In this hobby sooner or later you are going to have to do some soldering – especially if you are into electric vehicles. You may need to do some repairs that require wire replacement or want to change out existing wires for a heavier gauge. A proper soldering job will give you a better electrical connection and a joint that isn’t going to fall apart during a race.
Soldering is like gluing pieces of metal (wire/solder tab/etc…) together with solder. This tutorial will show you how to solder a piece of wire to a copper tab but the techniques are identical when soldering in general.
What you will need:
- The parts to be soldered
- Soldering iron
- Rosin core solder
- Wire cutter/ knife
- Vice/helping hand (something to help hold components in place)
If you will only be soldering wires here and there you will not need a very powerful or sophisticated iron. A 25 watt to 40 watt iron will generally be sufficient. If you are going to be doing a lot of soldering a temperature controlled iron may give you better performance. You will want the higher wattage irons if you are going to be soldering to thicker metal surfaces. A lower wattage iron will be more suitable to printed circuit board (PCB) work since the excessive heat from the higher wattage irons could damage PCB components. I’ve used a 25 watt iron for a few years and it is more than sufficient for soldering wires together as well as the occasional PCB task.
For electronics work you will want some rosin core solder and not the plumbing kind. The rosin flux in the solder will help prepare the surfaces to be joined to accept the solder. This type of solder is generally composed of tin and lead. The type I mainly use is made of 60% tin and 40% lead (60/40) but any of them will be fine.
- Soldering irons get very hot – keep away from flammable materials
- Fumes from the rosin core solder is toxic – work in an area that is well ventilated
- Solder/flux have a tendency to ‘splash’ – wear eye protection
- Solder contains lead – make you wash your hands after handling and DO NOT EAT!
Step 1: Determine the length of wire you’ll need
Keep the wire length as short as possible but long enough so that it has a bit of slack. Keeping the wire length appropriate will put less stress on the wires while optimizing conductivity.
Strip the insulation off the wire with the wire cutter or knife. The amount you’ll want to remove will depend on the application – generally 1/8 – 1/4 inch is sufficient. Twist the stripped wire to keep all the strands together.
Step 2: Prepare the surfaces to be joined
To make it easier when soldering the two pieces together, tin the surfaces to be joined. Tinning is the process of coating the surfaces with some solder. This is like ‘pre-soldering’ the individual pieces. Since the two pieces will now have melted solder on them, it will be a much quicker process to join them later.
If the surface you want to solder has oxidized, scrape it with a knife or some sand paper to remove the oxidation. The oxidation will not allow the joint to form effectively leading to what is known as a cold joint. Cold joints will look grey in colour and may come loose/ lose connectivity unexpectedly.
With the surfaces cleaned, proceed to tin with solder. It is helpful to have a vice or something to hold the wire in place while you work with it. If you are tinning the wire, apply the tip of the hot iron on one side of the stripped wire while holding the solder against the opposite side. The heat from the iron will conduct through the wire and melt the solder in 2-3 seconds. If it takes longer than this to melt the solder, you may not be applying the iron correctly or you may need a higher wattage iron.
Tin the other surface in the same manner. If it is not possible to get behind a surface, you may put the tip of the iron directly on the surface along with the solder (keeping the solder away from the tip).Properly tinned surfaces will look shiny and silvery. If it looks dull or grey you have a cold joint…clean the surface and try again.
Step 3: Solder the joint
With the tinned wire on the tinned surface, place the iron on top of the wire for 2-3 seconds. This will melt the solder on the wire along with the solder on the surface – joining them. Once you see the solder flowing remove the iron while keeping the wire in place for a few more seconds to allow the solder to solidify. Moving the wire before solidification could produce a weaker/cold joint.
Inspect the soldered joint. If there is not enough solder holding the wire to the surface you may repeat the step above while applying some new solder to the joint. DO NOT OVER DO IT WITH THE SOLDER!
You should not see gobs or balls of solder on your joint. If you do you have used too much solder! A gob of solder is no more effective than a sufficient amount.
Again, the joint should be silvery and shiny. If it is not you likely have a cold joint.
Practice tinning and soldering with some scrap wire until you are comfortable before doing it for real. If you can successfully solder two pieces of wire together, you are well on your way!