Electronics FAQ – Your Multilingual Guide to Electronics

Importance of a current-limiting resistor in an LED circuit LED is basically a forward-biased diode: Like a revered biased zener, it has a fairly constant voltage drop of 1.5V to 3V. If you supply more than this voltage, even slightly more, a large current will flow through it, as there is no mechanism to absorb the excess voltage (LED - supply). Result: LED damage from overcurrent. Mechanism of current limiting resistor:  A resistor in series absorbs the voltage difference and sets a safe current through it. A series resistor also has a secondary purpose of setting the light intensity of the LED. Especially in a battery powered gadgets, it is important to conserve battery.

How to find out the remaining life of lead acid battery?    Judging a battery's remaining life from its terminal open circuit voltage wont give you a clear picture. Have you heard the story of ‘ Blind Men and the Elephant’? You need to know the battery's ‘ internal resistance’ . As the battery becomes old, its internal resistance increases. If it crosses the maximum allowable value, the battery is due for replacement. Find the maximum allowable internal resistance for your battery type from its manufacturer. A telltale sign of a weak battery is that it heats up under high load. Battery internal resistance:  Battery internal resistance:   It is formed due to the chemical composition of the battery. It is very easy to calculate internal resistance by applying a predetermined known (resistive) load on the battery. Measure load current and load voltage to calculate the internal resistance of the battery by applying simple Ohm’s law. Circuit to find out the internal resis...