Weekend Project: Build your own budget-friendly electric bicycle for under $500
Electric bicycles make commuting around cities and urban areas much easier, but the good ones can be quite hard on your wallet. High quality electric bicycles by top brands like Trek’s Super Commuter 8s or Raleigh Redux IE offer both high performance and high quality in a sleek package. However, with top-end electric bicycle prices from $3,000-$5,000, that extra quality does not come cheap.
On the other end of the spectrum, cheap electric bicycles imported directly from Asia and shipped domestically in the US offer the most affordable options, starting at around $500. We’ve previously reviewed these super-budget electric bicycles, and the verdict often comes back the same – ebike parts: decent; bike parts: mediocre at best.
To put it simply, there just aren’t that many different electric bicycle motors, controllers or batteries out there for manufacturers to choose from, so they all basically draw from the same pile of mass produced, decent quality components. But to keep the price of these cheap electric bicycles as low as possible, corners must still be cut. And in these cases, the only corners left are the bicycle components.
The frames on these bikes are usually not bad, but the bolt on components leave much to be desired. Suspension is little more than a spring in a tube, seats are harder than park benches and brake components bend and creak in ways that, well, just don’t inspire confidence.
While these budget ebikes are often adequate for short trips and as a backup form of transportation, they just don’t cut it for most seasoned cyclists looking for higher quality bikes with added electric assist. For anyone looking to replace their car for many of their around-the-town trips, a better quality bike is a necessity.
Thankfully, for those creative individuals out there that don’t mind turning a few wrenches, you can easily combine the best of quality bicycles and quality ebike components to build your own high quality yet budget-friendly ebikes.
Electric bicycle conversion kits are available that allow a cyclist to convert a standard pedal bike into an electric bicycle with the same performance as retail electric bicycles, but at a fraction of the price. A decent electric bicycle conversion can be performed for the cost of a budget ebike, sometimes even less. The benefit to this method is that you can start with a bike you already own, which will almost always be much higher quality than the bikes used in budget electric bicycles. You also have much more room for customization and choosing the exact bicycle to fit you best, or even go with something odd or unique, like a two person tandem bicycle. I actually performed a DIY electric bicycle conversion on a tandem bicycle and it was a hoot – when I could find a partner to ride it with me!
Most electric bicycle conversion kits include everything you need except for the battery. The battery itself is probably the most important and expensive part of an electric bicycle, so it’s nice to be able to choose it separately. We’ll discuss both of these components in more detail below, starting with the battery.
Choosing an electric bicycle battery
The main parameters you’ll need to consider for your battery are the voltage and capacity. An electric bicycle’s battery voltage is usually measured in 12V increments ranging from 24V to 72V. The higher the voltage, the higher the ebike’s power and speed. 24V ebikes are fairly weak and are really only sufficient for low speeds and flat ground with light riders. My wife isn’t what you’d call a thrill seeker, so I built her a nice, low power ebike with this 24V battery designed to mount easily on the seat tube of folding bicycles.
My wife’s ebike with its 24V seat post-mounted battery
For those desiring a little more speed and power, 36V and 48V are the most common options for electric bicycles, and are both good for up to approximately 28 mph (45 km/hr). This is a good quality 36V ebike battery made from Samsung battery cells, though I usually prefer 48V ebike batteries for my personal rides because I like that extra speed on the flats and the extra power for hill climbing. Lastly 60V and 72V options are ideal for those building ebikes that reach high speeds of 30-45 mph (48-72 km/hr). However, I wouldn’t recommend going this fast on your first ebike unless you have light motorcycle-riding experience, as that’s basically what you’re creating. Also, keep in mind that the higher the voltage, the larger and more expensive the battery will be. You’ll also want a good quality, dual suspension mountain bike for speeds over 30 mph (48 km/hr).
Next, you’ll need to choose the capacity of your battery. Capacity is usually measured in amp hours or watt hours, and will determine how far you can ride. 10Ah is a common starting capacity, and increasing up to 20Ah will buy yourself more range. More than 20Ah is rare, and mostly reserved for touring ebikes and cross country-style trips. My longest XC trip was 500 miles around Florida, and I used two 72V 20Ah batteries for a total battery capacity of approximately 3 kWh. But for around the town trips, 10 Ah is usually sufficient.
When in doubt, I always recommend choosing a higher capacity battery if possible. Not only will you be less likely to run out of battery, but a higher capacity battery also runs cooler and lasts longer because the individual battery cells don’t have to work as hard individually. However, the higher the capacity, the heavier and more expensive the battery will be.
Many retail electric bicycles don’t list voltages and amp hours for their batteries, and instead only list watt hours. To compare the two, simply multiply the voltage and amp hours together to determine the watt hours.
For example, a 48V 10Ah battery is equal to 480 watt hours (Wh). However, when comparing batteries meant for electric bicycle conversions, you’ll usually find the voltage and amp hours listed instead of watt hours.
To determine the range of your electric bicycle without pedaling, you can use a rough approximation of 25 Wh/mi. Using this approximation, a 480 Wh battery should carry most people around 20 miles (32 km). However, factors such as rider weight and terrain can have a significant impact on range. And you can always increase your range by pedaling along with the motor power.
Lastly, you’ll need to choose between two styles of electric bicycle batteries: a frame mounted battery or a frame bag/rack mounted battery. The former (pictured below) bolts onto the frame, usually using the holes for the water bottle holder. The latter mounts into a rack or frame bag. If you’re using a battery with a voltage above 60V, you’ll likely be limited to a frame bag mounted battery, as higher voltage batteries rarely come in cases designed for easy mounting. This 72V battery is typical of most high voltage ebike batteries and requires a triangle frame bag or rear rack for mounting. Most people prefer frame mounted batteries for their simplicity. By mounting the battery between your knees in the front triangle of the frame, you keep the center of gravity lower and in the middle of the bike, improving handling. I personally like to use a triangle frame bag in my bikes, but that’s mostly because I’m a battery nerd and I like to build large, custom battery packs to fill up the available space.
Electric bicycle conversion kits
Once you have your bike picked out, you’ll need a simple, bolt-on electric bicycle conversion kit. The electric bicycle conversion kit will have all of the electronics you need (except for a battery, usually), including the hub motor in a wheel, a throttle and a speed controller, plus a few other accessories such as displays, gauges, fancy brake levers, etc., depending on the kit. This specific electric bicycle conversion kit is a good quality, budget kit that I’ve used many times. It comes in both 500 W and 1,000 W options, and can work with both 36V and 48V batteries (great for if you want to upgrade to higher speed later). If you shop around, you’ll find other electric bicycle conversion kits with similar or identical looking motors. In truth, most of the motors of this style, even from different vendors, generally use the same parts coming out of just a few factories in China. There simply isn’t very much diversity in the ebike conversion parts market. The mindset has essentially been, “if it works, keep producing it.”
There is also a second type of electric bicycle conversion kit that uses a mid-drive motor to replace your bottom bracket and provide power directly to the crank. The advantage of these mid-drive kits is that they allow you to run the electric assist through all of your gears instead of having a single gear ratio like hub motors. Having multiple electric-powered gears can be a big help on massive hills. However, these kits are more complicated to install, fit a fewer percentage of stock bikes and are 3-5x more expensive, so I don’t normally recommend them for your first electric bicycle conversion.
While most hub motor-based electric bicycle conversion kits are quite similar, there are a few parameters you’ll need to consider, namely the power level and which wheel has the motor, as well as choosing a kit with the proper size wheel for your bike.
Some kits offer different power options, measured in watts. Unless you’re traveling above 20-25 mph (32-40 km/hr), power levels above 750 watts won’t have as much impact on your speed as they do on your acceleration. For flat ground, 250-500 W is plenty of power to get most people up to speed, albeit with slower acceleration. If you are light and don’t mind taking a few more seconds to reach cruising speeds, a 250 W ebike could be for you. If you live in a hilly area though, you’ll likely appreciate a bump up in power to 750 W, or even 1,000 W for extremely hilly areas. Also, larger riders will benefit from higher power levels even on flat ground.
Personally, I find that a 48V and 750-1,000 W system is the perfect amount for most people. This combination provides a bit more speed and power than most will use, meaning you aren’t riding your ebike with the throttle constantly pegged at 100%. Imagine a car that you drove that way!
Lastly, you’ll need to decide between a front or rear motor. A front motor is better for smaller installs, usually in the 250-350 W range. Changing the tire is easier with a front motor, and can be a bit more annoying with a rear motor. However, many front bicycle forks aren’t designed to take the power level of large motors. For motors above 500 W for an aluminum frame or 750 W for a steel frame, rear wheel drive is best. Also, powerful motors mounted in the front can leave you performing burnouts due to the lower weight on the front wheel. Whether or not this is desirable is up to you. Or you could get fancy like me and have both front and rear motors for an all wheel drive ebike. Swooon
Installing the electric bicycle conversion kit
Once you’ve chosen your kit, installation is actually fairly simple, especially if you’ve ever changed a flat tire on a bicycle before. To install the hub motor, simply remove your old bicycle wheel and transfer the tire and inner tube to the electric hub motor wheel. Then bolt the speed controller (the brain of the ebike) onto the frame and add the throttle to the handlebars. All of the kits should come with compatible plugs to make the connections easy.
The trickiest part of the conversion can be connecting the battery to the speed controller, since they might not have matching connectors if they were purchased from two different vendors. In this case, you’ll just need to change the wire connector on one or both components. If you’re halfway decent with a soldering iron, this won’t be much of an issue. Simply cut off the old connector and solder on a new one. You can find electrical connectors with pre-connected wires that make this job even easier. This is likely the only soldering you’ll have to do in the project. Just be careful not to touch the battery wires together when you have them temporarily exposed, or you could create a short circuit. If you’ve ever short circuited a 9V battery by touching the two terminals to a metal object, imagine the same spark but much, much bigger. I’ve seen gold electrical connectors literally vaporized by doing this. There one minute, and just gone the next. Poof.
But don’t worry, that shouldn’t happen to you as long as you keep the wires apart while you replace the connectors.
Once you have your battery installed and connected to the speed controller, your ebike should be ready to ride. Simply ensure that all of the wires are out of the way and zip-tied or velcroed to the frame so they don’t catch on the pedals or other obstacles, and then you’re ready for a test ride. Oh, and don’t forget a helmet – safety first!
Do-it-yourself to save money
You may be surprised by how effective a DIY ebike can be, and how closely the specs of a name-brand ebike can be matched or exceeded with nothing more than a kit and a few hours in your garage. The Trek SuperCommuter 8s reviewed by Electrek is a beautiful electric bike, but costs $5,000. You could reproduce a very similar speed DIY ebike using this conversion kit and this 36V battery. With those parts, you’d have a more powerful motor and slightly larger capacity battery, all for around $450, not including the cost of the donor bicycle. Sure, it doesn’t have all of the bells and whistles of the Trek like the built-in headlight, internally routed cables and integrated bottom bracket motor, but you can trick out your own DIY electric bicycle with the $4,500 you saved!
Keep in mind though that when you build your own electric bicycle, you don’t get the same warranty and support as you would from a retail electric bicycle company. Those multi-thousand dollar price tags cover more than just the bike itself. But for those brave enough to strike out on their own, there are plenty of options to build your own electric bicycle and save a pile of cash while doing it.
[Edit: There’s a great discussion going on in the comments section about electric bicycle laws. Not only does nearly every country have different laws and regulations regarding power limits and other parameters affecting electric bicycles, but every state in the US also have unique ebike laws. You should check your local electric bicycle laws to determine what types of ebikes are legal in your area. This wiki is a good place to start, but may not always be entirely up to date with the ever-changing laws.]
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