# How to read current from a non invasive split core transformer AC current sensors

I was looking for a simple AC sensor and found this. It would seem to be a good option since it is not invasive. The problem is how do you read data from these type of sensors? Im having a hard time looking for a good guide on these sensors. it would seems that they output current(?) which will make reading them difficult with the basic analog GPIO

Further questions:

• How accurate are they?
• Can they be place beside one another if you want multiple of them?
• Will this still work if it will be placed in the distribution board where there are a lot other wires that produces magnetic fields
• I only see a current rating (100A) and not the voltage what does this mean?
• The datasheet for that CT is here. Someone else asked a question about it earlier today. – brhans Sep 24 '19 at 19:33
• Thank you for the datasheet, – Jake quin Sep 24 '19 at 19:56

From what I've seen from oscilloscope probes (i.e. much more expensive and hopefully accurate and sensitive than the unit you are referring to), these are sensitive to a tens of mA but I wouldn't really trust them below 10 or 20mA, even for units that max out at lower currents let alone 100A. There are, however, very low current level ones that are 1-5A but I've never used those.

You can place them beside each other if you need more than one.

But they are sensitive to surrounding magnetic fields which can create things like offsets. Once at work I thought I had a leakage current and I couldn't figure out where it was coming from. It turns out just having a nearby transformer powered produced enough of a magnetic field to influence the current sensor.

Why doesn't it have a voltage rating? Well, it doesn't have a datasheet provided either so does that really surprise you information is missing? No datasheet no buy. Another reason...it doesn't connect directly to the line nor does it take a power supply so what type of voltage rating are you expecting?

• may i ask around what distance is your transformer? although i dont plan on putting it near one , it just helps me scale how sensitive it is. – Jake quin Sep 24 '19 at 19:58
• It was a 120/VAC/240VAC/480VAC 1.5kVA transformer. I forget what was running through it but it was nowhere near capacity. The distance was maybe about 2 feet. The offset was some mA. No more than 20mA if I remember right. I think it was 7-12mA. – DKNguyen Sep 24 '19 at 20:02
• oh the transformer is very close i thought it was in the range of 20-30 feet. how about my last question how to do you read the data from these sensors? On the datasheet provided by brhans under the rated ouput there are 2 units used A and V. which now makes it even more confusing. – Jake quin Sep 24 '19 at 20:08
• @Jakequin It's a current transformer. Which means the primary has a very small number of windings (maybe just one) and the secondary has a very high number of windings. run current through the primary, place a resistor (load) on the secondary and measure the voltage across it. Never run a current transformer open-circuit with no load on the secondary. It is very dangerous since the voltage can be extremely high. So you may find out information on how to use your current transformer just by looking up how to use current transformers in general. – DKNguyen Sep 24 '19 at 22:29

It's a current transformer with 2000 turns. $$\N=\dfrac{I_{sec}}{I_{prim}}=\dfrac{100A}{0.05A}=2000\$$. At least that's what should be, the real situation is that numbers of turns are not exactly 2000, who knows why.

Inside a plastic enclosure, there is also a voltage limiting zener diode, so you can unplug the cable without destroying the CT. Normally the CT has to have a load connected, always! That's mandatory, otherwise the voltage in CT builds up and destroy it. Well this one has a protection as said, so leaving it without load won't harm it.

simulate this circuit – Schematic created using CircuitLab

How accurate are they?

Very accurate.

Can they be place beside one another if you want multiple of them?

Yes.

Will this still work if it will be placed in the distribution board where there are a lot other wires that produces magnetic fields

Yes.

I only see a current rating (100A) and not the voltage what does this mean?

There is no voltage rating, use this device for household wiring, let's say max 300VAC.

• Thank you very much for your answer good sir. Do you know how to interface it with a basic 3.3v or 5v microcontroller , so i can read the current in the microcontroller. I have done a bit of research but still not enough, I already know that the output signal is a sine wave so i have to rectify it, but i do not know the proper resistance and capacitor value, may i use a rectifier IC for this one? – Jake quin Sep 25 '19 at 12:32