how do power(Dc/Ac) inverters work ?

[hussain]

Hi,

I allways wondered how dc/ac power inverters work ?

Do you really get more power than what you put ?!

I saw inverters that's supplied with a 12VDC and will give 7000 W !! How come ?

 

[Tim]

"hussain" <ahussain@mop.gov.kw> wrote in message
news:3fbedc74.0401172311.457d8079@posting.google.com...

Hi,

I allways wondered how dc/ac power inverters work ?

Do you really get more power than what you put ?!

I saw inverters that's supplied with a 12VDC and will give 7000 W !! How
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:
7000 watts / 120 volts = 58.33 amps out
7000 watts / 12 volts = 583.3 amps in

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

 

[CWatters]

"hussain" <ahussain@mop.gov.kw> wrote in message
news:3fbedc74.0401172311.457d8079@posting.google.com...

Hi,

I allways wondered how dc/ac power inverters work ?

Do you really get more power than what you put ?!

Answer No.

I saw inverters that's supplied with a 12VDC and will give 7000 W !! How
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.

 

[JeffM]

I allways wondered how dc/ac power inverters work
hussain
http://www.google.com/search?num=100&hl=en&lr=lang_en&ie=UTF-8&oe=UTF-8&safe=off&q=%22DC-AC+inverter%22+circuit+-posted+-prices+-products&btnG=Google+Search

Do you really get more power than what you put ?!
No. Go to the library; read a Physics book.

I saw inverters that's supplied with a 12VDC and will give 7000 W
Nonsense. Physics book (see above).

 

[Tweetldee]

"Tim" <tim@prolectron.com> wrote in message
news:ryrOb.2307$ZJ1.1866@lakeread01...

"hussain" <ahussain@mop.gov.kw> wrote in message
news:3fbedc74.0401172311.457d8079@posting.google.com...
Hi,

I allways wondered how dc/ac power inverters work ?

Do you really get more power than what you put ?!

I saw inverters that's supplied with a 12VDC and will give 7000 W !! How
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:
7000 watts / 120 volts = 58.33 amps out
7000 watts / 12 volts = 583.3 amps in

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

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!!
--
Dave M

Never take a laxative and a sleeping pill at the same time!!!

 

[hussain]

jeffm_@email.com (JeffM) wrote in message news:<f8b945bc.0401180941.7641993d@posting.google.com>...

I allways wondered how dc/ac power inverters work
hussain
http://www.google.com/search?num=100&hl=en&lr=lang_en&ie=UTF-8&oe=UTF-8&safe=off&q=%22DC-AC+inverter%22+circuit+-posted+-prices+-products&btnG=Google+Search

Do you really get more power than what you put ?!
No. Go to the library; read a Physics book.

I saw inverters that's supplied with a 12VDC and will give 7000 W
Nonsense. Physics book (see above).

Thanks all,

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

 

[~^Johnny^~]

On Sun, 18 Jan 2004 20:04:21 GMT, "Tweetldee" <masondg4499@comcast99.net>
wrote:

the old inverters, which
produced a square wave.

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?
~~~~~~~~