How-To: Soldering

One of the many skills required for the rc hobbyist is soldering. Having the correct equipment and good basic skills can aid greatly in the hobby. Some get around this by having the local hobby shop or a friend solder for them. This is a valid solution but then you have to work around their schedule and you have to have faith in their abilities. Just because someone owns a soldering iron does not mean they can use it properly and this includes hobby shops. I personally like to do everything myself. That way I know it is right or if it's not, at least I learn from it.
Equipment and Supplies
Before you can solder anything, you have to have the right equipment. This includes the obvious items like a soldering iron and solder, but should also include heat shrink tubing, something to shrink the tubing (heat gun, lighter, match, etc), wet sponge, holding/clamping device, wire strippers and/or cutters, wire of various sizes and connectors. Now let me show you what I use.

My tools and supplies include a Weller soldering station, a pair of needle nose pliers with some elastic webbing on them, 60/40 lead based solder, various heat shrink sizes and a lighter to shrink the tubing. I keep a supply of several sizes of noodle wire and several sets of spare connectors of various types.

For cutting/stripping wire I use several tools including my pocket knife, scissors, dikes or a wire stripper. Which one I use depends on what type and size of wire I am using.

Hint: A pair of needle nose pliers with something elastic around the handles works great to hold the parts while you solder, or do any other task where you need the pliers to be "spring loaded".

Suggestion: Some use lead-free solder and this can make soldering much more difficult. I would recommend using a lead based solder. Just be sure to wash your hands after you solder.

Hardware suggestion: It has been brought to my attention that there is an alternative to using a sponge to clean your soldering iron tip. There are other types of cleaners that have little brass/copper curls in them and others that are brass/copper pads. These work very well for cleaning the tip without cooling it like a wet sponge.

Teaching by example
This article is going to be based on examples, the best way to learn in my opinion. I will start with a step-by-step how-to for soldering a T-Plug. Then the rest of the page will be filled with other examples as well as a few tips and tricks. Hopefully this collection of examples will cover all the various soldering concerns an rc hobbyist might encounter.

Step by Step soldering of a T-Plug connector
T-Plugs are very popular. They are not the easiest to solder but there are several things you can do to make it easier. So let me work through the steps needed.

1) Get everything setup and ready.
This usually starts with getting the soldering iron out, getting it plugged in to warm up and wetting the sponge.

Lay out all the parts so you have everything you need in one place. Next trim the insulation off the wires to match up with the connector tabs. You can trim the wires shorter but try not trim them too long.

Note: I suggest connecting the male and female connectors together for soldering. This will greatly reduce the chance of melting/distorting the housings due to the added thermal mass.

2) Prepping the surfaces, tinning
When tinning, try to do it quickly but well. Make sure your soldering iron is hot and clean. Before touching a part with the iron, add a small amount of solder to the tip.

Touch the part to be tinned with the wet solder and feed new solder into the angle between the two. Sometimes moving the iron around will help spread the solder more quickly. Once the part "takes" the solder, remove the iron. The solder should be smooth and shiny, if it is not shinny then add a tiny bit more.

Be careful how long you hold the iron on the parts. For smaller wires it should not take any longer than about 1/2sec to tin the wires. For larger wires it can take 2-3sec. If you heat the wires too much then solder will wick up the wire under the insulation and make it rigid. The prolonged heat will also boil off all the flux and then the solder will not melt/flow well. The same applies to the tabs on the connectors. For these you should just need to wipe the solder across them to leave the surface tinned with just a little bump of solder on them.

3) Complete the solder joints

This is going to be a very quick step. Before you solder anything, make sure your heat shrink tubing is on the wire. How far down the wire the shrink tubing it continues, how long you cut it, is your choice. The heat shrink does provide some strain relief on the wire.

Clean your iron tip well and add a little bit of new solder. Then while holding the soldering iron in one hand, get your wire exactly where you want with other hand. In the situation below, lay the wire on the tab and get it lined up just like you want. Then place the part of the tip with the newly added solder directly on top of the wire and hold it until everything melts together. Once everything melts nicely together, remove the iron but continue to hold the wire in place while it cools enough to harden. The iron should not be in contact with the wire more than 1sec for smaller wires or more than about 3sec for larger wires.

Next comes a very important step, check your work. Take a good look at the solder joint and make sure it is smooth and clean. If not then try it again. Once you are happy with the new solder joint, it is time to shrink the heat shrink tubing.

Now do the other side.

Soldering an XT60 connector
The XT60 connectors are new to the RC world and are quickly becoming popular. Most of this lies in the fact that they are much easier to plug/unplug but they are also a little easier to solder than T-Plugs.

Soldering XT60s is very similar to T-Plugs. First get everything laid out and ready. Next tin everything and then slide the heat shrink tubing over the leads. Only add enough solder to just coat the inside of the solder cups.

To complete the joint, clean the iron and add some new solder. Hold the wire in place and lay the soldering iron on the wire to melt everything together. Again this should take very little time. Once everything looks good then slide the heat shrink up over the solder cup and into the relief molded into the connector, and shrink it.

Note about XT60s: These connectors are made of a fairly soft plastic that has a moderately low softening point. Be sure to only solder them while connected to their mate and be sure to be quick with the iron. They are not "fragile" but it should just me noted.

Soldering bullets
Not all rc connectors are molded plastic like T-Plugs and XT60s, many are either just a metal connector like bullets or are metal connectors that are housed in a plastic housing like EC3s, EC5s and Power Poles.  The good news is that soldering bullets can be much simpler than other connectors. I am going to show how to unsolder a bullet and then re-solder it again. Then I will cover covering it.

The following connector came on a battery I recently ordered. Notice the lack of solder inside the hole? I would have never known it was not soldered well unless I had exposed the metal connector and seen that the solder cup was empty. As such I wanted to re-solder it to make sure I had a good connection.

Clean your iron and add a bit of fresh solder to it. Then hold the iron on the top edge of the connector until solder melts and you can remove the wire.

Now clamp the connector vertically and fill the cup 1/3 to 1/2 full of solder. Also re-tin the wire. Now heat the connector up for a few seconds and then place the wire in while keeping the iron on the side. When the two meld, you should see the solder pull in the hole some. At that point you can remove the iron but hold the wire in place until the solder cools.

Caution: If this bullet is to be installed in a housing, take care not to get solder on the outside of the solder cup, as it can cause problems when installing the bullet into the housing. You can wipe off excess solder with a wet towel. Just get the bullet nice and hot and wipe it off.

Covering the bullet
Because we are soldering a bullet there is no need to slip heat shrink over the wire before soldering, as we can slide it over the front. Cut the heat shrink tubing to the proper length, slide it over the connector and shrink it. I like to leave it hanging over the front edge of the bullet a touch.

In this case I have a problem. The heat shrink I used was just a tiny bit too small but I have a trick for that. In this case it is just a little too small. So I take the needle nose pliers and spread the heat shrink just enough to fit over the connector. Then I shrink it like normal.

Soldering new connectors on battery packs
Why do I have a special section for soldering a connector on a pack? Well simply put it's because I see too many posts about people causing shorts when soldering and many times it ends with a ruined pack. The #1 rule when soldering packs is to only have one wire exposed at a time. Done properly, the chance of causing a short is nearly zero.

Start by getting everything ready. Now remove the cover from the one lead and leave the other covered. Tin the lead and the connector.

Make sure the heat shrink is slid onto the wire and solder the lead to the connector. Once you are happy with the solder joint, shrink the heat shrink over it. Before working on the other lead, it may be a good idea to cover the opposite connector's tab to prevent shorts from your clamping device.

Now remove the cover on the other lead, tin it, slide heat shrink tubing over the wire, solder it and then shrink the tubing.

The finished product.

Fixing a bad solder joint
During your soldering you might find that you have a rough looking joint. This is usually caused by the solder being over-worked or from a lack of heat in the solder joint. If you find this to case don't panic, simply remelt the connection with some new solder and it will clean right up.

An easy way to remove extra solder
Many times you will find that you have too much solder on a wire or connector. The simplest way to remove the excess is to heat the solder and then tap the wire/connector on the workbench. Most of the liquid solder will come right off. It takes a little practice, so don't be discouraged if you have to do it several times to get the excess off. Also adding a touch more fresh solder before trying to tap off the excess solder can make it easier.

Extra layer of protection
Sometimes I like to shrink some larger heat shrink tubing over the whole back of the T-Plug connector and up the wires a little ways. It adds some extra protection and adds more strain relief to the wires. It can also give you some additional material to grip when disconnecting.

Soldering 10awg to a T-Plug connector
More and more rc batteries and escs are shipping with 10awg or even larger wire on them. In 99% of the cases this is totally uncalled for but they do it anyways and now the hobbyists have to deal with it. Unfortunately soldering 10awg is non-trivial, especially when soldering it to a T-Plug, but it can be done. To make is easier, people have come up with a few tricks you can employ to make the job much easier.

Basically the biggest problem is that most modelers have fairly low end soldering irons and do not keep them in good shape. So before attempting this, make sure you have at least a 40W soldering iron with a medium to large tip and make sure the tip is in good shape. My Weller station does it very well but I still have to be careful. Making sure you have some fresh clean solder on the tip before you try to heat anything makes a huge difference.

Here are several different methods you can use.
1) Soldering 10awg normally. Make sure you tin both well. Then I would heat the wire up separately until the solder just melts. Then add a tiny bit of new solder to the wire. Immediately place the wire on the tab and place the soldering iron on top of the wire. Heat the wire until the whole joint melts together. You will likely need some fresh solder added to the joint during the soldering process or it won't smooth out. If you can't get the solder to smooth out in less than 5sec, remove the iron or you will likely melt the connector. Let everything cool down. Then recheck everything, add a little fresh solder to everything and try again.

2) Trim the wire down to a more manageable size. I do this with my wire strippers. I just cut a little deeper when I strip the wire and take some of the outside wires off with the insulation. Once you get the wire to the size you want, tin it like normal and complete the solder joint. Just make sure you don't take too much material off. (This is the method I recommend)

3) The next method requires a saw or Dremel tool. You start my tinning the wire. Next you cut a slot wide enough and deep enough to fit the T-Plug tab into. Be sure the tab is cleaned off well to keep it as thin as possible. Then you slide the slotted wire over the tab and solder it. I had not tried this until writing this and I found the cutting part to be more difficult than I expected. It is doable but it is not easy. Once completed though, it is trivial to solder and makes for a nice looking solder joint.

Soldering 10awg to an XT60 connector
Most of the same difficulties exist when soldering 10awg to XT60 connectors but they are slightly easier. The solder cups make it easier to hold everything in place and they are made of a thinner material so they heat up more quickly. Make sure you don't use too much solder or it will bulge out when you put the wire on the cup. Also the wire is too large to fit into the cup, so just set it in the cut out area and slide it as far forward as possible.

Soldering both an ESC & BEC to a connector
Many times multiple devices need connected to the same connector and this can be a real challenge. For example lets say you need to solder both a 10awg wire from a ESC and the smaller wire from the BEC to a T-Plug connector so they can both be powered by the flight pack. Here is the method I use to pull this off.

Strip both wire a little longer than you need and then slide some heat shrink over the pair, lining the insulation of each up, and then shrink the tubing to hold them together. Now work the wires of both to make then one and then tin them. Once you are happy with the union, clip the excess wire off. I then added a little extra solder because the wires are so big. Slide some heat shrink up the pair of wires and then solder the pair onto the tab like you would 10awg wire. Shrink the tubing and you are done.

Now with an XT60 connector
Now lets do the same thing but on an XT60 connector. This is where this connector's design starts to shine a little.

Strip and tin both leads as well as the connector. Slide heat shrink over both wires. Now solder the small wire to the connector being sure to keep it in the bottom of the cup. Place the 10awg wire on top of the smaller wire and solder it on as usual. Finish by shrinking the tubing over the solder joint.

Soldering 2 wires together
Many times you need to connect 2 wires together. There are a couple of methods one can use but this is how I do it but this is how I do it. I start by stripping the wires, then I tin each end, slide shrink tubing over one wire, solder them together and shrink the tubing.

Soldering 2 large wires together, using a bullet
You can solder 2 large wires together using the method above but the resultant solder joint can be bulky and can catch on things. Another approach is to use something to help connect connect the 2 wires inline, a female bullet works great in this situation. Trim and tin both wires. Insert both wires into the bullet and heat the bullet, adding solder when it gets hot enough. Let the whole joint meld, making sure to get everything lined up correctly. Let cool and cover with shrink tubing.