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Soldering iron not working

  1. Feb 14, 2012 #1
    Hi all,

    i have ordered a 30W/230V soldering iron for doing some hobby projects online. First instance when i tried to use soldering iron i found the time it took to get heated up was very huge, some how i managed. After some several uses now when i am trying to use it is not getting heated. I am tempted to buy the new one but now want to understand why is it not working.

    1. what is the general internal circuitry of the soldering iron? i opened and found one diode probably i think to convert AC to DC.
    2. How much time it should actually take to get heated to some X temp. is it possible to calculate using some equations to measure the time?

    Please provide me some advice.

    Thanks in advance,
  2. jcsd
  3. Feb 14, 2012 #2


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    A 30 watt soldering iron should have a resistance of 1763 ohms when hot and probably a little less than this when cold.

    The power used by a resistor like your soldering iron is given by the voltage times the current

    So, 230 volts times current = 30 watts. So the current is 30 / 230 or 130 mA

    Resistance = 230 volts / 0.130 A = 1763 ohms.

    You will really need a multimeter to work out what has happened, however I am surprised that there is a diode in there. I wonder if it is really a 120 volt soldering iron and they have half wave rectified this to give DC so that it could be used on 230 volts.?

    Anyway, diodes are pretty cheap and you could easily replace the one in there with a 1000 Volt 3 amp diode to give plenty of safety margin. Are you sure it is a diode?

    If the heating element has been destroyed, you will need another soldering iron. Couldn't you take it back to where you got it and get a refund?
  4. Feb 14, 2012 #3
    Thank you very much for the reply. The information was very much useful to understand. i have verified whether it is diode. It is tightly soldered to a small pcb so the name i could see is 1n4007s. i think it is a rectifier. As you said maybe i should try for replacement.

    thanks and regards,
  5. Feb 14, 2012 #4


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    Even a very cheap digital multimeter would help you work out what has happened here.

    If the diode has gone open circuit, then this would just stop the soldering iron working.
    However diodes do not normally go open circuit. They short circuit.
    Maybe you could have got one which was faulty from the manufacturer.

    So, maybe you could try to get a multimeter. It will then be something you can use in the future for repairs, checking batteries etc.

    Note that most multimeters have a "diode test" function as well as resistance measurement.
    This is because resistance can be measured at low voltage while diodes need to be tested at a higher voltage.
  6. Feb 15, 2012 #5


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    If it's a cheap soldering iron with a correspondingly cheap tip, they tend to get coated with flux / gunk very rapidly and take a very long time to heat up (as well, the heating element is usually broader, meaning the heat is not as concentrated).

    If you're new to soldering, you can find some tips on tip maintenance and care here:

    Clean the tip frequently during use, and if you absolutely must (due to high blackening of the tip), use the very fine emory paper instead of sand paper.
  7. Feb 15, 2012 #6


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    It was taking a long time to heat up, even when it was new, but now it is not working at all.

    Being only 30 watts, it could take a few minutes but not much more than, say, 4 minutes.

    I don't really understand why it would have a diode in it, though, unless it was a crude way of giving it only half wave pulses to suit a 120 volt heater element.
  8. Feb 16, 2012 #7
    Thank you for the replies. today i will try to analyze the complete circuit inside the soldering iron, then i will share the details i do have a multimeter and check if the diode (?) is working or not. my initial thought when i saw the diode is that may be it was for avoiding reverse current or something like that i don't know. today i will post the complete circuit.

    Thanks and regards,
  9. Feb 16, 2012 #8


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    Is that 'diode' the only component in the iron apart from the element? It may be (have been) a thermal fuse? There is no reason for a diode (unless it was designed for 230V and the diode has been used to reduce the volts. In which case, take it back to the shop and get a better one. A poor one may well cost you in spoiled components and bad solder joints.
  10. Feb 19, 2012 #9
    Hi all,

    sorry for my mistake. now i have shown the actual diagram in the soldering as an attchment. Actually the red wire comes to the iron rod through a pcb and the negative wire also comes to the pcb and a diode is inserted between the negative wire and the iron rod. hence the diode is actaully coming in the path of the negative wire. There is also a green wire which i did not shown but also comes directly to the iron rod casing. I have completely dismantled the soldering iron and the wires are broken and hence now only option left for me is to buy a new one.

    sorry for the mistake.

    thanks and regards,

    Attached Files:

  11. Feb 19, 2012 #10


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    Is the break in the heating element, which you have shown as an iron rod at the right of your diagram?

    With a half wave rectifier, the power would be halved since there would be a pulse and then a gap in each full cycle.
    I suppose this might make sense if there was a switch across the diode to give you a burst of heat when you were actually soldering. This would help to keep the tip in good condition.

    Anyway similar soldering irons are not expensive:

    But I wouldn't get the same type again.
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