Automotive ?

All cars are DC only as are there lights

The Car lights are actually DC, not AC. The thing is that the battery itself is charged via the Alternator, and that in fact is AC. If you're using an older system of a car, then you'd most likely find a dynamo instead with commutators (both are types of power generators that constantly charge the battery, and yes that includes the time where the engine is just idling). As for everything else, from lights to battery, etc., Yes, that includes the Air Conditioner too (NOT referring to it as AC as in Alternative Current of course XD). Each of the impedances are actually calculated via Thevenin's law, stating that any linear circuit containing several voltages and resistances can be replaced by just one single voltage in series with a single resistance connected across the load. Of course, each of loads has their own voltage and power requirements too. 

As for the charging part, well:

Alternator is directly connected with engine power through a drive belt. When you start a engine, at the same time Alternator rotates with the help of engine power.

There are 4 important parts that are used in an Alternator:

1. Stator 

2. Rotor

3. Rectifier

4. IC Regulator. 

These 4 parts are necessary to develop electric power (AC current) and converts the power from AC to DC current then charging the battery while engine at running condition.

Stator : Permanent Winding Coil. There are 3 winding coils joined together.

Rotor: Electromagnet. Rotates with the help of engine power. Creates magnetic force at engine running condition. This EMF (electro magnetic force) pushes the free electrons (current generation) in the stator coils.

Rectifier: Made with diodes. Simply used for convert the AC current to DC current.

IC Regulator : It's used for control the current. For instance, when the battery is fully charged the Alternator management Sensor give signal to the IC Regulator. The latter stops the current supply to the slip rings (carbon brush) i.e. rotor.

FUNCTION : Alternator is a device it's only work with input current. Get 12v DC current from vehicle battery passed to IC Regulator. This will carry the current from battery and pass it to slip ring. Through the slip ring, current is passed to the rotor. Now the rotor develops EMF. These magnetic waves attract the stator coil and push the free electrons in the coil. This is the flow of free electrons (AC current) converted to DC current by rectifier. The DC current charges the battery and run other electrical components while engine at running condition.

Another way to explain it is that when the car is started the starter motor makes the crankshaft rotate along with the alternator whose rotor is connected to the crank with belt. When the engine starts and runs there is always a residual magnetism in the stator as the alternator starts producing electricity a part of the electricity is fed to the Stator to produce a larger magnetic field. This continues up to a point till the voltage required is obtained. The AC voltage is rectified and conditioned to DC required for the lights, ECU of the car.