Enter Resistor Split Details
The reference end is ground. The tap voltage is measured relative to this end. Leave the load blank for an unloaded divider.
Example Data
| Input | Example value | Meaning |
|---|---|---|
| Total resistance | 10,000 Ω | Complete resistor track |
| Track length | 100 units | Reference length for the tap ratio |
| Tap position | 40 units | Lower section is 40 percent of the track |
| Supply voltage | 12 V | Voltage across the complete divider |
| Load resistance | 4,700 Ω | External circuit connected at the tap |
For this example, the calculator first creates a 4,000 Ω lower section and a 6,000 Ω upper section. It then includes the 4,700 Ω load in parallel with the lower section.
Formula Used
The model assumes a uniform resistor track. The tap position is measured from the grounded reference end.
Tap fraction = tap position ÷ total track length
Rlower = Rtotal × tap fraction
Rupper = Rtotal − Rlower
Rlower, effective = (Rlower × Rload) ÷ (Rlower + Rload)
Vtap = Vsupply × Rlower, effective ÷ (Rupper + Rlower, effective)
P = V × I and P = I² × R
When no load is entered, the effective lower resistance equals the lower section resistance. The loaded and unloaded voltages then match.
How to Use This Calculator
- Enter the resistance measured across the two end terminals.
- Enter the complete physical track length in one unit system.
- Enter the distance from the grounded end to the tap.
- Enter the voltage applied across the full resistor track.
- Add the receiving circuit resistance when it loads the tap.
- Select calculate and review voltage, current, power, and loading error.
- Use the CSV or PDF buttons to save the current results.
Working With Partial Split Resistors
A partial split resistor divides one resistive track at a selected point. The selected point is called a tap. A uniform track has resistance spread evenly along its length. Moving the tap changes the resistance on each side. This behavior appears in potentiometers, trim controls, sensor tracks, and adjustable voltage dividers. The calculator treats the reference end as ground. The supply connects across the full resistor. The displayed tap voltage is measured from ground to the chosen point. This model also works for fixed resistor strings.
The split position creates two resistors. The lower section runs from ground to the tap. The upper section runs from the tap to the supply. Their sum equals the stated total resistance. A center tap produces equal sections on a uniform device. A tap closer to ground produces a smaller lower resistance. A tap closer to the supply produces a smaller upper resistance. These relationships are simple, but practical circuits add an important complication. A connected load can change the divider result.
Loading occurs when another circuit draws current from the tap. That circuit behaves like a resistor across the lower section. The parallel combination becomes smaller than the original lower resistance. The tap voltage then falls below the unloaded value. A low load resistance creates a larger voltage error. A very high load resistance causes little error. This is why measuring equipment and following circuit stages matter. Their input resistance becomes part of the divider network.
The calculator shows both loaded and unloaded tap voltages. Comparing them helps assess loading sensitivity. It also reports loading error as a percentage. This comparison is useful when a divider feeds an analog input. A small difference may still be unacceptable in a precision system. Increase resistance carefully, reduce load demand, or add a buffer stage. A voltage follower can isolate the divider from a demanding load. Always check whether the load remains stable during normal operation.
Power checks are equally important. Every resistor section dissipates heat when current flows. The total source power equals useful load power plus resistor losses. A partial segment may carry more power than expected near one tap position. Examine reported segment power before choosing a component rating. Leave a sensible safety margin. Resistor ratings also change with temperature, enclosure design, airflow, and nearby hot parts. Do not use the calculated minimum rating without margin.
The length field supports a physical resistor track. Use millimeters, centimeters, inches, or another consistent unit. The result depends on tap fraction, not the named unit. For a fixed divider, set total length to any convenient value. Then enter a tap distance matching the intended resistance ratio. Good measurements improve real results. Disconnect power before measuring resistance. Some loads change with voltage or temperature. Treat this as a steady-state resistive model. Confirm results with suitable test instruments. Careful setup keeps resistor calculations clear, safe, and repeatable.
Frequently Asked Questions
1. What is a partial split resistor?
It is a resistor track divided at a selected tap. The tap creates upper and lower resistance sections whose values depend on position.
2. Does the calculator require millimeters?
No. Use any length unit. The tap position and total length only need the same unit because the calculation uses their ratio.
3. What happens when the load field is blank?
The calculator treats the tap as unloaded. It uses the normal voltage-divider equation without a parallel resistance at the tap.
4. Why is loaded tap voltage lower?
A load draws current from the tap. It lowers the effective lower resistance and changes the divider ratio, reducing the tap voltage.
5. Can I calculate a potentiometer?
Yes. Enter the potentiometer resistance, total track length, wiper position, supply voltage, and any load connected to the wiper.
6. Is the model valid for nonuniform tracks?
Not directly. The calculator assumes resistance changes evenly with position. Use measured section resistances for a nonuniform track or taper.
7. What does loading error show?
It shows the percentage change between unloaded and loaded tap voltage. A negative value means the load reduced the expected voltage.
8. Why are power results important?
They help you choose safe resistor ratings. Excess power can cause overheating, drift, permanent damage, or reduced component life.
9. Can I use a zero-volt supply?
Yes. The resistance values still calculate, while current, voltage, and power results become zero.
10. Does this replace circuit testing?
No. It provides a steady-state estimate. Confirm important designs with real measurements under expected voltage, temperature, and load conditions.
11. Can the CSV and PDF files include inputs?
The exports contain calculated results. Keep a copy of your input values with each export for complete design records.