The Temperature rise by resistance method needs accurate measurement of armature resistance.
We want to test a small - sub - fhp ( around 50 w) motor having very few com bars ( around 12)
The problem is that the resistance at motor terminals changes as we rotate the motor shaft through a fraction of a turn.This is possibly due to the brushes covering more than one segment at some angular position and covering only one segment at some other position. The resistance measurement is therefore not accurate enough for the calculation by rise of resistance method.
One of the methods suggested in Kenjo and Nagamori's 'PM and Brushless Dc motors' is to measure the volts and amps at locked rotor at two points and determine the armature resistance as Ra = (V2 - V1)/(A2 - A1). This method is time consuming and also may not lead to correct resistances for temperature rise.
Is there any better method ? Is there any STANDARD method as per AIEE or IEC etc?
KASTURY rn snipped-for-privacy@vsnl.com