Friday, 19 June 2015

Why does my 12 volt soldering iron not melt?

Note, please understand that the soldering tip worked fine, my question was related to the fact that with 110 amps and around 13.6 volts dc, why does the entire soldering iron kit not just melt and fuse???

A mail to an electrical expert I know is below:

I have a teaser for you?

When I use the 12 volt soldering iron I have in the past connected to an Ellies220v ac to12v dc power source with a max rating of 5 amps, which works fine.
The same power source is upstairs and so when I want to solder on the bench downstairs I have to unplug it, switching power off to the VHF and the SSB radios, a bit of a mission downstairs then back upstairs etc.

I needed to solder yesterday and used a massive motive battery, 110 amps and charged to over 13.6 volts, a gift and a nice one too.
Question, why does the soldering iron not just melt!
Whats in the yellow handle I wonder, a resistor ?



Notty has replied as I hoped he would.

Hi Roy,

The soldering iron is designed to work from a nominal 12-volt D.C. supply. Nominal means that there is a safety margin designed in usually around at least 10 percent. In any case the element that causes the tip to heat up is similar to the element in your electric fire or kettle. Suitable for the purpose would be a high resistant alloy of metals used so that the tip gets hot enough to melt solder but does not glow red, that would be too hot and burn the job.

You would need to up the voltage to around 18-volts D.C. to cause serious damage but there is probably a fusible link built in to fuse at that level. If you hear the iron clicking now and then it will have bi-metallic link to control the temp of the tip within 10 degree or less, the more expensive irons are temp controlled by electronics in the iron or its base station.

Hope that helps.


Thanks Notty!

And just in from Justin:

! I understand – I suppose it’s the same reason 12v light bulb doesn’t melt – the current allowed through is determined by the resistance – plus of course the factors Notty mentioned like thermostats etc.


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