24vdc alternator to sine wave inverter

Re: 24vdc alternator to sine wave inverter

cptdondo wrote: »

I'm doing some thought experiments along the following lines:

Install a 140A, 24VDC alternator on a car engine (secondary to the engine alternator)
Run the output of the alternator to a 2500-3000W sine wave inverter

Use that to run various appliances - microwave, air conditioning, etc

There are no batteries between the alternator and the inverter.

Any thoughts on this? Is it feasible? Any potential for damage to the inverter?

The idea is to replace a 2.8kW 120VAC generator. I'm looking at 24VDC to reduce the size of the wiring; otherwise I could use 12VDC.

Many years ago I bought a "conversion kit" for my car alternator which included a switch that both disconnected the alternator from the battery and the rest of the car electrical system and replaced the voltage regulator with one in the kit box. When you revved the engine to a high enough speed, you got 120V DC from the kit to run tools, etc. with "universal" (AC/DC) motors. It worked right up to the point where it fried the alternator diodes one day.

So most alternators can work (although not very well) without a battery attached. There will be some residual magnetism to start the alternator producing current or it will use a permanent magnet.
The regulation will certainly not be as good and I would worry about damaging the inverter too.

The regulated field current system, requiring a battery, was commonly used in auto generators which produced DC directly, back before alternators were invented.

Re: 24vdc alternator to sine wave inverter

Cariboocoot wrote: »

Nit-pick: generators also produce AC, not DC. It is rectified to DC by the relation of the commutator and brushes: the positive brush always aligned with a section of armature coil that is positive and the negative brush always to negative. Since they are a series of connection points this amounts to switching on/off in relation to the coil energizing. It also means they are sometimes connected across two and tend to arc and spark and grab the full Voltage output for only part of the waveform. In other words they're inefficient and wear more compared to a modern alternator design with its constant-contact slip rings and solid-state rectifiers.

Picking right back: Since the commutator and brushes are in integral part of the generator, you can also say that the generator produces DC even though the rotor windings are carrying AC.
By the same nit, alternators either produce AC or, because the bridge rectifier pack is internal, they produce DC at their output terminals.

Just so the overall operation is understood, either labeling standard works. It is when people start mixing the two that problems develop.