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# how do you convert DC to AC? Answered

please will you tell me how to convert DC to AC?

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DC to LOW VOLTAGE AC! - Here is the problem: I live off-grid, my power source is a 12V battery bank. Inverters are very inefficient and drag the battery power down quickly. I have a cordless telephone and a modem which operates on LOW VOLTAGE AC.
What I need is not on the market as a unit, which is a means to convert my low voltage DC to low voltage AC (6 to 9 VAC)

OR, is it possible to simply run low DC voltage directly to these units. The telephone base charges a battery, so it converts the low power AC BACK into low power DC anyway.
I am assuming that there is an internal rectifier in the phone base, and just wonder if running DC directly through it will hurt it at all?

Depending on how picky your equipment you want to power you may need a pure sine wave inverter or a Modified sine wave inverter rather than a square wave inverter.
You should check out my Modified Sine Wave Signal Generator.
It shows the basic circuit for power boosting as well as it shows how to build the signal circuit.

Conceptually, an inverter is just a 60-hertz oscillator, a hefty power amplifier stage to pump out the needed wattage, and a step-up transformer.

An inverter, I am building one myself it's going to cost me about \$80 for the 50 2n3055 transistors I need to buy. You can buy an inverter they range form 150-3000 watts.

With 50 NPN bipolar transistors, you will be running a lot of them in parallel.
How are you going to insure they share current equally.
Im very interested and would like to know how you solve the problem.
I don't want to expose a secret or something.

A

I am not quite sure how to balance the transistors with resistors yet but I will find out.

Great Attitude !
Building bipolar ( NPN, PNP ) power circuits was an eng nightmare.
These transistors improve their gain and reduced forward voltage drop as temperature increases.
Say we put two 8 amp devices in parallel with a combined current of 10 amps ( 5 amps each ).
Device (A) has a has a little more gain and soon is carrying 6 amps while (B) is down to 4 amps.
This makes (A) get hotter, lowering its forward voltage, raising its gain, getting hotter still.
Now, device (A) is is carrying 7 amps approaching 90ºC and device (B) is loafing at 3 amps.
The progression is; device (A) over heats, goes into thermal run-away, shorts and burns out like a fuse.
Then device (B) has to suddenly handle all the current and it also fails.
This is called a cascade failure and works as bad with three to thirty parallel devices !!
Resistors heat up and waste energy even though they are useful in series with bipolar devices.
Resistors increase in value as they get hot reducing current just the Opposite of bipolar NPN, PNP.
The resistor in series with a device increases as a device tries to hog the current preventing failure.
The engineering hard part is balancing bipolar protectionwithwasted power ?!?!
Today inverters use MOSFETs and IGBT  that have fewer problems.

A

What would you suggest I use? Keeping in mind that that the cheapest and second best way I have found is with 2n3055's (best was IRFP260), I really don't want to buy \$80 dollars worth of transistors only to find a better way of doing it.

The IRFP260 is nice MOSFET 200V, 46A with heat sink.
Whats are input/output  voltages ?
How much current output ?

When working with a New kind of transistor, it is standard practice to make
a low power prototype testing out your gate drive circuitry at the same time.

A

The input of the MOSFET or transistor will be about 12V with a 65Ah battery which I hope to draw about 200Amps from. The 50-60Hz pulse will go through a modified microwave transformer to be stepped up to 230-260V AC 7-9Amps.

The cash to Amp ratio isn't as good for the IRFP260 (constant drain current) than for the 2n3055.

I know I will need two groups of 15 2n3055's for this to work but I will use two groups of 25 to be sure.
At 50-60Hz will the pulsed peak current for the IRFP260 mean anything, or is the frequency to low to consider?

you buy a converter they have them online you just need to google it

At the price of an electronic inverter, you'd be pretty crazy to use a mechanical system these days.

Depends on what you have kicking around the back yard, or if you have a friend at the junkyard. It would be difficult but it would make an interesting project.

An older more mechanical approach is to us a DC motor to drive an AC generator.