Electrical Fundamentals
Source Internal Resistance Calculator
Estimate internal resistance with Source Internal Resistance. The page keeps the formula, assumptions, and example values visible.
Enter values for internal resistance
Use one consistent electrical operating case for all fields.
How Source Internal Resistance works
The governing expression is r = (Voc − Vload) ÷ I. Source Internal Resistance uses Open-circuit voltage, Loaded voltage, Load current to report Internal resistance.
With the loaded values, internal resistance evaluates to 0.0400 Ω. Vary one measured quantity so the source of the difference stays clear.
Inputs for Source Internal Resistance
Open-circuit voltage, Loaded voltage, and Load current belong to Source Internal Resistance. Keep source units with open-circuit voltage. For output voltage, use Voltage Divider Calculator.
Actual ratings and readings should replace the demonstration values.
- Open-circuit voltage
- Example entry: 12.6 V.
- Loaded voltage
- Example entry: 11.8 V.
- Load current
- Example entry: 20 A.
Reading the Source Internal Resistance result
This output represents Source Internal Resistance.
A numerical answer cannot replace the rating and protection checks for the real equipment.
Measurement and units
Use measured values and keep prefixes such as milli, kilo, and mega consistent before calculating. Check prefixes on open-circuit voltage.
Normalize units before judging one electrical case against another.
Limits of this calculation
The source must be measured at a stable temperature and state of charge.
Additional electrical behavior needs its own measurement or calculation. Unentered effects remain outside Source Internal Resistance.
Source Internal Resistance record notes
Record source and operating details for open-circuit voltage.
Retain raw internal resistance beside its selected rating.
Questions about Source Internal Resistance
What does Source Internal Resistance calculate?
Source Internal Resistance reports internal resistance.
Can Open-circuit voltage be zero?
For Source Internal Resistance, measure any zero open-circuit voltage directly.
Why can internal resistance differ from measurement?
The source must be measured at a stable temperature and state of charge. Recheck open-circuit voltage.
Should the result be rounded?
Keep extra digits while comparing cases, then round to the precision supported by open-circuit voltage.