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Originally Posted by brent777
Well ya in away but like it take less energy to turn a fan motor then it does a alt
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How do you figure that? around 750 watts is one HP the rest of the mechanical energy that it takes to produce 750 watts is lost in the form of heat, if you put 1 hp of energy in to a wide range of generators and alternators you can measure the electrical output and see what you have for losses.
DC generators tend to be less efficient because they are mechanically rectifying the AC power to DC via the brushes and commutator, my understanding is that permanent magnet alternators and generators tend to have a narrower range of speed that they produce usable electricity at so you are going to have to have a gear ratio that spins your little generator faster to get 13.4v out of it, but at some point it's going to spin fast enough that it will just fly apart so don't spin it to fast! also the faster you spin it the more energy is going to be wasted in the bearings and just the friction of the parts moving in the air, so after you have those losses from using a permanent magnet DC generator you still have to regulate the voltage so you end up with more losses and when your battery reaches full charge your generator windings are still spinning inside of a magnetic field that you can not turn off.