نقشه ساخت اینورتر سینوسی کامل

DG 5 SGA

Power Inverters 12V to 230V

contents: construction plans, technical description

Version of Nov.8th,1999

Rev. 3.1

Fig. 1: 1000 VA-Inverter 12 Volt -> 230 Volt

An inverter allowes the use of 230V electrical appliances from a car battery or a solar battery. It must therefor supply a voltage that corresponds to an rms of 230 Volts sine-wave like household main supply or similar. Sine-wave voltages are not easy to generate. The advantage of sine-wave voltages ist the soft temporal rise of voltage and the absence of harmonic oscillations, which cause unwanted counter forces on engines, interferences on radio equipment and surge currents on condensers. On the other hand, square wave voltages can be generated very simply by switches, e.g. electronic valves like mosfet transistors. In former times electromagnetical switches, that operated like a door bell were used for this task. They were called "chopper cartridge" and mastered frequencies up to 200 cycles per second. The efficiency of a square wave inverter is higher than the appropriate sine wave inverter, due to its simplicity. With the help of a transformer the generated square wave voltage can be transformed to a value of 230 Volts (110 Volts) or even higher (radio transmitters e.g.).

Fig. 2: Sine-wave voltage and conventional square wave voltage with both 230 Volt rms

Fig. 2 shows a sine- as well as a square wave voltage with in each case an rms of 230 Volt. In both cases an electric lamp would light with the same intensity. This is, as we know, the definition of rms. As we recognize in Fig. 2, however the peak value of the sine-wave voltage is 325 Volts, i.e. factor Ö 2 more than rms. For electric lamps this is insignificant and electric engines are appropriate for it. Electronic devices were even designed for the peak voltage of sine-wave voltage, because internally they generate DC voltage from the AC supply voltage. A condenser will be loaded on exactly the peak value of the sine-wave voltage. Electronic devices thereby usually cannot be operated on 230 Volt square wave from fig. 2. The industry nevertheless manufactured square wave inverters according to this principle in former times.

Our inverter works with a trick, to obtain the same results from square wave voltage as for sine-wave voltage.

Fig. 3: Square wave voltage with duty cycle 25% for 230 Volt rms ("modified sine")

Square wave voltage in fig. 3 developes the same peak value as sine-wave voltage of 230 Volts, i.e. 230 Volt * Ö 2 = 325 Volts and nevertheless thereby obtains the demanded rms of 230 V. Square wave voltage as shown in fig. 2 (full half wave) with peak value of the corresponding sine-wave voltage would cause double amount of electrical power on electric consumers. The electrical power rises by square of voltage, and square of Ö 2 results in factor 2. The trick is, to switch the output power only for one half of every conducting cycle, thus resulting on a duty cycle of 25% on behalf of the complete oscillation period. If the calculated double amount of electric power will be generated only half the time, effective power remains the same. Industry called this cam shape "modified sine", in order to be able to differentiate the devices from conventional square wave inverters.

The inverter may feed nearly all electrical appliances, designed for 230 Volts, with exception of rotary field engines, that use condensers for generation of an auxiliary phase (condenser engines). Engines of this type are used in most refrigerators, washing machines, dishwashers and some few machine tools. Fluorescent lamps with a series inductivity to limit the operating current also won't work correctly on our inverter. This problem can be solved by increasing the duty cycle on more than 25% while decreasing the peak voltage to 275 Volts. Instead fluorescent lamps with electronics (energy saving lamps) will work very well on the inverter. There may also be problems with some small plug power supplies. An increased magnetizing current results on square wave voltages, while there would be an predominantly inductive load (cosj << 1). Duty cycle 25% and cosj =0 will result in load currents up to factor p /2 (approx. factor 1.5). But don't be confused: Cosj of most electrical appliances is between 0.8 and 1 and would be harmless.

Our inverter is suitable for:

• electric drills, fret saws, circular saws, electric chain saws, grinders

• Vacuum cleaners, coffee machines,irons, dryers, mixers, sewing machines, electric razors, etc.

• lamps, energy-savings lamps

• Electronic devices, e.g. music amplifiers, battery chargers

• Computers and accessories, UPS

• Televisions and radios