Harbor Soaring Society

As a long time R/C Modeler and one time Aerospace soldering Instructor, I think that there should be a “sticky” on this specific subject. Read “Safety Considerations” and “Wire and Connector Polarity” below very carefully. I recommend that the “beginning solderers” read this entire set of recommendations at least twice, as some steps are critical and must be done in a particular manner to avoid frustration and even danger of serious injury or damage to battery packs and speed controls. If possible, practice soldering wires to an old Deans connector, carefully following these directions, until you develop a feel for it. Using a small “bridge” of molten solder to conduct heat from the soldering iron tip to connector terminals and wires is a major “secret” that is learned with practice.

Choices of Soldering Iron and Tips- It is necessary to accomplish soldering quickly and to let the work cool to avoid heat damage to plastic connector bodies. Use of a 37 watt or a somewhat higher wattage standard type soldering iron for this kind of soldering is recommended for quick enough heating and promoting good solder flow. A thicker soldering tip with flat sides works better than a thin tapered cone-shaped tip intended for printed circuit soldering. Use of a 30 watt iron requires more practice and skill for these types of connections. Soldering guns are not appropriate for this delicate kind of soldering, somewhat unwieldy and too much heat 

1.      Solder and Flux - Use “electronic-type” 60/40 or 63/37 tin/lead alloy rosin core solder and electronic soldering flux as sold by Radio Shack, etc. Avoid use of lead-free solders, they require more skill to get good solder joints. 1/16 or smaller diameter solder on a roll is best for connector/wire soldering.

2.      Connector and Wire Holding Devices- A pair of vice-grips can be adjusted to gently but firmly hold the plastic body of a Deans or similar connector while soldering connections. A small model-work vise or pliers with a rubber band around the handles can also work as a holder. Devices to grip and hold wires in position can be bought or made from stiff copper or aluminum wire and alligator clips. An assistant can also provide a “third hand “to hold a wire or feed solder. With practice, you will often not need assistance or wire holding devices.

3.      Damp Paper Towel -Keep a slightly damp pad of paper towel handy while soldering. Tip of iron must be wiped often to keep it clean and shiny and able to transfer heat well, and not contaminate the solder joint.

4.      Safety Considerations - Every precaution must be taken to keep from shorting battery pack wires or connector terminals together. Leave insulation on one wire while stripping, tinning, installing heat shrink tubing, soldering to the connector terminal and shrinking the heat shrink tubing, Then, do the same to the other wire as described below avoiding any shorting of the battery pack with wire strands, excess solder or the tip of the iron. (See Wire and Connector Polarity, item 8 below)

5.      Stripping Wire Insulation - The object is to remove insulation from wire without cutting or damaging wire strands. If you disturb the strands, twist them back into position with tissue to avoid contamination. Strip, tin, and solder only one wire at a time to help avoid shorting the pack. (See Safety Considerations 4. above). There are number of wire stripping tools available. Inexpensive strippers are not much better than a sharp hobby knife. Cut through the insulation, without cutting the wire strands, and twist insulation off of the wire strands.

6.      Tinning Wire Strands - The object is to fill the exposed wire strands with solder to promote good solder flow during final soldering of wire to the connector. It is not desirable to overheat the wire causing solder to “wick” up under the insulation and make it stiff and subject to breakage when flexed like a single strand wire. Apply a dab of soldering paste to the wire , melt some solder onto the tip of the iron, lay the wire onto the iron tip and quickly feed a little more solder to fill the wire strands then remove from heat as soon as possible to prevent “wicking” ( stiffening of wire under the insulation)

7.      Heat Shrink Tubing – Heat shrink tubing is available from electronics suppliers like Radio Shack and auto supply stores. Use of electrical tape instead of heat shrink tubing is not as neat or reliable as it can tend to unwrap over time and expose soldered connections. Keep a supply of heat shrink insulation tubing in various diameters from 1/16” to 1/4”. Use a hobby heat gun to shrink the tubing tightly over soldered connections to insulate them and prevent any possibility of shorting the battery pack wires together. You must remember to slide the tubing over the wire up and away from soldering heat before soldering wires to connector terminals. If you accidentally shrink the tubing, you may be unable to slide it over the connection. If you forget the tubing, you will need to unsolder the connection, install the tubing up and away from the heat of soldering, re-solder the connection then slide tubing over the connection and shrink it.

8.      Wire and Connector Polarity – (Very Important) Looking at the end of a Deans Ultra connector, the slots or terminals are positioned to resemble a letter “T”. The top of the “T” or horizontal terminal is normally the positive terminal to which the red or positive battery wire is soldered. The vertical terminal is normally the negative terminal to which the black or negative battery wire is soldered. Battery packs and speed controls with pre-soldered connectors follow this industry standard. Battery charger cables with Deans Ultra connectors also follow this standard polarity. You must not solder a red wire to a vertical terminal or black wire to the horizontal terminal. To do so could result in destroying a speed control or battery pack, possibly causing a fire or injury.

9.      Soldering Wires to Connector Terminals – Clamp the plastic connector body gently but firmly in a small vise, a pair of vise-grips or a pair of common pliers with a rubber band around the handles. Apply a small “blob” of solder the connector terminals by putting a dab of soldering paste flux onto the terminal, touching the clean shiny iron tip to the terminal and feeding a enough solder to the junction of the iron tip and the terminal to form a small “blob” of solder. Important, now slide a piece of heat shrink tubing onto the wire up and away from soldering heat. Now wipe the iron tip, position the wire against the terminal and touch wire and terminal with iron tip while an assistant feeds just enough solder to the junction of the iron tip and terminal to form a nice solid connection. If you don’t have an assistant, there are various holder devices you can buy or make using stiff heavy guage copper or aluminum wire with an alligator clip to hold wire in position while you hold iron and feed solder, You will need to hold the wire very steady for about one second to let solder solidify after you remove the iron tip from the connection. If you move the wire while solder solidifies, you may have a fractured unreliable solder connection. You would need to reflow the solder and hold wire steady to make the connection good. Once the solder joint has cooled for about 5 seconds, you can slide the heat shrink tubing over the connection and shrink it to finally insulate the connection. At this point you have soldered one of the wires to one of the connector terminals and insulated the connection. Check to make sure that you have soldered the wire to the correct terminal per 9 above. Slide heat shrink tubing onto the other wire, solder remaining wire to the other connector terminal and shrink tubing over the connection with the heat gun. Job completed