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Frequently Asked Questions:

Alternative Power Sources & Regenerative Braking

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Can I charge my electric car from solar panels?

Yes, but not mounted on the car. There is not enough surface area on a car to generate enough electricity to drive the car more than a few miles, even in a very sunny climate. However, the car could be charged from a stationary solar array at your home base.

For more detailed information about batteries, see the Tech Paper on Solar Charging.

Can I charge my electric car from a windmill?

Yes, you could charge from a stationary wind generator at your home. The charger will accept any source of 110VAC input, preferably in the 15-20 amp range.

You can't charge by putting a windmill on the roof to catch the wind as you go down the road. The amount of drag created by the windmill would cancel out the energy it generated.

Can I charge the batteries from an alternator driven by the wheels as I drive?

No. It's a law of physics that you can't get more energy out of a system than goes into it, in one form or another. A gas car has a relatively powerful engine moving the car, and incidentally powering a small alternator to recharge a single 12V battery. Except during the few seconds when you are starting the car, the draw on this battery is very low, less than 50 amps.

An electric car can have anywhere from 96V to over 300V of batteries. During cruising, the car will draw up to 200 amps, and up to 400-500 amps for acceleration. It would take a huge alternator/generator to put out that much power. And if all that energy was going into the batteries, there would be none left to move the car. The car's motor can provide enough energy to move the car, or to charge the batteries, but not both at the same time. It would be like pumping water from a swimming pool to supply all the house's needs (dishwasher, laundry, shower, toilet), then running a hose from the house to refill the pool.

To put it another way, an alternator or generator creates a drag on the motor. The more energy the alternator/generator puts out, the greater the drag on the motor, and the more energy the motor needs to suck up from its power source: the batteries. Have you ever ridden a bicycle with a generator headlight on it? Turning on the headlight makes it a lot harder to pedal and keep the bike moving at the same speed, and that's just for a very tiny amount of electricity.

Can I capture the energy of braking to recharge my batteries?

Sometimes. This is called "regenerative braking". The drive motor temporarily becomes a generator driven by the wheels. When this happens, it generates electricity to charge the batteries, and creates drag to slow the car down. This feels very much like "engine braking" when you take your foot off the throttle in a gas car in a low gear.

Regenerative braking is easier to do with AC systems, such as the major manufacturers use, than it is with the much more affordable DC systems that are in most conversions. It requires modifications to the motor, a special speed controller, and some extra contactors and wiring. The controllers that provide this are more expensive, and are not available for all battery pack sizes. Most conversions do not use them.

Regenerative braking may not be effective for all driving conditions. For example, most people who have a long downhill in their commute usually have it as they leave home with a fully charged battery pack. In this situation, regeneration won't do you any good at all, because the batteries are full already, and there is no place to store any electricity that might be generated.

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