Perpetual Motion Solved! Regen Alternator.

by Ben N on May 29, 2010

One of the most common questions I get about my electric car is if I do regenerative braking on it.

The answer is “No”. Like many other home EV builders, I’m using a plain, series-wound, DC motor. Those motors are just not designed for regenerative breaking. So of course the next comment is “Couldn’t I just put an alternator on the motor to recharge the batteries?”.

The answer to that is also “No.”

The batteries drive the motor, which drives the alternator, which charges the batteries. Something doesn’t add up there. There’s no external energy input, therefore, energy can only be lost in the form of heat, but not gained anywhere. Also, alternators are only designed to recharge a 12V battery, whereas most EV battery packs are 72 to 144V for DC systems (AC systems can be 300 volts or more!)

While Hybrids have regenerative braking, and also can charge the batteries from the engine, keep two things in mind – ALL energy on a hybrid originates from the gasoline engine, and they use an AC motor, which can generate voltage HIGHER than the pack voltage to recharge it.

So, for a home-built DC series-wound motor vehicle to regenerate power, what we really need is an alternator that will put out pack voltage (rather than just 12+ volts) and only gets it’s energy from somewhere other than the battery pack – in this case the momentum of the car WHEN YOU WANT THE CAR TO SLOW DOWN.

That’s exactly what our friend Adam is doing. He re-wound an alternator so that it puts out a higher voltage, and is then rectified to DC. The alternator will be designed so that it only activates (thus causing drag) when the car is braking.

Here’s Adams latest video.

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