# Does the peak torque decrease at rated speed for BLDC motor?

Does the below BLDC motor have the same Peak Torque(short time) at the rated speed?

1. Rated_Voltage: 24V
2. Rated_Speed: 4000RPM
3. Back_EMF_Constant: 3.7Vp/KRPM
4. Peak_Current: 4.4A
5. Peak_Torque: 20oz-in
6. Resistance: 1.5Ohms
7. Inductance: 2mH

Here is my calculation:

• VOLTAGE = Rated_Speed * Back_EMF_Constant + Peak_Current * Resistance

If the above "VOLTAGE" exceeds Rated Voltage, then the motor can not exert Peak Torque(20oz-in) at the rated speed.

For the above motor:

• 21.4V = 4000RPM * 3.7Vp/KRPM + 4.4A * 1.5Ohms

Because 21.4v is less than Rated Voltage(24v), so it can exert the same Peak Torque at the rated speed.

Is my calculation correct ?

Thank you.

In your case, given the information you've provided, the stall current should be $\frac{24 V}{1.5 \Omega} = 16 A$. So the peak current of 4.4 A that you've listed must be something else. The rated current should be $24V = 4000 RPM * 3.7\frac{Vp}{kRPM} + I *1.5 \Omega => I = 6.1 A$.