Soldering Techniques

If you want to get into the R/C hobby, sooner or later, your going to have to learn how to solder. For beginner's, this can be intimidating. The idea of working with 600-800°F hot soldering iron tips and poisonous molten metal that can seriously injure you isn't something most people are eager to learn about. I hope that last sentence sunk in, because soldering is not something that should be done without the proper tools and safety equipment. Soldering irons get very hot. They instantly burn skin and can cause permanent scars. Solder, which is primarily lead, has been shown to cause kidney failure, cancer, and all sorts of other horrible things. So, if this article teaches you anything, let it be the safety precautions you should take when you solder. To make soldering easier, let's make some rules:

Rule #1 - BE CAREFUL! Irons are hot, and solder is poisonous. Keep the iron in a coil stand or a leaning stand that is meant to hold the iron. This will keep you from burning yourself. Wash your hands when your done after you handle solder. This will prevent lead poisoning. Do not solder in an area where there isn't good air flow. The fumes that come from soldering should be avoided. It's a good idea to have a small fan to blow them away from you to keep you from breathing them. It's also a good idea to wear eye protection. It's not uncommon to have small bits of solder or rosin "flicked" off the end of the tip. Getting a molten glob of solder in your eye isn't pleasant.

Rule #2 - Use the right tip for the job. This is critical. Even if you have a very nice soldering iron, it's not going to work if you have the wrong tip at the end of it. If you look at the two tips below, you can see they are very different. Both of them are temperature controlled, so they will both be the same temperature. So what makes them different? Surface area! The more surface area the tip has, the quicker heat is transferred to the metal you are trying to solder together. If you use the wrong tip, you will transfer the heat from the tip to your work too slowly, and it will either take forever, or ruin your work. When you solder battery bars on cells, the heat needs to be transferred quickly to prevent cell damage. The top tip is used for delicate soldering jobs, such as repairing circuit boards. The bottom tip is for larger jobs, like soldering battery bars or 12 gauge wires. The tip you will need for about 90% of your R/C needs is the tip on the bottom. It's commonly known as a "Chisel Tip".

Rule #3 - Always tin your tip before you use it for the first time. Most tips come pre-tinned, but some aren't. "Tinning" is simply getting the new tip nice and hot, then melting a lot of solder on it. This will prepare the tip for use and make soldering easier for you. It will also protect it and make it last longer.

Rule #4 - Clean your tip BEFORE and AFTER you use it. Nothing will ruin a tip quicker than not cleaning it. The best way to do this is to use a wet sponge. Simply rub the tip of the iron in a damp sponge and the shiny tinned tip will transfer heat better. There are special sponges you can buy to clean your tips, but you can use a regular one and it will work just fine. Most coil stands (like the one pictured above) have a space meant to hold a cleaning sponge.

Rule #5 - Human beings are not octopuses. We only have two arms, so if you need help holding something, either get someone to help, or use something to hold what you are working on for you. You will find that as your soldering skills get better, you won't need to rely on other people to help hold your work.

Rule #6 - Heat the work, NOT the solder. When you solder two pieces of metal together, your goal is to use the least amount of solder as possible. Clean solder joints are strong joints. If you heat the just the solder, the joint will not be strong, the resistance will be high, and you will end up with a gloppy metallic mess.

Rule #7 - Insulate your work if necessary. If there is even the slightest chance of two exposed solder joints touching each other, use either heat shrink tubing or electrical tape to prevent shorts.

Rule #8 - ALWAYS use a battery jig when you solder cells together. It's virtually impossible to solder battery bars and keep the cells in place at the same time. I recommend the W.S. Deans Speed Jig. It will hold the battery bar in place for you so you can hold the solder in one arm and the iron in the other. And we know from Rule #5, we are not octopuses.

OK, now that we have the ground rules set, let's talk about equipment. There are basically two types of irons you can buy. You can get a soldering iron or a soldering gun. Personally, I think soldering guns are useless, especially in the applications it would be used for in the R/C Hobby. Irons are lightweight and are easier to use. I use a Weller W60P iron. It's a little more expensive, but I think in the long run, it's worth the money. The W60P is temperature controlled and has a wide variety of tips available. It comes with a small point tip, so you will need to get a chisel tip for it. You want Weller Part # CT5E8. It sells for about $6. The W60P costs about $63. The best place I have found on the internet to get this soldering iron is through a store called WASSCO. They also carry the CT series tips for the W60P. The CT series tips come pre-tinned. You can find them HERE. There are cheaper soldering irons out there, but they won't last as long, and the tips need to be replaced frequently. Cheaper tips are made of solid copper with a zinc coating. After about 10 uses, the zinc coating wears off, and the tip becomes useless. I have been using the same CT tip for about a year now, and it still works great. Just remember - You get what you pay for.

There are all kinds of solder available - 60/40, Silver, Rosin Core... I like to use 60/40 rosin core solder from Radio Shack. Rosin core solder is usually a 60/40 mix - 60% Tin, 40% Lead. A one pound spool of 60/40 rosin core solder will cost your about $12 at Radio Shack. You can also get smaller spools of silver solder for about $4 from W.S. Deans. I prefer the rosin core, because it's cheaper and the rosin helps the solder flow between the two pieces of metal you are trying to join together.

OK, here are a few of the types of joints you are going to have to make if you are involved with electric R/C cars. The first thing we need to learn is how to tin wires. 99% of the wires we use the the R/C hobby are what are known as "stranded" wires. These are wires that are made up of tiny strands that are twisted together. This makes them highly flexible. If you take a piece of 12 gauge wire and strip off the insulation, you'll get something that looks like this:

	Notice how the wires are all twisted together. Tinning the wire will make it easier to solder it to whatever we want to attach it to. Take the exposed end of the wire and pinch it between the thumb and pointer finger. Use your other hand and twist the insulated part of the wire to bring all the strands into a nice tight twist.
	You can use a pair of pliers to hold the wire while you tin it. Notice how my iron is on one side of the wire and the solder is on the other side. This is an example of Rule #6. 12 Gauge stranded wire can sometimes be a little hard to tin. To make the heat flow from the tip better, you may want to melt a TINY bit of solder on it. When the wire heats up, the solder will melt. The rosin core will help the solder get "wicked" into the wire strands. When the strands are all covered with solder, remove the iron and the solder.
	This is what you will end up with. The wire strands should be wound tight and covered with solder. That's all there is to tinning a wire. Pretty simple, huh? This is pretty easy to learn how to do with some practice. Once you can tin wires correctly, the rest comes pretty easily.
	The first joint we need to learn how to make is a T-Joint. This joint can be seen in Electronic Speed Controls that have only three outputs - Black (Goes to Negative Battery), Blue (Goes to Negative Motor), and Red (Goes to Positive Motor and Positive Battery). To create this type of joint, you need to remove about 3/16th inch section of insulation from the Red wire coming from your motor. The end of this wire will be connected to the positive battery terminal. Tin the section of the wire that you removed as shown in the picture. (NOTE - the pictures are for reference only, your wires will be different lengths due to the layout of your chassis. Make the wires as long as they need to be so they can reach what they need to be connected to, but try to keep them as short as possible to eliminate resistance and clutter. It's a good idea to measure how much wire you will need and mark where your T-Joint will be before you solder the wire to the motor.)
	Tin another wire on both ends to connect the exposed section to the red terminal of the ESC and the motor wire. Again, make this wire as long as it needs to be to make the connection, but try to keep it as short as possible. You shouldn't need any more solder to connect the two wires, but if you need it, just add a little. It's OK to leave this type of joint exposed, since it's pretty unlikely to short out under normal conditions.
	Now that you have learned the T-Joint, I will show you how to eliminate it completely if you want to. Sometimes it's easier to solder the exposed section of the wire directly to the red post of the ESC, like the Associated TC3. This is sometimes a little harder to do, since the wires get a little cramped in a small space. Use which ever method is easier for you.
	Now I'm going to show you how to solder wires to a high performance connector. This is a W.S. Deans 2 Pin Ultra Plug Connector. I have tinned the connectors already, but we need to add the wire leads. Just a warning. Connectors (any kind) get VERY HOT when you solder them. NEVER hold the connector with your fingers when you solder the wires to the tabs. You will get burnt. Let the connector cool for a few minutes between soldering the tabs to keep it from melting. Now we need to strip about 1/8th inch of insulation off the wires and tin them.
	Before you solder anything, remember to slide on any heat shrink tubing if you are going to need it. Nothing is more frustrating than having to unsolder a joint because you forgot the heat shrink tubing to insulate the joint. Use your pliers to hold the connector while you solder. When you pre-tin the connector and the wire, put just a tiny extra amount of solder on the wire and the connector tab. Since we know from Rule #5 that we only have two hands, we can elimiate hoding the solder by letting the extra solder we tinned on the wire and the tab make the connection for us. Notice again, I am heating the work, not the solder. When the tab gets hot enough, the solder will melt, then the solder on the wire will melt, and the joint will form. You will need to keep the wire in place for 5-10 seconds while the solder cools and the joint hardens.
	Now do the same with the negative wire. Be careful not to make a "solder bridge" between the negative and postive wires. This would cause a short - and possibly a trip to the hobby shop for a new ESC and battery.
	Here's the completed joints. Notice they are a nice shiny color, and they are solidly connected to the tabs. You should be able to pull pretty hard on the wires without breaking the joint. If the joint breaks, you probably have what is refered to as a "rosin joint". This is a joint that looks ok, but the only reason it is connected is because the rosin is acting like a "glue". This type of a joint has a very high resistance and will eventually fail, maybe even cause a short. You should ALWAYS insulate this type of joint to prevent a short.
	Slide the heat shrink tubing over the joints and shrink it. Now you have a professional looking solder job! Just another bit of advice. If you decide to use connectors instead of hardwiring (soldering the wires directly to the battery pack), NEVER use male connectors on batteries. The terminals on a male connector are usually more exposed, and are more likely to short out.
	The last thing you are defiantely going to need to learn how to solder are battery bars. The first thing your should do is get the cell surface prepared. Rough-up the surface of the negative and positive ends of each cell with a Dremel tool or some sandpaper. This will make it easier for the cells to bond to the solder. After you have prepared them, tin the ends of the cells. If you end up with a lot of rosin on the cells, don't worry, you can clean it away with a wire brush later.
	You can pre-tin the bar if you wish. It will make it easier to solder the bar onto the cell. The W.S. Deans Speed Jig's clip wil hold the bar in place for you.
	Press down on the ends of the battery bar with the soldering iron. The chisel tip will cause the solder to melt and make a nice joint without heating up the cell too much. Do the same with the other end of the battery bar.
	Remove the clip, and the joint is finished. You can use a wire brush to clean away the extra rosin. If you want to prevent the bars from shorting out, you can cover the whole pack in shrink wrap if you want, however, if you do this, you won't be able to equalize your cells.

Well, those are the most common joints you will have to make in the R/C car hobby. It takes a while to learn how to solder well. Practice makes perfect! I hope this helps you become a better solderer, and don't forget when your done cleaning up - WASH YOUR HANDS. This will get the lead off your fingers. Have fun soldering

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