Various types of dc motors for traction application

Thread Starter

Electro nS

Joined Feb 20, 2016
i am doing a research on which motor is better suited for Small EV or kart conversion using a fixed gear (single stage).

the options available are : PMDC , SepEx , Series , BLDC . ( No ac motors )

I have found so many information regarding BLDC motors and their advantages , but no useful info on the other types .

So assume 4 motors of each type that can rated continuously (S2 duty) to work on 96v 100A , what which motor is better for traction ? my initial guess is Series or SepEx , since you can design the fixed ratio gearbox for maximum torque required (hills). and get extra speed when torque is not needed (flat road) by "Field Weakening" ( something like electrical gearing) . while with PMDC or BLDC you cannot do that .

1-is my logic correct ?
2- what are the criteria in choosing one of these motors ?
3- how much you can weaken the field and how much extra speed you will get (to stay in safe zone) , most motors shops donot provide much scientific information for an engineering or academic approach for example Netgain motors.


Joined Jul 18, 2013
A shunt field motor can be field weakened, but obviously with a series motor, it cannot.
The main reason for field weakening is higher RPM at lower torque. If you weaken too much you may get run-away condition.
A series motor, starter motor etc, has very high torque at low RPM.