Experimental Electric Vehicles

January 3, 2010

Laying Out the Power Grid

Filed under: 1 — tonyhelms @ 7:43 pm

After a much needed holiday vacation that gave me plenty of time to work on the motorcycle, I can finally post what I have been doing to it.

The speed controller finally arrived in the mail, this is the Alltrax AXE 7245. When considering where to mount the speed controller, especially when high current will be run through it, it is most important that it not be tucked away. The controller is actually constructed of three sides being a heat-sink, therefore it is important that it has ample air flow around the controller at vehicle speed and while at a stop.

While the largest unit being the Alltrax speed controller, it is important to have all of the main electrical components ready to mount so you can organize the entire space accordingly.
The four main components I had to arrange were the speed controller, main fuse, main contactor, and shunt resistor. Keeping the power wiring short was another consideration that went into where they were placed. Keeping the power wiring short will help reduce wiring resistance power losses. Even after making strong quality power wiring and connections there will still be power losses from the wiring alone. To help reduce these minimal losses, simply try to make all the connections as short as possible.

As you can see in the picture above the Master positive from the battery is routed directly to the main fuse holder (black wire on left), this wire is critical that it cannot rub or short ANYWHERE! This wire is completely un-fused, meaning if a short ever occurred on this wire nothing will stop the build up of energy and heat, until a power wire or battery completely melts down, this will usually end up becoming a fire. Proper wire crimping, heat shrinking, wire-looming, and taping is crucial here.

These neat little things are often referred to as “buss bars” or “rigid wires” there essentially the same as a traditional “power wire” but these can supply just as much, if not more current then the equivalent wire size. and they will stay exactly where you install them, therefore they will not rub through, or short to ground.

Buss bars are very easily fabricated, simply get a sharpie marker out and start marking and bending the steel to whatever shape you need, and remember you can use 2 pair of pliers and twist it to make it conform to different shapes. Whenever making these you should use a highly conductive material such as copper or steel, these materials can usually be found at local hardware stores and dont cost too much. Remember to use a wire wheel to clean the contact areas before installation, otherwise it may end up being a poorly conducting surface. When youre all done take the part back off and simply wrap the piece with high quality electrical tape, if you do this in front of a space heater it will help the tape conform to any bends or odd shaped the buss bar has been formed into.

Dont forget to take your master negative battery to a part of the frame, only do this if you are going to be running a negative frame ground source like an automobile.

While you are wiring the power circuits in your EV it is very important to make it look neat and tidy, a messy wire job will end up in a disaster, especially when you have to service or diagnose a problem in the future. Not only that but your fellow EV friends will be very impressed when they see a super professional wire job.

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