Cabling it up!
Wiring up the power system of the motorcycle is fairly straight-forward. It just requires using thick power cables that are connected with nuts on the motor and batteries, and nuts and bolts on the motor controller.
You will want to use what’s known as welding cable. Welding cable has many fine strands of copper cable inside. It’s designed to carry high current, but it is also very flexible, making it easy to work with. Other types of copper cable are very stiff, may not have the right type of insulation, and aren’t as easy to crimp to. Welding cable is available at welding suppliers, good full-service hardware stores, and some building supply stores.
The thicker the cable, the more current a cable can pass through it without heating up. Cable is commonly rated by American Wire Gauge. That measurement is a number wherein the higher the number, the skinnier the wire, and the lower the number, the THICKER the wire. Typical household electric wiring for 15 amps might be 14 ga, but electric vehicle cabling might need to be able to handle hundreds of amps. The motorcycle uses 4 gauge cable. It’s thick enough to carry the required current, but still be affordable. Thick cable can get pricey fast. (My electric car project uses recycled 2/0 cable!)
Get crimp-on power lugs that match the size of the cable you are using. They are available at the same place you got the welding cable from. 4 gauge is common enough to find locally. Make sure that the bolt hole in the lug is the right size to match up with the power connectors on the motor, the controller, and the batteries. If the various connectors are different sizes, get the appropriate number of lugs required so that you have enough lugs to fit all system components correctly.
You will need a mechanical crimper designed specifically for these heavy lugs. They usually come in two styles – “bolt-cutter”, and hydraulic.
The ones that look like large bolt cutters (long handles, small, jaw, almost always painted red for some reason….) work well and are fast and easy. They can be a bit pricey to purchase. They can sometimes be rented from full-service hardware stores. I borrowed one from a friend.
Hydraulic crimpers are typically hand-held with a small cylinder like a mini bottle jack. You pump the handle repeatedly to make hydraulic fluid crush the lug onto the cable. They have interchangeble jaw inserts for various diameter cables. The can be purchased fairly affordable at import tool stores like Harbor Freight.
To make power cables for the cycle, you need to know how long each cable is. Measure the distance between the two components using a flexible table measure or a piece of string (it’s almost NEVER a straight line between anything) You might want to account for having cables follow the shape of the frame or all be on the same side. In general keep cables as short as possible.
Cut the cable to length. Thick power cable usually can’t be cut with a small wire cutters. A bolt cutter will work fine, but the best tool I have used is a Sears Robo-Cutter. Any other type of large, sheering cutter will work fine.
On the end of the cable, slide on a piece of shrink tube, large enough diameter to go around the lug, and about an inch or so long. Then, cut back the insulation of the cable so that the lug can fully slide on, without having any left over bare wire. I used a utility knife to trim back the insulation, but if you plan to do lots of this in the future, you can buy a special wire stripper designed for heavy cable.
Crimp the lug on with the crimper of your choice. On some styles of hydraulic crimpers, they won’t release until you have FULLY crimped the lug. On “bolt-cutter” style crimpers, certain sizes require you to crimp twice.
Slide the heat shrink tube forward to cover the crimped part of the lug and the beginning of the cable insulation. Hit it with a heat gun or hair dryer set to hot so that it shrinks into place.
Physically connecting the cables
Connect all the cables, following the diagram provided in the motor controller manual. All four batteries in series – one to the next to the next to the next. Batteries to the controller. Controller to motor.
Without the main power turned on, the only concern electrically is that the batteries themselves always have power and that anything attached to them can carry current. Do not touch any power cables to the frame of the cycle, as that is the easiest accidental short-circuit. (Wear safety glasses whenever working with batteries and power connections. I also highly recommend wrapping the handles of wrenches that you use on the project with electrical tape, heat-shrink tubing, or other non-conductive material.)
Once the cycle is cabled up, you only have to check things over and test it all out before you can go for a ride!