How to Measure AC Current

Is the mk.1 eyeball not good enough, then?

Use a shunt resistor and feed to rectifier and put a zener diode according to the variance between running and idle condition. then amplify with a transistor circuiit and connect to a micro relay.

Temperature sensing of the motor body will tell very good the difference between the motor running and the motor jammed.

A digital ammeter should be accurate enough to show the difference between normal running and locked rotor current (for what sounds like a small shaded pole motor).

If current monitoring is not viable (using either a fixed ammeter or a temporary clamp ammeter when performing maintenance), you could monitor the air flow.

What's the fans actual function and why is it jamming in the first place?

Please provide more information.

HI,

I am using hall effect sensor for confirmation of fan is rotating, but mechanical fitment of sensor is not simple for end user.To avoid this problem i am trying to check current in the live ckt . but the results are not satisfactory.

Take a couple of bicycle handlebar streamers and glue 'em where you can see 'em. When they're vertical, the fan is jammed; when they ain't, it ain't.

Actually, instead of streamers, use a flap of thin metal. run a current to it, so when the fan stops, the flap drops and activates a buzzer,siren, horn, whatever.

How small is the variation in current?

Hi,

The fan is used in control panel for removing hot air inside panel.It is lexon ac 230v/0.1a fan.Normal mode fan current is approx 100ma,in fault condition the current is 94 ma approx.The same current variation found if line voltage also changes.

vinayakj

With the current variation being so small and also susceptible to variation with line voltage, any current monitoring system may be prone to false triggering.

If your main objective is to simply identify the fact that the panel cooling fan has seized or stalled, it might be worthwhile considering a different type of fan. There exists DC fans which have a third terminal that give a tachometer feedback (pulses basically) which can be monitored to indicate fan status, similar in operation to PC cooling fans. As you stated, you have a 230v supply. This can be transformed to provide a supply for the fan. All you need now is a pulse monitoring circuit.

Hope this helps.

Hi.

I am using schmitt trigger retriggerable timer with hall effect sensor for input pulses.Timer 'on' time adjustment gives adjustment to detect mimium fault rpm level.The ckt works properley.But to avoid additional sensor wiring i am searching for new thing. I dont think exactly that superimposition of operated rpm freq is available on ac input or not. thanks to all of you.

The current variation will be difficult to monitor and will give a lot of false alarms.

The method you currently use is the best method for fans with no speed output. I personally have only seen DC fans with a speed output though.....

Why not supply the spare fans with the sensor you are now using, already installed, with a plug connection. I personally would just drill a hole in the frame and add the sensor, maybe using epoxy or similar.....

Firstly, there are special sensitive chips around to do this work if you need an operator free environment.....24/7....

Secondly, we might be more helpful if we knew AC or DC, 110V 240V or what ever.....

If you don't state the exact environmentals, you get bad answers. GIGO is the old name for this!!!

Is it 24/7, or no operator presence etc etc etc etc........

BE SPECIFIC AND ACCURATE PLEASE!!!!

Use a digital clamp-on-Ammeter.Set the meter to the lowest current range say 20A or lower range if your meter has it.Start the fan and clamp on the life wire side and read off your values.

Secondly,if u are not ok by this method,use a digital multitester that has the current range of 10A,200mA,40mA and some μA.Since your ac current is 100mA,connect the red lead of meter to the mA jack and the black lead to the common(com) jack.Cut one side wire or cable supply to the motor(u hv two open ends say A and B).Connect one end A to the red lead open end and the other end B to the other open end of the black lead.Select the meter to the 10A current range.Start the fan as usual,when it has run up,select the 200mA range and u will get a good value of the current drawn.

Patrick Whowha

... in addition... better DMM's will also have a button for "peak" reading. You can check the peak current in starting, running and stuck; although if it's stuck to begin with you'll get that peak reading only. A fan that occasionally sticks may draw more current because of the sticking being probably worn bearings. The average will be higher than for a fan without the problem. Detecting this difference may or may not be easily done with a DMM on low current ranges. At 100ma you'll probably be on a 400ma range of the meter, so the resolution may not be great enough to show such a variation.

Using a higher voltage for the fan, if you have access to an appropriate variable AC supply, with a dropping resistor of the right value (you'll need to figure the right combination of the two for best sensitivity) you might see the variations better.

Google also:

Application Note AC Current Monitoring EOCR-AR

If you can afford it, an added transducer for voltage could allow you to monitor the power factor of the motor. If not turning, the power factor will be very low compared to a running condition. There are monitor relays available that do this, but I doubt you can afford to use a +$100US relay on a small vent fan like that. But you may be able to roll your own if the volume warrants it.

Example: Siemens 3UG4 relay