# Mechanical Power (Application) and Electrical Power (Stepper Motor) Discrepancy

For my application I need a torque of $\tau=0.87 \, Nm$ and a speed of $w=140 \, RPM \approx 14.65 \, rad/s$. This gives me a mechanical power $P_m=12.75 \, W$. $$P_m=\tau w$$ I have selected this stepper motor, which gives me the desired speed torque characteristics. Now, I want to double check that the motor will generate enough electrical power to match or exceed the mechanical power requirements ($P_m<=P_e$). $$P_e=UI$$ From the motor spec $I=6.37$, $R=0.3$. As recommeded here, I obtain $U=IR$; this gives me a value $U=1.91 \, V$.

Now this gives me an electrical power of $P_e \approx 12 \, W$, which is lower than my $P_m$. Looking at the graph I would expect a $P_e$ considerably higher than my $P_m$ requirement. Question: why is $P_e$ not higher?

• 12w is the electrical power consumed by one coil when operating as a space heater - what you might call the "parasitic resistance loss". – Chris Stratton Nov 18 '14 at 13:49