Calculator Inputs
Example Data Table
| Branch | From node | To node | Resistance ohm | Meaning |
|---|---|---|---|---|
| R1 | P | A | 100 | Input resistor from supply to node A |
| R2 | A | N | 220 | Load path from node A to return |
| R3 | A | B | 330 | Bridge branch between two junctions |
| R4 | B | N | 470 | Second load path to return |
| R5 | P | B | 680 | Alternate feed branch from the supply |
Formula Used
The calculator uses Ohm's Law, Kirchhoff's Current Law, and conductance matrix solving.
Branch conductance is G = 1 / R.
For every unknown node, the current sum is zero.
The nodal equation is G matrix times V node equals I source.
Branch current is I = (V from - V to) / R.
Branch power is P = I squared times R.
Equivalent resistance is R eq = V terminal / I source.
With source resistance, I source = V ideal / (R eq + R internal).
How to Use This Calculator
First, enter the ideal source voltage. Then enter the positive and negative source node names. Use short labels, such as P and N.
Next, describe each resistor branch. Type the branch label, start node, end node, and resistance. Use the same node name wherever schematic wires join.
Enter source internal resistance when the supply has a known series resistance. Enter power and current limits to get warning messages.
Press Calculate Current. The result appears above the form. Use CSV or PDF buttons to save the same calculation.
Current From a Schematic Article
Why Schematic Current Matters
Reading a circuit schematic is more than finding one resistor. Real diagrams may contain several paths, shared nodes, and branches that join again. This calculator treats the entered network as a resistive direct current schematic. You define each branch with two node names and a resistance. The tool then builds the conductance matrix and solves every unknown node voltage.
Mixed Network Solving
The method is useful when a circuit is not purely series or parallel. A bridge, divider chain, or mixed network can be entered by naming the same junctions consistently. The positive supply node is fixed at the terminal voltage. The negative supply node is fixed at zero volts. Other nodes are solved from Kirchhoff's Current Law.
What the Result Shows
After the node voltages are known, each branch current is found from Ohm's Law. Power is calculated from current squared times resistance. The total source current is the sum of currents leaving the positive source node. Equivalent resistance is voltage divided by total current. When internal source resistance is entered, the terminal voltage is reduced before branch currents are shown.
Good Node Naming
Use clear node names. Common labels are P for positive, N for negative, A for a junction, and B for another junction. A branch is active only when both nodes are filled and resistance is greater than zero. Leave unused branches blank. Avoid using the same node name for both ends of one resistor.
Practical Use
This calculator helps with study work, repair notes, and quick design checks. It can show why a current path is heavy, why one resistor runs hot, or why a supply may sag. The CSV export is helpful for spreadsheets. The PDF export is useful for sharing a compact calculation record. A saved report also creates a repeatable trail. You can change one resistance, compare source current, and document the effect. This makes troubleshooting faster. It also helps students connect schematic symbols with node equations and measurable branch currents during lab practice and homework.
Limits
The result should still be reviewed against the real schematic. Inductors, capacitors, diodes, transistors, meters, and alternating current effects are not modeled here. Convert those parts into an equivalent resistance only when that assumption is valid. For safety critical work, verify values with test equipment and applicable standards.
FAQs
1. What does this calculator solve?
It solves current in a resistive direct current schematic. You enter resistor branches between named nodes. It returns source current, branch currents, node voltages, power, and equivalent resistance.
2. Can it solve mixed series and parallel circuits?
Yes. It does not need a simple series or parallel selection. Shared node names let it solve mixed paths, bridges, and divider networks with nodal analysis.
3. What node names should I use?
Use simple names like P, N, A, B, OUT, or GND. Use the exact same name for points connected by a wire. Different names mean different electrical nodes.
4. Why is my branch current negative?
Negative current means current flows opposite the branch direction you entered. The magnitude is still useful. Swap the from and to nodes if you want a positive displayed direction.
5. What is terminal voltage?
Terminal voltage is the voltage applied to the external resistor network. It can be lower than ideal source voltage when internal source resistance is entered.
6. Does it handle capacitors or inductors?
No. This tool models resistors in direct current conditions. For capacitors, inductors, diodes, or transistors, use a valid equivalent resistance only when the circuit assumption allows it.
7. Why did it ignore a branch?
A branch is ignored when it is not connected to the source node group. Check its node names and make sure it connects into the active schematic.
8. Are CSV and PDF exports calculated again?
Yes. The export buttons submit the current form values and recalculate the schematic. This keeps downloaded reports matched to the latest entered data.