Detecting 120V motor running

[windozeuser]

I've built a counter on the arduino, and used a 120V relay coil wired in parallel with the 120V motor to detect when this device powers on. The problem is the motor runs very brief anywhere from 800mS to 2 seconds at a time ( varys with the material) (only when the operator does something to operate it). I need to count only once every time it powers up so I made a NAND RS debouncer circuit which helps a lot, but it seems to still not count sometimes, I'm polling 4 times a second in the code for the trigger.


Is there a better way to do this? To detect the 120V motor running depite the time its running for and only counting it once for sure? It needs to be somewhat accurate not medical accurate but at least 98% accurate

Thanks

 

[alec_t]

What type of motor is it? AC? DC? Brushless?.....
What current does it draw?

 

[windozeuser]

Its a 120V AC motor draws around 10A but since its only switched on briefly it goes up to 15Amps only runs when an operating pulls a label and the IR sensor energies the motor for up to 2 seconds to advance to the next label. Its a label dispenser and I'm making a counter to count the labels. The IR sensor itself operates on 120Volt too..

 

[alec_t]

Relay contact bounce may be the culprit for the mis-counting, despite the debouncer. Have you considered using the IR sensor instead to trigger the counter?

 

[ronsimpson]

I measure when my motor is on by watching current. I use a current transformer. In my case there is no need to know 1A or 2A or 10A but if the current is above 1A. The current transformer turns a transistor on at 0.6 volts and the transistor swings 0/5 volts for the computer.

 

[windozeuser]

The current transformer idea is very interesting! how much do they run?

The IR sensor runs on 120V and has an IR emitter and receiver pair that picks up if there is a white piece of paper in front of it basically. I'm wondering how I could trigger using this? Theres no where to really put my own sensor in along with this one and a piece of paper is floating over near it too

 

[alec_t]

the IR sensor energies the motor

Then could it energise the counter too? Can you tap into the sensor output?

 

[ronsimpson]

Digikey.com has 100s of CTs.
A part from pulse eng. is $3.00
Coilcraft has good white papers on how to use them.

You need a part that works down to 60hz. (some do not).
I am using a part with a hole in it. You pass the motor wire through the CT.

 

[windozeuser]

Well the output is 120V it goes into relay that turns the relay on and the motor turns a little and then when the IR sensor picks up a white paper it shuts off the relay and the motor turns off. The motor is only energized for maximum 3 seconds at a time. The problem I'm having tapping it is dealing with the 120VAC to the 5VDC counter to count accurately Thats the whole device its really simply made, just a motor, relay, power switch, and IR sensor that actually outputs 120V. The device dispenses white labels for the operator to pick off easily and fast

 

[alec_t]

I'm surprised the IR sensor output is 120AC. I would have expected a lower, DC voltage, e.g. 12V, for operating the relay coil.
So, as another option if you don't take up Ron's suggestion, perhaps you could drop the 120V at the relay coil down to ~5V with a potential divider, then rectify and smooth the result with a fat cap. The cap would need a resistor across it so that the cap volts decay between successive activations of the relay.

 

[windozeuser]

Sounds good guys I'm gonna try rons idea and get back to you thanlks