SECRETS OF SUCCESSFUL SOLDERING
by David Eidell (02/12)
“I HAVE NEVER HEARD A COMPLAINT THAT AN ELECTRICAL CONNECTION HAS LASTED TOO LONG”
With few exceptions there is no more secure way to join a wire or terminal than by soldering. The connection is one piece of metal. Corrosion is blocked forever from attacking from inside-out (in the center where copper strands touch the terminal). But most RV'ers (myself included) started off on the wrong foot. I remember trying out an old soldering iron, and a roll of plumber's 50/50 solder. It seemed like forever before anything happened. Instead of sticking to the terminal or wire, gobs of lead dripped off the roll of solder. It spattered into little star shaped droplets that resembled thick aluminum paint. The mess I made of the pair of twisted wires was too sad for words.
A horrified friend who was a television repair technician told me I was doing it all wrong. After I rectified several basic mistakes and found out other vital secrets by trial-and-error, the solder started sticking and not long after that I started producing easy-as-pie, pretty, soldered wire connections.
ONLY ELECTRONIC SOLDER WORKS WELL
This point is critical. Ordinary hardware store solder is extremely difficult to work with on electrical parts. Plumber's solder is designed to be used with a torch and extremely strong acid flux. Such a high temperature is necessary to melt this class of solder that it would char plastic wire insulation, and damage the copper or tin finish on wire and terminals. Solder must flow onto perfectly bright and shiny metal or it will bead-up and fall.
The best place to find electronics solder is at an electronics supply house. Frys Electronics and Radio Shack sell good electronics solder. On the web you can Google, Kester 44®, Ersin Multi-Core® or Standard® solder and follow the link permutations.
LET'S GET TO WORK
The only way that you're going to get motivated is when you see your first really pretty solder joint completed before your eyes.
I use a paste acid flux knowing that all those warnings about “not using acid core flux on electrical circuits” really should read “Don't use acid core solder on delicate electronic circuits”. I have examined 30-year-old work where I used acid core paste flux and never bothered to wash it off. The joint and surrounding area was just as bright as the day the work was done. Butane cigarette lighters don't work because they do not burn with a blue flame. Yellow flame soots up whatever it's heating almost instantly, and that casts a death knell for soldering success. I've used a stove top burner many times – the clean blue flame insures success. This is a good example of just how touchy solder is with regard to cleanliness
• A solder gun with at least 140 watts rating is enough to solder 10-gauge wire. A 270 watt gun is good for wire as large as 8-gauge. Huge sizes including battery cables and lugs require a propane torch. My micro torch works quickly on wire lugs and battery terminals to 1 gauge. A torch with an adjustable flame is indispensable, but make sure the flame is a clean blue color.
• Hot tools and RV's make poor companions. I use an eighteen-inch square of fiberglass cloth to protect against surfaces from the flame of a torch or hot soldering iron tip and splatters. Meticulous caution is called for – so is common sense; a torch may not be the best choice when soldering in the middle of a gaggle of wires or near expensive finish or upholstery. I set my solder gun in a wooden tray. It can be bumped around without danger of the gun spilling out onto upholstery or finishes.
• I fill a sprayer bottle with clear water. Wetting down larger gauge hot terminals can really speed up the soldering process. Battery terminals and lugs can take 5-minutes or more to air cool down enough to touch them without getting a burn. Dribble droplets of water on a freshly soldered cable or lug. Too much water too soon turns the solder into something resembling aluminum paint and simply ruins the work. A rag placed atop the fiberglass flame mat will sop up any dribbles or splashes.
• Razor sharp box knife blades can be used to carefully scrape dull copper wire strands to their original brightness. Keep revolving the bared strands and scraping and soon they will be clean enough to apply acid flux and then be soldered. The box knife scraper is much easier and more effective than a wire brush.
• A soldering iron tip must start out as bright copper. To rejuvenate a crusty solder gun tip, scour off the dark scale with a swatch of rough sandpaper. Apply a bit of flux, then pull the trigger while holding a sprig of solder to the bright copper tip. Good quality solder will melt and flow onto the tip before it overheats and turns brown or purple. It's hard to not dribble solder while “tinning” a solder gun tip, so you might as well give up and place a cloth or other protection under the work. Now touch the tip of the gun to the wire or terminal. Touch the end of the solder sprig to the tip and let a little drop of solder to droop onto the work. Not too much. The droplet helps to transfer heat to the work. When the solder gun heats the work up to the correct temperature the droplet will suddenly spread out all over the work – quickly now, touch more solder onto the work until you have enough to fill the hidden places. If you gob on too much solder, tap it with the end of the gun and knock off excess solder before it cools. Beware of flying droplets of molten solder. One of the things you will learn is to back off on the heating. When solder flows onto the work, release the trigger or move the torch flame away.
• I use a sopping wet sponge or rag to wipe off the icky crust of the heated solder gun tip. The tip must be kept coated with silvery solder for it to work right. If the tip turns black it's time to stop and clean it. On really marginally clean connections I have had to stop and clean a tip a couple of times.
• It's best to mechanically buff and scrape a piece to be soldered than to rely on flux. Even the strongest acid core flux will be sorely challenged if it should face even a modest amount of corrosion. As flux bubbles and picks up corrosion and oxides it weakens. I have had to simply gob on the flux in really bad cases. Liquid acid flux is stronger and flows into tighter spaces than paste flux, but I always keep in mind it's going to drip and heated acid can be very unfriendly to many surfaces.
• There is a downside to acid fluxes; they corrode hot copper and eat away at solder gun tips. Use of acid flux is an aid and not a mainstay – once again, it is far more effective and faster to scrape parts bright, then use just a dab or drop of flux.
• When I want to add more corrosion resistance to a bare copper terminal I'll continue soldering after the joint is done and coat the whole terminal. The trick here is to quickly tap the terminal sharply with solder gun tip to knock off excess solder out of the hole of a ring terminal. Otherwise the screw won't fit. A solder coated terminal will be a lot more corrosion resistant than a factory tin plated terminal right out of the box.
• There's been hype about “how much better silver solder is” as compared to regular solder. Don't get conned into spending a small fortune for a roll of lead and tin wire that contains merely 4% silver. If you have an ohm meter and too much curiosity you can buy a quarter pound roll of “silver” solder, unwind it, measure the resistance across the full length of it and then compare it to that of 60/40 solder of the same diameter and length. Oh sure, there's less resistance on a laboratory scale but it doesn't add up to a hill of beans on automotive circuits. The silver doesn't even add to corrosion resistance. If you replaced all the copper in the wire, all contacts, switches, everything with pure silver, you'd gain only 20% more or less in conductance. Silver plated switch contacts however resist arc burning better than bare copper.
• Gold plated terminals solder just as easily as bare copper terminals. If you use adhesive lined heat shrink tubing over the joint and then coat everything with corrosion compound like LPS-3, the finished connection is good for decades.
• I mentioned “60/40” solder earlier. It's sixty percent tin and forty percent lead. It melts at a much lower temperature than 50/50 solder which makes all the difference in the world for soldering electrical parts. You can find rolls of 63/37 solder, and it melts at a slightly lower temperature and seems to be even easier to use. Beware of buying solder that is really skinny – it's made for tiny electronic circuits and you'll be scrambling to feed the melting solder fast enough into an automotive-size joint. I like .035” solder for small wires and .060” for large wire and lugs.
• Parts that have been freshly soldered must remain motionless until they cool. A good solder joint has a good luster to it. A bad solder joint looks like a gob of flat aluminum paint. This type of failed solder job is often called a “cold solder joint”. You might as well have stuffed the wire into the terminal with window putty.
• If solder won't flow well onto a properly cleaned solder gun tip, it sure won't flow onto the work. If you can't tin the solder gun tip easily, stop right there and figure out why. Solder oxidizes like most metals, and old solder can be a real bear to use. In a pinch I have used sandpaper to wipe down a length of solder. Beginners always try to overheat their way to a good solder joint. A lot of heat just causes things to get worse. Every metal in the world of soldering has to be brand-new-shiny and free of grease and oil including oil from your skin and perspiration.
• Solder guns like the Wen and Weller, use a formed copper rod for the tip. It is very common for the nuts clamping the rod to loosen. When they loosen it causes the gun to lose a lot of heating potential. If you have good solder and can't “tin” the solder gun tip easily, perhaps the nuts are loose. If they're already tight, I would unscrew the nuts, remove the tip and scrape the ends shiny bright. Don't forget to clean inside the barrel where the tips fit to the gun (this is a very common problem and I have seen many solder guns thrown away because the holes for the solder tip were oxidized but the owner thought the gun died!).I use a nail (flatten a nail with a hammer to make a miniature scraper) on the aluminum barrels and scrape them clean. How do you know you are starting out with solder that's going to work? If there is any doubt, like a missing label I would buy a new roll from a trusted source like Radio Shack.
• Protect your work by using adhesive lined heat shrink tubing on top of the soldered joint, and then spray down exposed metal with corrosion compound like LPS-3. Soldering can be fun, but once is enough.
Here's a parting idea: Spread your new found talent around the RV community and teach a friend!