what is a pure sine wave inverter ?

[ilanko]

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  Inverter  http://goo.gl/1x7QYn  price tag is $ 81  and other http://goo.gl/eiQX7p 600 Watt is $175.
Maybe Teardown video. 

[wraper]

First outputs almost square wave and second normal sine wave.

[ilanko]

First outputs almost square wave and second normal sine wave.

Is that what pure sine is ?

[AmmoJammo]

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.

[Marco]

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 search will give you plenty of references to see how the sine wave inverters work.

[wraper]

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 search will give you plenty of references to see how the sine wave inverters work.

But then it gets filtered so no square on the output. Like class D amplifier.

[Whales]

Like class D amplifier.

Interesting 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.

[Carrington]

Basically consists in integrating a frequecy modulated PWM square wave.

        -----------     -----------------------------
         |          |     |                                  |
DC---|  PWM  |---| Induction Trasformer |--- AC
         |          |     |                                  |
        -----------     -----------------------------

[fcb]

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 search will give you plenty of references to see how the sine wave inverters work.

They 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).

[A Hellene]

Why  1100 Watt  Inverter  http://goo.gl/1x7QYn  price tag is $81 and other http://goo.gl/eiQX7p 600 Watt is $175?

Something (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 the full-fledged second solution CAN NEVER BE as cheap as the half-assed first 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/appliances are designed to be running on a sinusoidal AC power supply.

After understanding the terms 'pure sinewave' and 'modified sinewave' of the power inverters, you can watch our fellow blogger's 'Tesla500' the excellent video analysis of the APS true sinewave UPS:





-George

[Whuffo]

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.

Have you ever scoped the mains in your house?

[AmmoJammo]

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.

Have you ever scoped the mains in your house?

should I?

[wraper]

Have you ever scoped the mains in your house?
[/quote]
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).

[Fsck]

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 one

but 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

[mtdoc]

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's a 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" 

[wraper]

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 one

but 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

You 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.

[A Hellene]

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:

[...]

Now, here is an interesting waveform I captured, using my 100 MHz DS1052E:


Ch1 to the mains line; Ch2 floating

Channel 1 was reading the mains voltage directly¹, using a 100x probe, and
Channel 2 was reading whatever it could pick up while unconnected, using the standard 10x probe, floating.

Please note that it made no difference at all turning ON or OFF the 75W monitor (a DELL U2410) right in front of me, or the 250W halogen roof lamp (driven by a traditional and noisy phase-control TRIAC dimmer), or the 1.3KW room air-conditioning unit (the thermometer outside my window now reads 37 deg.C!). The captured waveforms were exactly the same, either the noisy units above were powered on or off.

For those who will notice it, the mains voltage was externally measured to be 228.7 VAC RMS, while the DS1052E measured it to be 218 VAC RMS (DS1052E error: -4.7% or -3bit); in defence of the DS1052E, I will have to state that I did not warm it properly up before taking these readings, neither have I recently run auto-calibration².

The interesting parts in the captured waveform above are the time points -1.7div (-3.4 ms) and +3.3div (+6.6 ms), where Ch1 captures a couple of seemingly innocuous mains disturbances, which are absolutely synchronised to the Ch2 obvious spikes. The problem is that, though the Ch1 and Ch2 waveforms are out of synch by ~1.4div (~2.8 ms), the Ch1 and Ch2 spikes are in perfect synchronisation. Channel crosstalk, do I hear some of you murmuring? Well, maybe. But, by disconnecting the Ch2 probe, the second trace became a nice and clean flat line while the spikes at the first trace remained as they were exactly, and of the same shape and amplitude. So, I suppose that my scope is not really lying to me...

This means that:
1. The depicted spikes are probably generated erroneously within the oscilloscope front-end amplifiers.
2. Our mains lines are actually that dirty.
3. We are both being bombarded by who-knows-what kind of electromagnetic weapons (I am kidding!).

What I can only say is that, in order to trust what my DS1052E tells me about my mains line spikes, I would have to repeat those readings with a higher class oscilloscope and not with another entry-level one.


EDIT:
1. DO NEVER TRY doing that if you are not absolutely sure of what you are doing, because the probe ground clip is the instrument's ground, which is hardwired to the mains power supply ground! Be very careful when messing with the mains line.

2. More than half an hour later, the mains line was reported by the DS1052E to be 221 VAC RMS, while it was measured to be 223.2 VAC RMS.

-George

[NiHaoMike]

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:

[...]

Now, here is an interesting waveform I captured, using my 100 MHz DS1052E:


Ch1 to the mains line; Ch2 floating

Channel 1 was reading the mains voltage directly¹, using a 100x probe, and
Channel 2 was reading whatever it could pick up while unconnected, using the standard 10x probe, floating.

Please note that it made no difference at all turning ON or OFF the 75W monitor (a DELL U2410) right in front of me, or the 250W halogen roof lamp (driven by a traditional and noisy phase-control TRIAC dimmer), or the 1.3KW room air-conditioning unit (the thermometer outside my window now reads 37 deg.C!). The captured waveforms were exactly the same, either the noisy units above were powered on or off.

For those who will notice it, the mains voltage was externally measured to be 228.7 VAC RMS, while the DS1052E measured it to be 218 VAC RMS (DS1052E error: -4.7% or -3bit); in defence of the DS1052E, I will have to state that I did not warm it properly up before taking these readings, neither have I recently run auto-calibration².

The interesting parts in the captured waveform above are the time points -1.7div (-3.4 ms) and +3.3div (+6.6 ms), where Ch1 captures a couple of seemingly innocuous mains disturbances, which are absolutely synchronised to the Ch2 obvious spikes. The problem is that, though the Ch1 and Ch2 waveforms are out of synch by ~1.4div (~2.8 ms), the Ch1 and Ch2 spikes are in perfect synchronisation. Channel crosstalk, do I hear some of you murmuring? Well, maybe. But, by disconnecting the Ch2 probe, the second trace became a nice and clean flat line while the spikes at the first trace remained as they were exactly, and of the same shape and amplitude. So, I suppose that my scope is not really lying to me...

This means that:
1. The depicted spikes are probably generated erroneously within the oscilloscope front-end amplifiers.
2. Our mains lines are actually that dirty.
3. We are both being bombarded by who-knows-what kind of electromagnetic weapons (I am kidding!).

What I can only say is that, in order to trust what my DS1052E tells me about my mains line spikes, I would have to repeat those readings with a higher class oscilloscope and not with another entry-level one.


EDIT:
1. DO NEVER TRY doing that if you are not absolutely sure of what you are doing, because the probe ground clip is the instrument's ground, which is hardwired to the mains power supply ground! Be very careful when messing with the mains line.

2. More than half an hour later, the mains line was reported by the DS1052E to be 221 VAC RMS, while it was measured to be 223.2 VAC RMS.

-George

I 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.

[Paul Moir]

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.