Written by: Newton C. Braga

 

 

I want to power a 60 W x 110 V lamp with 4 small alkaline batteries. I need an inverter circuit that converts the 6 V of the batteries into 110 V, keeping the current …

 

This type of question is more frequent than many people think. In the first place you can not create energy. If the batteries can supply 6 V x 1 A, you cannot increase the voltage by keeping the current, i.e., you cannot get 110 V keeping the 1 A, as this would create power and there is a principle of physics that says that energy cannot be created or destroyed ... Thus, when we increase the voltage of a battery of 12 V x 1 A to 120 V, we only obtain a maximum current of 0.1 A, for 12 x 1 = 12 x 0.1 = 12 W. For this reason, the inverters used to increase the voltages of batteries have such limited power. They depend on what the source of energy the batteries can provide. Even so, if we "pull" too much of a battery with an inverter, the result will be a decrease of its autonomy. For example, if you use a 12 V battery to get 120 V and power an appliance that needs 0.2 A (24 W), the inverter should operate with 12 V x 2 A. This is also loss since the transistors and inverter transformer heat up. In other words, we can change the voltage of a circuit, increasing or decreasing, but always maintaining the power, because power is energy per unit of time, and energy cannot be created. To finalize: the requested project is unfeasible