AC motors #2

kishorebilla111

Joined Nov 1, 2015
1
HI
I AM CHECKING IN 3 HP NEW MOTOR WINDING RESISTANCE FOR COIL TO COIL =8.8 Ohms
but ohms law is telling 3 hp motor resistance is 76.95 ohms why.....

AlbertHall

Joined Jun 4, 2014
10,366
HI
I AM CHECKING IN 3 HP NEW MOTOR WINDING RESISTANCE FOR COIL TO COIL =8.8 Ohms
but ohms law is telling 3 hp motor resistance is 76.95 ohms why.....
See post #2

ericgibbs

Joined Jan 29, 2010
10,736
Hi,
Something is causing a hiccup, in post move operation.
Looking into it.
Mod.

I expect you saw that the original Thread is 5 years old.!
So a new Thread was Created, for the new poster in order to clear the Thread hijack

Last edited:

Joined Jul 18, 2013
21,378
Re-post:
HP of practically all motors, AC or DC, cannot be discerned from a simple resistance reading.
Max.

crutschow

Joined Mar 14, 2008
25,367
The motor resistance determines the stalled rotor current (starting current), not the running current.
A running motor generates back EMF which reduces the current.
The running current is determined mainly by the motor load.

Joined Jul 18, 2013
21,378
I AM CHECKING IN 3 HP NEW MOTOR WINDING RESISTANCE FOR COIL TO COIL =8.8 Ohms
Also you should be seeing two coils of different resistance, as a 3HP motor is too large to be a identical winding, 1ph PSC motor.
Unless it is a 3ph motor, then 3 winding's should be identical.
Max.

CBTech_Joe

Joined Sep 9, 2020
39
The motor resistance determines the stalled rotor current (starting current), not the running current.
A running motor generates back EMF which reduces the current.
The running current is determined mainly by the motor load.
Yup, this is spot on.
The windings in a phase to phase measurement (all three in a three-phase motor) should read low but not zero ohms. The smaller the motor, the higher this reading will be, but it should not be open. It will usually be low enough (under 30 Ω) for the audible continuity indicator on your meter to sound.
Testing a motor phase to phase only has value if you suspect unbalanced current loading. Each phase to phase reading should be within a few percentage points of each other.

Joined Jul 18, 2013
21,378
The windings in a phase to phase measurement (all three in a three-phase motor) should read low but not zero ohms.
The OP has not stated the motor technology so far!
Max.

CBTech_Joe

Joined Sep 9, 2020
39
The OP has not stated the motor technology so far!
Max.
You are correct. I thought I read 3 phase, but I see all he stated was 3 HP.

So, my information is only pertinent to a 3 phase induction motor which does happen to be the most common format for motors. If however OP has something different, then all bets are off.