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How to Convert a Gas Moped to Electric

by Richard Rowe

While the word "moped" is a amalgamation of "motorized" and "pedal powered," the vehicle type's connotation and legal status has changed somewhat. While most people now associate the word with the street-legal, step-through scooters common in cities worldwide, the motorized bicycle is more of a moped in the truest sense. Converting a gas-powered moped to electric is not a simple project, nor is it especially cheap if you use new parts. However, some smart shopping and fabrication experience can make this a worthwhile project for the mechanically inclined.

Unbolt the original engine, transmission, rear and front wheels; procedures will vary depending on the make and model. Once you have the moped stripped down to the frame, remove the throttle and clutch linkages, but not the control assemblies, from the handlebars.

Acquire from an online kit retailer a motorized bicycle kit utilizing a hub motor. Locate a kit retailer by entering the words "bicycle hub motor" into your browser. Hub motors are brushless DC (direct current) motors, meaning that they're functionally identical to AC (alternating current) motors. Hub motor kits are not cheap; you can easily spend more than $500 on the motor, motor controller and required running gear before spending anything on batteries. See the Tips section for sizing recommendations.

Obtain a set of batteries from an electric mobility scooter supplier; enter the words "mobility scooter batteries" into your browser to find a retailer. An electric moped will use about 10 amps per hour of current to maintain 20 mph, or 23 amps to maintain 35 mph. As such, you'll need a battery (or set of batteries) with at least 90 amp-hours of storage. A set of 12-volt, 33-amp-hour mobility scooter batteries will cost about $60 apiece as of 2011, which is about 1/15th the cost of the same storage capacity using the more expensive lithium ion batteries sold with many hub motor kits.

Cut and re-weld your frame to fit the batteries. Mobility scooter batteries are about 6 inches wide, which gives you enough room to pedal if you mount them on the bike frame where the engine previously resided. Make a new frame section out of 1/16-inch plate steel. Cut two pieces of plate and sandwich your batteries between them. Weld tube steel across the top and front to connect the handlebars to the seat and pedal housing. Enlist the help of someone with experience, if necessary.

Mount your motor controller to the top of the frame, and connect the batteries in series; that is, the positive terminal of one battery to the negative of the next, then again with the third battery. This will give you the 36 volts that your motor requires. Connect your wires to the motor controller and follow your kit manufacturer's direction for installing the rest of the assembly. The wheel/hub motor assembly bolts to the frame the same way your original wheel came off.

Re-install the brakes by bolting them to the front and rear frame and fabricate a cover out of sheet metal to cover the motor controller. You may opt to install an on-board charger and a length of extension cord behind the motor controller and under the cover so you can recharge anywhere.

Tip

  • Motor sizing is crucial, especially if you want to maintain the same 35 mph that your moped was originally rated for. If you want to maintain the same amount of power, multiply your original motor's horsepower by 746 to get the motor power in watts. For example, if you want to keep your original 6 horsepower, you'll need a 4,476-watt motor or a pair of 2,238 watt motors. However, this will make your moped capable of about 60 mph, which is probably illegal in your state. You'll only need about 300 watts to go 20 mph and 1,000 watts to go 35 mph.

Items you will need

About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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