Is it TRICKY to measure armature winding resistance?
Is it TRICKY to measure armature winding resistance?
(OP)
I've a brushed DC shunt wound machine with the following specs:
Rated Speed: 3000rpm
Rated Power: 0.25kW
Armature Voltage: 180V
Armature Current (full load): 1.6A
Field Voltage: 210V
Field Current (full load): 0.2A
I did some calculation as follows:
w = n*2*pi/60 = 3000*2*pi/60 = 314.1593 rad/s
Rated torque, Torq = P/w = 250/314.1593 = 0.7958 Nm
K = Torq/Ia = 0.7958/1.6 = 0.4974
E = K*w = 0.4974*314.1593 = 156.2628 V
Armature resistance, Ra = (Va - E)/Ia = (180 - 156.2628)/1.6 = 14.8358 ohm
Field resistance, Rf = Vf/If = 210/0.2 = 1050 ohm
Then, I carried out some measurements. I measured the resistance with 4-wire method using Agilent 34410A. The measured field winding resistance is about 976 ohm, which is not too far from the calculated 1050 ohm. However, I found out that the measurement of armature winding resistance is not consistent (8~100 ohm). May I know why? Is it because of the 'brush/commutator' assembly? Any good approach to measure armature winding resistance?
Thank you very much
Rated Speed: 3000rpm
Rated Power: 0.25kW
Armature Voltage: 180V
Armature Current (full load): 1.6A
Field Voltage: 210V
Field Current (full load): 0.2A
I did some calculation as follows:
w = n*2*pi/60 = 3000*2*pi/60 = 314.1593 rad/s
Rated torque, Torq = P/w = 250/314.1593 = 0.7958 Nm
K = Torq/Ia = 0.7958/1.6 = 0.4974
E = K*w = 0.4974*314.1593 = 156.2628 V
Armature resistance, Ra = (Va - E)/Ia = (180 - 156.2628)/1.6 = 14.8358 ohm
Field resistance, Rf = Vf/If = 210/0.2 = 1050 ohm
Then, I carried out some measurements. I measured the resistance with 4-wire method using Agilent 34410A. The measured field winding resistance is about 976 ohm, which is not too far from the calculated 1050 ohm. However, I found out that the measurement of armature winding resistance is not consistent (8~100 ohm). May I know why? Is it because of the 'brush/commutator' assembly? Any good approach to measure armature winding resistance?
Thank you very much





RE: Is it TRICKY to measure armature winding resistance?
RE: Is it TRICKY to measure armature winding resistance?
RE: Is it TRICKY to measure armature winding resistance?
Thanks for your reply. I have no access to the brush/commutator assembly. There are two pair of leads out of the motor. One of them is for field winding, whilst another pair is for armature winding. I place the 4-wire probe across the armature winding and I find out the measurement is not consistent, ranged from 8-100ohm when the rotor of the motor is turned manually by hand. Is that normal?
RE: Is it TRICKY to measure armature winding resistance?
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