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Thread: New guy here(first SMPS build)

  1. #1

    New guy here(first SMPS build)

    Hello everyone, i am starting a project to build a high power switchmode supply that will act as the power source for a homemade plasma cutter, i don't want to hear start with something easier and lower power since i am new to this, i have made the decision that the best way to learn is to just jump right in and just do it, i also understand all the necessary safety precautions. This power supply i plan to build will have 330v open circuit voltage and need to be limited at 40 amps short circuit current. I am still in the research and design phase. I have decided to use a half bridge inverter design, and i will be driving it with an IR2153. So far i have purchased a lot of EE80 ferrite cores, the mains rectifiers, large filter capacitors, the IR2153 chips, and a lot of large 1200v, 150amp IGBT half bridge modules, i will post my schematic shortly for all to see. i dont have any specific questions as of now, just posting to see if anyone has any input or pointers that could help me along with this project

  2. #2
    Quote Originally Posted by twenglish1 View Post
    Hello everyone, i am starting a project to build a high power switchmode supply that will act as the power source for a homemade plasma cutter, i don't want to hear start with something easier and lower power since i am new to this, i have made the decision that the best way to learn is to just jump right in and just do it, i also understand all the necessary safety precautions. This power supply i plan to build will have 330v open circuit voltage and need to be limited at 40 amps short circuit current. I am still in the research and design phase. I have decided to use a half bridge inverter design, and i will be driving it with an IR2153. So far i have purchased a lot of EE80 ferrite cores, the mains rectifiers, large filter capacitors, the IR2153 chips, and a lot of large 1200v, 150amp IGBT half bridge modules, i will post my schematic shortly for all to see. i dont have any specific questions as of now, just posting to see if anyone has any input or pointers that could help me along with this project

    I like the EE80 for this project, but I recommend to replace the IR2153 with SG3525 as at least you have SS. witch IR2153 dont have.

    Also a full bridge SMPS would be better option for 330Vx40 AMPS SMPS 13200W

    I am not sure if you take into account harmonics will be injected and EMI

    Hope that helps.
    www.diysmps.com & www.Micro-Audio.com

  3. #3
    How much power can the EE80 cores handle at say 40khz? If one isn't enough I could parallel two cores, right? And what is the advantange of the sg3525 over the ir2153? One more quick question is what is the best way to determine the value of the capacitors in the half bridge? Not talking about the main filter capacitors, I'm talking about the half bridge output capacitors that are connected between the positive and negative rails and the point between them goes to one side of the primary winding, not sure what they are called

  4. #4
    The SG3525 has “soft start”, it is a real SMPS controller chip with a lot of design examples and good ap notes.

    The EE80 core can deliver a theoretical power of 8KW at 40 khz, if you can find room to wind that much copper.

    You can stack cores. Each core is a set of E cores. One set is 8KW at 40Khz. Two sets would give you 16KW. Realistically though, over 3 or 4 KW you usually go to multiple transformers and series or parallel the outputs to get the power you want.

    You gave the short circuit current of 40 amps. What is the maximum working current and voltage you will see.

    As a general rule a half bridge is good for 1KW. But it can be pushed to 2KW or so if you really want to do it. Also If you want to do KW’s of power then a half bridge is a poor choice. As Microsim said go full bridge.

  5. #5
    Quote Originally Posted by twenglish1 View Post
    i don't want to hear start with something easier and lower power since i am new to this, i have made the decision that the best way to learn is to just jump right in and just do it
    Much like the multi-kW TIG welder project elsewhere on this forum I admire your guts and naive determination. You know people with some experience in the field will tell you it's an unthinkably difficult project nigh-on-impossible for an amateur especially a beginner, a couple of orders of magnitude more power than might be reasonable, but you continue anyway. Cudos.

    I can't really give you much advice except to say be very careful, don't kill yourself or burn down your house etc. Don't be too disappointed if the project turns out to be more expensive and poorer performing than the commerically available alternatives or you never get it working at all as you know going into in that these are all distinct possibilities. And finally, good luck!

  6. #6
    I will probably start at less than 40 amps for a start, maybe 10 - 15 amps Say i design my transformer to draw 15 amps at the rectified line voltage which is around 330v, that is just under 5000 watts, less turns on the primary means a higher current draw correct, but also a higher saturation level, i calculated around 11 primary turns will be a good starting point for one EE80 core, 11 turns puts the saturation level at about 4500 gauss, which is getting close to the max saturation of the core, so for a start should i go with more than 11 turns?

    Question about doing a full bridge, will i be able to drive a full bridge with one of the SG3525 drivers? i know the chip only has two outputs but could i connect the gates together of the two opposite transistors and just use the two drive signals? or will i need 4 separate drive signals?

  7. #7
    “Will i be able to drive a full bridge with one of the SG3525 drivers?”

    With a full bridge you usually use a gate drive transformer with separate output windings for all 4 gates. The gate drive transformer is driven by auxiliary transistors and the gates are assisted with more circuity.

    Here is a good example showing the whole setup, but not necessarily the only way to do it.

    EDIT, i do not know why this forum is making the image so small but i will try to upload again in next post.
    Attached Images Attached Images
    Last edited by wally7856; 04-26-2014 at 12:41 AM.

  8. #8
    2nd try, converted PNG to JPEG.
    Attached Images Attached Images

  9. #9
    "I will probably start at less than 40 amps for a start, maybe 10 - 15 amps Say i design my transformer to draw 15 amps at the rectified line voltage which is around 330v, that is just under 5000 watts, less turns on the primary means a higher current draw correct, but also a higher saturation level, i calculated around 11 primary turns will be a good starting point for one EE80 core, 11 turns puts the saturation level at about 4500 gauss, which is getting close to the max saturation of the core, so for a start should i go with more than 11 turns?"


    My semi educated input would be as follows. Pressman’s switching power supply book says not to use more than 1600 Gauss unless you really know what you are doing. He also says large cores have a problem dissipating heat. His book does not cover big cores like the EE80 so i would go less than 1600 Gauss, more like 1200 to 1400 maximum at 40khz.

    Also using your 5000W as a guide, i would say the EE80 might be good for 3KW continuous duty. So use two of these cores with the primaries in parallel and put the secondaries in series, one winding for each core. You can then wire up the secondary’s with a full wave center tap configuration.

    Now each primary only has to see 1/2 of the current, instead of 2x the current for a half bridge. Also with a full wave center tap you wind each output winding for the full voltage you want out but each winding supplies half the current.

    To sum things up, you would have on each core one primary winding and one secondary winding.

  10. #10
    Thinking some more, it would be better to use a split primary. This is how the best transformers are wound.

    Primary, Secondary, Primary

    This will give you the best coupling and give you more room for your primary winding.

    340vdc Primary voltage
    40khz
    1200 Gauss
    Ae 3.925 cm^2
    = 45 turns

    So you have a choice of 22 or 23 turns for each half winding.

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