Mini Inverter. Design Note 41


Here is a simple Mini Inverter circuit to light 11 Watts CFL from 12 volt battery. It is an ideal gadget to check the vehicle engine or electrical circuit in night. It can be hooked in the vehicle’s battery and the CFL will light. It can also be used in home as emergency lamp using the 12 volt UPS battery. An AC socket provision is also added to charge Mobile phone or other low watt gadgets while travelling. The 12 volt DC can be tapped from the Cigarette lighter socket of the car. The Inverter has maximum 18 Watts power.
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Simple Inverter. Utility Gadgets.9

An Inverter circuit converts DC to high volt AC for driving high power devices. The principle of simple emergency lamp circuit and the heavy load inverter circuit is the same. The DC voltage is converted into AC using an oscillator circuit. A driver transformer then step up this low voltage AC to 230 volt AC. The output waveform from the oscillator depends on the type of circuit. In simple inverter, it is square wave but in microprocessor based types, it may be quasi sine wave or pure sine wave. Pure sine wave AC is similar to the AC available in the mains power supply so all the instruments usually running in Mains power can be connected in Pure sine wave inverter. The appliances connected to Square wave and quasi sine wave may not work well as seen in the humming of fan, flickering of tubes etc. This circuit is meant for explaining the method of  an inverter.

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Inverter Capacity Tester

With this tester, you can assess the capacity of Inverter to handle the load. It gives a warning beep, if the inverter load exceeds above its load handling capacity. Inverters are available in different ‘Size ratings’ from 50 VA up to 50000 VA. VA indicates the ‘Size’ (capacity) of the inverter which represents its maximum load capacity. Commonly available inverters are 500 VA, 800 VA, 1000 VA, 1500 VA etc. An inverter needs Peak or Surge power and Typical or Average (Usual) power to handle the load. Peak power is the maximum power that an inverter can supply usually for short time. If the load increases above the rated capacity of the Inverter, it will over load the inverter that may leads to its permanent damage.

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Home Inverter

Home inverter is to provide uninterrupted power to run household electric devices. These are available in different voltage and load capacities. In the basic design of the inverter a DC (battery) source is connected to a transformer through the center tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the battery following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit. This will be 230 /110 Volt AC and can operate all the electric devices.

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