Modfied sine wave to a pure sine wave

Discussion in 'General Electronics Chat' started by low, Mar 28, 2013.

  1. low

    Thread Starter New Member

    Mar 27, 2013
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    I plan on using a wind turbine or alternator to produce electricity. The inverter will be a modified sine wave as a pure sine wave is very expensive for a house.

    My question is this: I have been told that electronics such as televisions, computers, microwave's etc., can malfunction on a power supply that is using a modified sine wave.

    If I were to plug the electronic devices listed above into a line conditioner/cleaner, or ups backup, would that give me a pure sine wave, to prevent damage/malfunction to my devices?
     
  2. richard.cs

    Member

    Mar 3, 2012
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    Most, but not all, electronics works OK on modified sine wave. I would expect modern TVs and computers with switchmode power supplied to function ok, although it can be a bit harsh on the input capacitors - a bit of series inductance can help there. Motors and things with mains-frequency transformers generally buzz and hum a bit more and can run warmer. Microwaves are a bit of a special case - they're very sensative to peak voltage and so can give significantly reduced output, even though the peak voltage of modified sine wave isn't that low.

    Most UPS's just pass the input to the output largely unchanged when power is supplied, the exception is "dual conversion" UPS's which continuously step the voltage down the the float level for their internal battery, and then continuously run their internal sine wave invertor. These are probably more expensive and definately less efficient than just buying a sine wave invertor.

    Most line conditioners that I'm aware of remove some high frequency noise and clamp voltage spikes but don't do a lot else. They might round off the edges of your modified sine wave (which is really a square wave with a dead time chosen to minimise harmonics).

    Also worth considering is pulling the DC out of the invertor before its output H bridge and using it to run devices with a switching power supply.
     
  3. low

    Thread Starter New Member

    Mar 27, 2013
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    Thanks for your response Richard. I am not versed in electronics as you are, studied electrical installation in high school, and one year of trade school.

    Just trying to find some means of saving money on my electrical bill.

    My house is wired for 240 volts. If I were to use a 110 volt invert, (they usually come with three or four circuits) and use two circuits to feed the panel, That is use the hot from each circuit, and run one to the hot on the breaker bus bar(to prevent overloading a single circuit) can I use the neutral from both outlets, tie them together, and place them on the neutral bar of the breaker panel? The same thing would apply to the ground as the neutral.
     
  4. richard.cs

    Member

    Mar 3, 2012
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    I'm finding it difficult to visualise what you're describing (a diagram might help), but I think you are assuming that you can buy a 110 V invertor that has multiple independant outputs. Usually if they have multiple outputs they are not independant of each other.
     
  5. low

    Thread Starter New Member

    Mar 27, 2013
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    Thanks Richard. I am thinking of something like this. http://www.powerbright.com/pw6000-12.html

    Plug heavy duty plugs into the receptacle, and take the hot line and connect it to the hot busbar on the breaker panel. Do this for the next receptacle and take the neutral lines from both and connect them to the neutral bus bar in the panel.
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Think you will find that two 120VAC inputs do not a 240VAC out put make. The timing of the wave form also has to match. How are you going to synchronize the wave form to have them 180 degrees apart? This is what electrical appliances are expecting, not a haphazard wave form.

    Link to our Ebook about AC voltage - http://www.allaboutcircuits.com/vol_2/chpt_1/2.html
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    What you are trying to do. Will require quite high investments. And also proper qualifications to do. This is not by far a DIY project. If you want to reduce your electrical bills. Start by using this
    [​IMG]
    And also try to be economic in any other way. Like do not heat rooms you are not using or then you are not using them. Can you lower the indoor temprature a degree or two (if you live in a cold climate). Google "lower electrical bill" you will find a lot of tips.
     
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  8. richard.cs

    Member

    Mar 3, 2012
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    And the other end? Are you planning on using two separate 110V inverters?

    That might be doable if 1) the inverters produce an output isolated from ground or with neutral tied to ground (many cheap ones aren't like this and the two outputs alternately swing between gnd/bat- and 170V) and 2) you modify the inverters so that one acts as master and drives the other with the same frequency and opposite phase.

    You would need a lot of knowledge of the internal workings of the inverters to get that to work.

    Do you need to run both 110 V and 220 V appliances? If only 110 V you could just tie the two "hots" together. Any 110 V appliance would work but anything on 220 V wired between the two legs won't see any volts at all.
     
  9. timescope

    Member

    Dec 14, 2011
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    DC is extremely dangerous and can give a LETHAL ELECTRIC SHOCK.
    Do not do this.

    Timescope
     
  10. timescope

    Member

    Dec 14, 2011
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    This type of inverter is not reliable because of it's poor surge handling capability. I am currently repairing a 3000 watt modified sine wave inverter that destroyed 32 of the 48 mosfet transistors used.

    I have found pure sine wave inverters with transformer output to be the most reliable.

    Also, select a 24v or 48v inverter for power levels over about 1000 watts. The 6000 watt, 12v inverter you referred to would require a DC input current of 500 Amps at full load.

    Timescope
     
    Last edited: Mar 28, 2013
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  11. ramancini8

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    Jul 18, 2012
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    Why is DC more dangerous than AC?
     
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    They are both capable of killing you BUT

    DC in general is considered more dangerous because of its effects on the muscles in the body. Muscles will 'clench' tightly and because of this effect, it is sometimes impossible for the person experiencing the electric shock to let go of the wire, where AC because it passes through zero allows the muscles to relax for a fraction of a second.

    This is only for special cases where a person has (usually) closed their hand around the electrified object.
     
  13. t06afre

    AAC Fanatic!

    May 11, 2009
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    In medical safety regulations they differ between AC and DC current. In case of single fault condition. Much higher AC current(RMS) than DC are allowed to pass through patient.
    [​IMG]
     
  14. BillB3857

    Senior Member

    Feb 28, 2009
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    Unless you are talking about installing a totally separate breaker panel and circuits dedicated to being run from the inverter, I would strongly suggest this thread be closed. Connecting inverters to an existing panel requires a proper transfer switch, knowledge of how to connect it, etc, etc.
     
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