Connectors and Cable

By Paul Williams.
Article posted 6th March 2009.

Connectors

The most popular type of connector used in FE powerboats is the gold-plated "banana" plug that you can buy in 2, 3.5, 4, 5.5 and 6mm sizes. This type of connector is widely used due to its low electrical resistance. Not all banana connectors are the same. Although one gold-plated plug might look much like another, there can be quite a difference in the quality - and therefore the current handling capacity and voltage drop - of one plug to another.

Gold-plated power plugs.
Gold-plated banana plugs. Left to right: 2mm, 3.5mm, 4mm and 5.5mm.

I would tend to avoid unbranded cheap chinese plugs for high current applications or when you want the ultimate performance. Instead, go for plugs made for the likes of Schulze.

No matter how much you pay for connectors, if you're completely cack-fisted at soldering then any advantage in buying the better quality types is wasted. Sound, low resistance solder joints are vital. Here's how you do it:

A minimum of a 50 watt soldering iron
Multicore electrical solder
Thin-nose pliers
Heat shrink tube
Hot air gun

Get the soldering iron well up to operating temperature. Tin the ends of the 4mm cable with solder. Holding the plug with the pliers, fill the solder "bucket" on the end of the plug with solder. With the plug still hot, insert the tinned end of the cable and hold the plug and cable in contact with the soldering iron to re-melt the solder in the bucket end. When the solder flows, remove from the iron and allow to cool holding the cable and connector together until the solder solidifies. If you move the cable around as the solder cools, this can cause the joint to assume a crystalline appearance that can indicate a poor joint. You need the joint to be smooth and shiny. File off any excess solder and insulate the plug with heatshrink tubing.

Cable

The basic advice regarding power cables is simple: you want the least amount of cable in your boat as possible, of the greatest practical cross-sectional area . Cable has resistance, resistance causes a voltage drop and a voltage drop reduces motor rpm. So, the more cable, the greater the voltage drop and the less motor rpm you have. Lower motor rpm = slower speeds.

Three different sizes of power cable. Left to right: 2.5mm square, 4mm square and 6mm square. Use the thickest gauge cable appropriate to the type of model.

Use the thickest gauge of cable appropriate to the type of model. For mini oval boats, 2.5mm is more than adequate, for most everything else 4mm is usually ok, but for high performance models use 6mm cable and 5.5 or 6mm connectors.

Excessive cable lengths are not only bad news where performance is concerned. Long cables kill speed controllers. This is a quote from Allan Shillitto on the Astec Models forum:

"The reason is that at the frequencies that the controllers work at the wires have an impedance. The impedance is caused by the inductance of the wires which is directly proportional to the length and the inverse of the diameter. So long thin cables are worst."

Long, thin cables place a huge strain on the capacitors of a speed controller. It cannot be overemphasised how important it is with modern high frequency 3-phase brushless motors and speed controllers to keep cable runs as short as is practically possible, especially given the requirement to include an isolation loop in the power circuit. So, be ruthless. When planning the layout of a new boat, keeping the power cables as short as possible should be a major priority when deciding where everything goes, especially the isolation loop. Place the loop as close as possible to the motor and speed controller, while observing the requirements of the rules regarding loop location on the boat.

This article may not be reproduced wholly or in part without the written permission of the author and www.fastelectrics.net. If you would like to use this article or the accompanying pictures/diagrams please email articles@fastelectrics.net.

Last modified: 08th July 2010 @ 09:05