hello, i am new here and i need help with my project. i have to create a proto that measures stator current from an induction motor. i tried arduino uno r3 w/ acs712 as the main hardware for data acq but I don't think the sensor is right. can u guys suggest any other sensors or anything that could make my proto work? thank you.
Hi, @panonymous
Welcome to the forum.
How big is the induction motor?
Can you please post a schematic of how you connected the 712 sensors?
Thanks.. Tom.. 
the single-phase induction motor has the following specifications: 1 HP, 220 V, 60 Hz, 4-poles, 1720 RPM, and 7.5 A. And I just connected the current sensor in series with the motor and ac supply.
have a look at SCT_013 current clamp - comes in various current ratings - don't even have to break into the cable
I use three 100amp clamps to monitor current/power to the house, e.g.
How often are you reading the sensor? I think you need to measure many time faster than the motor rotation and then average the readings.
Hi, @panonymous
Can you please post your code?
To add code please click this link;
It looks like you are sampling the actual real time AC current, when I assume you need RMS current.
Thanks.. Tom...
yes, I actually need instantaneous current instead of rms that's why I don't think acs712 is the right sensor. can u guys suggest a sensor that outputs instantaneous current?
the ACS712 gives you the instantaneous DC or AC current when sampled
if you require RMS of AC you read a series of samples over several cycles and take the square root of the mean of the sample values squared
this what I do with the SCT-013 current clamp to get RMS current and hence power
The ACS712 does measure the instantaneous current.
Measuring RMS current is more involved, you need to take multiple readings throughout a mains cycle and process the results to get the RMS value.
Thanks.. Tom..
Panonymous,
Are you just taking a single reading, at random, and expecting that to be the required result?
If so then depending upon whereabouts in the mains cycle you happen to take the measurement, the result can be anywhere between the peak forwards current and the peak negative current. It might even be zero.
Is this the problem you are experiencing?
tbh I haven't tested the proto yet but based on my research, the data acq devices that have the acs712 current sensor produce small/few current signals only, and I don't think that can detect the bearing fault in motors coz ill be needing the acquired current signals to detect the bearing faults in motors. also, how would I know that the current signals I'm acquiring are stator current?
Hi,
Do you have access to a scope, so you can see the output of the 712?
This will help you understand the waveform you are sampling.
Tom...
If the motor is the more common squirrel cage induction motor, then the only current you can measure is the stator current.
If the motor is a wound rotor induction motor then it will have slip rings and terminals to connect resistors to. Don't connect the ACS712 here. (I'm not sure that these even exist as single phase motors)..
The current measured on the mains input wiring is going to be the stator current in either case.
Hi,
Can you post a link to specs/data of the motor?
Does it have a capacitor mounted on it?
Thanks.. Tom..
hello, I already posted the IM specs here, and it doesn't have any capacitor mounted on it. do I need to mount a capacitor in my IM to acquire instantaneous current?
No need to add a capacitor.
If the motor needs one it should already be fitted.
Some motors have two separate, but similar windings. A capacitor is used to alter the phase of the signal going to one of the windings. This ensures that the motor starts and runs in the right direction. By altering which of the windings has the capacitor connected you can change the direction of rotation.
Usually you use a vibration sensor and or a temperature sensor connected to the bearing casing.
That is how most underground mining operations monitor their electric motors.
Tom....
yes i know that but our project is about detecting bearing faults using motor current signals. anw do u guys know how to adjust the parameters of the serial plotter in arduino ide because I cant see the totality of the current reading like I still need to plot it manually in excel to see the up and down trend of the current reading
What type of bearings does your motor have? How often are they lubricated? Or are you trying to discover when lubrication has failed?
Ball bearings will make noise when they need lube. Sleeve bearings will get warmer when they lack lube.
A varying load on a motor will have a direct effect on current values, so the load on your test motor will have to be constant.