Electronics FAQ – Your Multilingual Guide to Electronics

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...

How Long Can a 9V Battery Power an LED using a 4.5K current-limiting resistor? Calculations and Practical Tips A good quality alkaline 9V battery pack has an AH capacity of 500 mAH. Calculation:  Assuming a drop of 2V across the LED, the current drawn by the battery for the LED circuit would be 7V/4.5K 1.5 mA So LED will be ON for 500/1.5 = 333 Hrs. Conclusion:  An LED will stay lit for 333 hours or approximately 14 days.  FAQ Set: Q1: How long can a 9V battery power an LED? The runtime depends on the battery capacity, LED current, and any series resistor used. It can be estimated using   battery capacity/circuit current . Q2: How do you estimate the battery life? Battery life (hours) ≈ Battery capacity (mAh) / Load current (mA). Example: A 9V alkaline battery (~500 mAh): Battery life ≈ 500 1.56 ≈ 320  hours Battery  life ≈ 1.56 500 ​ ≈ 320  hours Q3: What factors affect battery life in this circuit? Actual battery capacity LED forward voltage var...

Why Do some Batteries Connected in Series Heat Up? Causes, Safety Risks, and Prevention Tips. Internal resistance of the battery is explained.  To understand this, let’s solve a quiz.   Higher resistance dissipates more power in a series circuit: Two lamps. 40W and 100W are connected in series. Which one will give more light? Popular to the misbelief that having more wattage, 100W, will give more light.   No, exactly apposite, 40W will give more light. Why? Because a 40W bulb has more filament resistance than a 100W bulb. In a series circuit, the current remains constant, so the I^2 x R product, i.e., heat, is greater for a 40W lamp than for a 100W lamp, hence producing more light. Batteries are connected in series for the Inverter and UPS:  Why all this rant? Because batteries are commonly connected in series, especially in UPS systems. Every battery has an Internal resistance:  Why do some batteries have more internal resistance? It depends on the age of the b...