Square Wave Inverter versus sionodal Inverter

Discussion in 'OnBoard Electronics & Controls' started by BertKu, Jun 19, 2015.

  1. BertKu
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    BertKu Senior Member

    I am considering to use a 1 Kw transformer to use in a 1 Kw square wave inverter. Apart of possible sharp spikes, produced by the MOSfets, has anybody any experience what a square wave inverter does to equipment like modern TV, chargers etc. versus a sinusoidal wave. Assuming that in both cases the 230 Volt AC rms is the same. Bert
     
  2. jehardiman
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    jehardiman Senior Member

    Modern electronics do poorly and can be damaged by square wave inverters. Square wave inverters should only be for incandescent lights, heaters, and universal (I.e. commutator with brushes) motors. Induction (i.e. squirrel cage) motors will run poorly if at all, with more heat and noise.

    If you want to run electronics, spend the money for a good pseudo-sine wave inverter.
     
  3. yam_fzr
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    yam_fzr Junior Member

    I'll second that.
    Square wave, or more correctly called modified sine, produce far more harmonics than a sine inverter which has technically only the fundamental frequency.
    Some applications have no problem with modified sine, others do. The advantages of the modified sine are that it is lighter and has high efficiency.
    The disadvantage is that it can cause problems running some equipment, in particular motors don't much care for them running more inefficiently thus negating the efficiency gains one got with the true sine.

    True sine inverters will set you back more dollars, will be heavier but will run whatever the mains would as there is no difference other than power capacity.

    Which brings us to the next point, always overrate the inverter. If you need 1kW, then get something that can put out at least 1.5kW continuously. Although all inverters offer initial start up currents higher than the continuous, they do so by compromising both the power train and the distortion of the waveform when doing so. Overrating will make a big difference.

    There are also newer PWM/PCM style inverters that combine the advantages of both the true and the modified sine inverters but they are still pretty rare and expensive. As for why that is so, I have no clue. It may also have changed since I last looked and if you can get one cheaply then that would be my choice. They provide a true sine wave output at high efficiency.

    Hope that helps.
     
  4. BertKu
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    BertKu Senior Member

    Thank you Jehardiman, I suspected that already that the upper harmonics, will play havoc with the 230V AC conversion to the DC level of the 50 Inch TV flat screen. Pity. Thanks for your help. Bert
     
  5. BertKu
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    BertKu Senior Member

    Thank you for your input. I have that transformer lying around and considered, to build an inverter from it. Indeed the upper harmonics, 4th,5th, 6th, 7th etc will give the 50 Inch TV a hard time. Pity, All what I can do then, is to build a Mains to 12 Volt/ 80 Ampere DC power supply from it. Thanks Bert
     
    Last edited: Jun 19, 2015
  6. yam_fzr
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    yam_fzr Junior Member

    It depends greatly on the TV itself. many now use a switching supply which is the same as a computer or laptop supply. It simply rectifies the AC and then does a DC/DC conversion down from there to run the electronics. If it has a switching supply, it really won't make any difference if it's true sine or modified sine as an input as the rectification and subsequent filtering takes care of it.
    If however they use any part of the mains input directly, then you may have issues. Unfortunately that's going to be model by model variation specific and no rules apply.
    An engineer would make a DC/DC conversion so it can use a universal power source. Your TV may be marked 85-260VAC or so, with or without a switch. If this is the case you're probably going to be ok with a modified sine inverter.
    If the accounting department got to make some design decisions, then that may or may not be the case.

    You can have fun building an inverter, though I'd recommend simply buying one. It'll be far more cost effective and way less time consuming. That's free advice from an electronics design engineer so take it for what you think it's worth and how much you paid for it ;)
     
  7. CDK
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    CDK retired engineer

    Any modern device will work on whatever waveform you offer. The input stage is always a rectifier followed by a large capacitor that converts everything to DC.

    Only motors that rely on phase shift spoil the fun, like the compressor in a fridge. Central heating pumps do work, but produce a lot of noise. I've been using a square wave inverter for 15 years, just added a filter with two toroids and a capacitor to keep the pumps quiet.
     
  8. BertKu
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    BertKu Senior Member

    Hi yam_fzr, I have all the components lying around and do not have any expenses. I thought already that it would be a front end rectifying part and then a switch mode power supply. If it comes to the fine crunch, I have to dig my study notes out from 55 years ago on the calculations on T filters etc. Then filter the square wave to a more perfect sine wave. Not very efficient, but sunlight is very patient. I have to block the 3rd, 5th, 7th harmonics of a Square wave. I assume the even harmonics are too low to have an influence.
    You are totally correct in that some models use the AC input as reference point, maybe for zero cross detection etc. in anyway thank you for your valuable advice. Bert
     
  9. yam_fzr
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    yam_fzr Junior Member

    That's not really correct. Most, I use the term carefully there, will work correctly on a modified sine inverter, particularly the better ones that do some filtering of the input/output and get a much cleaner waveform.

    There are however electronics devices that don't use a switching supply on the input stage as well as other devices that assume a very clean sine wave input and then don't use quality filtering in their input stages which may or may not end up affecting the device. Other devices will be affected by the low voltage noise generated. By affecting, I'm meaning that the device will almost always work, whether it will work satisfactorily however is another matter. For example, a TV may have unacceptable interference with the video or the audio that the owner may find bad enough to negate the use of it. Whistling audio or banding video are typical.

    As an example, I have a 1.5kW modified sine inverter. Every time I use it I lose considerable dynamic range and sensitivity on my Icom SSB radio. To use the SSB, I have to turn off the inverter, even if that inverter is only running to supply 60W to a laptop or the small bar fridge (120W) I use.
    A true sine inverter won't generate the harmonics and thus won't affect the SSB performance. This is with the SSB running off the 12V side and not connected in any other way to the inverter. The power lead effectively becomes an antenna transmitting interference very effectively through the boat.

    As further example on the way devices can interfere unintentionally, one laptop I have I can't be charging even on shore power if I want to use the SSB at the same time. The quality of the laptop's universal charger is poor and it generates enough noise to swamp the SSB reception. Imagine what an inverter connected to the boats 12V supply pumping near 20 times more current at the output, and 200 times at the input will do.
     
  10. yam_fzr
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    yam_fzr Junior Member

    You're welcome Bert.

    There are other ways to generate a since wave that have far less interference and don't use a true sine wave input.
    If you do a search on (sine inverter pwm microchip) you'll get already made reference designs. Plenty of others around too. I'd recommend not going for a modified sine inverter design but a pwm type if you are going to build one. You'll be far happier with the results.
     
  11. sdowney717
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    sdowney717 Senior Member

    I have no trouble with a MSW inverter running the LED TV, the desktop PC, the Laptop PC, fluorescent lights. GFCI breakers. fridges, electric motors, fans
    It has run everything ok
     
  12. BertKu
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    BertKu Senior Member

    Hi Sdowney717, what is a MSW inverter? Is this a pure Square Wave inverter with only the odd harmonics, i.e. 3rd, 5th,7th,9th etc harmonics and not the even harmocis i.e. 2nd, 4th, 6th 8th etc.. only?
    Bert
     
  13. sdowney717
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    sdowney717 Senior Member

    Adding it runs the microwave and DVD player ok also.
    I have not found anything it wont run, but a pure sine wave is obviously a better inverter but it does cost more money.

    MSW inverter is a modified square wave. So whatever they produce is basically what I have. I know it does have the odd harmonic distortions. They offset time the base of the wave at the zero point, so it gives it a stretch step which helps approximate a sine wave.
    it certainly is possible my MSW inverter has a better wave pattern than the standard MSW inverter. It is a peak power products made by old world industries. I dont have an oscilloscope to see.

    knurlgnar24 has a lot of interesting inverter repair videos
    phase corrected versus non phase corrected MSW inverters.
    I have noticed under heavier loads, my inverter output voltage seems to rise a little.
    https://www.youtube.com/watch?v=CEeKlcL7kMo

    West marine video and notice they say MSW may not run a laser printer or high end audio equipment, but I dont have that on a boat, likely none will.
    Mine is a 3000 watt MSW inverter. I got a big one so that it could power the things I want. A microwave takes a lot of power and a fridge startup takes a lot of power. I bought it for $150 from an ebay seller.
    http://www.westmarine.com/WestAdvisor/DIY-Selecting-an-Inverter-or-Inverter-Charger

    Also adding this MSW inverter does not interfere with my TV antenna or the antenna 30db amplifier.
    True that inverters can create EMF interference. I have not noticed it with mine.
    I did have to do a major repair on this inverter when it shorted the output trying to run a 16k BTU cruisair heat pump.

    I really don't know exactly what happened. I have since added a disconnect relay, so if the inverter powers on, it disconnects the heat pump from the power. I don't like not knowing why, perhaps the inverter protection circuit is bad. But makes me more careful with keeping loads under 25 amps output. And not switching to inverter if the heat pump is on, just in case, even with that relay, there would be time in ms involved since a relay takes time to open.
     
  14. BertKu
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    BertKu Senior Member

    Hi yam_fzr, Yes I am aware that microchip has a number of Sine wave examples. However I do most of my programming still in assembler and stills struggle to master C with the Microchip C modules. One day, one day!! Look, yam, the square wave inverter is so simple, 1 x Microchip PIC12F675 for generating the 50 Herz , 2 x IRFP064N, 2 BC377-40 and a few resistors. The transformer came from a customer who went burst, some 30 years ago. I have it standing around in the workshop and I may as well use it, to make something I could use on the boat once in a while.
    Thanks for your suggestions and experience with the upper harmonics on your equipment, if I really make a 10Kw inverter one day, I will certainly look at a more cost effective and power efficient one with a 32 bit Microchip core.
    Bert
     

  15. BertKu
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    BertKu Senior Member

    Thank you Sdowney, that is of great help. I am planning to delay the zero crossing on both sides to get some better type of sinus wave shape. Thanks Bert
     
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