3P motor to 1P with capacitor - Page 1
Forum section: electronics / projects

author: Saull
author_rank: Contributor
timestamp: September 24, 2020, 11:36:46 am
content: Hi,I would like to convert 3P motor 1,5kw to single phase with capacitor.I would use 120uF working capacitor.(can I use 90uF I have it at home)Will the currents stay the same as is noted on the motor plate for delta 220V and 5.9A? We have 230V single phase.I need to know so I can chose correct motor protection switch.Any help is appreciated.

author: PaulAm
author_rank: Frequent Contributor
timestamp: September 24, 2020, 02:17:41 pm
content: Google for static phase converter schematicYou need to use the cap as a start capacitor and switch it out of circuit after the motor comes up to speed. Once it's running, it will continue on single phase, although with less than rated power.

author: drussell
author_rank: Super Contributor
timestamp: September 24, 2020, 03:34:59 pm
content: If you actually want the full output from the motor, why don't you just spend the $100 and buy one of the cheap Chinese VFDs? They work fine.

author: TheMG
author_rank: Frequent Contributor
timestamp: September 24, 2020, 03:50:39 pm
content: I second that suggestion.... Just get a VFD. They're cheap enough these days and pack all sort of features including but not limited to speed control, soft start, overload protection, etc. Most of those options are user adjustable too so you can tailor the setting to suit your motor and application.

author: Saull
author_rank: Contributor
timestamp: September 24, 2020, 06:34:04 pm
content: This solution with VFD is interesting. I went on ebay and foundhttps://www.ebay.co.uk/itm/2-2KW-3HP-VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-VSD-220V-SINGLE-To-3-PHASE/303248544676?epid=6029832779&_trkparms=ispr%3D1&hash=item469b0593a4:g:j6wAAOSwRs1dTSKH&amdata=enc%3AAQAFAAACYBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkpFtSR0CGv%252Bh98r8Yb9quS2r2%252F5WL3SsVpiaRiO%252FMbep9g%252Fu%252B8yXooPj0O0PUaIbDc%252Fg1KJZob5z9O2%252Fmm2owDrnsy4tsysq5nNj%252F8smQRG%252FX8R8%252B9iXH99cZq5MYsHi8QY%252BpnYzCZ08CyJhgc5ex8fCJ%252Fo1oY35qo0e%252BK8kCCTFL%252BdBLPgaFPGqBKppTixIT2Ka9w8bnQzO8TAQb%252FAtaPK%252F%252By726HyOyIaPbxA8nwEhA4VBno%252BM8U8isGf8y486nuL8MzI9L3J6dIuQeEATMOOxYXA1ap5UWFfAvTjtHC7HRNjwTa2Yo8n0yNZ03oV%252F3TVvV0JaGFp8ndfNRJF%252Fa1CuTZ42SpkjT%252BuIzc4J0Kg9aS2Axam3itJnawGOusZcoozn2Lbih8kmMqI938sI8wUHIPqMLHOSiL0VOCIao6sFQCTSYZUHAQcOqRWUL1YaOFn18goEN0%252B6F7QVGbaqPWE0ON6kpGs2vrZl0hzHuN3%252Fyxvu7JrNJsLKrWo56m1uXlpvB7EyWnB68x2AG8t%252Btxru1aX4VQYIJG5KbrolQukn8ZdRuEEJYDKmggYdOBvp%252FverCgsUx8YMLLVtElp9WPCTtIzLVbA9RUnRcVio%252FwqJmrz6a2vSsxOBXq7tRgDOpmpE%252BzGJw4bci%252B06cUIophhYCX32UoMpIvAjUQapHz8vx%252FfQz7M7wPRzipV5U%252BK3jKN6QelksGuhpRc0PBY34x6orKoCHyOgD9tU%252B2cP36wRO6j%252F0QKbOUaahrLL54UC7%7Ccksum%3A303248544676bba0a52785f94370a7846e2340faa96a%7Campid%3APL_CLK%7Cclp%3A2334524The only thing bothering me is the fact that output is 240v and not 400V.Can I drive 3P motor that is made only for 400V with this VFD. What current will motor draw if the voltage is 240V ?

author: TheMG
author_rank: Frequent Contributor
timestamp: September 24, 2020, 07:26:00 pm
content: If the motor is 400V star, if you can wire it in delta configuration that would make it 230V.If it can't be re-wired from star to delta, you will either need a different motor or a 400V VFD and step-up transformer.You can't run a motor at significantly less than its rated voltage without a HUGE reduction in performance (else you end up over amping and overheating it). It's not practical at all to do so.

author: JohanH
author_rank: Frequent Contributor
timestamp: September 24, 2020, 08:42:41 pm
content: There are one phase 230V to three phase 400V converters. This says 220V/380V (close enough):https://www.aliexpress.com/item/4000449258851.html

author: JohanH
author_rank: Frequent Contributor
timestamp: September 25, 2020, 07:45:31 am
content: Note also that many 3-phase motors can be configured both in star and delta configuration (if specifications say so). Especially older motors before the time of VFDs. Smaller motors (lower than 4 kW) could be designed to utilize either or both of them. Usually Delta (D) for 3-phase 230V and Star connection (Y) for 3-phase 400V. But don't drive it with 400V in Delta if it is specified for 230V in that configuration. Note that 3-phase 230V connection is meant for countries that have 3-phase 230V (not 400V!). But it would work fine with a 230V 3-phase VFD.Larger motors above 4 kW in the past could utilize Star/Delta configuration to start the motor with lower inrush current. They could typically then be specified 400V Delta and 690V Star. That means when starting them with 400V in Star, they would start with a much slower current and after spinning up you would switch to Delta configuration for full power. In industrial applications they could be used with 690V Star, but then you would need other means of limiting inrush current. Not a problem today with VFDs.

author: Saull
author_rank: Contributor
timestamp: September 25, 2020, 08:11:05 am
content: Thanks for replies.The situation is that I have three 3 phase devices that I would need to run off the single phase. For 2 I know that I can connect them in delta and run off 230v.The third device is Kircher high pressure wash. This I need to check how it is wired now and if I can rewire it.I like the solution with VFD because the price is similar to other solutions and there is no significant power loss.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2020, 10:07:18 am
content: VFD is the only proper solution, really.Even if you are unable to configure the motor for 230V windings, you'll still get some 60% of the rated power; and full torque at low RPMs.If you run it single-phase with a small run cap, you'll get maybe 20% of the rated power and maybe 10% of the torque it can really deliver, if even that.

author: Saull
author_rank: Contributor
timestamp: September 25, 2020, 12:12:10 pm
content: Wouldn't motor draw bigger current if I run it in 400v config ?Or can VFDs limit the current and still run the motor?

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2020, 12:15:36 pm
content: VFD can and will provide the exact motor current (~ torque) you want and need, and do that from 0Hz upwards so that you get good torque and low losses at low RPMs as well.