Why is AC not usable to power lighting? Every light in my house is powered by AC.
Small, Home made generators have a tendency to be made from electric motors or car alternators.
They have a tendency to have 'Cycle' counts that cause 'Flickering' or detectable 'Blinking' of the lights we have now.
(Incandescent)
Wrong cycle counts can burn up all sorts of electronic devices, but are especially hard on motors wound specifically for a specific cycle count,
And on transformers that like to overheat when subjected to higher cycle counts...
A capacitor will stop or at least minimize that flutter, but you will still see it,
And with electric motors, you will find that that many of them aren't compatible with the 'Cycles' of the generator.
They will do strange stuff, or just burn up when you try to run them directly off a home made generator.
Grid energy is a very constant 60 cycles a second,
Where your generator might be 400 cycles a second, or 10 cycles a second.
(Cycle is where current flips form positive to negative and back again,
AC does this 60 times a second from the grid,
Where DC power doesn't do it at all)
If the motor is built correctly, you can run it on about any type of current,
Amount of current will determine speed.
Low current = Low speed...
If the motor is build specifically for AC current, it will melt down when you try to run it on DC current.
Same if it's the other way around,
You have a DC motor and try to run it on AC current.
Some motors are wound for specific input cycles,
Can't run them on anything else correctly...
--------------------------
For instance, your cordless drill works great on DC current,
But if you plug it into an AC outlet, no matter if the voltage is dropped down to 18 volts or whatever,
It's going to burn that DC motor up in short order!
Generator has to match equipment to run directly off the generator...
That's why batteries and converters/inverters that put out SPECIFIC current type are very handy to have...