Variable wattage vs temp control in a soldering iron?

Question

Presently, I am looking into soldering irons because I am considering making a purchase. I am considering features in order to find something that is usable and versatile for the value.

One factor I am struggling with a bit has to do with temperature vs. wattage. I have already checked out a number of resources:

https://www.circuitspecialists.com/blog/selecting-a-soldering-iron-temperature-wattage-and-tip/

How does power affect soldering irons? Is 30 Watts enough?

As such, I do get the basic idea about wattage being an issue of the tool's capacity to heat the tip and replace heat that has been lost or sunk. Where it becomes a bit confusing to me, though, is when it comes to varying one or the other. For example, the Vastar Full Set 60W 110V Soldering Iron Kit features adjustable temperature, whereas the Weller WLC100 has a dial for you to vary the power (5 to 40 watts).

So, I guess I am wondering: Is there a reason to prefer adjustable temperature over adjustable power? Or vice versa? Or am I overthinking the matter?

Your input on this is appreciated, so thanks in advance!

Answer 1

Once you try proper temperature regulated soldering gear, you never go back.

Dumb constant power tool:

• Takes a while to heat
• Temperature is unknown
• Either too hot (burns your PCB) or not powerful enough (soldering takes a long time, and you also end up burning your PCB)
• You need a 20W one for SMD, a 30W one for thru hole, a 50W one for connectors, a 100W one for big wires...

Dumb variable power tool:

• Same drawbacks as above, except you only need one.
• Does everything... but does it wrong.

High power regulated tool:

Get more than 80 watts. More power means better reaction time, faster and more accurate soldering, and counter-intuitively, less chance of burning the PCB, because the job is done quickly. Mine heats up in 20 seconds. There is no need to change the settings, whether it's a 0603 capacitor or a big banana plug. It just works.

Now, soldering iron or soldering station?

Stand-alone Iron:

• Cheaper
• Easy to transport
• Wire rated for mains voltage, thus thick and not flexible
• No space on a soldering iron for temperature display and knobs

Station advantages:

• Smaller, nimbler, lighter iron
• Thinner and more flexible wire
• Nice temperature display and controls

I have a XYTRONIC 90W station, which cost 90€. Very cheap!

Also, look at the price and availability of tips! Tips can be anywhere between 3€ and 20€ depending on brand, this is important both over the long run, and when you need a special tip to do the job. Although a standard flat tip is adequate for most work.

If you get an obscure brand station which uses special tips which are impossible to find... or you can't find replacement irons or heating elements... you'll regret it later, when you have to throw it away because you can't find the spare parts.

I believe the tips for mine are identical to Weller WES51 tips, so even if the manufacturer goes bankrupt, I won't have problems finding them.

I also have a €9 30W dumb soldering iron, which uses Weller tips. With one soldering iron in each hand, de-soldering SMD resistors and capacitors only takes a second. It is well worth having a cheapo second iron for this reason.

Answer 2

I suggest you get a Metcal , used ones are available. No bell no whistle , just an on off switch. I use only two tips ; a small pointy one , and a bigger broad one. The Metcal heats up in a few seconds and can solder surprisingly thick heavy metal objects as well as tiny leads, and traces . Use a small blob of melted solder on the tip to transfer heat to the joint being soldered - this helps the heating tremendously. Remove the heat source the moment the joint shines with shiny flowing molten liquidity , but without moving the joint , or you may get a “cold solder” joint .

Answer 3

Ideally, you want a soldering iron that keeps the tip at some constant temperature. This would be regardless of how much the iron is heating something else.

In reality, doing that better costs more money. As a result, there are products out there with various tradeoffs. The three primary ones are:

1. No control at all. The heating element is a fixed wattage. The heater has to be sized to still allow soldering with some reasonable heat flow, so the tip will get very hot when just sitting there doing nothing. This leads to more rapid tip degradation, and can damage parts and even boards when soldering. Of course this type is the cheapest since it's very simple.

   In the old days of point to point wiring between eyelets of tube sockets, this type was acceptable. The high heat didn't do much damage to the eyelets.

2. Manual control. This is what you seem to be asking about. There is some way for the user to roughly set the power level manually. Often this is not calibrated in terms of actual power, but just numbers from 0 to 5 or something giving you a rough idea how to repeat something that you found to work previously. The actual power is usually not regulated. Usually the knob just adjusts a PWM duty cycle.

   These cost a bit more than fixed wattage types since there is a little more complexity in them.

3. Temperature control. This is the most complex, the most costly, but also the best for usage. This is like the variable power type, but adds a temperature sensor in the tip and closed loop control. In effect, the temperature control circuitry tweaks the power knob for you in real time to try to keep the tip at a constant temperature.

I realize there are always budget realities, but my recommendation is to get even a low end temperature controlled iron. It really makes quite a difference during use. If you are a EE student, professional, or otherwise expect to do soldering in a professional environment, then there is no choice at all. Anything less than temperature controlled is unprofessional.

I would not get a fixed-power soldering iron at all. Those just don't mix with modern circuits where over-heating parts is a real possibility.

If you're a student or a hobbyist on a limited budget, perhaps suggest to someone that a temperature-controlled soldering iron would make a great present.

Take a look at the Weller WES51. Last time I looked around, this was the least expensive "real" soldering iron out there. There are definitely more fancy ones with more bells and whistles, but this one is "good enough", even for many professional uses. Its the kind of iron you can put one on every engineer's bench, then have a more sophisticated soldering station available in production or wherever.

Answer 4

For consistant work temperature control is best. That can either be regulated or variable. Variable wattage will put your tip temperature all over the map depending on how much soldering you are doing and what you are soldering.

The real question though is what you want to use it for and what temperature range you need to accommodate that. Since you are on this forum I am going to assume it is for electronic work and not say soldering jewelry. If you want to solder a variety of solder types, then you should chose a variable one of the right range.

You don't really need a meter though, just start low and slowly wind it up till a bit of solder starts to melt on the tip.

Wattage really comes into play if you plan on soldering larger metal pieces, like heavy cable ends, metal wire taps etc. Those can soak up a LOT of heat before you ever get the solder to melt.

Both of those are good brands, but I highly recommend a heavier "station" type.. like the Wellers (But not the one you mentioned). Nothing worse than fumbling and juggling around with a loose soldering iron that was resting on a flimsy holder. Plus, one with a good sponge reservoir really helps you keep your tip clean... (Can I say that one here?)

Addition Three great answers here, and because I was going to mention it anyway I'll add this too. Soldering is usually a delicate manipulative art. As such the best tool for the job is a lightweight ergonomic "business end". One piece soldering irons are fine if you just want to solder a few ring terminals on the end of a few cables, but if you are planning on soldering 1,000 p.c.b. connections you will quickly wish you had forked out the extra cash. for a soldering station.

Answer 5

I would echo what others have said about temp controlled irons. However, I would add my own experience with power controlled irons.

I built a variable power iron from a dimmer switch. 10 USD all in. It doesn't provide fine temperature control and you may have to adjust it in the winter vs summer, for example. To some this is a huge inconvenience but I don't personally find that a big deal.

So I would summarize too say that if you have the money, go for a temp controlled iroon. Otherwise, a variable power iron is a big step up from fixed. Wattage iron.

And pay attention to the tips - should consider then consumables when pricing an iroon.

Edit: just in case you need a quick way to reduce power, you can out a diode in serial with the iron (non temp controlled iron) and you would have halved the power to the iron. With a switch, you can then quickly cut in and out of the diode.