27-06-2012, 05:37 PM
Power Inverters 12V to 230V
Power Inverters.pdf (Size: 934.67 KB / Downloads: 71)
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.).
Transformer:
A transformer will provide best characteristics when the primary coil, that takes over magnetization of the iron core,
fits closely around the core. For industrial transformers this would be the 230 Volts coil, on our inverters however it
will be the 12 volt coil.
Wire strength:
Current densities from 3.5 A/mm2 to 4 A/mm2 are used on industrial transformers. If our inverter is not beeing used
excessivly, current densities may even be higher. A transformer with 1000 VA needs approx. 84 ampere from the 12
Volt battery on nominal load. Since the two primary coils alternate mutually, we may count from 42 amperes. (This is
strictly not correct, since the acceptance applies only if both windings would exhibit double surface for heat
emission). For a round wire this would mean a diameter of 4 mm. Such wire is hardly to wind, also automats can't do
it perfectly. A solution may be wires with rectangular cross section or several smaller wires in parallel.
After winding the transformer, the sheet metals must be inserted again. With each layer we change the direction of
the sheet metals, while in the original condition several sheet metals were probably summarized into packages, in
order to increase the air gap and linearize magnetizing currents. This effect isn't needed for our inverter. Magnetizing
currents are always extremely nonlinear in square wave transformers, and they are asymmetrical also. This has no
effect on the performance of the inverter and the output voltage.
Power Inverters.pdf (Size: 934.67 KB / Downloads: 71)
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.).
Transformer:
A transformer will provide best characteristics when the primary coil, that takes over magnetization of the iron core,
fits closely around the core. For industrial transformers this would be the 230 Volts coil, on our inverters however it
will be the 12 volt coil.
Wire strength:
Current densities from 3.5 A/mm2 to 4 A/mm2 are used on industrial transformers. If our inverter is not beeing used
excessivly, current densities may even be higher. A transformer with 1000 VA needs approx. 84 ampere from the 12
Volt battery on nominal load. Since the two primary coils alternate mutually, we may count from 42 amperes. (This is
strictly not correct, since the acceptance applies only if both windings would exhibit double surface for heat
emission). For a round wire this would mean a diameter of 4 mm. Such wire is hardly to wind, also automats can't do
it perfectly. A solution may be wires with rectangular cross section or several smaller wires in parallel.
After winding the transformer, the sheet metals must be inserted again. With each layer we change the direction of
the sheet metals, while in the original condition several sheet metals were probably summarized into packages, in
order to increase the air gap and linearize magnetizing currents. This effect isn't needed for our inverter. Magnetizing
currents are always extremely nonlinear in square wave transformers, and they are asymmetrical also. This has no
effect on the performance of the inverter and the output voltage.