How to Solder- the basics Richard Perez Soldering insures permanent, low loss, electrical connections. A soldered electrical connection is not difficult to make, it only requires a little practice and the right tools. If you're making your own power, then your system's wiring and its maintenance are critical. Without good electrical connections, even the finest system will perform poorly or not at all. Here's what you need to know to make effective soldered connections for your system. Interconnection- the electric pipeline In order to use the electricity we make, we need wiring. Wiring transfers power from its source (PVs, Hydro, Wind or what have you), to the batteries for storage, and from the batteries to the appliances which consume the power. The chain of wires and connections that eventually leads to say turning on a light, must remain intact if the light is to operate. It only takes one weak or bad link in this chain to render the entire circuit inoperative. Electrical wiring is made of copper and aluminum because both metals have low resistance to electron flow (electric current). The major problem with mechanical connections is the formation of oxides on the copper or aluminum. These oxides are poor conductors of electricity and the resistance of the mechanical connection increases. The pure copper or aluminum on the surface of the wire gradually changes to copper oxide or aluminum oxide by chemical reaction with the oxygen in the air and in the water. I shudder to think of what acid rain doesÉ Why Solder? Mechanical connections are made by twisting the bare wires together or by compressing a wire into a connector or terminal. Wire nuts make mechanical connections that, while better than twisted wire connections, still don't prevent oxidation within the electrical connection. As the wires that make up the mechanical connection oxidize, the electrical resistance of the connection increases. This results in a voltage loss across the connection. This voltage loss is directly proportional to the amount of current flowing. The loss of voltage (and thereby power) across the connection manifests itself as heat- the oxidized mechanical connection gets hot. On the other hand, a well made soldered connection will have about half the resistance of a new mechanical connection and will not oxidize with time. Years down the road, the soldered connection will have many times less resistance than the oxidized mechanical connection. In 120 Volt wiring, the voltage loss due to oxidized mechanical connections is negligible because the input voltage is so high- 120 vac and thereby the current flow is low. Here, mechanical connections are standard and perfectly acceptable. In 12 Volt systems, however, the voltage loss is appreciable. For example, consider a 120 Watt load being powered via a mechanical connection with a resistance of 0.2 ½ ( a fairly typical funky connection's resistance). At 120 vac, the 120 Watt load will consume 1.0 Amperes of current (I=P/E, I=120 Watts / 120 Volts, I=1.0 Amperes). At 12 VDC, the 120 Watt load will consume 10 Amperes of current (I=P/E, I=120 Watts / 12 Volts, I=10.0 Amperes). In order to transfer 120 Watts of power, we must move ten times the current in a 12 Volt circuit as in a 120 Volt circuit. Increased current produces increased voltage loss across a bad connection. The voltage losses and power losses for this scenario are in the spreadsheet below (calculated at a variety of voltages and using Ohm's Law). INSERT SPREAD Note that the voltage loss for the 120 Watt load is only 0.2 Volts at 120 Volts input. However the voltage loss for the same 120 Watt load at 12 Volts is 2 Volts. The 120 Volt system shows a percent loss of 0.2%, barely worth mentioning. The voltage loss in the 12 Volt system is large- 16.7 % of the initial input voltage. The net result of this scenario is that the 120 Watt load will barely function on the 10 Volts leftover after the bad connection gets its share of the power. Low loss, low resistance electrical connections are essential in systems using voltages under 30 Volts. Soldering a connection insures that it will not oxidize and increase in electrical resistance. Do it right once, and it will work right forever. But you must do it right. A bad soldered connection can have more resistance than a mechanical connection. When to Solder Any low voltage electrical connection, involving copper wire, where oxidation or corrosion is a potential problem is a candidate for soldering. Obviously, there will be some mechanical connections in the system. It's not prudent or possible to solder to battery terminals, inverters, and controls- here mechanical connections are appropriate. Here is a list of appropriate places for soldered connections. ¥ Any connection that lives outside in the weather, especially wire to ring connector connections. ¥ Low voltage distribution wiring where it connects to the main DC buss. ¥ Any low voltage appliance's power wires where the appliance is stationary and thereby doesn't need a plug. For example, a ceiling light doesn't need a plug. ¥ Connectors on all battery or cell cables. The corrosive environment surrounding batteries will ruin mechanical connections very quickly. The connectors used to bolt to the cells must be soldered to their cables. See HP#7, page 36 for a detailed article on building these cables. ¥ Any place you want to save money. Not only is soldering more permanent than mechanical connections, but it's far less expensive. Connectors, wire nuts, crimpers and the like cost at every connection. Once the soldering equipment is paid for, the soldered joint is far less expensive as well as more durable. What is Soldering Soldering is the process of bonding bits of copper together by flowing a molten mixture of tin and lead over the copper. The solders used will be detailed later, but they are mostly mixtures of tin and lead with a flux added. A flux is a chemical compound that, when hot, will chemically strip off the deoxidized surface layer of copper and allow the solder to bond to clean, pure metal. The Tools The tools needed to solder are few: a source of heat (soldering iron), solder, and flux. The soldering iron should fit the job at hand. Just as you can't remove a 1 inch nut with a 1/2 inch wrench, you can't solder big cables with a small iron. Soldering irons are mostly electrically powered and come in sizes from 4 Watts to over 300 Watts and available with input voltages of either 12 and 120 Volts. Some are butane or propane powered. If you are serious about soldering, then you will need several sized irons, just like you need different sized wrenches or screwdrivers. After all, Rembrandt didn't use just one brush. Low Wattage Irons These little jewels are designed for use on electronic printed circuit boards/wiring or small sized house wires (up to 14 gauge). They put out between 4 and 25 Watts of heat to a tip that does the soldering. Pictured below is the Weller TCP-12 which consumes 2.3 Amperes at 12 VDC. The TCP-12 is thermostatically controlled to keep tip temperature in line (700¡F.) and prevent the iron from burning up its tip when not in active use. The TCP-12 costs about $50. and is professional quality, we've used the one pictured for over eight years in heavy service. Tips come in all sizes and are easily replaced. Another iron pictured below is a PortalSol unit powered by butane. It is adjustable from about 4 to 75 Watts (see HP#16, page 39). A similar model is available from Radio Shack (RS# 64- 2161 for $29.95). INSERT PHOTOS Medium Wattage Irons These irons are usually 120 vac operated and produce between 45 and 260 Watts. The large Weller soldering gun (Model D550) below is our favorite and runs on inverter produced power very well. It produces enough heat to quickly solder several 10 gauge copper wires. Soldering ring connectors and tinning wire up to 8 gauge is easily accomplished with the Weller gun. It has two heat levels- 200 and 260 Watts, but we run it wide open almost all the time. This soldering gun and others are available at hardware stores for under $40. INSERT PHOTO The Heavy Weights For heavy duty soldering it's hard to beat a propane torch with soldering tip. These are universally available from hardware and discount stores for less than $30. See the article in HP#7, page 36 for detailed info on torch type soldering. Care must be taken in torch soldering not to burn the flux with the open flame. INSERT PHOTO LAYOUT What Kind of Solder to Use The chemical composition of solder varies greatly. The quality and utility of solder sadly also varies with its content. The best type to use is made from ³60% tin and ²40% lead, with a built-in rosin (that's tree sap) core for flux. This type is becoming less common in favor of the 40% tin and 60% lead varieties. The types with less tin than lead are not only more difficult to use (poor wetting characteristics), but make a joint with less mechanical strength. Under no circumstances use a solder with a tin content less than 40%. Don't use solder with acid core flux, it is for plumbing. Rosin core fluxes are noncorrosive over time and should be used on all electrical work regardless of solder composition. The Ritual of Solder Soldering is a skill that has seven basic steps. If you follow these steps, you will get a permanent, good connection every time. ¬ Use a soldering iron sized to fit the job. Use low wattage irons for small connections with small thermal mass and high wattage irons for big jobs with large mass. Á Solder only clean copper. Soldering will not work on corroded, greasy or dirty copper. Sand or polish all the parts of the connection bright before soldering. Â Make a tight mechanical connection before soldering. Soldering is not a substitute for mechanical connection, it merely makes it permanent by sealing out oxidation. Twist wires together firmly, or crimp wire into a connector before soldering. Ã Heat up the iron, clean (wipe with cloth or paper towel), and re-tin its tip with fresh solder just before making a solder joint. It is impossible to effectively transfer heat from a funky soldering iron tip. ° Place the hot iron on the work and melt a small amount of solder on the tip where it meets the work. This small puddle of molten solder between the tip and the work greatly increases thermal transfer. Å Then place the solder against the work, NOT against the soldering iron's tip. This melts the solder on the work where its flux will deoxidize the copper. Melting the solder against the tip causes the flux to eat up the tip instead of the copper oxide on the work. This makes a poor soldered joint and wears out tips rapidly. ² Flow only enough solder into the joint as it will easily accept. Is it a good soldered connection? If the connection is a good one, then the solder will be bright and shiny. All solder surfaces will be concave (valleys) indicating good wetting of the solder. This means that enough heat was used to make the joint and that all parts were hot enough to suck up a good, yet thin, coat of the solder. Connections made with too little heat will show convex (hills or blobs) solder surfaces indicating that the solder didn't get hot enough to flow easily. Solder joints made with too much heat have a grey, dull appearance. Practice make Perfect Soldering is a skill. It takes practice. Work with scraps until you can get good joints. Under heat the work and see what happens. Overheat joints until you can see the effects of too much heat. These skills can be learned by anyone willing to pay attention for a single afternoon. The Advantages? Your work lasts. A soldered connection is good forever. Do it right once and future generations can use the connection and and sing songs in your praise.