Soldering fail. Ok... what am I doing wrong?

[Marlin]

Hmmm, some good advice given below (above for those that old school setup your threads with newest at the bottom), seeming that I teach soldering here at the Naval Nuclear Power School. I rarely solder anything at home. I prefer crimp on connectors as they are far superior in longevity and strength. They have a lower resistance at the connection, therefore generate less heat. They are also almost dummy proof, and can't have unseen internal flaws. Where vibration is involved, such as a vehicle, terminal lugs are 100% the way to go, hence the fact that virtually every connection in your car is via terminal lug of some type vice soldered. JMTC as a soldering instructor. If you really want to do it, get some eutectic alloy (60/40 tin lead) and a Pace unit. Its like comparing a Harbor Freight 90A flux welder to a Millermatic. You can be the best welder in the world, and not do anything useful with the crappy HF welder.

[SlowPro48]

Haha! TomDude that's beastly - using inorganic acid flux from the plumbing aisle for electronics! I hope you're not in the satellite business! I'm no electronics repair expert so maybe Marlin can confirm or dispel this - but I've heard it's better to stick with rosin or some other organic-based flux (i.e., less acidic) when soldering electrical stuff. Corrosion and circuit boards generally don't mix well...

[Marlin]

X10, we only use rma flux, rosin, mildly activated. Anything stronger will eat the connection.

[tom4bren]

Haha! TomDude that's beastly - using inorganic acid flux from the plumbing aisle for electronics! I hope you're not in the satellite business! I'm no electronics repair expert so maybe Marlin can confirm or dispel this - but I've heard it's better to stick with rosin or some other organic-based flux (i.e., less acidic) when soldering electrical stuff. Corrosion and circuit boards generally don't mix well...

True ... but most of my soldering is just connecting some wires together or fixing jewelry or stained glass stuff that broke. Soldering on a circuit card is another matter entirely. It's been so long since I've done any of that, I don't even have a temp controlled soldering iron anymore.

[SlowPro48]

Tom, yeah I've never done enough electronics work to justify one of those variable temp irons - my soldering tool collection is rather sparse too. A 40 year old Sears 25W chisel tip for wires and a 15W/25W conical tip from The Shack for the occasional fried resistor/diode/transistor, etc., some 60/40 rosin core and a roll of Chemwick. The chisel tip works better for wire joints since it has a lot more surface area available and can dump the heat more quickly. Plus it's much easier to balance some molten solder on the flat of a chisel tip than on a cone!

Rick, you said "finally" but it really shouldn't take very long for the solder to flow after you hit it with a hot, wet iron. Think of the end of the iron as a repository of heat - you let the temp build up and then you have a certain mass at a certain temp and (in the short duration it should take to solder 18ga wire) it's almost irrelevant whether the iron is 25W or 40W - all that matters is the temp differential, the mass of the hot body, and how well the heat can be conducted. You can't do anything about the mass of your tip so to minimize heating time (maximize heat transfer) you work with the other two variables - let the iron get good and hot, i.e., give it enough time to heat up initially and let it recover between joints - this will maximize temp. As for maximizing conduction, you already know about using a dab of molten solder to help transfer heat. There's not much difference in the temp of a 40W iron and a 25W iron it's just that, given the same mass, the 40W iron will recover and be ready to solder the next joint more quickly.

Now, if you've got a small iron that doesn't store enough heat to solder 18ga wire then you're relying on the output of the element itself and yeah that will take a while. Need a bigger iron if that's the case. But I doubt it. Never seen a 25W iron that wasn't physically big enough to solder 18ga. The bigger the wire, the more heat it sucks up thus the bigger the iron required. Bigger irons have more mass to re-heat so need more power to get back up to temp in a reasonable timeframe and once up to temp they dissipate more heat so need more power to maintain temp.

Yeah, I know blah blah blah - OK I'm done.