Electric bike conversion basics
By Daryl Neal
Electric bikes are rapidly becoming popular. They offer faster commuting, no sweat, no struggling on hills, more responsive negotiating of traffic and a balance between fitness and fun. They are also one of the most efficient modes of powered transport, costing about 0.5 cent per kilometer.
‘Off the shelf’ e-bikes are available, but converting an existing bike is more cost-effective (about $1500), allowing you to keep the bike you love with the specs that you want.
Most conversion systems provide 500 to 600 watts of peak power, averaging about 300 watts to comply with government regulations. This is enough to allow you to ride up hills that would otherwise need granny gear or make you walk. Standard kits have a top speed of about 30 km/h (to match the gearing of most bikes) and a range of about 35 km.
A custom conversion can give your bike more range, power or speed for touring, load carrying or off-road use.
A basic conversion kit comprises battery, motor, speed controller and throttle.
The Battery.
The battery is the heart of the system and where most of the cost lies. Today’s batteries are lithium based, of two types: lithium ion and lithium iron phosphate. Both can be recycled.
Lithium ion batteries are slightly smaller and lighter, with a useful life of 800 to 1500 recharges.
Lithium iron phosphate batteries have a life span of about 3000 recharges and will not catch fire if damaged or incorrectly charged.
Battery capacities are measured in amp-hours. A 36 volt 10 amp-hour battery gives about 36 kilometers of assisted riding on the flat. A 36 volt 20 amp-hour battery gives about 72 kilometers. The range depends greatly on hills, load, speed and how much pedaling you do.
Most chargers charge a battery in about five hours from a standard wall socket.
The motor
Three types of motor are available: the direct drive hub motor, the freewheeling (or geared) hub motor and the mid mount motor.
The direct drive hub motor is the simplest and most reliable. It runs silently and needs almost no maintenance. It turns even if not in use, creating a small amount of resistance.
A direct drive motor can provide regenerative braking (recharging the battery while slowing or descending) and can drive in reverse. It is ideal for a cargo bike, trike or off-road machine.
The freewheeling hub motor or geared hub motor does not turn when not in use, creating no resistance when pedalling unassisted. It provides no regenerative braking and cannot drive in reverse. It has reduction gears, making it a great hill climber. This motor is ideal for a commuter bike.
The mid mount motor fits in front of the pedals and connects to the chain, using the bike’s transmission so the rider can choose suitable gears. It is more complex to fit and causes increased chain wear. However, it provides provide great performance and keeps the weight central in the bike.
The speed controller
The controller is a small box that plugs between the motor and the battery to regulate the flow of electricity; the bigger it is the more it can handle. A standard controller has a flow rating of about 20 amps. The controller can do clever things like cruise control, reverse and regenerative braking. It also protects the battery and motor.
The throttle
The throttle is usually a handlebar-mounted twist grip like that on a motor-cycle or a thumb lever like that on a quad bike. A lead connects it to the controller. Another option is a pedal sensor, which activates the motor when it detects movement of the pedals.
You can convert a bike in an afternoon, but mechanical knowledge is an advantage because improper installation can cause expensive damage.
If unsure engage a specialist, who will also shorten cables and waterproof the system to ensure a tidy and reliable job.
EVLAB is happy to answer any questions you have and work out the ideal kit for your needs.
