At the same time as sizing the motor, you need a good donor bike.
There are a couple of things to keep in mind:
1. If you use a front motor, take a magnet and place it on your forks. Are they magnetic? If so you have steel forks; this is usually good. Some e bike motors are powerful enough to literally bend aluminum forks. Anyway, check to make sure your forks are steel and strong.
2. Pick a bike that you want to ride. We converted bikes that we had already been riding.
The conversions feel just like our old bikes but with plenty of power!
3. Finally, choose your range. How far do you want or need your DIY electric bike to go? Remember that hills and wind will take more power, although you get to come down energy free. Although a few kits offer regenerative braking, it is not that common just yet. Hopefully ultracaps or other technology will help solve this in the future.
One thing to remember about the energy for your DIY electric bike: batteries are still pretty heavy. Li-Ion battery packs are about 1/3 lighter than Pb-Acid, but if you use a 15-30 AH Li-Ion pack, you will definitely notice the weight. Our 36V 15AH packs weigh in at about 12 pounds. They hold the energy in just a few ounces of gasoline.
An average of 200 different ebike battery packs/motors and resulting efficiencies gives a working average of around 15 watt hours of energy used per mile. So, if you need a range of 20 miles, take 15 WH/Mile x 20 Miles = 300 Watt Hours of energy needed. Remember to add in a little (20 percent) for battery draw down since battery packs do not like to be pulled down past 80% full. To do this divide 300/0.8 = 375. You need 375 watt hours of energy.
375 watt hours is close to a 36V battery pack x 10 Amp Hours = 360 Watt Hours. From the example, this would get you 19 miles. Since battery packs are sold in common sizes you would want a 10AH pack minimum. Other common sizes are 12AH, and 15AH. It is your choice to go lower or higher.
Remember that this is 19 miles with no pedaling. If you pedal some, the power savings add up, and your DIY electric bike range gets extended.
Also, the efficiency can vary a lot! Some Schwinn bikes for example claim a 60 mile range and a 240 watt hour pack which turns out to be less than 4 watt hours per mile! This seems low, and messes with our average, but those are the published numbers.
Kits come either with or without batteries. The batteries are usually Lead Acid, Nickel Metal Hydride, or Lithium-Ion. Costs range from around three hundred dollars USD for a kit with no batteries to three thousand dollars for a powerful motor with high output Lithium-Ion battery.
At the present time, ebike batteries cost as much or more than the motor and other parts combined. The following table gives the cost of some common kits sold today.
A battery table cost comparison chart is here.
Keep in mind that motors, wheels and batteries are heavy. A complete kit with battery can easily weigh in at 30 pounds or more, and fill several cartons. Shipping these parts can be a sizeable fraction of the kit cost, perhaps 5% or more. Remember too that if you get a defective part, it may need to be shipped back to the retailer or manufacturer.
The Bionix kits are considered by many to be top of the line. The kits and prices shown are basic and can be supplemented by many other matching parts like custom made racks.
Amped conversion kits are quality kits designed to be lower priced, but with quality still built in.
The eZeebike kits are shown for contrast. Finally, the Crystalyte kits shown are some of the more powerful ebike kits on the market. These kits are noted to not meet most Federal or State ebike definitions and regulations, but do represent the upper end of the spectrum in ebike kit performance. Crystalyte does make a lower power Sparrow kit.
Last, there are several good links to check out that have a lot of other kits:
The DIY conversion kit for electric bike can save you big while giving the builder the satisfaction of building their own e-bike. A little planning and shopping can get you
a quality e-ride for about 1/2 retail or less. Read ahead before you buy a kit.
The first step is (boring) planning, but important, especially if this is your first
conversion. What do you want your future conversion to do? Do you want range,
speed, hill climbing ability, or just cruising around a bit? Check out our page
on motor sizing to see how much power you might need and some other kits
on the market.