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I have a cheap, 40W 120V soldering iron with no temperature adjustment. Given the internal circuitry seems pretty simple would it generally be safe to run it on 240V?

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  • \$\begingroup\$ Define "pretty simple" \$\endgroup\$
    – User323693
    Feb 14 '17 at 2:31
  • \$\begingroup\$ I can't put an answer down because the question was closed, but I would say give it a try; these soldering guns are usually very underpowered. They are just a transformer. Hold the trigger down for less time than normal. \$\endgroup\$
    – Elliot
    May 9 '19 at 15:23
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A big NO. What would you expect a 120V lamp to do if you powered it from 240V! The results could be similar.

A simple soldering iron is just a resistor - if you put twice the voltage into it it will produce 4 times the heat - rather than heating to 700°F it could get to 1000° or more. It could cause a fire, the insulation could break down and cause electrocution danger.

You could run it from a step down transformer - one capable of powering it should no be expensive but neither would a 240v soldering iron.

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  • \$\begingroup\$ Ah, forgot about V squared.. It wouldn't have a thermal switch that would effectively let it run at a lower duty cycle? Or is the resistor simply matched to the voltage to give the correct temperature? \$\endgroup\$
    – 101
    Feb 14 '17 at 2:31
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    \$\begingroup\$ I wouldn't count on that. These are generally a resistive element attached to mains. (If it had any active circuitry it would probably be rated for 110~240V.) \$\endgroup\$
    – Wesley Lee
    Feb 14 '17 at 2:34
  • \$\begingroup\$ These usually are PTC heaters, meaning they are self-controlling. It doesn't work for a completely out-of-range operation of course. \$\endgroup\$
    – Janka
    Feb 14 '17 at 4:35
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    \$\begingroup\$ @Janka - It is very uncommon to use PTC heaters in a soldering iron - I have never heard of one. Simple soldering irons are plain resistive heaters. More sophisticated non-electronic ones usually use a thermostatic switch based on the curie point of a magnet in the tip. \$\endgroup\$ Feb 14 '17 at 4:49
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    \$\begingroup\$ You could also use a simple lamp dimmer to reduce the power. The soldering iron doesn't care about the waveform -- just the average power. \$\endgroup\$
    – Dave Tweed
    Feb 14 '17 at 11:57

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