how do power(Dc/Ac) inverters work ?

come ?

You do not get more power out than in. 7000 watts is a lot for an inverter. The DC formula is P = IE (or P/E = I).

Considering no conversion power loss:

Almost 600 amps of 12 volt is quite a load. Your standard automotive alternator and battery will have a tough time keeping up with that. It would take almost 10 horsepower to drive the alternator!

I will let someone else cover how they work, but I would use an oscillator that activates a GREAT BIG MOSFET that drives a GREAT BIG step-up transformer at 60Hz :)

Hope that helps,

Tim

Answer No.

come ?

Easy. They draw a lot of current from the battery!

You are comparing Volts In with Watts Out and they aren't the same thing. You need to look at Power In and Power Out....

The power going In = Input Voltage x Input Current The power coming Out = Output Voltage x Output Current = 7000W

The ratio of Output Power/Input Power is called the power conversion efficiency and is always less than 100%, however if you assume it is 100% for the moment then...

Power In = Power Out

or put it another way...

Input Voltage x Input Current = Output Voltage x Output Current = 7000

Since the input voltage is 12V the input current must be > 7000/12 = 583 A !!!!

Better use very thick wire!

If you have a 100 AHour 12V battery (eg a Battery that will supply 100A for an hour at 12V) this will run this inverter for 100/583 Hours which works out at about 10 mins.

No. Go to the library; read a Physics book.

Nonsense. Physics book (see above).

inverter.

would

Welllll, almost!!! Modern inverters operate on a different principle than older designs. The older designs did, in fact, use a transistorized oscillator that drove a massive 60 Hz power transformer. Modern inverters are switchmode designs that convert the incoming 12 volt supply into a higher voltage, such as 300 VDC. This stage runs at 40 Khz and higher. The high voltage is then switched by power transistors or MOSFETS using a PWM scheme to produce a stepped waveform that is more sinusoidal than the old inverters, which produced a square wave. This stepped waveform is the output of the unit. The result of the modern design is a much smaller unit, weighing a fraction of the old heavy iron inverters. Consider that an old heavy iron inverterr capable of producing 150 watts squarewave would probably weigh around 20 pounds. A modern switchmode inverter capable of 150 watts modified sinewave would weigh in at a couple pounds. Hope that helps more, Cheers!!

Thanks all,

I,actually, thought so. However, I never thought that you can draw such amount of current from a 12VDC battery

Not necessarily. They can run at other than bistable-astable (i.e: binary astble). Pulses with a period of 16.67 ms, fed to a class C amplifier, with a low Q, and PWM feedback for load regulation, could provide a pretty stable sine waveform at the ouput. :-)

ALso, there're "magic sinewaves". Then you got multiple-stepped "psuedo-sinewaves", which is the type my low freq stanby UPS uses. There is enough self-resonance in the large output transformer to filter out most of the harmonics, even in a modified low freqency switching mode.

The cheapies pump out square waves.

-- -john wide-open at throttle dot info

~~~~~~~~ Maybe I should ask Radio Shack. They claim they've got answers; but frankly, if Radio Shack were our provider, we'd _really_ be in trouble now, wouldn't we? ~~~~~~~~