Supercapacitor Internal Resistance Calculator
[Image of parallel resistance circuit diagram]
Reverse Calculating the “Truth” of Supercapacitors
When you connect a supercapacitor in parallel with your car battery, the total internal resistance ($R_{total}$) decreases according to the parallel resistance formula. Some sellers use the resulting lower number to claim their product is “ultra-low resistance.”
By using the formula below, you can find the actual internal resistance of the capacitor ($R_{capacitor}$):
\[R_{total} = \frac{R_{battery} \times R_{capacitor}}{R_{battery} + R_{capacitor}}\]Rearranged to solve for the capacitor:
\[R_{capacitor} = \frac{1}{\frac{1}{R_{total}} - \frac{1}{R_{battery}}}\]1/RCap = 1/RTotal - 1/RBattery
Why Use This Tool?
When a seller claims that adding a “Supercapacitor” dropped your system’s resistance from 4.0mΩ to 3.8mΩ, you might think it’s a great improvement. But if you plug those numbers in:
- $R_{battery} = 4.0$
- $R_{total} = 3.8$
- Result: $R_{capacitor} \approx 76\text{m}\Omega$
You will realize the capacitor you just bought has a 76mΩ internal resistance—which is extremely poor. In contrast, a high-quality LiFePO4 battery typically has an internal resistance of around 1.5mΩ to 3.0mΩ. This tool helps you see through the marketing and make informed decisions about your car’s electrical system.