Electric Conversion Kits - What you need to know before you start the hunt.
Electric bicycle technology is growing and improving at a rapid rate. A state of the art e-bike component this year is probably not going to be the state of the art component for next year. That’s not to say e-bikes are subjected to “Moore’s Law” in the way that your PC is, but, if you’re picking up on your e-bike research where you left off a few years ago, you would be wise to update your findings. The following is a list of the words and terminology used throughout the e-bike industry. By familiarizing yourself with these words and terminology you’ll be better able to understand the information provided by the e-bike kit companies and you'll be able to ask the proper questions.
I broke the list down by listing some generic terms used to describe many of the individual components of the e-bike system first and then a list of those specific e-bike components. The terms Amps, volts, watts, and ohms are standard units of measure used in the specifications for any electrical device.
Amps, volts, watts, and ohms are the main units of measure used in measuring electricity. Ohms is a measurement of resistance that is critical for measuring electricity, but it’s rarely used so I will leave it at that. Most e-bike kits will be advertised using volts & watts to explain their size as it compares to the competition, i.e. 36v 800w wheel motor kit. This number can be easily manipulated and as such is not very reliable. Some of the better quality kits will use volts, amps and watts i.e. a 36v 25A 900w wheel motor kit. This is better as it takes the capacity of the controller into consideration. Sadly these too can be fudged. If you remember the formula volts x amperes = watts you will be able to accurately determine the real output of your motor based on the components and batteries you’ll be using.
MOTOR (Electric) = An electromechanical device that converts electrical energy into mechanical energy. It’s the part of your e-bike that, along with you does all the work. Hub Motor Geared = Smaller, lighter, and with more torque it also free wheels. The down side is they are often more expensive, more complicated & slower. They cannot be used for regenerative braking. Hub Motor Direct Drive = Simple, inexpensive, faster, well tested and reliable. They can weigh twice as much and have less torque than a geared motor. If mountain biking is your thing consider a geared hub or mid-mount chain drive. If you want regenerative braking then a direct drive hub motor is your only option. Brushless or Brushed = Brushless motors account for about 90% of today’s e-bike kits making the brushless or brushed question somewhat academic. See Electric Hub Motorsfor a complete explanation of the two or click this Wikipedia articlefor more information on brushless DC motors. Chain Drive = A transmission system in which power is transferred to the wheels by means of a chain. Usually found in e-bike applications where the motor mounts in the middle of the frame. Usually in the area of the pedals. Friction-Drive (FD) = A very simple and inexpensive drive system which pushes an electrically powered roller against the front or rear tire. Regenerative Braking = An energy recovery mechanism which slows the bike down by converting its kinetic energy into either a braking action or by creating electrical energy to put back into the batteries. Although this can save wear and tear on the brakes it is probably not cost effective as far as increasing your range. Often referred to as ReGen. Your money would be better spent on a bigger battery pack. Watch this video for more information on regen braking and why it is not a relevant for electric bicycles compared to electric cars.
Motor Efficiency = Most e-bike kits advertise this figure at 80 to 85%. It basically means that the given motor can convert up to 80 or 85% of the available energy into forward motion. This figure is dependent on many things and can be measured in different ways. The overall efficiency of the e-bike is dependent on many things among them; the batteries, controller, wiring and wire connectors. So don’t hang your hat on this number. Amps = A measurement of current flow. Ah = One ampere-hour is equal to a current of one ampere flowing for one hour. For our use we are concerned with the ampere-hour capacity of our battery. That’s the number of ampere-hours which can be delivered by the battery on a single discharge. The higher the number the longer the run time, the bigger the battery and the more expensive it will be. 8, 10, 12, 15, and 20Ah will be the most common. Volts (v) = A measurement of the electric potential. The higher voltage the more power on tap & the more batteries you’ll need to carry. Watts = A derived unit of power or a measurement of power. I.e. 750 watts = one horsepower. Hub motors will typically be advertised as 250 to 1000 watts. To find the actual wattage your motor will be running at use the following formula. Volts x Amperes = Watts. Almost all of the motors being used in today’s e-bike kits are designed to work across a range of both volts and amps. Hence watts can be subjective number. Watt Hours = The energy capacity of a battery pack. To calculate multiply the voltage by the amp hours (Ah) of the battery pack. I.e. A 36-volt 10-Ah battery pack has 360 watt hours. Revolutions Per Minute (RPM) = The RPM’s given for a specific hub motor will be the maximum no load operating RPM. Higher RPM translate into more speed and less torque. Lower RPM is less speed and more torque. Conversely a small diameter rim will require a higher RPM motor to achieve the same travel speed as a larger diameter wheel. Horsepower (HP) = 1 Hp, between 735.5 to 750 Watts BLDC Motor = Brushless DC motor using an electronic motor controller.
MOTOR CONTROLLER (The Brains) DC Motor Controller = an electronic device that reads the throttle setting of your e-bike and adjust the current being supplied to the motor. Other functions usually include a low-voltage cutoff, a high temperature shut-off, over-current shut-off. Some controllers will also have a brake cutoff to shut down the motor when the brake is applied. Some may also have a regenerative braking option. This will often be indicated with regen being listed somewhere in specifications. Most of today’s controllers will work with hall sensor motors and the newer sensor-less motors. Most DC motor controllers are designed to operate across a range of motor and battery sizes. This gives the kit builder a fair amount of flexibility in selecting a cost effective controller for their kit. However when you combine this flexibility with the rather broad operating range of today’s hub motors you can see how easy it would be to “play with the numbers” Power Management Display (PMD) = An electronic dashboard for you e-bike measuring things like amps, watts, voltage, temperature etc. Wheel/Rim = (Where the rubber meets the road.)
All e-bike kits with the exception of a mid-drive motor include a hub motor laced to a front or rear rim. Most of today’s e-bike kits will also include the tire. Standard rim sizes are 18", 20", 24", 26" & 700cm. (28") A front wheel drive is by far the simplest to purchase & the easiest to install. They should not be used with aluminum forks or forks with shocks. Check your front forks with a magnet. If it sticks your good to go. If it doesn’t you’ll have to use a rear drive unit. Here aluminum is OK. A rear wheel drive will come with a narrow gear sprocket in case your sprocket is too wide. You should look for double-walled rims with properly tension stainless steel spokes. Many cheap kits use a heavier zinc coated steel spoke. All front hub motors require some type of “Torque Arm”. These can be anything from a flat washer with a bendable tab to a true “torque arm” consisting 3 or 4 parts. Other useful information on rims and spokes can be found in Sheldon Brown’s article titled Wheel Building.
THROTTLE/BRAKES (Stop & go)
There’s not much to say here. You will usually have an option for a thumb throttle or a twist throttle such as you find on a motorcycle. A twist throttle gives you better control thereby increasing your run time. Most of today’s kits will accommodate the newer disc brake as well as the older V pull or center pull brakes. MAKE SURE YOUR BRAKES FIT YOUR E-BIKEKIT. Most e-bike kits will ship with brake levers to shut of power when the brakes are applied whether you want them or not. If you go with a “regen” option you will need an upgraded brake lever with a switch.
WIRE HARNESS (The Plumbing)
All e-bike kits will come with one. Many of the cheap kits will come with wire plugs and connectors in a plastic bag for you to install. These same kits often come with no instructions making the installation of these wire ends a very big challenge. One very nice feature that EBikeKit.com uses is a quick disconnect for the wiring that goes to the hub motor. I used to retro-fit my front hub motors with this option. It allows you to quickly unplug your front wheel to change a flat, put it on a roof top rack that requires removal of the front wheel or just to put your stock wheel & tire back on. Most e-bike kits will also have a quick disconnect for the battery pack. Between those two you can quickly take it apart to put into the back of your SUV, make it as light as original for lifting onto the bike rack or just to put it back to its original condition.
BATTERY (The Fuel Tank) Go to Battery University for detailed information on battery types.
Lead-Acid Battery = the type of battery in your car. This 100 yr. old technology is very toxic, very heavy & has a short life span. They are also very inexpensive and can be found just about anywhere. Go here for detailed information. SLA = Sealed lead acid battery. See above PbA = Lead acid battery. See above Li battery = Lithium battery. Go here for detailed information. http://batteryuniversity.com/learn/article/lithium_based_batteries Li-Ion = Lithium Ion battery. LiFePO4 = Lithium iron phosphate battery cells offering high power and energy density, excellent safety and life cycling. LiFePO4 is the safest and the most enviro-friendly chemistry make-up of lithium-ion batteries. Read “Electric Bike Lithium Battery Primer” for some very useful information on building LiFePO4 battery packs or here for detailed information on all lithium based batteries. See My Choice for Batteries for information on EZgo-Now’s new battery packs. NiH = Nickel hydrogen battery. Go here for detailed information. http://batteryuniversity.com/learn/article/Nickel_based_batteries NiCd = Nickel cadmium battery. See above NiMH = Nickel metal hydride battery. See above BMS = A Battery Management System is required for the safe operation of any multi cell lithium battery pack. All BMS’s are not created equal. They affect both safety and performance so pay attention to what you’re getting. PCM = A Protection Circuit Module that is part of a BMS.
BATTERY CHARGER (The Gas Pump)
Battery chargers are specific to both voltage and battery type. Many e-bike kits will include a charger for SLA batteries even though the kit does not include any batteries at all. TIP! PURCHASE YOUR CHARGER FROM YOUR BATTERY DEALER.
FREIGHT (you can’t get it from there to here without paying for this)
Freight can be a significant cost of your overall e-bike kit. Many of these kits and battery packs are coming from China. In addition to these regular freight charges you have additional charges for shipping batteries as they are classified as a hazardous material. (You probably wouldn’t want 50 lbs of poorly packaged lithium batteries sitting in the cargo hold of a plane you’re riding in)
EV = Electric vehicle. E-Bike = Stands for Electric Bicycle. Usually means that motor power is independent of pedaling and can be used as much or as little as the rider wants.
E-bike conversion kit = A complete conversion kit will contain everything required to turn an ordinary bicycle into an electrically assisted bicycle. Many of the low-end E-bike kits require the buyer to make-up and install wires, connectors and mounting brackets. You’ll have to buy or have on-hand zip ties, wire connectors and jumpers. Many do not come with a manual nor do they make any of the documents available on-line. Because of freight cost most conversion kits will make the battery an option or will not include it all. Finally a complete kit can take anywhere from 30 minutes to 1.5 hours. At the other extreme a bargain kit will take anywhere from 2 hours to the entire day and a trip or two to the hardware store. PAY ATTENTION TO WHAT’S INCLUDED. See Why Choose E-BikeKit for a listing of what E-BikeKit includes in their kits. Use this list when comparing other kits. Sadly Complete does not necessarily mean that you’ll have everything you need out of the box to ensure a smooth and aggravation-free electric bike conversion.