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It's a good question. How does a car charge its battery? Newer cars and trucks use an alternator to charge the battery. The alternator driven by a belt off the engine converts mechanical energy to electrical energy and charges the battery. Once the engine is running the alternator supports just about everything electrical on a new car or truck. So it gets back to an engine which in many cases is powered by fossil fuel like gasoline or diesel fuel. Rather than think about the fuel source let's put things in power. One horsepower equals 746 Watts of electrical power expressed in watts. Now in a perfect world a 100 Amp automotive generator would output 13.6 Volts and if we create a 100 amp load we get 13.6 Volts X 100 Amps = 1,360 Watts. That gets us 1360 Watts / 746 HP = 1.832 HP . Unfortunately this is not a perfect world and Alternators also have an efficiency factor we need to consider. The same is true of electric motors, they have an efficiency rating. So while we can say for example 2.0 HP = 2 HP X 746 Watts = 1492 Watts in reality we may only see 1193 Watts or 80% efficiency. I have a small generator out in my shed. It can continuously output 4,000 Watts which we would think can be done with about a 5.36 HP engine but it uses an gasoline engine running at 3600 RPM delivering 8 Shaft HP. Nothing is perfect.
Ron
