Display whether or not a line has current going through it

Using Arduino Project Guidance
#1

Hello everyone!!!

I want to be able to tell if there is a/c current going through a line. If it is than I want a counter to keep track of how long it is on for in seconds, because I am planning on doing this with a pretty thick gauge wire I was thinking of using an a/c current clamp like this one:

I am wondering is this is possible? (I hope it is)
If I cannot use the clamp, what else can I use to sense the current? I don't need the sensor to be accurate since I just want to keep a time of when current goes through the wire.

Any help would be much appreciated!!!

#2

What voltage AC is this, 120, 240 ?

There are several ways to test for current flow. One is to check the voltage across a low value resistor (or a length of the wire).

#3

The voltage is 240.

#4

How much current is going through the wire? It it's variable, consider the minimum current you'd like to detect...

The specs say -

Output: 40A: 1mV/0.1AC
400A: 1mV/1AC

On the most sensitive scale (40A), you'll need to have 1 Amp in order to get 10mV, which I would consider about minimum for the Arduino without amplification, assuming you use the optional 1.1V ADC reference.

You CANNOT put regular AC into the Arduino because it can be damaged by negative voltages. You can [u]bias[/u] the input at half the supply voltage (or half of the ADC reference) and then subtract-out the bias in software.

It's also a good idea to add some [u]protection diodes[/u] whenever connecting the the "outside world" where unexpected things can happen.

#5

Hmm, okay so would you suggest a better sensor to use??

#6

Question from DVDdoug: "How much current is going through the wire?"

Is it 240V * 40Amps = 9600 watts ?

#7

Measuring AC is not as easy as measuring DC.
The sensor has a 1mV/A setting. That is ~2.8mV peak/peak per amp.
That migh just be able to be detected with 1.1volt Aref in the code.
Remember that this is AC, so the sensor has to be "lifted" to mid-voltage.
And needs to be sampled many times per second.
Google "openenergymonitor Arduino"
Leo..

#8

May be best to have a preamp (op-amp) to increase the signal. Then a rectifier and small cap to smooth it a bit.

#9

Pass live and neutral in opposite directions through the clamp for twice the output.
Or loop one wire multiple times through the clamp.
Correct answer depends on the current to be measured.
Leo..

#10

Do you want to trigger if a 7 watt light bulb is on or off? Or is your expected load different from that?

#11

I have used this type of current transducer.

It is powered from 5V, The output is at 2.5V, with no current flowing.
The output voltage increases for a current in one direction, and decreases for a current in the opposite direction.
So you can use it to measure AC or DC.

#12

So it's for a welding machine. There is a negative and a positive wire coming form the front of the welding machine. If you put a multimeter to the positive wire it only shows current when the welder is welding. I want to capture the time that the welder is actually welding. So I'm not trying to get an exact measurement, I just want the arduino to see the current then keep a timing total in sec.

#13

So it's for a welding machine.

In that case, there's probably plenty of current to measure and the clamp should work. Just make sure to add the bias & protection circuits.

#14

The welding machine has a switch to start the arc (trigger on a MIG and pedal on a TIG). Have you thought about using the switch as a trigger instead of trying to detect the current going through the positive lead? Just a thought...

#15

chipreibel:
The welding machine has a switch to start the arc (trigger on a MIG and pedal on a TIG). Have you thought about using the switch as a trigger instead of trying to detect the current going through the positive lead? Just a thought...

If you aren't using an arc welder, this is your best option. Just find the hook up on the front of the feeder where the whip trigger wires plug in.

If you need to use a current sensor, I am using one of these to detect MIG current for an automatic torch height controller http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MT7185-ND&site=CA&lang=en

Or just drop 10+ thousand on a new Lincoln power wave. They will send you a weekly email with arc on time, wire used and even weld quality.

#16

Also, unless you are working with an aluminum welding tig machine, your current will be dc if you read it off the cables on the front of the unit.

#17

It took 11 posts to tell us this is for a welding machine.
The AC clamp from post#0 will only work on the mains power wires.
Leo..

#18