what is a pure sine wave inverter ? - Page 1
Forum section: electronics / projects

author: ilanko
author_rank: Contributor
timestamp: November 09, 2013, 01:00:32 am
content: Hi guys,I hope some one can explain what's a pure sine wave inverter and may bee to shed some light on DC to AC inverters.Why 1100 Watt Inverterhttp://goo.gl/1x7QYnprice tag is $ 81 and otherhttp://goo.gl/eiQX7p600 Watt is $175.Maybe Teardown video.

author: wraper
author_rank: Unknown
timestamp: November 09, 2013, 01:04:18 am
content: First outputs almost square wave and second normal sine wave.

author: ilanko
author_rank: Contributor
timestamp: November 09, 2013, 01:06:10 am
content: Quote from: wraper on November 09, 2013, 01:04:18 amIs that what pure sine is ?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 09, 2013, 01:08:08 am
content: http://www.energymatters.com.au/renewable-energy/inverters/Give a fairly good description I think, plus diagrams showing the difference in the outputs.Regular mains in your house is a pure sinewave, but its a more complex inverter to build, therefore costs more.

author: Marco
author_rank: Super Contributor
timestamp: November 09, 2013, 02:35:19 am
content: They're all square wave generators, some just use higher frequencies(Strictly speaking with three level signal it isn't square, but close enough.)This google searchwill give you plenty of references to see how the sine wave inverters work.

author: wraper
author_rank: Unknown
timestamp: November 09, 2013, 02:45:18 am
content: Quote from: Marco on November 09, 2013, 02:35:19 amBut then it gets filtered so no square on the output. Like class D amplifier.

author: Whales
author_rank: Super Contributor
timestamp: November 09, 2013, 07:13:22 am
content: Quote from: wraper on November 09, 2013, 02:45:18 amInteresting tangent: I've heard stories about amp companies advertising the output of their products by shoving 2400W at 50hz into a kettle to boil some water.

author: Carrington
author_rank: Super Contributor
timestamp: November 09, 2013, 02:20:12 pm
content: Basically consists in integrating a frequecy modulated PWM square wave.----------- -----------------------------| | | |DC---| PWM |---| Induction Trasformer |--- AC| | | |----------- -----------------------------

author: fcb
author_rank: Super Contributor
timestamp: November 09, 2013, 03:26:47 pm
content: Quote from: Marco on November 09, 2013, 02:35:19 amThey might me PWM based these days, but Valradio used to make a DC to AC inverter that was basically a big audio amplifier and transformer, these were used in things like early OB trucks that were sensitive to mains quality (we are talking 80's).

author: A Hellene
author_rank: Frequent Contributor
timestamp: November 09, 2013, 04:56:26 pm
content: QuoteSomething (or, better put, ANYTHING) can either be 'affordable' (or, better put, CHEAP) or be 'high end' (or, better put, PROPER/CORRECT/COMPLETE/ACCURATE). That is because thefull-fledgedsecond solution CAN NEVER BE as cheap as thehalf-assedfirst copycat of that solution.Do never let the corporate/commercial doubletalk/doublespeak confuse you!The inverters you mentioned above are designed to substitute the mains power supply when the mains cannot supply the devices/appliances with proper power. And the mains powered devices/appliancesare designedto be running on a sinusoidal AC power supply.After understanding the terms 'pure sinewave' and 'modified sinewave' of thepower inverters, you can watch our fellow blogger's 'Tesla500' the excellent video analysis of the APS true sinewave UPS:-George

author: Whuffo
author_rank: Regular Contributor
timestamp: November 09, 2013, 06:43:53 pm
content: Quote from: AmmoJammo on November 09, 2013, 01:08:08 amHave you ever scoped the mains in your house?

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 09, 2013, 08:01:12 pm
content: Quote from: Whuffo on November 09, 2013, 06:43:53 pmshould I?

author: wraper
author_rank: Unknown
timestamp: November 09, 2013, 08:26:31 pm
content: Have you ever scoped the mains in your house?That it not so easy to do because oscilloscope connectors are grounded. I scoped couple of times running oscilloscope from the ups or isolation transformer. But it is not safe to do because scope's case becomes connected to the mains. There was sine wave with some distortion on the peak (likely because devices connected to the mains have capacitors after rectifier).

author: Fsck
author_rank: Super Contributor
timestamp: November 09, 2013, 08:34:18 pm
content: it's easier than you think. use a portable oscilloscope (properly rated of course)a fluke scopemeter is an easy choice for this task, either borrow/steal/whatever onebut in regards to "pure sine wave", it depends on your definition of pure.mains fits the sinusoidal description but it tends to be noisier than what I'd consider the word "pure" to be

author: mtdoc
author_rank: Super Contributor
timestamp: November 09, 2013, 08:44:14 pm
content: For people who live off-grid, modified sine wave (really modified square wave) (MSW) inverters used to be the norm. True sine wave (aka pure sine wave) inverters were very expensive. Prices came down in in the 90s and now there's not enough difference in price to justify buying a MSW inverter for any mission critical type application. There are still some high quality MSW inverters made by Magnum Energy and Xantrex (Schneider Electric).MSW inverters can work fine for resistive loads but inductive loads can have problems and run noisy and less efficient. Since most electronics run on DC via regulated power supplies they can often tolerate MSW inverters ok.HERE'sa nice article from 2001 Home Power mag about inverter choices.Pretty much any inexpensive auto 12V lighter inverter for running laptops, charging phone, etc will be "MSW"Here's a shot of the output from a cheap Duracell branded (made by Xantrex) 300W inverter made for auto 12V. Notice the "modified sine wave"

author: wraper
author_rank: Unknown
timestamp: November 09, 2013, 08:47:59 pm
content: Quote from: Fsck on November 09, 2013, 08:34:18 pmYou have to have one in the first place, most people don't. Not so easy to borrow and not worth to rent. I'm personally not going to acquire one for just occasional thing.

author: A Hellene
author_rank: Frequent Contributor
timestamp: November 09, 2013, 08:57:41 pm
content: Regarding someone having 'scoped the mains (utility) waveform, this is a very interesting recording I made in July 29, 2012:Ch1 reading directly my home's mains power outlet, and Ch2 reading whatever electrical signals existed in the air by using the ~3cm probe tip extension as an aerial:Quote from: A Hellene on July 28, 2012, 01:25:27 pm-George

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 10, 2013, 02:31:47 am
content: Quote from: A Hellene on November 09, 2013, 08:57:41 pmI remember reading about some PLC standard that outputted pulses similar to that.A modified square wave inverter is plenty for general purpose use. Most electronics don't really mind it (the peak current is actually lower than with sine waves, and even lower with a square wave of the same peak voltage) and motors run noisy but rarely have problems. (The Prius inverter actually outputs square waves at higher speeds where noise is not an issue.) While the fancy sine wave drive computer fans are more efficient than the cheap square wave type, that's actually because they use FOC, which an off the shelf sine wave inverter will not do.The EMI and standing wave issues can be solved by adding series inductance at the inverter. A passive PFC choke out of an old PC PSU works well. If it's only for running switching power supplies, you can open it up and there'll often be a trimpot to increase the output duty cycle to the point where it's almost a square wave,, along with another trimpot that lets you turn down the frequency.What I would like to see in an off the shelf "smart" inverter is V/Hz soft starting/overload avoidance and automatic load characterization. For example, if it detects only a rectifier type load, it turns the output frequency way down and the duty cycle up in order to cut losses. The moment it detects a motor or transformer load, it quickly changes back to V/Hz operation.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: November 10, 2013, 03:18:29 am
content: Here's a shot of what's in a Magnum MS2812 2800W inverter. Note the big (in this case) transformer on the left to help reshape the wave into sine. It's easily 3x heavier than the 3000W square wave I also have because of that. Caps are Nippon Chemi Con if you're interested in that sort of thing. Total class act. Interesting use of stainless steel bolts on the high current leads, but these are often found on boats so that might explain it.