Horizontal and vertical RV generators were the old standbys within the generator industry until those new fangled inverter thingy’s showed up a few years ago. The horizontal RV generator has been around since generators were invented. They consist of some stator coils pressed inside a metal housing and a rotor attached to the engine rotating inside the stator. With the rotor making a strong magnetic field, the stator will generate electricity that can be used in our campers (“coaches” for the well-to-do). The generator end opposite the engine will have a bearing to support the rotor that is usually a sleeve bearing (for the cheap ones) or a sealed needle or ball bearings (for the good ones).
The rotors may have 2 magnetic poles and the unit will run at 3600 rpm to produce 60 Hertz. If they have 4 magnetic poles, the unit runs at 1800 rpm to product 60 Hertz. Graphite compound electric brushes riding on slip rings normally bring in controlled dc voltage and current that varies as the voltage regulator tries to maintain 120 volts and whatever current the load requires.
Most stators today will have four power coils that output through two circuit breakers and a neutral connection. On some generators, the coils are connected to add their current to a single output. On others, the coils are connected to output double the normal voltage such as 240 volts on a single circuit.
The horizontal generators are connected directly to the back of the engine. They are called “direct connected” generators and only have a generator bearing on the back end of the unit. Vertical generators have shown up in recent years. They work the same as the horizontal ones but they are mounted and driven differently. A vertical generator is mounted beside its engine and is not directly connected to it. Instead there are pulleys on the engine and the generator and a belt connected the two together. With this arrangement, manufacturers have some options that they didn’t have before. If the two pulleys are the same size, then the engine should have the same horsepower as before (at the rpm of the generator). If the pulleys are different sizes, then the engine can be run faster than the generator and either a smaller engine or a larger generator could be used. Engines usually produce the most power at speeds different from that at which generators must be run such as 2300/1800 rpm. The arrangement also allows the manufacturer to produce the genset in a more compact package than before.