Part of the RC Airplane Electric Power System Center
I used to think of connectors as the simple part of an RC airplane because they do not make power or move a control surface. The trouble is that they only have to fail once to bring the whole airplane down. I want every connector to be correctly sized, properly soldered or crimped, protected from vibration, and standardized enough that a polarity mistake is hard to make.
This guide belongs to the Electric Power System Center.
Main Connector Jobs
- Main battery connector: Carries the power-system current from the battery to the ESC.
- Motor connectors: Usually three connections between a brushless ESC and motor.
- Servo-style connectors: Carry signal, positive, and negative between receivers, servos, and accessories.
- Balance connector: Lets a charger monitor and balance individual lithium cells.
- Charging connector: May be the main battery connector or a dedicated lead in receiver and ignition systems.
Choose for Current, Not Popularity
A connector must handle the expected continuous and peak current without excessive resistance or heat. The wire, solder joint, mating surfaces, and adapter all become part of the circuit. Oversized connectors add weight and can be awkward in small airplanes; undersized connectors create voltage drop and heat.
Use the battery, ESC, motor, charger, and connector manufacturer ratings as the starting point. Verify the completed electric power system with a wattmeter.
Polarity and Standardization
Choose a consistent battery-connector family for each current range when practical. Standardization reduces adapters and makes it easier to bring the correct batteries to the field. It does not eliminate the need to check polarity. Never assume two connectors are wired alike because they physically mate.
Mark unusual installations clearly. Before connecting a new or modified pack, verify polarity with a meter and compare it with the airplane and charger.
We once had a charger with connectors that looked exactly like the others in the shop, but they were wired with the opposite polarity. The result was smoke. Matching plastic housings told us nothing about the way the wires were connected, and that is why I check polarity any time a pack, adapter, charger lead, or connector has been changed.
Soldering and Crimping
A good joint is mechanically sound before it is protected. Use the connector manufacturer’s recommended method, adequate tool capacity, clean materials, and heat-shrink tubing that fully covers exposed conductors. Avoid allowing solder to wick far up flexible wire, where it creates a stiff section that can fatigue at the end.
Crimp connectors need the correct terminal and crimping tool. Crushing a terminal with general-purpose pliers may look secure while producing poor electrical contact.
Adapters and Extensions
Every adapter adds contacts, resistance, bulk, and another possible polarity error. Use an adapter for testing or an occasional legitimate need, but do not build a high-current power system around a chain of adapters. Servo extensions should be the appropriate wire size, secured at joints, and supported so vibration cannot work the plugs apart.
Inspection
- Look for darkened housings, melted plastic, loose pins, corrosion, or damaged insulation.
- Feel for unexpected warmth after a ground run.
- Tug-test wires gently at the strain relief, not by pulling connectors apart by the wire.
- Replace questionable parts rather than repeatedly bending pins back into place.