You can use the standard controls that are on your donor bike, with the addition of a kill switch that controls the power to the contactor and a high-voltage main cutoff switch. Often, you’ll see the addition of some fairly sophisticated monitoring devices like the Cycle Analyst, which reports battery state of charge and estimated range, along with speed. It even serves as a data logger and provides GPS information for plotting data over the course of a ride. Some owners just run a simple voltmeter.
Lead-acid batteries can indicate state of charge by their voltage, to the practiced eye, but lithium-ion technologies need more sophisticated monitoring to provide an accurate state of charge. Because the voltage stays pretty high throughout the charge/discharge cycle, it’s not a very good indication of lithium SOC.
For this motorcycle, the throttle is a simple twist-grip Magura matched to the controller we’re using. It slips over the bars, just as the stock gas throttle did, and is controlling a fairly simple 0- to 5-ohm potentiometer inside the twist grip. This gives you direct electrical control of the motor speed controller, eliminating any cabling other than a relatively fine electrical wire.
The battery propulsion pack voltage is too high to power the lights and horn, so you’ll need a 12 VDC power source. Do not just connect the lights to one of your 12 V batteries, since it will dramatically affect the balance of the pack, leading to premature battery failure.
A simple solution is to just add another battery, independent of the main pack. (Naturally, you’re going to have to add another simple 12 V charger for this, but a simple 12 V “wall-wart” type charger does nicely.) Another common and less heavy method is to add a DC/DC converter, which will take the high voltage of your main pack and step it down to 12 V.
The controller, along with the contactor and the main fuse, is usually mounted on the top part of the frame and covered by the tank. Neatness translates into safety—if you give this some detailed consideration, there’s less chance of making the wrong connections and high-voltage connections are less likely to come undone. Well-routed wires also minimize chafing and breakage.
On a medium-sized bike, there’s likely room to mount the chargers onboard, in our case above the controller and contactor. This allows you to plug in wherever you park the bike to get an “opportunity charge.” Even if you give it just a little boost when you’re having your morning coffee and donut, it can make the difference between an exhilarating ride home or finding yourself babying the bike back to the garage.
Typically, you need to use at least 4 AWG high-voltage cables for all of your propulsion applications. In some cases, 2 AWG is used, and if you have doubt, err on the side of bigger. If your cables heat up at all in use, they certainly need to be increased.
It’s essential to work with a good wiring diagram. You may be able to find information on various wiring configurations on common EV controller manufacturer websites. The Alltrax AXE controller site, by far one of the most commonly used, is where we started, and then made slight modifications.
The devil is in the details, and as you build your electric motorcycle, you’re undoubtedly going to have questions and challenges. The best place to look for help (and do your basic research) is in online communities. ElMoto.net is a very authoritative online group for electric motorcycles—a great group of generous people with vast experience. For general EV technology, Endless Sphere Technology has an enormous amount of information.
Sign up, and start reading. Almost every question will probably already have been asked and answered, so start with the online search feature. Once you get a feel for the group, introduce yourself and your project, and ask away. Just prepare to be bombarded with advice and opinions. Be prepared with photos of your build, too. As the saying is often repeated there, “Photos, or it didn’t happen!”
Another great resource is the EV Album site where you can browse hundreds of projects like your own, and review the specifications, component combinations, and performance results. There’s a lot to be learned from seeing what others have done—what’s worked, and what hasn’t.