Ohm's Law for Model Railroaders

Ohm's Law is the foundation of all electrical work in model railroading. Understanding this simple relationship will help you wire your layout safely and troubleshoot problems effectively.

The Basic Formula

V = I × R (Voltage = Current × Resistance)

**V (Voltage)** - Measured in Volts (V) - The electrical "pressure" pushing current through the circuit
**I (Current)** - Measured in Amperes/Amps (A) - The flow of electricity through the circuit
**R (Resistance)** - Measured in Ohms (Ω) - Opposition to current flow

Practical Applications

LED Resistor Calculations

When adding LEDs to your layout (signals, building lights), you need a current-limiting resistor:

R = (V_supply - V_LED) / I_LED

For a typical 12V supply with a red LED (2V forward voltage, 20mA current):

R = (12 - 2) / 0.020 = 500Ω (use 470Ω or 560Ω standard value)

Wire Gauge Selection

Longer wire runs have more resistance, causing voltage drop. Use our wire gauge calculator to select appropriate wire sizes for your track feeders.

Power Supply Sizing

Total current draw determines power supply requirements. A typical HO locomotive draws 0.5-1A, so a 5-loco layout needs at least 5A capacity.

Safety Considerations

Never exceed component ratings
Use appropriate fuses or circuit breakers
Heat is a sign of excessive current - check connections if components get warm

Ohm's Law for Model Railroaders

Ohm's Law is the foundation of all electrical work in model railroading. Understanding this simple relationship will help you wire your layout safely and troubleshoot problems effectively.

The Basic Formula

V = I × R (Voltage = Current × Resistance)

**V (Voltage)** - Measured in Volts (V) - The electrical "pressure" pushing current through the circuit
**I (Current)** - Measured in Amperes/Amps (A) - The flow of electricity through the circuit
**R (Resistance)** - Measured in Ohms (Ω) - Opposition to current flow

Practical Applications

LED Resistor Calculations

When adding LEDs to your layout (signals, building lights), you need a current-limiting resistor:

R = (V_supply - V_LED) / I_LED

For a typical 12V supply with a red LED (2V forward voltage, 20mA current):

R = (12 - 2) / 0.020 = 500Ω (use 470Ω or 560Ω standard value)

Wire Gauge Selection

Longer wire runs have more resistance, causing voltage drop. Use our wire gauge calculator to select appropriate wire sizes for your track feeders.

Power Supply Sizing

Total current draw determines power supply requirements. A typical HO locomotive draws 0.5-1A, so a 5-loco layout needs at least 5A capacity.

Safety Considerations

Never exceed component ratings
Use appropriate fuses or circuit breakers
Heat is a sign of excessive current - check connections if components get warm