Why soldering stations use step down transformers ?

Discussion in 'General Electronics Chat' started by IcedFruits, Jan 15, 2014.

  1. IcedFruits

    Thread Starter Member

    Jan 15, 2014
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    I was browsing some soldering station tear-down videos in youtube, and say almost all of them have some high watt step down transformer inside.

    But I would like to know why the manufacturers do this step down, instead of controlling the 230v directly by triac ? :confused:

    (Also some of them actually use the stepped down AC to power the iron, with the help of a triac)
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you are referring to the Weller style gun type, they have a single turn extremely high current secondary that heats up at the point of smallest area.
    It is the same principle used in spot welding, where the electrode points are very small diameter compared to the secondary conductor.
    It is a very economical, non-electronic way of heating.
    Max.
     
  3. IcedFruits

    Thread Starter Member

    Jan 15, 2014
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  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The transformer you would still need is in the High VA range (>600VA).
    And I suspect they use the lower voltage for safety reasons.
    Max.
     
  5. IcedFruits

    Thread Starter Member

    Jan 15, 2014
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    those transformers are mostly 24v/upto 5A secondary powering some 50-70w iron.

    safely could be a reason, but there could be more .....
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    Usually a soldering iron is resistance wire wound on to some kind of heat conducting former - lower voltage means less turns (shorter total length) of thicker resistance wire = more robust element, it greatly simplifies arranging insulation that can withstand high temperature too.

    The most popular Antex model is straight 230V into the element, which is very fine resistance wire - its a very good iron, but I always plug mine into a surge protected socket or mains transients finish it off!
     
  7. vk6zgo

    Active Member

    Jul 21, 2012
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    Hardly big,bulky or expensive!

    Small transformers as used in most soldering irons are really quite economical to use,compared to the cost of producing real temperature control using the Mains direct.

    You can buy El Cheapo soldering stations,which use a triac---in fact they use the same circuitry as lamp dimmers.
    They are not really temperature controlled,as you need to wind the "temp" control up in order to keep any sort of reasonable temperature when soldering.

    Like lamp dimmers,the peak voltage doesn't change,just the duty cycle,so the iron handpiece has to be insulated for Mains voltage.

    If you add the Electronics to provide real temperature control,you are stuck with providing a low voltage supply,which in the transformer case is already halfway there!
     
  8. IcedFruits

    Thread Starter Member

    Jan 15, 2014
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    That would be kinda strange, cause they could just use normal irons those come with a direct mains socket, and still they last pretty long.

    please see hakko 936 schematic. its pretty popular and temperature controlled by 24v ac with triac.

    http://dalincom.ru/datasheet/HAKKO_936_schematic.pdf
     
  9. vk6zgo

    Active Member

    Jul 21, 2012
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    I have nothing against triacs-- the HAKKO appears to use it to control 24vac,not 240/120,as used in the irons I referred to!
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    mostly for isolation from the ac lines. anti static soldering came into favor with integrated circuits and cmos back in the 70's.
     
  11. IcedFruits

    Thread Starter Member

    Jan 15, 2014
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    thanks for sharing all ur views. i am thinking about doing something similar, will post for some design suggestions later in some other thread. :)
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Isolation is how Weller used to advertise the benefits. If power or test equipment is still connected to the circuit (even if turned off) voltage can flow to undesired routes.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    A lot of manufacturers trumpet about isolation - at the end of the day, the exposed metal bits are connected to earth.
     
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