsims on February 26, 2023, 01:02:09 pmDefinitely no. If it runs off just two wires, this is still a single phase. If you have 3-phase 220VAC available, then the single-phase 220VAC motor would be connected between a phase and neutral. Between any two phases, there would be 380VAC, so one could run a 380V "single phase" motor from that.Higher voltage is just that, higher voltage. It's still called "single phase motor"."Two-phase motor", as a term, is rarely used, because two-phase electricity has never widely existed (although to limited degree over a 100 years ago). People prefer to choose the term based on what it practically runs with, not how it's internally driven. This is also why BLDC motors are called BLDC, even though they are AC motors. But one supplies the inverter with DC.Many motors are actually two-phase motors, they are not just called that way. In addition to single phase induction motors,stepper motorsare two-phase motors, as are many computer BLDC fans.The distinctive feature of something being 2-phase is the optimum phase shift of 90 degrees (think about sine and cosine and how you can draw a rotating vector with them). This is also why thesplit-phasesystem (as common in the USA) isnota two-phase system. The "phases" are just inversions of each other (i.e., 180deg phase shift), so they cannot define a rotating vector. No "dynamics" are added beyond what single phase already does; motors can and do create this 180deg offset winding internally, just by wiring in opposite direction.

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 02:26:25 pm
content: Quote from: Siwastaja on February 26, 2023, 01:59:18 pmNot fully understood you're answerHere in my country we have 3-Phase 220 volts meaning the voltage between L1-L2, L2-L3 and L1-L3 is 220 volts. The voltage between a line and neutral is 120 volts. A capacitor start induction motor running on 120 volt (L1-N) is called a single phase induction motor. What is the name of a 220 volt induction motor using a start capacitor and running on two phases like L1 and L2? Is it still called a single phase induction motor?

author: alpher
author_rank: Frequent Contributor
timestamp: February 26, 2023, 03:43:20 pm
content: Yes, single phase. Are you sure about 220 phase voltage? If so phase to neutral will be 127v not 120.

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 03:48:42 pm
content: Quote from: Siwastaja on February 26, 2023, 01:59:18 pmI understood you're answer completely now Siwastaja. Many thanks. Yes it is still a single phase motor even when the motor uses two lines for example L1 and L2. It still needs a capacitor to make a phase shift. Another question, in a single phase induction motor which coil rises to max voltage first? The coil without the capacitor or the coil with the capacitor connected on it?

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 03:52:37 pm
content: Quote from: alpher on February 26, 2023, 03:43:20 pmMany thanks alpher. Yes, i understood it. It is still single phase. Yes the voltage should be 127, but the voltage varies between 115 and 129 volts. I asked another question in my last post (reply on Siwastadja's post), maybe you can help me out with that one too. Many thanks

author: Siwastaja
author_rank: Super Contributor
timestamp: February 26, 2023, 04:24:36 pm
content: Quote from: robsims on February 26, 2023, 02:26:25 pmOK, you were referring to phase-to-phase voltage. If it is 220V, then phase-to-neutral voltage must be 220V/sqrt(3) = 127V, not 120V. It'd be a good idea, to avoid confusion, to round that up to 130V (or just use one more digit and say 127V).QuoteJust two wires go to the motor? (plus possibly protective earth to the motor case - that does not count.) Motor is connected between L1 and L2, and no neutral? Then, between L1 and L2, there is bog standard sinusoidal AC waveform, just like between L1 and N, just with higher voltage. So it's definitely a single-phase load, and will be called single-phase motor.

author: robsims
author_rank: Frequent Contributor
timestamp: February 26, 2023, 04:30:06 pm
content: Another question, in a single phase induction motor which coil rises to max voltage first? The coil without the capacitor or the coil with the capacitor connected on it?

author: amyk
author_rank: Super Contributor
timestamp: February 27, 2023, 01:43:29 am
content: Quote from: robsims on February 26, 2023, 04:30:06 pmBoth and neither. There is no "first", because the motor rotates continuously.As an interesting historical note, early Westinghouse refrigeration equipment used 2-phase fan motors, with the 2 phases being generated by the compressor motor windings being used as a transformer.

author: james_s
author_rank: Super Contributor
timestamp: February 27, 2023, 03:06:24 am
content: Quote from: amyk on February 27, 2023, 01:43:29 amSounds like the compressor motor doubled as a rotary phase converter. That's clever.