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DIY off-line transformer winding ?

Discussion in 'Electronic Design' started by Adam Seychell, Jan 5, 2004.

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  1. Is it common for people to hand wind their own transformers when
    prototyping an off line isolated switching power supplies ?

    The construction seems quite labor intensive, considering the
    insulation requirements, EMI shielding, and safety regulations.
    As a home brewer so I don't have the money to purchase official
    standards for insulation and EMI regulations nor do I have the
    specialized equipment to test insulation breakdown or accurate winding
    machinery, so I've been collecting data from various application notes
    on transformer design and dismantling transformers from old computer
    power supplies. One of the requirements is a 5 to 6 mm "creepage
    distance", and is usually made by creating a gap between each winding
    layer and the bobbin side wall, while the insulation layers of
    polyester film tape occupies the full width of the bobbin. The
    professional built transformers I've seen use a 3 mm width tape as a
    margin for each winding layer, and is wound to same thickness of the
    copper layer.
    With all this work do people go to the trouble or this just one of the
    reasons why building off-line SMPS don't make popular hobby pojects ?


    Adam.
     
  2. Adam Seychell wrote...
    The issue is dealing with the occaisional 3 to 10kV spikes that
    occur on the ac power lines. These must NOT be allowed to start
    carbon discharge tracks. One aspect that helps in this situation
    is the input RFI-noise spike-filter components.

    OK, you've learned some of the principles of practical insulation
    integrity, so don't you feel more comfortable to make some of your
    own ac-line switching transformers? Be sure to use good fuses!

    BTW, an easy way to get 0.2" or more of total creepage distance is
    to use two-section bobbins and avoid winding all the way to the top.
    If you stop 0.1" below the edge on each side, there's your 5mm.

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  3. henryf

    henryf Guest

    No, most people have a self-preservation instinct.
     
  4. You can make really tiny transformers using triple-insulated wire.

    Best regards,
    Spehro Pefhany
     
  5. Sure. There are usually very few turns and winding a transformer or
    two is no big deal. It's expensive getting ahold of all the required
    materials in small quantity though, IME.

    Best regards,
    Spehro Pefhany
     
  6. Sure, it's a Prototype after all. Personally, I prefer to find a
    commercially made transformer with the right credentials and design around
    that. If there are no special needs, one cannot beat those Chinese assembly
    lines!
    However, If you must roll your own, you can get quite far with Planar
    Transformers!

    In many ways they are easier to design & build than the "normal" types. The
    downside is that the switching frequencies are higher than one would
    probably like and it costs a PCB if you get it wrong. The cores are
    difficult to get in small quantities - the best way is to buy an "evaluation
    kit" with a few of each size.
    It's simply not worth the effort anymore - you can buy decent supplies below
    USD 100 for the typical power/voltage ranges up to about 200W or so. The
    excuse for building your own would be special requirements such as High
    Votage f.ex. - in which case you could try to work with a commercial CCFT
    transformer and leave the isolation to a commercial power cube.
     
  7. Spehro Pefhany wrote...
    Or even quad-insulated wire, http://www.vipwire.com/power.html :>)

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     

  8. *Buc buc buc...*

    Hark, what is that I hear? It sounds an aweful lot like a chicken. Hmm...
    Speaking of which, chicken sounds pretty tasty right about now.

    Don't be insulted. Chickens are quite respectable creatures. In fact, they
    are quite noble even though most of us just take them for granted. They
    give the ultimate sacrafice just so we can fill our bellies. Rather than
    thinking of this as flamebait, think of this post more as a tribute to
    chickens.
     
  9. "The rooster stared back at me, his power and confidence almost
    overwhelming. Down below, a female paused warily at the coop's
    entrance. I kept the camera running. They were beautiful, these
    "Chickens in the Mist." -- Gary Larson

    Best regards,
    Spehro Pefhany
     
  10. Spehro Pefhany wrote...
    Yes, indeed.

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  11. henryf

    henryf Guest

    Fritz, I admit it. I'm very careful when building circuitry
    that could become lethal if done wrong, such as an off-line
    SMPS, and I wouldn't advise the homebrewing of such circuitry
    just to save a few "bucs".
     
  12. Active8

    Active8 Guest

    It also sounds like a rip-off from one of the final episodes of
    MASH.
     
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