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View Full Version : Non-Invasive current sensor usage....?



Javalin
02-27-2012, 11:29 AM
Hello all,

A little help please. I bought a non-invasive current sensor to monitor my home current consumption - http://www.seeedstudio.com/depot/noninvasive-ac-current-sensor-100a-max-p-547.html?cPath=6 with the aim to connect it to a propeller via an ADC.

Connected it up as per http://openenergymonitor.org/emon/node/59 and all I get from my multimeter is 0.1mv and 0.050hz. Tried various burden resistor sizes and no change. I am connecting it around the red mains feed between the fusebox and the meter. Tried without the "dc bias" - same result. The openenergymonitor site seems to imply a voltage output proportional to the current flowing....?

I notice that on its "datasheet" the current sensor model has a internal diode and the voltage sensor has an internal resistor. Mine as a resistance of 100ohm across the outputs - does that sound right?

Any ideas?

Thanks,

James

erco
02-27-2012, 04:32 PM
James: I can't help with that sensor, but I wanted to point out this nice B&D finished unit: http://www.ebay.com/itm/Black-Decker-EM100B-Energy-Saver-Series-Power-Monitor-/330688255246?pt=LH_DefaultDomain_0&hash=item4cfe8e550e

I nabbed one off Ebay for $30 and it works great as a standalone unit.

Duane Degn
02-27-2012, 04:53 PM
The openenergymonitor site seems to imply a voltage output proportional to the current flowing....?


James, I just want to make sure noticed from the chart, your model (SCT-013-000) apparently outputs a current proportional to the current flowing. All the other models listed look like they output a voltage.

Javalin
02-27-2012, 05:00 PM
yes it should.

Mark_T
02-27-2012, 05:53 PM
Hello all,

A little help please. I bought a non-invasive current sensor to monitor my home current consumption - http://www.seeedstudio.com/depot/noninvasive-ac-current-sensor-100a-max-p-547.html?cPath=6 with the aim to connect it to a propeller via an ADC.

Connected it up as per http://openenergymonitor.org/emon/node/59 and all I get from my multimeter is 0.1mv and 0.050hz. Tried various burden resistor sizes and no change. I am connecting it around the red mains feed between the fusebox and the meter. Tried without the "dc bias" - same result. The openenergymonitor site seems to imply a voltage output proportional to the current flowing....?

I notice that on its "datasheet" the current sensor model has a internal diode and the voltage sensor has an internal resistor. Mine as a resistance of 100ohm across the outputs - does that sound right?

Any ideas?

Thanks,

James

That datasheet is awful... Wouldn't trust it to be right.

Let's assume its right about the turns-ratio of 1:2000, in which case 100A in gives 50mA out. In that case try a 22 ohm resistor for 1.1V output at 100A input (all rms, of course). This would be 3.1V pk-to-pk.

The "diode" is a bidirectional TVS device to protect the secondary against over-voltage should you leave it output unconnected (CT's have to be connected to a load otherwise they become step-up transformers).

The 100ohms you measure is probably just the winding resistance which is irrelevant to its function.

To get appreciable output voltage for lower input currents you might want to use a higher-valued burden resistor (useful for testing/calibration?) 220ohms for instance.

Make sure your multimeter is on AC voltage setting.

Javalin
02-27-2012, 05:59 PM
excellent - thanks mark will check it out shortly!

Javalin
02-27-2012, 06:20 PM
Thanks Mark - that works. I think I need a 70ohm resistor to give me a 50amp range based on half load output at 50amp would be 25ma. V=IR = 3.5v = 0.025 * 70.

Gives a nice range.

I think the main trick was to use the multimeter on AC voltage - DOH! Also its wasn't 0.050hz, but 0.050khz.

Thanks again for your help!

Javalin
02-28-2012, 01:38 PM
Hello,

A little more help if I may...!

Reading an AC voltage with a ADC... I appear to have two options:

(a) Filter the signal to be 0-2.5V AC and DC bias it on 2.5vdc so that I get a 0-5 volt sine wave centered at 2.5vdc. Then pick the biggest point on the wave as my voltage

(b) Rectify the AC signal to DC, which means I can have a 5vac signal as a 5vdc signal so I get better range. Problem is how to account for the "upto 1.1v" diode drop, as I don't want to scope the AC signal to run 0-6vac then find it turns into anything from a 4.9vdc to 5.5vdc signal and blow the ADC?

If (b) is the better option, can somebody recommend a recifier IC or the best approach? (max 6vac and 50ma required)

Thanks,

James