Phase Rotation - Page 1
Forum section: electronics / projects

author: Spark-Doctor
author_rank: Contributor
timestamp: March 08, 2021, 09:49:06 pm
content: Hi AllI am trying to build a 3 phase, Phase rotation tester powered from a 12V DC battery. This is for validating phase rotation testers in the field where there is not a 3 phase supply available.My thinking so far is a simple inverter using 2 x 2SC5200 transister's to get me the 230V AC and then to split the 230V via 3 small transformers to get the 3 phases but i then realised that i would not have any phase rotation, just 3 phases at the same phase angle.Can anyone suggest a way to get 3 phases out of this setup at 120deg rotation or a better way?Many thanks in advance.Ian

author: richard.cs
author_rank: Super Contributor
timestamp: March 08, 2021, 10:46:54 pm
content: Perhaps take a look at the micropower three phase inverters people have done for driving aviation instruments.If you really like the discrete approach, perhaps something like a phase shift oscillator driving three buffers, and then three transformers. If not most people would probably generate three phase PWM with a small micro, drive some power fets, filter and then into the same transformers. You could do it with a single transformer, but then you have to do all your waveform generation at high voltage which is less convenient.

author: Spark-Doctor
author_rank: Contributor
timestamp: March 08, 2021, 11:11:37 pm
content: Many thanks Richard. Need to do some research on RS phase shift oscillators.From what I just looked at, am I right in saying I split the one single phase into 3 circuits and then by adjusting the amount of caps and resistors, get 3 different phase angles?Ian

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 08, 2021, 11:23:29 pm
content: Probably the easiest would be a pair of small transformers to step up the voltage from a stereo audio amplifier, driven by two sine waves 60 degrees apart and the output wired in "open delta" configuration.

author: Circlotron
author_rank: Super Contributor
timestamp: March 09, 2021, 12:35:42 am
content: If the frequency and voltage doesn't have to be exact, what about a hand cranked brushless model motor feeding 3 transformers?

author: themadhippy
author_rank: Super Contributor
timestamp: March 09, 2021, 01:25:49 am
content: QuoteThat sounds like work,as theirs 12 v available put that to work on a DC motor thats driving the 3 phase generator ,old skool rotary convertor style.

author: Manul
author_rank: Super Contributor
timestamp: March 09, 2021, 01:50:12 am
content: Quote from: Circlotron on March 09, 2021, 12:35:42 amCould also be mechanically coupled to a DC motor to save the hand.Once I build 3 phase 400Hz inverter, and it was a bit of a pain. There was also a need for clean sine, low harmonics. I used MCU with 3 timers fed by DMA for high frequency SPWM. The output stage was full bridge for every phase, so 12 mosfets, then filters and transformers. Can not say, that I recommend building such inverter, too much effort for the task.There are also cheap class D audio amplifier boards available. These can be used to drive transformers. The source signal might be from MCU or a phase shift oscillator.

author: richard.cs
author_rank: Super Contributor
timestamp: March 09, 2021, 09:34:39 am
content: I have also seen an approach where three square waves with the correct phase relationship are generated and fed through a high-order switched capacitor filter to get good quality sine waves. Not that it's clear if waveform quality is important in this application, though as the phase rotation testers to be tested are a bit of an unknown black box we should probably assume they care to some extent.

author: Circlotron
author_rank: Super Contributor
timestamp: March 09, 2021, 11:31:22 am
content: From Don Lancaster's CMOS Cookbook.