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I have a cheapo Weller 40W unregulated soldering iron. $20 at the local everything store. I've gone through quite a few soldering irons/tips in my life, this is just the latest one. I'm fairly certain I know why my tips get chowdered after just a little while of use: it gets too hot. There's nothing I can really do about that, seeing as it's unregulated...or is there?

I'm wondering, is there anything I can make that will at least give me some control over the temperature of the tip? I'm using regular .032 diameter, 60% tin/40% lead solder. It seems obvious, but would simple voltage regulation (perhaps from a variac) work to lower the total power? It seems fairly obvious to me that if 120VAC is giving me a 40W output, then, say, 60VAC should give me half of that, but it's rarely that straightforward. Given that it's a cheap piece of crap, the idea of monitoring the temperature seems a little out there, but a calculation on input voltage/current vs output power should get me somewhere, right?

Now, I'm asking this question as a (for now) hypothetical "what if". I don't have a variac, or any way to test my theories, I'd just like to know if something like this is possible.

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  • \$\begingroup\$ The problem is that temperature is not a direct function of input power -- it also depends on how much heat is being drained from the tip by touching it to other things. That's why if you want temperature control, you need a temperature sensor, which is the key thing that an unregulated iron is missing. There are some people who have figured out how to use the temperature coefficient of resistance of the heating element itself as a temperature sensor. However, this only allows you to regulate the temperature of the element (not the tip), but this might be enough for you. \$\endgroup\$ – Dave Tweed Sep 30 '16 at 23:26
  • \$\begingroup\$ are you cleaning the tip with flux and keeping it properly tinned? It's not just temperature that affects tip life. \$\endgroup\$ – Brian Drummond Sep 30 '16 at 23:31
  • \$\begingroup\$ This whole discussion is not applicable to PWM-based devices, which heat differently (and I guess they are out of scope because they are not "cheap") \$\endgroup\$ – Anonymous Sep 30 '16 at 23:35
  • \$\begingroup\$ A Variac will certainly work, but 60VAC will give you 10W, not 20W. \$\endgroup\$ – Spehro Pefhany Oct 1 '16 at 4:04
  • \$\begingroup\$ @SpehroPefhany That's interesting, could you explain why that is, exactly? \$\endgroup\$ – HaLo2FrEeEk Oct 1 '16 at 5:49
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The solution is to use a Triac dimmer set to about 60% -80% after fast warmup.

Then increase for heavy soldering on ground planes, , heavy wires etc.

Tin and clean tip daily with damp sponge after use.

In Japan operators would measure tip temperature daily before work.

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  • \$\begingroup\$ By that do you mean the same type of dimmer used in a simple light dimmer? I could pick one of those up from the hardware store pretty cheap. I was actually wondering if something like that would work as well. I clean the tip as I work with a damp piece of denim material (because that's what I had on hand at a moment's notice.) I keep it tinned, but like I said it's also a cheap iron, so probably not a quality tip either. \$\endgroup\$ – HaLo2FrEeEk Oct 1 '16 at 5:50

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