Stepper Motor Vref Calculator

Target Vref

Set Multimeter To

1.200 V

Target Peak Current1.20 A

Target RMS Current0.85 A

Sense Resistor0.11 Ω

Formula:
Vref = (I_rms × √2 × (Rs + 0.02) × 2.5) / 0.325

Safety: Use a ceramic (non-conductive) screwdriver to adjust the potentiometer. A metal screwdriver can short the board and destroy the driver. Always adjust with the printer powered on but motors idle.

What is Vref?

Vref (Reference Voltage) is the voltage on your stepper driver's potentiometer that sets the maximum current the driver will deliver to the motor. Setting it correctly is critical:

Too high: Motors and drivers overheat, potentially causing thermal shutdown mid-print, skipped steps, or permanent driver damage.
Too low: Motors don't receive enough torque, causing missed steps, layer shifts, and failed prints — especially during fast travel moves.

The relationship between Vref and motor current depends on your driver chip and the sense resistors on your specific board. The same driver chip (e.g., A4988) can need very different Vref values on different boards — always verify your sense resistor value.

Peak vs. RMS Current

Stepper motor datasheets almost always list peak current per phase — the maximum instantaneous current through one coil. However, Trinamic drivers (TMC2208, TMC2209, TMC2225) regulate RMS current, which is lower:

I_RMS = I_peak × 0.707 | I_peak = I_RMS × 1.414

This calculator accepts the peak current from your motor's datasheet and automatically converts to RMS when needed for TMC drivers. No manual conversion required.

How to Set Vref

1. Find Your Sense Resistor

Look for two small SMD resistors near the driver chip. They'll be marked with a code like R100 (0.100 Ω), R068 (0.068 Ω), or R110 (0.110 Ω). If you can't read them, check your board's documentation.

2. Calculate Vref

Enter your motor's rated current from its datasheet or sticker (typically 1.0–2.0 A for NEMA 17 motors). Select your driver and sense resistor value. Start with 70–80% current limit — you can increase later if you get layer shifts.

3. Measure & Adjust

Power on the printer with motors idle. Set your multimeter to DC voltage. Touch the positive probe to the potentiometer and the negative probe to a ground point (motor power supply GND). Adjust with a ceramic screwdriver until you read the target Vref.

4. Test & Fine-Tune

Run some test prints. If motors feel excessively hot after 10 minutes (too hot to touch), lower Vref by 5–10%. If you experience layer shifts or missed steps during fast moves, increase it slightly. Motors should be warm but comfortable to touch during normal operation.

Tips & Troubleshooting

TMC Drivers in UART Mode

If your TMC2208/2209 is configured via UART (through firmware like Marlin or Klipper), Vref is overridden by software. In that case, set the current in firmware instead. The potentiometer only matters in standalone (STEP/DIR) mode.

Different Axes, Different Currents

Your X/Y axes may need higher current than Z for fast moves, while the extruder often runs lower to avoid grinding filament. It's common to set X/Y at 80–90%, Z at 70–80%, and E at 60–80% of rated current.

Cooling Matters

Stepper drivers generate significant heat. Ensure your driver heatsinks are properly attached and that your electronics enclosure has adequate airflow. Overheating drivers will thermal-throttle and cause random layer shifts.

Common NEMA 17 Currents

Typical rated currents for 3D printer NEMA 17 motors: Creality stock motors are 0.84 A, the popular 17HS4401 is 1.7 A, and pancake extruder motors (like LDO-36STH20-1004AHG) are around 1.0 A. Always verify with your specific motor's datasheet.

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