How to Build a 72Volt Electric Motorcycle

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Introduction: How to Build a 72Volt Electric Motorcycle

No gas, no oil and almost silent. 72 Volts, 70mph of pure fun. This is how I built an electric motorcycle.

Step 1: Why and How

I only work 3 miles from home but with gas prices getting out of control, I thought it would be great to have an electric vehicle. I've always wanted a motorcycle and decided that making an electric motorcycle would be a good EV project, keeping costs down, and be fun to ride.

This project took about 3 months of research and development (not counting waiting for parts to come in or help from a friend with the welding). All in all, it cost about $3000 to buy and build. This may take a long time to pay off in gas savings, but if you add the fun of building and all of the environmental benefits, it was well worth the effort. With a top speed of over 70 mph and 10 miles per charge, this vehicle is perfect for me. The following instructable will not give you exact step by step instructions, but if you have some mechanical skills and welding ability you should be okay. A little knowledge of motorcycle maintenance wouldn't hurt, too. However, I just read the user's manual and learned as I went.

Step 2: Components and Tools

Every motorbike is different but the basic components can be the same. Below is a list of the parts I used and where I got them, but you will have to do some research to figure out what fits your bike and requirements. Check out the photos at the bottom to see what I bought and the EVAlbum for other electric vehicle projects.

Frame: I looked at many different bike styles and decided on a 1984 Honda Interceptor for a few reasons:
1) I like the style of bike, not a total crotch rocket but not a hog either, with room for batteries inside the frame.
2) The seller on Ebay was close to my house. And the bike didn't run, so it only cost $600. If you have an old bike or someone will donate one then that's great--but for the rest of us, try the local paper, junk yards, Craig's List or ebay motors.

Motor: After reading other EV bike specs (and knowing that I wanted to go faster than a moped), I chose a 72V Advanced DC motor, because it's weight and dimensions where good for my frame. I ordered it online fromthunderstruck-ev.com.

Batteries: I went with 6 Yellow Top Optima batteries from remybattery.com because they are sealed and have received great reviews. After making cardboard mock ups of the D23 model I realized that there was no way six full sized batteries would fit and still look good. I ended up getting the D51 model. Half the size and weight but also half the storage.

Controller: You have to match your controller to your voltage but the amperage is up to your budget. More amps = more power and more cost. It seems that there are only two real choices: Alltrax or Curtis. You'll have to decide for yourself, but I went with the 72V 450Amp Alltrax from cloudelectric. Don't waste your time trying to build a potimeter on an old throttle--just buy a pre-made one and be done with it. I got the Magura 0-5K Twist grip throttle from cloudelectric.com

Charger: You have to match your charger with your voltage but the speed of charge in Amps is also up to your budget. I went with a Zivan NG1 from EVAMERICA I have recently switched to six individual 3amp Soneil chargers to help balance the batteries.

DC/DC Converter: It's safest to run with a DC/DC converter and an extra 12V battery backup but motorcycles have limited space so I am only using the converter. I purchased a Sevcon 72V Input 13.5V output from evparts and it has working perfectly.

Fuses: You'll want to get a fuse that matches your setup. I bought model ANN 400 w/ holder from EVAMERICA.

Contactor: This is a device that you hook up to your existing key ignition on 12Volts and it will close the loop so you get the full power to your controller. I bought an Albright SW-200 from EVAMERICA

Battery cable and connectors- I bought about 10 feet of 2 GA wire from WAL-MART and cut it to length. Using Lugs from cloudelectric I soldered and used heat shrink tubing on each end. I highly recommend battery terminal covers for safety.

Instruments I chose an E-meter(Link 10) w/ Prescaler add on for 72V use instead of a bunch of different meters. As an added feature I wired up the ignition switch to the neutral indicator to show me when the bike was on.

Other parts
Wire - 12GA different colors and heat shrink tubing (large and small sizes)
Electrical tape
Wire connectors
Wire wrap

Tools
Basic shop tools are required such as a socket set, screw drivers,wire stripper, etc. Additionally a volt meter, metal grinder and crimper are used in this project.

Step 3: The Build

Start by removing all of those nasty internal combustion engine parts. Remove the gas tank and using your grinder or other cutting tool to cut out the bottom. This makes room for extra batteries or components. (Make sure all gas is out before cutting) Reference your owners manual so that you don't cut any necessary wires, and try to sell some of the parts to help pay for this project.

Next, make cardboard mock ups of all of your batteries and electronic components to see how and where things are going to fit. Take a look at my pictures to see how I fit everything, believe me that taking the time to make accurate cardboard mock ups is well worth the effort.

Now for the hard part. You need a secure battery box and motor mount. I had a friend weld it up for me and he did a fantastic job. From the photos you can see that he first strung up the motor to allow for minor adjustment to be made before cutting the motor mount plate. After that was cut he made a nice chain and sprocket enclosure with a door and welded them onto the frame.

Next he fabricated the battery rack and gave each battery a swing arm closure to give a tight fit yet still allow me to get them out easily. Half inch foam padding spacers are between each battery to help cushion the stack--but believe me, they aren't going anywhere. The last thing
he did was weld in metal plates for mounting my electrical components.

After you get your motor mount and battery compartment all welded up, take some time to clean up the frame of your bike. I removed any rust spots and chipped paint that I could find. Then I used some metallic gray and black spray paint. This makes a world of difference and costs very little.

I made a fake gas cap and ran the power cord from the charger up the frame and out the top.

Now that you have all of the welding done and your frame looks great, let's install the electrical components and start wiring it up.

Step 4: Wiring

If I tried to explain where to connect every single wire I would get writers cramp. View the wiring diagram that I put together and let me know if you have any questions. This diagram should be pretty accurate to how I built mine, but obviously you are responsible for your project.

Step 5: Last Few Things

Double check all of your connections and tighten every bolt.

I wanted my bike to look as good as it rides, so I had all of the panels painted and custom graphics made up by worldsendimages.

Using a serial cable and laptop, tweak the speed controller program for your riding preferences.

Lastly, I got the bike inspected and insured. (Be prepared for the dealership mechanics to swarm and hit you with a bunch of questions and jokes about failing the emissions test).

I know these weren't step by step building instructions, but that's because of the complexity of this project and variables in component use. My intention was to give you the motivation to build your own by seeing how I did it and make it easier by supplying the parts list and a wiring diagram.

For more photo's and a build commentary visit my website at http://ben.cbccinc.com.

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We have a be nice policy.
Please be positive and constructive.

Tips

I saw on your other thread that you had problems with batteries...did you know that you have to have a special charger for charging Optima Batteries? if you use anything else you will burn up batteries. Even most AGM chargers are not made to charge up optimas....just thought I bring that up.....

Questions

579 Comments

I've finished an EV bike of my own, however, I cannot find a drive sprocket and no guide talks about what sprocket they used. I am running an eTek motor with a 7/8" output shaft and a 3/16" keyway on a 520 chain, likely a common setup... what sprocket did you use? Where did you get it? My project is sitting in the garage until I find one :(

1 reply

Hi, Sorry but I don't know much about the gearing. I had a friend who works in a machine shop get the sprocket for me. It fit so we used it. I thought about changing tooth ratio for more range, but never got around to it. Try asking a few of the people that built bikes over at EVAlbum motorcycles section. http://www.evalbum.com/type/MTCY

I owned the '83 intercepter... Fastest track bike of 83... I miss it too... Hopefully you were able to sell parts from the bike to help not only yourself with funds, but someone who needed parts to get their bike going again... Great motor on those. Hope you had fun

user

i really hope the parts from that interceptor went to a good home to give life to another. Very valuable and rare bikes...

Exactly what I've been looking for to get my own conversion off the ground. Thanks very much for taking the time to post

is there an advantage to wiring the batteries in series and converting the voltage for the bike systems down instead of wiring them in parallel and converting the voltage up for the motor

7 replies

You would get killed on Booster inefficiency going from 12V to 72V.

With 72 volts you can use smaller wires since you wont be carrying as much current. All of your design concerns will be based on Ohms law, Voltage = Current* Resistance. Always best on a mobile system to use as high a voltage as possible where possible. A fighter uses 400 Volt motors for example.

Better off only converting back to 12 Volts to run lights and control things where necessary. Or alternatively use a smaller 12 volt battery that is not part of the 72 volt system.

Wraithsquad, since nobody ever really answered your question, I'll put in my two cents. There is indeed a tremendous advantage. The power that is downconverted to 12 volts to power the control system, lights, etc., is a very small percentage of the total power of the batteries, and therefore a relatively small and inexpensive DC to DC converter will do the job. If you went the other direction the converter would have to be much larger and much more expensive. It would have to handle the lion's share of the load and battery power. This conversion is not 100% efficient, therefore the power lost in conversion would much higher. The current from the battery pack would be at least six times as high, therefore would require larger conductors and would be much more susceptible to resistance losses. I realize your question is almost a year old, but I am new to Instructables. Hope you get a chance to read this reply, and I hope it helps to answer your question.

I think some of you may have missed one of the points regarding the voltage converter. Only the motor is operated directly from the 72-Volts through the controller. The voltage converter is only there to operate the 12-Volt lights, turn-signals and such. The author's approach is probably the best trade-off in efficiency vs. weight, as opposed to a separate 12-Volt battery for the accessories.

Thanks. That makes it make a lot more sense now.  I was not thinking about the inefficiency of the converter

The batteries are connected in series, (pos to neg) to increase the voltage. Voltage is electrical pressure, comparable to PSI in a hydraulic system. The higher the voltage, the better efficiency and performance of a product. That's why you saw cordless tools go from 3V to 7V to 14V and now 18Volts. Wiring in parallel ( pos to pos and neg to neg) is how you jump a car battery. Parallel increases the amperage or capacity of the system while keeping the voltage the same. Flashlight batteries are connected in series (a 5 cell would be 7 1/2 volts). That's why electrical companies transfer power in thousands of volts, less resistance is greater efficiency.

I don't understand what you mean. But I'm no electrical engineer so I doubt I could answer it if I did understand.

user

Assume 12V deep cycle batteries.

Series Connection
6 x 12 = 72 V
72V x 100A = 7.2kW (or ~10 HP)

Designing a motor/controller combination to handle this voltage and current range is pretty easy and relatively inexpensive. There are MANY currently available.

Parallel Connection
1 x 12 = 12 V
12V X 600A = 7.2kW (or ~10 HP)

Although a DC-DC converter can be designed to convert 12V 600A to 72V 100A, it will add significant cost and weight, and will reduce efficiency of the overall system.

A motor could be designed to use 12V 600A, but it too would be less efficient because...

Resistive losses are a function of I*I*R, so as current increases resistive losses go up FAST. The lower you can keep the current, the better. That is one reason why AC power is transmitted over the grid at very high voltages and then stepped down locally.

What power batteries and motor do I need to get in order to get at least 50 miles per charge

1 reply

I'm not sure, but I would say a lot......

sir,i want to build a electric motor cycle which should have top speed of 50-60mph and it should have a mileage of 70-80 miles per charge would anyone can suggest me required motor,batteries and controller set ups

Glad I came across this site. There really is hope. How much does the motor weigh?

3 replies

72V Advanced DC AC4-4002 10”x 6.7” 47 Lbs from thunderstruck-ev.com

Just out of curiosity, have you ever thought about a good generator, like off of a car or something?

Car alternators really aren't all that good. There are better options, though with something like this, one might like to go custom. Maybe use permanent magnets instead of coils, that also would aid in battery life. That's kinda intentional though, like the 18% fuel efficiency they have so you have to buy more gas and your engine wears out sooner.