Depends on size. If you plug in two irons, 30 and 40W, both the same size, the 40W iron is always going to run hotter. The $10 Radio Shack irons available around local stores have basically only one difference and that's the element and tip size. As such, the 40W runs a lot hotter, increasing tip loss and risk of overheating things. On the other hand, it makes quick(er) work of soldering heavy wire and desoldering most anything.
Those big 100-300W irons (often used for soldering sheetmetal) are well, big. They don't need to vaporize the solder, just melt it. The rest of the power is there to keep the thing at that temperature, and speed up heating when you suck out heat with some work.
Soldering guns typically run a whole lot hotter, but only if you clamp it down on max with nothing to melt. Best idea with these is to get good at clicking the switch on and off to regulate temperature.
-- Deep Fryer: a very philosophical monk. Website:
Temperature unregulated irons can vary greatly on the temperature they get to. Wattage alone is not a good indicator of whether one iron will be hotter then the other.
Temperature regulated irons hold the temp they are set to. In that case the wattage will determine how MUCH heat can be applied to whatever is being soldered. Generally the more material you are trying to heat, the more powerful an iron you need.
In your case I would strongly recommend getting a temp regulated model. The wattage you need will then depend on what you want to solder. From your comment "soldering undemanding things like a fine wires to a small tag" I'd say something in the 50-75W range will suit you perfectly (overkill for the small tag, useful when soldering bigger things).
The best part about temp regulated irons is they won't heat small things up to much, something a temp unregulated iron will do.
Larger irons usually have a larger thermal mass and thus need more watts to recover in a reasonable length of time. The larger thermal mass allows them to handle larger jobs ... such as sheet metal or large wires and terminals.
Ideally, the unloaded temperature (not in contact with any work) should be about the same regardless of the watts.
You are assuming the iron has a thermostat. Basic units don't. Just like a basic electric 'bar' fire, they heat up and stabilise at the point where the heat loss from the iron, matches the input power.
If you are doing a lot of joints in succession, with an unregulated iron, then the tip will get cooler with each one. Also, you must be careful to be using the right solder. The iron will have a 'design' temperature, and some solders will require less heat than this, while others require more.
Get the smallest shafted temperature controlled iron you can find. Two basic designs, 'single temperature' units, like the Antex TCS50 (trimmable with a screwdriver), or fully adjustable units, like the 660TC, with the TC50. Antex irons give better heat transfer to the joint (I also use a 100W Weller TC iron, and the Antex 50W will out solder it on some jobs), than many competing designs, and I like the weight.
As others have said, irons come as uncontrolled or temperature controlled.
The temperature of an uncontrolled iron is dependant on the wattage and ambient conditions. Wave one around in the air and it will be substantially cooler than if you put it in an insulated stand. One of my irons is 250W, uncontrolled, and will soon start to glow red-hot, unless in contact with a LOT of metlwork being soldered. Great if you are doing plumbing - not so great for electronics work. The tip is about 1 1/2" across. It dates back to the 1940s - they may not be avialble anymore...I got given it by my great uncle, an RN submariner electrician in WWII.
The temperature of the tip of a controlled iron in its stand should be near enough the set temperature, irrespective of iron wattage. Once you start using it, the tip temperature will fall. The key point is how much.
The end of a very long, thin, tip, in contact with a large chunk of cold metal, will quickly fall in temperature and stay at that low temperature. It is simply not possible to transfer enough heat down a very long thin tip, irrespective of the wattage of the iron. So, if you only use very long thin tips, practically any wattage of iron will do. I have a very tiny 15W temperature controlled iron which is as comfortable and easy to use as a 'scope probe. The element tube is about
1/8" in diameter and so is the thickest part of the tip.
However, if you have an iron with interchangeable tips and can use a thick, short, tip, then the tip is capable of transferring much more power - so you can make good use of a higher wattage iron. Hence my next bigger iron up from the teeny one is a 40W. The element tube is about
1/4" in diameter and so is the thickest part of the tip. But the business end varies from something about 1/16" across for one tip to
1/4" across for another.
I could do with something to fill the gap between the 40W and 250W - I sometimes end up with an iron in each hand and feeding solder in from a tube clenched between my teeth...
I reckon that it is the tip that makes the iron. My favourites are a weller 40W that takes interchangeable tips, each tip with a preset temperature. But there are places where those irons are simply too big or too small.
I have a Maplin
BP53H soldering station that I hate - I can't get along with any of the tips. Unlike plain copper tips, you can't just shape them the way you want. They also do a very cheap one N78AR, which I haven't tried. It may be worth a look - it's a 50w variable temperature adjustable model for
On Wed, 22 Mar 2006 16:18:03 -0500, repatch Gave us:
Not true. An UNregulated Iron IS related to heat output by wattage. Almost directly and proportionally.
So a 35W will be MUCH hotter, and almost always physically bigger than a 15W. The 15W is akin to a bench assemblers model, and the 35W is typically akin to someone doing stained glass that needs to dump a LOT of heat into a connection or seam without dropping the iron temp much.
No... really? :-]
They are usually limited by the tip shape and size. It is very hard to fill a small, long, thin tip with enough heat to say... solder a shield can seam onto a PCB. Place a larger tip in the same Iron though, and input consumption will go up (and thus output) when trying to do the same task.
OR the larger thermal mass at the tip (read tip size).
For electronic PCB mixed technology assembly... definitely.
50 to 75 Watts seems huge for PCB soldering irons. A regulated unit may rate that on its consumption label, but the tool itself will never use that much (short of huge desoldering tips being applied).
Again, that depends on the thermal mass (goes with physical mass) of the tip itself. It gets pulse modulated (pumped) by the station.Once up to temp, a large tip is quite capable of dumping a huge amount of thermal energy into the work.
The wattage rating would be more of the heating capacity. The larger the wattage, the greater the mass that it can heat. Use a lower wattage for the smaller jobs. Use a higher wattage for the larger type soldering jobs.
I have one, now non-working! I used it all of three times at 3/4 max setting and it burned out. They are rubbish- they're not temperature controlled- they're simply a tacky, clumsy, cumbersome mains iron hardwired into a lightweight, cheap plastic dimmer box. There's no thermostat, you simply have to whack up the 'dimmer' knob when the tip temperature drops, and the iron seems very inefficient- more like a 30W than a 50W.
My advice to anyone wanting a temperature controlled iron is to look out for proper temperature controlled irons on eBay, or better still a low voltage soldering station like the Weller TCP series or Antex 660 with a TC50 iron. They cost a lot more even secondhand, but they are immeasurably superior in every way. I have both and can't fault them at all.
We've seen some good thoughts on soldering irons. I learned that wattage is a unit of capacity. Temp is important but you also need wattage to match the job. After all, the temperature of the spark in your cars ignition is in the thousands but the wattage is way too low to melt solder (in normal sizes) Let me offer a simple analogy about wattage. If a common match will raise a one inch strip of metal to a certain temperature, would it not require 12 matches to raise a 12 inch strip of metal to the same temp, placing one match at each inch of the strip. Keep in mind the temperature of the matches are generally some consistent number, so it is clearly the higher wattage of the 12 matches as a whole that makes the difference between one match and 12.
More important than the physics of the issue, experience really makes a difference. You'll find using a similar soldering station like my old Weller WTCPN make a world of difference. It's undersized for big jobs but perfect for circuit board work. The temp controlled tips click on and off as necessary. For bigger work, I use a higher wattage station not neccesarily a higher temp tip, all else being equal.
Not really, convection and geometry being what they are, it'll be hotter in the center because the heat can't really "get out", while on the edges, the heat just rolls up and away. But that's just being pedantic; ignoring such effects, yes, you're absolutely right, power per area is temp, roughly speaking.
I should build an induction heated soldering iron. I've heard of Weller irons that work like that. Mmmm, isolated tip. Tack on a thermocouple and I've got it made.
-- Deep Fryer: a very philosophical monk. Website:
On 23 Mar 2006 19:51:26 -0800, "distar97" Gave us:
Just to keep up at a given reasonable time rate actually. The at rest temperature is one thing. The thermal mass (size) of the tip is another. If it cannot maintain the "at rest temp" very well, then the wattage used to heat it is not sufficient for the tip's mass or rate of radiation (emissivity).