Soldering irons: Temperature relative to watts

Thread Starter

cheddy

Joined Oct 19, 2007
87
Hi.

I am wondering how the watt of a soldering iron is relative to the temperature of the tip?

I did a little experiment with a temperature sensor and my adjustable watt soldering iron. At the lowest 5watt the temperature seemed to continue to get hotter and hotter although the temperature increase slowed down as it got hotter although it never seemed to stop getting hot.

At the higher setting the temperature seemed to get hotter, faster, even at a high temperature.

So another question I have is that is it not a good idea to keep a soldering iron turned on for a long period of time? For example if I am doing a project should I only turn the iron on before I need to use it then turn it off if I don't need it for 5 minutes so it doesn't get too hot?
 

zane9000

Joined Mar 16, 2007
19
Generally the max temp is listed on the irons spec sheet. I usually leave my irons on for the duration of my project construction (which can be a few hours if i get distracted) so I dont have to wait for it to heat up over and over, and I have never seen a problem with it
 

Salgat

Joined Dec 23, 2006
221
Zane is correct, the pencil can only get so hot before it starts to dissipate heat faster than it can create it, think of it as the "terminal temperature" I guess. I often leave my soldering pencil on for as long as needed.
 

mrmeval

Joined Jun 30, 2006
833
Clean the tip on a damp (not wet) sponge then apply more solder to the tip. The ball of solder will oxidize rather than the metal while it's on.
 

GS3

Joined Sep 21, 2007
408
Roughly speaking, the increase in tip temperature above ambient temperature will be directly proportional to the power (watts) being consumed. That is with the tip at rest, obviously. The instant the tip touches metal and solder a lot of heat is transferred away and temperature drops.
 

bloguetronica

Joined Apr 27, 2007
1,372
The wattage does not correlate directly with the temperature of the iron (unless it is an adjustable iron). It has more to do with the heating capacity. Higher wattage irons have a bigger thermal mass, and thus can solder bigger metallic parts that absorb more heat than, say for example, small components. I would recommend no more than 30W (20W would be great) for electronics and 60W for thick cables and other appliances.
 

GS3

Joined Sep 21, 2007
408
My response was assuming everything else being equal. In other words, same tip with different wattage applied.

If we are talking about different irons then a bigger iron will have a bigger mass, ergo bigger thermal mass and will also have greater xchange surface which means lower thermal resistance to the surrounding air.

With the iron at rest the temperature differential from the iron to air is equal to the power (watts) being disspated multiplied by the iron to air thermal resistance (ºC/watt).
 

bloguetronica

Joined Apr 27, 2007
1,372
My response was assuming everything else being equal. In other words, same tip with different wattage applied.
Even though, it depends on what you're soldering. With a higher wattage iron you are just ensuring that you'll have more heating capability. So it will attain higher temperatures depending on the size of the object to be soldered. Such objects always act as heatsinks.
 
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