Why transformers rather than switch mode power supplies?

Discussion in 'Electricians' Talk' started by Joshua_S, Jul 11, 2018.

  1. Joshua_S

    Joshua_S New Member

    Hi,

    I am currently looking for my first low to mid range soldering stations (recommendations welcome). And every teardown I see of Hakko, Weller, Atten, Circuit Specialist, Ersa and any other, they all have 110/220V to 24V transformers. Why? Wouldn't it make much more sense to use DC-DC converters, as they would be smaller, more efficient, lighter and cheaper (which is comprehensively explained by this SMPS fundamentals: http://www.apogeeweb.net/article/85.html )? especially for the > 60W range.
     
  2. CGN

    CGN Well-Known Member

    Why does it concern you?
    These manufacturers have built these for decades and have a track record for reliability, and prob has something to do with the need for a variable output in the 2 to 3A range, which is perhaps better suited to a more traditional design.
    Also, the Tx adds a fair bit of weight to the station to make it stable, but I suppose you could always substitute that with something else...perhaps a tin of spam or sumthing.
     
    Last edited: Jul 11, 2018
  3. Vin

    Vin Member

    I'm going to stab a guess.

    I'd say it's a combination of the need for galvanic isolation between the mains supply and the metal probe of the soldering iron coupled with the need to earth the soldering iron.
     
  4. rogerk101

    rogerk101 Well-Known Member

    Where would the input DC come from that you're wanting to convert to an output DC of a different voltage? You would still need to have converted the 240V AC of your home to whatever you think of as the input DC, and the best way of doing that is with a transformer.

    FWIW, I have now had my transformer-equipped Weller soldering station for over 40 years, and it's still working as well as the day I was given it by my electrical engineering father. It is proof of his only advice for tools ... to buy the best tool you can afford, as anything less will likely mean buying twice ... once to buy rubbish and the second time to buy what you should have bought the first time round.
     
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  5. Pollowick

    Pollowick Well-Known Member

    Mine is of a similar age (possibly coming up 40) and still working well - I still have a range of 5, 6, 7, 8 (hundred degrees) temperature control tips from fine through to spade size. An excellent 24V 50 W tool that was last used yesterday. I also have a 12V iron only of the same type which can be used on a car battery.
     
  6. Joshua_S

    Joshua_S New Member

    That is also the thing that bothers me to the point if wanting to make my own controller...Going from ebay, i can get an Arduino, 2.4in color LCD, buttons, and instrumentation op-amp for temperature sensor, all for less than 10$. I have 65W 20V supply from a laptop charger. Arduino is fully capable of running LCD and PID loop.
    There can be less noise from DC/DC converters, right? Low to low mid range stations tend to use essentialy triac dimmers to control the output power. That is really noisy. But if it's bypassed good, DC-DC can give low noise.
     
  7. Joshua_S

    Joshua_S New Member

  8. rogerk101

    rogerk101 Well-Known Member

    Have you ever looked at the 'supposedly flat' DC waveform of the output of a switched mode power supply with an oscilloscope?
    Whether you look at it with zero load, full load, or anywhere in-between, the waveform is far from flat.
    What would you consider "low noise" for a DC supply?
    The next question to ask yourself is what it is you're trying to power with it. A soldering iron doesn't care about the shape of the waveform supplying it. It just wants to convert electrical energy into heat. A laptop also doesn't really care about the shape of the waveform feeding it because it has a whopping great battery smoothing the input supply to be nice and steady for the laptop's electronics. By contrast, something like an Arduino wants a pretty smooth waveform, so unless you use a huge capacitor (or a battery) to help with the smoothing, it's unlikely to be happy.
     

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