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What happened to toroid power transformers?

Discussion in 'Electronic Components' started by Usual Suspect, Mar 8, 2007.

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  1. 15 years ago there were (if I remember correctly) lots of toroid power
    transformers available. It seems that most of what is available now is the
    same old steel lam cores.

    Did the market price for tor go up? (c:

    Just curious...
     
  2. Dave Platt

    Dave Platt Guest

    15 years ago there were (if I remember correctly) lots of toroid power
    www.toroid.com
    www.avellindberg.com
    www.amveco.com
    www.plitron.com
    www.nuvotem.com
    www.atc-frost.com

    Mouser Electronics carries Hammond toroidal power transformers.

    I don't know whether toroidal power transformers are more or less
    common than 15 years ago. They always seem to have been a specialty
    item, with higher costs than EI-core or similar traditional types.
     
  3. Eeyore

    Eeyore Guest

    If anything, the general availability of toroids in the UK from broad line
    distribution has actually improved in recent years.

    Graham
     
  4. I'll guess that since they cost more, designers are opting for less
    expensive types. Also, thanks to switch-mode power supplies, the market is
    shrinking for line transformers.
     
  5. Ed

    Ed Guest

    There are many advantages to using this type of transformer.

    I've been cleaning out lots of parts after years of building and have
    a few for sale.

    They are listed in the 'parts for sale' page on my web site at:

    http://mysite.verizon.net/topossibilities/
     
  6. Guest

    |>15 years ago there were (if I remember correctly) lots of toroid power
    |>transformers available. It seems that most of what is available now is the
    |>same old steel lam cores.
    |>
    |>Did the market price for tor go up? (c:
    |
    | www.toroid.com
    | www.avellindberg.com
    | www.amveco.com
    | www.plitron.com
    | www.nuvotem.com
    | www.atc-frost.com
    |
    | Mouser Electronics carries Hammond toroidal power transformers.
    |
    | I don't know whether toroidal power transformers are more or less
    | common than 15 years ago. They always seem to have been a specialty
    | item, with higher costs than EI-core or similar traditional types.

    They do have specialty uses, such as:

    http://www.equitech.com/products/industrial/xfmrs/toroid.html
    http://www.equitech.com/products/industrial/wall.html
     
  7. Don Kelly

    Don Kelly Guest

    Possibly the toroidal transformers that the original poster was referring to
    were "pole pig" traansformers rather than the more specialized (isolation?
    ,auto?) transformers indicated by your references. These were/are(?) made
    but are considerably larger than the units shown.
     
  8. Guest

    | |> |>15 years ago there were (if I remember correctly) lots of toroid power
    |> |>transformers available. It seems that most of what is available now is
    |> the
    |> |>same old steel lam cores.
    |> |>
    |> |>Did the market price for tor go up? (c:
    |> |
    |> | www.toroid.com
    |> | www.avellindberg.com
    |> | www.amveco.com
    |> | www.plitron.com
    |> | www.nuvotem.com
    |> | www.atc-frost.com
    |> |
    |> | Mouser Electronics carries Hammond toroidal power transformers.
    |> |
    |> | I don't know whether toroidal power transformers are more or less
    |> | common than 15 years ago. They always seem to have been a specialty
    |> | item, with higher costs than EI-core or similar traditional types.
    |>
    |> They do have specialty uses, such as:
    |>
    |> http://www.equitech.com/products/industrial/xfmrs/toroid.html
    |> http://www.equitech.com/products/industrial/wall.html
    |>
    |> --
    |> |---------------------------------------/----------------------------------|
    |> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
    |> |
    |> | first name lower case at ipal.net /
    |> |
    |> |------------------------------------/-------------------------------------|
    |
    | Possibly the toroidal transformers that the original poster was referring to
    | were "pole pig" traansformers rather than the more specialized (isolation?
    | ,auto?) transformers indicated by your references. These were/are(?) made
    | but are considerably larger than the units shown.

    I've never seen one of those. But that would be interesting.
     
  9. John Larkin

    John Larkin Guest

    We use toroidal power transformers in some of our products. They're
    small, don't leak much field, and don't cost much more than regular
    ones. But they are sure hard on line fuses.

    John
     
  10. John E.

    John E. Guest

    We use toroidal power transformers in some of our products. They're
    For those of us not familiar, 'splain, please?
     
  11. John Larkin

    John Larkin Guest

    A conventional laminated core has corners and stuff. Some parts run at
    lower flux density than others, so are sort of buffers against hard
    saturation. Toroids have nice uniform cores, so can be designed to
    have all of the core material run near saturation. That's one reason
    they are so small and light. The geometry favors low copper
    resistance, too.

    So switch off a piece of gear that uses a toroidal line transformer.
    If you're unlucky, the switchoff will happen at maximum flux density
    in one direction, and leave some residual magnetization. Now, more bad
    luck, turn it on at the ac zero crossing in the same direction. All
    the core saturates and a huge primary current flows. This cheerfully
    takes out mdl or even slo-blow fuses, and sometimes power switches.
    We've measured 1000 amp peaks on modest-sized transformers, and you
    could hear the wiring jump inside the wall.

    CE requirements don't allow over-rating fuses a lot, so that can be
    really nasty. The super-slow TT fuses help, but are sometimes hard to
    get.

    John
     
  12. Dave Platt

    Dave Platt Guest

    A conventional laminated core has corners and stuff. Some parts run at
    lower flux density than others, so are sort of buffers against hard
    saturation. Toroids have nice uniform cores, so can be designed to
    have all of the core material run near saturation. That's one reason
    they are so small and light. The geometry favors low copper
    resistance, too.

    So switch off a piece of gear that uses a toroidal line transformer.
    If you're unlucky, the switchoff will happen at maximum flux density
    in one direction, and leave some residual magnetization. Now, more bad
    luck, turn it on at the ac zero crossing in the same direction. All
    the core saturates and a huge primary current flows. This cheerfully
    takes out mdl or even slo-blow fuses, and sometimes power switches.
    We've measured 1000 amp peaks on modest-sized transformers, and you
    could hear the wiring jump inside the wall.[/QUOTE]

    Seems like a good application for an NTC-thermistor inrush current
    limiter, with a few ohms of "cold" resistance?
     
  13. Jim Thompson

    Jim Thompson Guest

    Seems like a good application for an NTC-thermistor inrush current
    limiter, with a few ohms of "cold" resistance?[/QUOTE]

    I used to use NTC-thermistors at GenRad until some weisenheimer came
    by and toggled the ON/OFF switch at a rapid rate and blew my PS all to
    hell.

    So I rigged it so that turning OFF forced a 15-second wait before ON
    would function ;-)

    ...Jim Thompson
     
  14. John  Larkin

    John Larkin Guest

    Seems like a good application for an NTC-thermistor inrush current
    limiter, with a few ohms of "cold" resistance?[/QUOTE]

    Absolutely. They work very well.

    John
     
  15. Seems like a good application for an NTC-thermistor inrush current
    limiter, with a few ohms of "cold" resistance?[/QUOTE]

    What happens if the power blips with the NTC hot? Short blips in AC
    power are pretty common, and there would be negligible time for the
    NTC to cool.


    Best regards,
    Spehro Pefhany
     
  16. John  Larkin

    John Larkin Guest

    We were concerned about that, and did some tests, on a 1000 watt CAMAC
    crate power supply. It ate power switches before we installed NTCs,
    and after that was fine. We tried teasing the power switch all sorts
    of ways, and it still worked. Ditto on an NMR gradient driver. Don't
    quite understand why.

    John
     
  17. There's not a lot of thermal inertia in an NTC. How much slower than a
    lightbulb, say, is it really?
     
  18. They have poor line-to-output AC isolation. They usually have low
    leakage inductance, that's bad for direct bridge-rectifier storage-
    capacitor setups. Plus, it's not so easy to add a grounded primary-
    secondary inter-winding shield. But hey, what the hell, I like 'em.
    Low ac magnetic fields spreading out into my sensitive electronics.
     
  19. Paul Mathews

    Paul Mathews Guest

    Other approaches commonly taken include a series power resistor
    shunted by relay contacts or a triac turned on after a delay. Another
    approach is to use SCRs in 2 legs of the secondary bridge rectifier,
    using phase control to ramp up the secondary current. This often
    works, since part of the turn-on surge....sometimes a big share of
    it....is actually the charging current for the secondary side
    capacitors reflected back to the primary side, with very little
    leakage inductance in series. ST makes a part designed to switch the
    line at zero crossings.

    Paul Mathews
     
  20. Eeyore

    Eeyore Guest

    It also has a small distributed air gap.

    John, you can fix this by running toroids at a *lower* flux or you can fit an
    inrush current limiting device / circuit.

    The absence of an air gap in toroids is a contributory factor to the problem
    btw.

    Graham
     
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