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Description: This non-invasive current sensor (also known as a "split core current transformer") can be clamped around the supply line of an electrical load to tell you how much current is passing through it. It does this by acting as an inductor and responding to the magnetic field around a current-carrying conductor. By reading the amount of current being produced by the coil, you can calculate how much current is passing through the conductor.

This particular current sensor will measure a load up to 30 Amps which makes it great for building your own energy monitor to keep your power usage down, or even building an over-current protection device for an AC load. This sensor does not have a load resistor built in, so in most cases it will be necessary to place a resistor across the output to convert the coil's induced current to a very small measurable voltage.

Documents:

Replaces: SEN-10341

Comments 47 comments

  • It uses a stereo plug, but i couldn’t find which pin is NC. I need to design a PCB, but I need this info first. I would apretiate if anyone could tell me.

  • Also, this is the current generating version, you need the burden resistor. The linked sites are confusing about this.

  • We all are still hoping to see the 100A ones! Get ones with the biggest holes possible. I think my grid wires coming in are .58" dia. Then I’ll take two!

    • http://www.crmagnetics.com/Products/Assets/ProductPDFs/CR3100.pdf

      I’ve used this device (a pair of them actually) to monitor the entire power use of my house. Linear up to 100A, 0.58 gate size, weatherproof.

      Here’s a simple circuit to do precision rectification, amplification and averaging.

      http://www.crmagnetics.com/Products/Assets/ProductPDFs/Precision%20Rectifier%20Circuit%20for%20CT%20Signal%20Conditioning.pdf

      • Can you recommend what size resistors and capacitors to use in this circuit if using it with Sparkfun’s current sensor.

  • Anyone have any tips on how to get this to work with a raspberry pi?

  • Hi, may i know when will this item be re-stocked? Urgently needed.

  • Hi, what is the bandwidth of this probe?

  • Hi thanks for the great price and product! may i know what is the bandwidth of this current sensor?

  • why there’s not an arduino shield or an interface board for this thing? Phone jack, needs an analog circuit and there is no board for this? There are boards for things a lot simpler than that…

  • I put a video up on youtube to show the setup needed to use this sensor. Hope it helps others with first time setup.

    http://youtu.be/IHozA4Ds5Ts

  • How long is the cable?

  • I checked the datasheet and the comments below but did not see any answers, anyone know what size jack I need for this?

  • does this work with DC current.. I think it should but just confirming, simple DC motor, DC voltage, will it measure current.

    THANKS

    • It WILL NOT work with DC. Current transformers rely on AC to function, as DC doesn’t create a time-varying magnetic field. You might try looking into Hall effect current sensors.

  • On mine it appears that tip and shield are connected to the transformer and ring is open, for some very strange reason.

  • I am struggling a bit with this sensor and I am hoping someone might be able to shed a bit of light for me. I have connected two of these sensors to a PIC24 that basically reads each sensor 1500 times and records the highest reading from each then forwards the value to a second PIC24 set up to display the values converted to amps using two 4 digit 7-Segment Displays. Amazingly, all works perfectly. Well under test conditions anyway. As soon as I disconnect the PICKit 3 programmer from the board it start getting spurious readings and my readings can be up to like 5 to 10 amps out and fluctuating. It must be something to do with noise or earthing or something as it only does it when not connected to the computer. But this is proving difficult to test as in works when under test. Cry. Any suggestions.

    Side note:- As already mentioned, bring on the 100 amp clamps. I have a few from eBay and there much more use. Sorry sparkfun. I do try to be loyal.

    Undated:- Spoke two soon as always, 10uF filter cap fixed it.

    • Can you post pictures and a diagram on how this was done. I recently purchased basically similar items … CR3110-3000 in hopes of doing what you have done. I recently learned how to transmit this data remotely with Arudino and nRF24l01 … so I want to make a complete set with remote transmission. Saman

  • are these 60 or 30 amps?, aleread have one i ordered to test,but my main lines are 3*40 amps and need to know if it will be linear to 40 amps.

  • This device does not seem to work. I’ve tried both the Arduino energy monitor project and simply adding a 10 Ohm burden resistor and then measuring with a voltmeter. Both the Arduino ADC and the voltmeter give me a reading of 0V (or in the case of the energy monitor project circuit, 2.5V).

  • What is the pinout on the audio jack for one of these? The datasheet doesn’t show anything about it. If I base myself on the product it replaces, the front and back connections are used and the center connection is NA. Does this apply to this one as well?

    • tip and ring, i have it working for 20 amp max at the moment don’t know the burden resistor out of my head but with the formula above or if you google there are calculators online to find the wright size

  • Am I just an idiot or does the datasheet not mention what parts of the TRS plug are what. This may just be obvious to everybody else…

  • Is anyone successfully using this CT? I am trying to use it with a 5 volt ADC and I’m having trouble sizing the burden resistor. The documentation suggests I need a 10 Ohm, however the formulas for 2000 turn CT’s suggest I need about 118 ohms.

    • I have been tinkering with this device. I’m using a 10 ohm burden resistor, but then I’m looking at measuring amperages that go up close to the maximum capacity of the CT (the spec sheet says 60A, even though the product description says 30A). The CT output seems to match pretty closely to what’s printed in the datasheet. You could feasibly play with the resistor values to tweak the output, but it will affect the accuracy for a given range of values.

      I tried using the precision rectifier circut referenced up above, but I had a lot of trouble with it at very low input voltages. I used the circuit emulator app at http://www.falstad.com/circuit/ to get the resistor values right, but in the actual circuit the amplification wasn’t at all linear down there, so it made measuring small currents impossible. I’m now playing with incorporating an AD636 true RMS to DC chip, which is working reasonably well, but still has issues at very low voltages (like a few mV).

  • Is there a 3.5mm jack on the wires? I’m designing a rig with 4 of this each with it’s own LTC1967 (true RMS to DC) and a 1wire Quad ADC DS2450…and i’m wondering what kind of connector should i use…

  • This is fantastic!

    FYI, if you are using this to measure the current in, say, a powerstrip wire, make sure you only clamp around one of the internal power wires, not both. Otherwise, you will read nothing, because while current in one wire is going one direction, the other is going the other direction, canceling each other’s effects out. If you look at the picture closely in the link, you’ll see this.

    Sparkfun should carry one of these: http://www.thehumansolution.com/exaclisp4.html?utm_source=Google%2BShopping&utm_medium=cpc&utm_medium=cpc&utm_campaign=Google%2BShopping&gdftrk=gdfV2929_a_7c132_a_7c5187_a_7c480172 , so you don’t have to cut wires. Obviously it’s trivial to make your own, but if you wanted to cut things, you might as well use an invasive sensor.

    Also, on the connector, you want the tip and the sleeve. You can verify this with a multimeter. The orientation does not matter.

  • WARNING! The plastic housing is badly made and the hinge and clasp break very easily on these units. I got one that arrived broken, and the hinge on another looks so weak that it will fail if opened and closed frequently. Current transformers require that the 2 halves be held firmly together for accuracy, so this is a major flaw.

  • Where’s the datasheet? The link above still doesn’t work.?

  • this only works for AC, right?

    • The datasheet states that the specifications are valid for use at 50/60Hz. And it looks like it’s actually rated for up to 60 amps. Too bad it’s not quite large enough to clamp on the usual residential home size power feeds or you could meter your whole house’s power use.

      For anyone that hasn’t worked with these yet, you must add a 10 Ohm burden resistor. On top of that an overvoltage (transient) limiter is a good idea too. And there will be high frequency noise, so a low pass filter of some sort is often needed if you want to digitize the 50/60Hz AC waveform.

      • This should only be clamped on one wire, so it should be large enough to go over stuff as large as 2 AWG, which can be used for up to 100A circuits. If your house is limited to 60A, this should be large enough to go over the whole feeder.

    • Since is is only a coil (vs. a Hall-effect IC), then yes, it is AC only.

      Alas even the official data sheet doesn’t show the frequency response. Presumably it is good for at least 50-60Hz which covers most of the consumer utility mains on this planet. But perhaps not for higher frequencies (such as switch-mode power supplies, etc.)

  • Datasheet, please! At the very least, we need to know the number of turns and the saturation voltage (point at which the output becomes nonlinear).

    • Haha, sorry, I know. When I was listing these products the engineer who has the only datasheet in existence (custom) wasn’t in the office so it had to wait until today.

      I just got it uploaded and there’s a link in the documents heading. Enjoy:)

      • Thanks! Unfortunately, the new datasheet only lists the “Turnn ratio”. I need to know the turn ratio; I assume these are comparable? (-:

        Also, the datasheet only gives specs for R_L < 10 ohms, and no indication of the saturation points with higher resistances. Using the equation

         V_out = ( I x R_L ) / T
        

        where I = 8 A ( the peak value for my equipment), R_L = 10 ohms (Load resistance from the spec), and T = 2000, (the turnnnnn ratio), I predict an output voltage of a measly 40 mV RMS. My ADC is only capable of about 4 steps in this range (8 bit, 3.3V reference = 12mV step) , which isn’t enough to do much of anything. :-/

        I’d like to increase this resistance by (30/8) = 3.75 times, to 37.5 ohms (realistically 37.4 ohms in the 1% E96 series). (or more if possible; I understand that the limiting factor in the 30 A specification could be saturation of the primary or overcurrent in the windings). 37.4 ohms would give me an output voltage of 150mV, or about 12.5 steps, but I need to know whether the transformer will saturate with this resistance.

        A graph like the one shown on the CR Magnetics datasheets: (CR8300 series datasheet, PDF) and the specs required to derive the values on that graph would be immensely helpful.

        • I know this might be silly but what about wrapping the current carrying wire around a couple more times to give a seemed higher amperage then divide it in the program/code? I believe if you wrap it twice around then it will read at 16A then divide it by 2 and you will have your value. 4 turns 32A divide by 4 etc. etc

          • I might be silly, but i THINK i read somewhere just before i came here that they cancel out each-others magnetic fields if the primary is wrapped. Dont quote me on that though.

            • look at page 5 and 17 of http://www.crmagnetics.com/Portals/0/main_cat.pdf it talks about changing the ratio and wire pass I was hopeing with my vagueness it would spur someone to do more research. To cancel out the the current threw the sensor place the neutral/return wire threw as well. That is the premise of a GFCI the Neutral and Hot wire pass threw the window and the ground does not. When there is current going to the device it will return on the neutral so nothing is measured in the sensor if there is a fault some current will be returning on the ground and it will no longer be balanced and the sensor will measure current.

        • I don’t think there is any way to use a current transformer without some sort of preamp.

          • I have used the CR 8348-2000 without a preamp. The maximum output voltage is given by

            V_L = V_max - (I * R_DC) / T
            

            where V_max = 13.7V (the saturation point of the transformer), I = 8 A (or 30A, or whatever the primary current is), R_DC = 106 ohms (the DC resistance of the transformer), and T = 2046 (the number of effective turns).

            This gives a maximum output voltage V_L of 13.2V, which is linear up to 10V. You’d probably need a resistor divider to get readable voltages, and that can be tuned with a pot for new maximum voltages. That’s much more flexible, simple, and cheap than most any preamp circuit.

            If we knew V_max for this transformer, we could increase the resistance to approach higher voltages like this. I’ll grant that this probably has lower specs than the CR part because it’s a split-core transformer, but 40mV seems extremely low.

    • +1


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