Soldering electrical connectors onto motor wires, battery wires and speed control wires isn’t hard to do when you know the steps, and the first step is to think clean. Metal, by nature, oxidizes, and the metal wire and connector must be bonded to each other, not to any corrosion that may be on the surface.
Quality connectors are gold plated because gold doesn’t corrode like copper, which turns green; aluminum, which turns white, or steal, which turns brown. Since electrical solder loves to stick to gold, there’s little you need to do to prepare that part of the job. If you have lacquer thinner on hand, just gently wipe the metal ends of the gold plugs to remove any oil or dirt.
The tip of the soldering iron should be “tinned.” Do this by touching solder to the hot tip of the iron to coat it with molten solder. If the wire you will solder has silicone or PVC insulation, it has been protected and won’t need any cleaning. The wire should also be tinned. Once the insulation is stripped from the wire, twist the braids to keep the bundle from fraying.
Apply flux to the bare wire, then tin the wire with a coating of solder. Flux is essential because it helps prevent the metal from oxidizing and helps direct the flow of molten solder. Touch the tip of the iron to the flux-coated wire. The point of contact will sizzle and smoke due to the fast transfer of heat, and the copper wire will quickly turn bright silver. The exposed wire should have a healthy coat of solder.
The tinned wire is now ready to be bonded to the connector, so tin the connector in the same manner as the wire. When the wire and connector are both coated with solder, they can be heated and bonded almost instantaneously.
With both the connector and wire tinned, slide on any heat shrink tubing now. Bring the two points together; flux is no longer needed. Use an Excel Extra Hands or similar vice-type tool to position the wire and connector so that they touch each other, then simultaneously apply heat from the iron to both parts. Make sure that the tip of the iron, coated with a tiny amount of solder, contacts both the wire and connector so they heat at the same rate. The wire and connector will bond when you see bright silver solder flowing between them. Remember not to leave the heat on too long or it will melt the connector. A little bit of heat, a little bit at a time, ensures a neat and solid connection.
Besides being neat and clean, the joint has to be strong. If the heated solder doesn’t turn bright silver, it will only surface-bond. It can crack and break off easily. Bright silver solder bonds securely. It’s smooth and has no jagged edges. Strong solder joints prevent broken wires from causing shorts and permanent damage.
Check your work
Always double-check your work before sealing the connections with heat-shrink tubing. First, check for correct polarities, then tug on each connection just firmly enough to ensure its security. Finish your handiwork by applying heat to the heat-shrink tubing.
30-watt soldering iron
25-gauge lead-free electrical solder
Electronic soldering flux
Excel Hobby Blades Extra Hands with Magnifier
Great Planes Wire Cutter/Stripper
Emery board or emery cloth
Damp sponge or soft damp cloth
1. Clean contact points
2. Apply electronic flux to contact points
3. Tin contact points separately
4. Slip on heat-shrink tubing
5. Join the two tinned contact points with solder
6. Insulate bare connection with heat-shrink tubing