A common source of problems when using motor controllers is wiring that is not terminated properly. This results in problems like shorts and poor connections. We will cover several solutions to these problems below.
Why Proper Termination Matters
Bare stranded wires might seem like the way to go when wiring your motor controller. After all, this is how your battery and motor wires are likely to come from the factory. However, this can present several problems. One such problem is that a strand or two may come loose and cause a short at the screw terminals. It only takes one loose strands for this to happen. Another potential issue is that the wire may not be secured and can come loose as your robot moves and jostles around. If the wire comes loose if can possibly cause a short somewhere else on the board. Loose wire ends can also end up touching the heat sink and result in the wire being heated.
Figure 1: This photo shows the wrong way of wiring an open screw terminal. The wire comes in from the right side and strands of wire are exposed.
The first solution to the mentioned problems is to twist and then tin the wire ends with solder. This will solve the stray strand problem and also ensure a solid connection at the screws terminal. This is one of two potential methods we will discuss.
Figure 2: The red wire is untinned and the green wire is tinned.
The second solution is to use crimp on terminals. These can be used with the open type screw terminals. They come in two broad types: the forked type, knows as spade terminals, and ones with a closed ring. If you only occasionally remove connections to the motor controller a ring type terminal works well. You will need the appropriate terminal connector and a matching set of crimpers to add these to your bare wires. Below is a table of suggested ring terminals based on wire size along with their Digi-Key part numbers.
Table of suggested ring terminals based on wire size. Diki-Key part numbers and links are included.
Figure 3: An example of ring terminals.
Photo by Mataresephotos / Wikipedia Commons
If you do need to use a bare wire connection on open type screw terminal there is a right way and a wrong way to do connect it. The right way is to loop the wire in a clockwise direction before you tighten the screw. This allows the wire to snug up as the screw is tightened. If you loop it in the counter-clockwise direction the wire will not be as secure and can also fray causing the shorts we mentioned earlier. Be sure to twist the wire ends together before you loop the wire around the screw.
Figure 4: This photo shows the proper wiring for an open screw terminal. The wire comes in from the left side and is carried around by the rotation of the screw.<
Now you’re armed with the knowledge of proper wire termination for your motor controller. You should experience no faults due to improper termination and should have reliable connections that don’t need tinkering with.