Purchasing an Electric Bike

by Geza Vamos 

In choosing an electric bike there are several important considerations. First, decide how far you would like to go before the battery needs to be re-charged, how much you want to contribute with pedaling, how much you will save on car mileage and parking, and thus how much you are willing to invest. 

The Drive 

There are a wide range of electric motor drives. Avoid motors that drive the bike by rubbing on the rubber tire, which are very inefficient and worse in rain or snow. Today, the most common motor is a hub motor built right into the wheel, but there are also motors which drive the wheel via a chain. Most electric bike systems provide speed control electrically through a twist grip or lever throttle which means you cannot change the gear ration between the motor and the wheel. A few which do allow you to change the gear between motor and wheel deliver a greater range of speed and torque for hill climbing and higher average efficiency. 

Power Ratings 

Efficiency means a lot because for a given weight of battery, the more efficient the electric drive, the greater your range. Efficiency measures how much of the electric power going into the motor is delivered at the wheels as mechanical power. Efficiency is not usually specified, and varies as the bike starts and accelerates. Typical full load efficiency may range from 40% for a brush type motor with internal gears, to better than 80% for brushless motors without internal gears. Motor power is critical to function and enjoyment. 

Don’t be fooled by incomplete power ratings: the rating should specify continuous or peak power delivered for a specified short period). For me, an electric bike has to get me up hills faster than I can pedal or it’s worthless, and I would not buy a motor weaker than 500 watts continuous rating.

 The law restricts power and speed that the motor is allowed to deliver (not including rider contribution), beyond which you need to comply with motorcycle rules. In BC it is 500 Watts, 32km/h, maximum 3 wheels. 

Batteries                                                                                         

Lead acid: cheap, toxic but recyclable, heavy, about 6 hours to charge, a life of several hundred cycles. 

Nickel cadmium: a little lighter, toxic but recyclable by return to manufacturer, charges in 2 hours, life up to 1,000 cycles. 

Nickel metal hydride: a little lighter still, less toxic, recyclable, charge time 2 hours, life of up to 1,000 cycles. 

Lithium batteries: all are light, less toxic, varied life cycles and charge times, the best promise many thousands of cycles, less than 1 hour charge, and fire safety (some lithiums catch fire if abused). 

Battery voltage ranges from over 72V to as low as 12V, most commonly 36V and 24V. Higher voltages improve system efficiency. 

Battery cycle life is the most important factor in cost. A cheap battery with 500 cycles is worth ten times less than an expensive battery with 5,000 cycles. 

You can buy a complete ebike or scooter (designed for mostly powered use), or install a drive kit onto most ordinary bikes, but seek advice first because the kits do not fit all bikes. Experienced cyclists know how much difference a little weight makes to the effort and enjoyment, so choose your bike and drive components carefully. Above all test drive several bikes on as long and challenging a route (steepest local hill) you can.

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When BC Hydro canned PowerSmart to boost private power, Geza Vamos became a forester, determined to help make forestry sustainable. Geza’s project is a two-person enclosed electric trike.

Links to established Vancouver ebike businesses: www.ebikes.ca Engineer, best advice for self builders, sells just parts, informative website www.cambiecycles.com Vancouver’s recumbent bike specialist, frame builder, excellent service, rentals, demos. www.jvbike.com Downtown, has good selection of ebikes, trikes, rentals.

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