Equation $(1)$ specifies the relationship between speed and armature voltage.

Evidently, according to the formula, the speed would be directly proportional to the

applied voltage, irrespective of armature $($load$)$ current if Ra $=0.$ In practice, Ra $0.$

We shall now see what effect this has on the idealised relationship at no$-$load $($brake

fully off$)$ and at full load.

E&EE$,$ NUI Galway $2$ Third Year Laboratories

Speed $($RPM$)$

Question

Is the brake a mechanical load $($what useful work is it doing$)?$

Answer

Question

$($a$)$ What is the full load current of the motor $($how do you find this out$)?$

$($b$)$ What would happen if this maximum load current were exceeded?

Answer

The following results show how the motor speed varies with armature voltage: $($a$)$

with no load $[$brake fully off$]$; and $($b$)$ at half$-$load current.