Calculate stepper driver Vref and current limit from target current, sense resistor value, and driver type.
Set driver, Rsense, and target current to calculate Vref or current.
Vref is the reference voltage used by many stepper driver boards to set phase current limit. Correct current limiting helps avoid motor and driver overheating.
A common formula is I ≈ Vref / (8 × Rsense). Rearranged: Vref = I × 8 × Rsense.
A practical formula is I ≈ Vref / (5 × Rsense). With Rsense = 0.1Ω this becomes I ≈ 2 × Vref.
TMC current setup depends on board design and firmware mode (standalone vs UART/SPI). This tool provides a practical estimate and should be verified against board documentation.
| Driver | Rsense | Target current | Vref | Notes |
|---|---|---|---|---|
| A4988 | 0.05 Ω | 1.0 A | 0.40 V | Common formula I = Vref / (8Rs) |
| A4988 | 0.10 Ω | 1.0 A | 0.80 V | Check board resistor marking |
| DRV8825 | 0.10 Ω | 1.0 A | 0.50 V | Common estimate I ≈ 2 × Vref |
| Generic | 0.10 Ω | 1.0 A | 0.80 V | Factor 8 example |
Clone boards may use different Rsense values. Always check resistor markings or board schematics before setting Vref.
After setting current, validate with real load tests. Monitor driver and motor temperature, and stay below rated current where possible.
Use Vref = I × 8 × Rsense. For example, 1A with Rsense 0.05Ω gives 0.4V.
Use Vref = I × 5 × Rsense. With Rsense 0.1Ω and 1A target current, Vref is 0.5V.
Current limit formulas scale with Rsense. If board Rsense differs from assumptions, the resulting current can be significantly wrong.
Not exactly. TMC boards and firmware modes vary. Treat simple Vref formulas as practical estimates and validate with board-specific documentation.
Drivers and motors can overheat, skip, or fail prematurely. Start conservatively and increase only as needed.