HOW TO BUILD AN ELECTRIC BIKE

How I Built My First Electric Bike

My goal was simple: build an electric bike that everyone can replicate with minimal cost, without electrical know-how, but be powerful and reliable at the same time.

• By Parker Jardine
• January 14th, 2015 1:01 pm
• Category Energy, Hacks

One day I became fed up with all of my excuses for driving to work every day. During the summer I would ride my bike, but it would come in waves without any consistency. There is one huge hill climb to get to my work that is quite daunting, and is the main reason why most people take a vehicle, especially when you are running late. One day I said, screw it — I am going to put together an electric bike.
I recently read an article about what the average person can do to prevent climate change and a green commute was at the top of the list. Besides everyone needs a project to work on during the winter or rainy months.
But how would I build a bike? What motor would I use? What batteries should I choose? All these questions and more can help you build your own bike.

Getting Started

If you type “diy electric bike” in your favorite search engine, you will find a barrage of information from electric drill bikes to the top 10 most expensive electric bikes. The information can be daunting and lead you in many directions, only to cause confusion with so many choices.

My goal was simple: build an electric bike that everyone can replicate with minimal cost, without electrical know-how, but be powerful and reliable at the same time. Another major goal was to decrease complexity over other builds, which in turn would make maintenance easier over time.http://youtu.be/sroxzNI4fmY

My Parts List

• Electric Mid Drive, 750 Watt Bafang BBS02 Kit with Led display and 25Amp controller and thumb throttle  eBay seller gregj8127 imports these to sell in the USA. Or you can view kits here
• Prismatic Lifep04 12 volt 20Ah batteries (4)
• Smart LED Balance Boards (16)
• Series Connector Bars (3)
• LifeP04 smart battery charger
• Battery  box
• Titan Straps (2)
• Key starter switch
• Inline 30 Amp Fuse and holder

Choosing a Motor

In my opinion, the first item you should decide on is the electric motor. Traditionally the hub motor has been the most popular choice for electric bikes. With the hub motor you have two choices, geared hub motors and direct drive motors. Each type has its own pros and cons which can be viewed here: http://electricbikereport.com/electric-bike-direct-drive-geared-hub-motors/
A relative newcomer to the scene is what is called a mid-drive electric motor. The mid-drive electric motor is not installed in your front or rear wheel hub, but attached to your front drive system. The main advantage to this system is the ability to use your own bike’s rear derailleur to change gears. The motor has its optimum rpm speed which you can sense when riding the bike. When the chain spins really fast, but your speed doesn’t increase, you simply change to a lower gear in the rear to get the perfect combination.
I chose to use the mid-drive Bafang BBS02 motor kit. The downside to this design and kit is the fact that the pedal-assist mode can “crunch” your rear chain rings in the back when shifting. You typically have to pedal your bike to get the rear derailleur to change chain rings. The controller then detects that you are peddling your bike and then spins the front ring. You then hear a “crunch” from the back chain sprocket as it is shifting gears. There are a couple of ways around this design flaw:

1. The manufacturer needs to detect not just the fact that you are pedaling, but also applying a certain amount of force at the same time before turning the front chain ring.
2. You can turn the pedal-assist mode off while changing gears, or turn pedal-assist mode off entirely.
3. Some people just tap the breaks, which kills the motor. Within this short amount of time you can shift several gears
4. Buy or use a Shimano Nexus 8 speed rear hub. This allows you to change your rear gears without pedaling.

For me, the benefits of this design outweighed the negatives. In the following videos, I demonstrate how the bike performs with the Bafang BBS02 mid-drive motor kit. I would like to make two notes: I am aware that I need lube for my chain (taken care of), and yes a bigger hill is needed. Enjoy!

(Most) Any Bike Will Do

The beauty of this electric bike is that you can install the kit on pretty much any existing bike with a 68mm bottom bracket shell width. Choosing the bike to convert into your new electric bike is really fun. If you have an existing bike to use, you can save a bit of money, which is what I did. You can also find a good bike at your local bike shop or even Craigslist. Here are some things to look for when choosing components for your next e-bike:

• smaller wheels generally means stronger wheels
• more spokes in your wheels means stronger wheels
• fat tires provide smoother ride when your bike is loaded down with weight
• front disc brakes are recommended for stopping on steep hills
• look for bikes that contain eyelets for rack attachments
• the more weight your rear rack can support the better for supporting batteries and other gear
• extra wide handle bars are good for mounting all of your e-bike accessory and lights
• If you buy a used or new bike, and you are going to use a mid-drive motor kit, don’t invest your money into the front derailleur or one with a nice double or triple crank set up front. You will be removing these components, if using the mid-drive kit. So, look for single speed bikes or fixies. The problem with fixie bikes is that they are generally a minimalist bike without eyelets for rack attachments etc.

After choosing your desired bike, the first step is to remove your chain, front crank set, and bottom bracket. Some chains are connected with a quick link which can easily be pulled apart. Other chains may require a chain tool to remove a link from the chain to get it separated.
The next step is to remove your crank set. This usually involves using a hex tool to remove your crank arms, and then using a crank puller tool to pull the crank assembly away from your bottom bracket. Once you have the crank set removed from your bike you will need to remove your bottom bracket. The bottom bracket will generally unscrew using a special tool that matches your specific bottom bracket as there are several different models. Now you are down to the hole in the bottom of the frame. This is a good time to clean this part of your bike before you attach the new mid-drive motor assembly.

Close-up of Bafang BBS02 motor installation on bike

Unless your number one love in life is bikes, you probably don’t have every bike tool needed for this project. It is a really good idea to make friends with a bike mechanic at your local bike shop. Tell them what you are building and see if they have any good ideas. I did remove my crank set myself, but did not have the bottom bracket tools. I took my bike to the bike shop to have them remove my bottom bracket and install the mid-drive motor kit. I could have purchased the tools to do it myself, but he was able to do it for me in as little as five minutes. They didn’t charge me because it was so quick — and because they would be making money on all of my bike accessory purchases (which is a really good business model and great customer support).
The mid-drive kit slides through your bottom bracket and is screwed down tight on the other side with 2 hex screws tightened to 35-40nm of force. This is quite a bit of force and is typically how much force one person can generate with a hand tool using all of their might. One thing to note is that after two weeks of riding my bike, I had to re-tighten the mid-drive hex screws. I also had to re-tighten the screws holding my rear rack to the bike. Re-examining your bike for loose components is necessary for any bike, but even more so for electric bikes because the forces applied to them tend to be higher over time. Once you have the mid-drive kit installed on your bottom bracket the rest is pretty easy. Simply route the cables coming out of the motor to the designated locations on your bike.

Stabilizing and Securing the Battery Box

The bike that I chose already had a setup for a rear rack. In the past this bike has been used for bicycle touring and I was confident in the rack’s ability to hold weight. I simply installed my rear rack and set the battery box on top of the rack. This was not a very good idea because the battery box was sliding all over the place.
I decided to make my own cargo-style rear rack with a wooden platform. To do this I took a 1″x 4″ board of “strong” wood, maple, I believe, and cut it to the desired length. I then determined the exact location for this platform on my rack and used perforated metal hanging strap that you can buy at any home improvement store to attach the bottom side of the platform to the rack. I used short wood screws and cut the strap to small lengths and screwed the rack and platform tight in several locations.

Battery-box holder: the top plate supports the weight, while the rectangle keeps the battery box in position

This platform now solved the weight and stability issue of the battery box, but the box could still slide side to side and fall off pretty easily. I measured the battery box and determined the length of small pieces of 1″x 1″ wood strips that would wrap around the battery box and be screwed together forming a rectangle. I then determined the desired position of the battery box on the platform and screwed down this wooden rectangle onto the platform using short 1/2″ brackets found at the hardware store. The battery box then fit right into the rectangle like a glove. All that is left is to use some Titan Straps to cinch down the battery box to the rack and she shall not move!

Side view of custom wood top mounting plate attached to rack

Engineering a Battery Pack

When building an electric bike, typically you want to keep your weight as low as possible. However, engineering a battery pack to fit between the frame triangle takes a bit of time, money and expertise. You can buy the em3ev battery triangle packs from Paul in Hong Kong, which offer high power and capacity. The ping battery is another option, however both of these batteries suppliers have to ship to the USA for around $100. It was really a toss-up between these two builders in the end.
I ran across a forum on http://www.bikeforums.net about using prismatic LifeP04 batteries for solar power storage (http://www.bikeforums.net/electric-bikes/900011-first-ebike-build.html). The second comment by turbo1859 caught my eye. I paid close attention to how he has previously constructed his battery packs using the prismatic cells. I ultimately chose these batteries for the simplicity of balancing the cells, and the ability to remove or replace cells in the future without having to rip apart the battery pack and remove the cells that are soldered together. I could simply replace a cell without having to solder a new one in series or parallel within the pack. The problem with these batteries is they are not lightweight. I believe all 4 packs weigh about 26 pounds.
The Need for Battery Management Systems (BMS)
Almost any time you build a lithium battery pack you need a BMS. A BMS requires a wire to connect to each cell to balance the voltage or state of charge across the battery pack. Each one of these wires connects to the BMS circuit board to provide overcharge protection, discharge protection, overheat monitoring, short-circuit protection, and balancing functions, etc. During high discharge and charge sequences, the cell voltage and capacity can differ between cells, thus the need for a BMS.
Using the balancing cells, a smart charger, and the motor cutoff thresholds, I would be able to get away with not having to use a BMS.
This modular functionality in my opinion is very important. And the fact that batteryspace.com’s products are designed and assembled in the USA is important to me. So I made my decision to go with these batteries. Of course I would have to buy four 12-volt packs and 16 LED balancing modules. I would also have to buy a 52-volt smart charger to charge all of the batteries when I wire them in series. A 52-volt charger would prevent me from having to babysit the batteries during the charging process, which was really important to me. The smart charger automatically cuts power when the batteries are full, preventing overcharging issues.

Batteries connected in series for the first time with battery charger hooked up to positive and negative terminals.

Once I received my batteries I tested each cell and each pack of 4 cells for voltage differences from the manufacturer. I then connected the four packs in series to quickly test the smart charger. Once I verified that the smart charger was working properly, I then started to install the LED balancer modules on each of the 16 cells. Each of these balance modules installed without any issues. Each 12-volt four-pack then needed to be connected in series to each other to make the 48-volt pack required to run the motor. The extra connector bars that I ordered didn’t quite reach from one battery to the other, so I flattened them down with a hammer to extend their length. The length was perfect and it also allowed me to put a small piece of cardboard between the batteries for shock protection.

12-volt battery pack with LED balancer modules

After the batteries were connected in series I then wrapped the battery pack with duct tape to secure them together. After adding sufficient packing material to the empty battery box, I slid the battery pack into the box with a nice snug fit. I decided to add a 30 amp inline fuse to the positive battery terminal of the battery pack. You could also add the fuse to the negative terminal, but I believe it is standard to be installed on the positive terminal.

Battery pack stuffed into battery box with foam packing for snug tight fit

I then drilled a 3/4″ hole in the battery box to mount the keyed switch, followed by connecting the positive lead cables to the appropriate terminals on the switch assembly as indicated on the package material. With each wire connection, I made sure to use heat-shrink tubing at each cable termination. I then measured, cut, and installed the positive and negative cables needed to extend from the battery box to the XT90 connector and cable that connects to the motor. The motor came with an extra female end XT90 connector which I soldered onto the negative and positive cables from the battery box. I also use this female XT90 connector when charging the battery pack using the smart charger, since it has alligator clips and connects quite easily.

30 amp inline fuse holder and key switch connections

View of battery box, keyed switch for a bit of added security.

Creating a Custom Kickstand

The only thing left was to add a double kickstand and some lights. The kickstand is really important for a bike of this weight. In my case, the kickstand makes it easier to unload and load my young son from the bike trailer I pull behind me. I simply flip down the kickstand and then the bike is stable.

Coolest mod to tire lever — double kickstand top mounting plate

The problem with my bike was that there was not a top mounting plate for a kickstand. There was, however, a small opening in my frame for the bolt to extend through. You have got to check out the tire lever that I modified to become the top mounting plate for the kickstand. It works really well, and I have not had to re-tighten or mess with it yet! Simply cut a tire lever with a hack saw to match the width of your frame. And then carve a similar curve with a knife or saw on the other side. Tire levers have this circular indention on one side, and that is exactly where I drilled my hole to fit the kickstand bolt. And voila! The kickstand works great!

Driven to Ride

In my experience so far, I have had to charge my battery pack once a week. Even with pulling my child behind me to school and back everyday. However, I only ride about 7 miles round trip each day, but there is one major hill that drains the battery juice.

First working version of e-bike, with built-in mounting system on rear rack.

Now that I have built this bike, I think that I overdid the battery pack a bit with the weight, but the increased capacity, once a week charge requirement, and other pros have justified my positive opinion of this design. The bike literally helped transform my life. I no longer drive to work everyday, I ride my bike instead. Even during the cold winter months, I bundle up my 2-year-old son and transport him to school. I’m riding 90% of the time, which has drastically cut the carbon emissions I was generating.