Square Wave Inverter versus sionodal Inverter

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

  1. yam_fzr
    Joined: Mar 2015
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    Location: Australia

    yam_fzr Junior Member

    Hey Bert, I meant no offense. I was going by your op request and giving you some advice as an electronics design engineer who has done high power control systems with motors and inverters for decades.
    You're welcome to take my advice or not, but it was given to save you heartache by using an already developed and engineered design.

    Here's the last bit of unsolicited advice I'll give you. The IRFP064N will burn up in a spectacular way shortly after you place a load on the transformer and possibly even before load, if you use the components you have listed. You also run a serious risk of blowing up any device on the output at low load if the inverter survives.
    The IRFP064N is not a device I would use for this application, nor are the BC377's going to be any good as level translators for the MOSFET driver stage.
    At least use a half bridge MOSFET driver rather than a simple common emitter level translator that will have very poor performance and asymmetrical drive capability.
    If you open up an inverter (MSW) of similar capacity, you will notice that it is a lot more complex than a CPU, an output stage and some front end drivers with a few discrete's thrown in. There are many reasons for that. A 1kW inverter is not a simple design to produce.

    You can take or ignore my advice or even tell me to stick it where the sun don't shine, but, I did this sort of stuff for a living for decades and am passing on free information to help you make something with the best chance of success and the least chance of disaster. Do with it what you like.
     
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  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    30-odd years ago I designed an inverter that more or less did as Sdowney describes. It had a stable 50 Hz source (can't remember exactly what it was), square wave to triangle converter and a dual opamp that compared the triangle with a DC level obtained by rectifying the inverter output. There also was a bias voltage to get the thing started.
    Without load, the duty cycle was approx. 30%, with increasing load it grew to almost (but not quite) 100% with just a small gap so the output stages had time to get out of saturation.

    We sold 1000's of these as a kit and a few 100's assembled ones under the name "Port-a-Quart". Because the output power increased with the load we never succeeded in reliable current limiting, so plugging a fridge in meant instant death for all output stages....
     
  3. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Yam_fiz, I am fully aware that you mean it in a good way and I appreciate that and like to avoid me "Blowing" things up. However I have made a number of inverters with small transformers and are surprised about you worrying me the IRF064N burning up, which I have been using in the hundreds. I do current sensing in a fast way and only work on 12 Volt with sufficient protection for spikes. Also, my load will only absolute a maximum of 250 watt and not 1 Kw. Although 250 watt is already no longer electronics but plumbing works, with the thick copper wiring.

    Thanks , I am aware about the inductive load with consequences.

    I am surprised as I have build more than 10 circuits with them without blowing any of them. Also with brushless motors of a few kilowatt.

    good idea, I will consider that, however I will have a switching delay between switching the 2 primary coils therefore I can use any BC337 or DC-DC inverters for the gates. (Done that many times)

    Yes, I have opened a few of them and will certainly build something similar one day.

    No, I will not ignore your advise, nor tell you to go to hell. Although my favorite rugby team lost yesterday from your country, I do have a bone to pick with you. Trust that you have a good sense of humor.
    Bert
     
  4. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Interesting CDK, maybe I should use the PIC18F2431, whereby I can instantaneously determine the current and go for a loop a few times and then cut the driver, if the situation hasn't normalized. The PIC18 has 4 AD Converters simultaneously, which can sense in nanoseconds any funny business. I did that for the brushless motors I have running in the boat. I wrote the program for the PIC12F675 for this 1 KW trafo, but after reading your experience and the warning from Jam_fzr, it maybe a better option.
    Thanks for your input
    Bert
     
  5. yam_fzr
    Joined: Mar 2015
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    Location: Australia

    yam_fzr Junior Member

    Bert, this is what I based my recommendations on.
    But it sounds like you don't need any advice.
    I do have a good sense of humour and aren't taking any offence.
    Good luck with your project.
     
  6. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Yam, I like people with a good sense of humor. Unfortunately I am nearly 75 and even today I am still learning. I can guarantee you that your advice is taken seriously. Because of your and CDK warnings, I do now implement current sensing, which I was not planning to build in. Thanks for your help. Bert
     
  7. yam_fzr
    Joined: Mar 2015
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    Location: Australia

    yam_fzr Junior Member

    No one stops learning, though some stop trying. Glad to read you're not.
    I never stopped teaching even though I gave up being a lecturer in electronics engineering a long time ago, but I still have plenty to learn myself. The person who has nothing to learn has already reached the end of their life because they already know everything they ever will.
    If you need any advice, or want me to elaborate on anything I've written, feel free to ask. I'm more than happy to oblige.
     

  8. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Yam, it is a pleasure to have a lecturer like you, advising us on this forum. With electronics, there are lots of different ways to solve a problem. The question always will be "Will it be the first time right" . Thus, most readers have the same problem and love to get a second opinion in what they are doing.
    Bert
     
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