Cleaning Modified Sine Wave

[Gnome]

Well an inverter producing "modified sine" and sine wave are essentially identical.

The first stage called the input/boost stage, takes the DC input, then uses transistors that turn on and off very quickly to feed this power through a transformer. Because the transistor turns on an off quickly the transformer boosts this voltage.

The voltage then goes through a rectifier bridge so you get high voltage DC. The ripple is cleaned with capacitors.

After this is where modified sine and sine wave differ.

Sine wave UPS uses high frequency pulse width modulation to create a sine wave. Modified sine uses low frequency pulse width modulation. Both work from a high voltage DC source.

The total cost difference between the two really isn't that big from a manufacturing perspective. Most of the cost is R&D and people always buying cheap crap.

To be clear you do get two types of boost stages, fixed ratio and fixed voltage. Fixed ratio is almost always used in modified sine, it is the cheapest and lowest quality. The DC output voltage varies with load and input voltage, it only boosts the voltage by a fixed amount. Fixed voltage is technically a switch boost converter targeting a specific voltage by using PWM to keep that voltage.

Hence converting is always less efficient than buying a quality sine wave product in the first place.

 

[tRoN]

Warning: A lot of UPSes do not like modified sine as their input - they show a mains failure.

^this
Tried, tested and failed

 

[Napalm]

Has anyone had issues connecting Simulated Sinewave/Modified Sinewave inverters (like the Mecer 2400va to LCD tv's )


I have an 47inch Sony LCD TV.

 

[Sonic2k]

Well an inverter producing "modified sine" and sine wave are essentially identical.

The first stage called the input/boost stage, takes the DC input, then uses transistors that turn on and off very quickly to feed this power through a transformer. Because the transistor turns on an off quickly the transformer boosts this voltage.

The voltage then goes through a rectifier bridge so you get high voltage DC. The ripple is cleaned with capacitors.

After this is where modified sine and sine wave differ.

Sine wave UPS uses high frequency pulse width modulation to create a sine wave. Modified sine uses low frequency pulse width modulation. Both work from a high voltage DC source.

The total cost difference between the two really isn't that big from a manufacturing perspective. Most of the cost is R&D and people always buying cheap crap.

To be clear you do get two types of boost stages, fixed ratio and fixed voltage. Fixed ratio is almost always used in modified sine, it is the cheapest and lowest quality. The DC output voltage varies with load and input voltage, it only boosts the voltage by a fixed amount. Fixed voltage is technically a switch boost converter targeting a specific voltage by using PWM to keep that voltage.

Hence converting is always less efficient than buying a quality sine wave product in the first place.

There are still many inverters out there that take a low-voltage DC and step that up with a transformer... the output of these is quite horrible to say the least. My UPS at home is such a candidate.

The boost topology is currently used yes, but the cost difference? Not so sure about that.
I stripped one of these inverters last year, they basically stepped 12VDC to 300VDC odd and then chopped that up with a rough H-bridge. What a piece of crap!

The pure sinewave inverter however was a very complex piece of kit though... and even there, the Chinese crap doesn't last.

 

[Mr.Jax]

Has anyone had issues connecting Simulated Sinewave/Modified Sinewave inverters (like the Mecer 2400va to LCD tv's )


I have an 47inch Sony LCD TV.

I'm using the MECER 1200VA inverter to power a LG 47", DSTV Explora and LED light with no problems whatsoever. The items consumes 150w (measured).

 

[Napalm]

That's basically similar setup to mine yes. (isn't your LG 47" an LED tv?)

 

[Gnome]

There are still many inverters out there that take a low-voltage DC and step that up with a transformer... the output of these is quite horrible to say the least. My UPS at home is such a candidate.

The boost topology is currently used yes, but the cost difference? Not so sure about that.
I stripped one of these inverters last year, they basically stepped 12VDC to 300VDC odd and then chopped that up with a rough H-bridge. What a piece of crap!

The pure sinewave inverter however was a very complex piece of kit though... and even there, the Chinese crap doesn't last.

Indeed, I didn't mentioned what is commonly referred to as a low frequency design. The newer designs use a high frequency PWM to cut down significantly on cost (eg. much smaller transformer), increase reliability and massively improve efficiency.

But yes, the older APC Smart UPS are an example of low frequency design. Well built but lacks efficiency and costs are crazy.

Good catch I totally forgot about that topology.

 

[Tacet]

You can build low-pass LC filters. Adding i.e. a 5th order Butterworth to your design will help in cleaning up the signal, and not only to a small degree. However, you'll waste a lot of energy in your filter components, and you'll mess up the power factor.

Thor's idea has merit. Yes, it's not a good solution here, and has a couple of drawbacks, but there's no need to ridicule him for it.

 

[Mr.Jax]

That's basically similar setup to mine yes. (isn't your LG 47" an LED tv?)

Yes it is. I don't think you'll have any problems though, CCFL backlit TV's should also work without a hitch.


On another subject, I'll capture the waveforms of 3 different UPS's this weekend and post the images (cheap modified sinewave PC UPS, proper pure sinewave PC UPS and the mecer inverter which is also modified sinewave of course).

 

[Napalm]

thanks mr.Jax. Will be interesting to see the price diff vs the Sinewave quality.

 

[Tacet]

Yes it is. I don't think you'll have any problems though, CCFL backlit TV's should also work without a hitch.


On another subject, I'll capture the waveforms of 3 different UPS's this weekend and post the images (cheap modified sinewave PC UPS, proper pure sinewave PC UPS and the mecer inverter which is also modified sinewave of course).

When you post it, would you please post the frequency responses as well, if your scope can do Fouriers?

 

[Mr.Jax]

When you post it, would you please post the frequency responses as well, if your scope can do Fouriers?

Good idea, will do.

 

[TheMightyQuinn]

I use a 1 000w Modified sine wave Inverter. My plasma gives off a very loud buzzing sound when I use it. Some people claim that "it shouldn't", but it does. Something to doe with the squarer sine wave causing resonance within the plasma's power supply's wiring. I use headphones anyway through a Yamaha receiver, so it doesn't really bother me. More concerned that this may cause damage. Any ideas?

 

[Napalm]

Mr jax, where is the results and pictures?

 

[Mr.Jax]

Oh fek. I totally forgot. Will do this tonight.

 

[Mr.Jax]

Here are the Oscilloscope measurements for the 3 UPS's I have.

RCT 650VA
MECER 1200VA
TESCOM SS Pro pure sinewave.

http://imgur.com/a/HbxTT

 

[savage]

Here are the Oscilloscope measurements for the 3 UPS's I have.

RCT 650VA
MECER 1200VA
TESCOM SS Pro pure sinewave.

http://imgur.com/a/HbxTT

Jeez - now one can understand why the Mecers and RCTs are so cheap. I'd be scared to connect expensive electronic equipment to that.

 

[bekdik]

What about using a CVT between the UPS and the load?

 

[Gnome]

Here are the Oscilloscope measurements for the 3 UPS's I have.

RCT 650VA
MECER 1200VA
TESCOM SS Pro pure sinewave.

http://imgur.com/a/HbxTT

That is perfectly acceptable for modified sine and exactly how all modified sine inverters look.

As I have said countless times, modified sine is simply pulse width modulation. When you push more current, the pulses get longer.

What is more concerning is the bad quality of the Tescom SS Pro Pure Sinewave. Clipping at the top and bottom somewhat. I'm wondering what the ripple looks like...

What about using a CVT between the UPS and the load?

Again, you cannot convert "modified sine" to sine wave. It just isn't going to happen.

 

[hexagon]

I know how to do it.
I would use two of these cheap modified sine wave UPS units to generate two DC rails of 150V each, and then use a nice, powerful set of transistors in push-pull to generate a clean sinewave.

I was going to do this for my house but the energy taken out the batteries proves to me that the mains is incredibly efficient at what it does. Although its not difficult to deliver upwards of 6kW continuous from the batteries doing it the Emerson way, it becomes a bitch to charge all of that from solar panels.

Push-pull is essentially Class B, so you're limited to a maximum of about 78.5% efficiency... So go and check out datasheets on transistors that will dump that sort of heat - it won't be pretty.

This is why audio amplifiers > 1kW will pretty much always be Class D (roughly like power inverters), although I'm sure there will be some audio nutcases who will be able to point to a 1kW Class A amplifier somewhere.