As You Probably Have Seen in One of My Previous Videos, I Like to Use This Current Clamp to Visualize the Current Flow in a Circuit on My Oscilloscope.
This can be very important when it comes to designing switched mode powersupplies like this buck boost converter right here whose job it is to efficiently convert 12V on the input to a lower or higher voltage on the output.
I recently decided to try out a DIY AC/DC current clamp project, and I must say it was quite an interesting experience.
You can get a DIY AC/DC current clamp for around $15 by combining some existing designs found online. The total cost of such a system should be suitable for lower frequency applications.
The DIY version takes a bit of time to make and the calibration process can be a bit cumbersome, but other than that it is a decent alternative in certain situations which is why for my both DIY and Buy are this time the winner.
To begin with, let me tell you about my experience with the commercial clamp. The commercial clamp worked well for measuring AC current with mains frequency, but while measuring the current consumption of a PWM driven LED with variable frequency, I noticed some problems.
As You Probably Have Seen in One of My Previous Videos, I Like to Use This Current Clamp To Visualize The Current Flow In A Circuit On My Oscilloscope.
The DIY version didn't seem to be suited for higher frequency applications at all but it was still a good alternative for lower frequency applications that could be used with a cost of $15.
When I decided to try out the DIY AC/DC current clamp project, I knew I had to get my hands dirty and experiment.
I recently decided to try out a DIY AC/DC current clamp project, and I must say it was quite an interesting experience.
The S49E is one example of a hall effect sensor that can be used for this purpose. When soldering a 100nF capacitor between its supply voltage pins, I powered the IC with 5V and had a look at its output pin on the oscilloscope while bringing a magnet close to it.
This means that the IC can show us how strong the magnetic flux inside our core is and therefore tell us how much current is flowing.
I decided to test this further by desoldering the diode from the secondary coil, removing a small part of the ferrite material, gluing the hall effect sensor there through the help of two component adhesive.
After that I added a couple of wires as well as some hot glue, my new DIY AC/DC current clamp didn't look half bad.
When testing with a constant current of 1.2 and 3A, flow through its core while writing down the output voltages after removing the offset voltage of 2.472V we could see that we got a pretty linear relation between those output values, Great!
So what we need next in order to use this DIY current clamp with an oscilloscope is a suitable circuit that gets rid of the offset voltage and amplifies the remaining linear section of the sensor voltage.
A schematic that I came across on the internet quite often for such a task looked something like this.
While we can adjust the offset voltage with this trimmer and fine tune the amplification factor with this trimmer, this circuit is still only suitable for a DC current clamp and not an AC/DC current clamp.
The reason is that as soon as a negative current is flowing through the core, the sensor voltage decreases beneath the offset voltage which means the Op Amp would need to work in the negative voltage area which due to a single supply voltage does not work.
So my solution was to create a dual rail voltage with a virtual GND.
While I know that such a voltage divider solution can be quite terrible for such a task, it was pretty stable in my design.
WEBVTTKind: captionsLanguage: enAs you probably have seen in one of my previousvideos, I like to use this current clamp tovisualize the current flow in a circuit onmy oscilloscope.This can be very important when it comes tofor example designing switched mode powersupplies like this buck boost converter righthere whose job it is to efficiently convert12V on the input to a lower or higher voltageon the output.Like the name switched mode power supply implies,we are working with switched voltages andalso currents.So needless to say using a multimeter to checkthose values does not make much sense.Instead we need an oscilloscope with a normalprobe to check the voltages and like I saidbefore a current clamp in order to show thecurrent waveforms.Now I was quite happy with this current clampmodel since it is acceptably precise and itsprice is also reasonable when you compareit to other models on the market.And I said was because I actually managedto destroy one of those clamps and the oneI was showing you up until now was the replacement.Not sure how I did it but I messed somethingup on the battery input and now the wholecircuit is dead.And since I needed a new current clamp immediately,I ordered a replacement but later while examiningthe old busted clamp I started to realizehow simple this tool actually is and whetherit would have made sense to DIY a solutioninstead of buying a new one.So in this episode of DIY or Buy I will showyou how we can create our own DIY versionwhich offered some rather unexpected challenges.And in the the we will be able to determinewhether it makes sense to DIY such a toolor whether we should stick to the commercialsolution instead.Let's get started!This video is sponsored by Brilliant whichis a website and app that I would describeas an interactive storyteller where you canlearn all about math, science and computerscience.I was having a look at a few different coursesfrom them and I have to say that in combinationwith all the interactive puzzles and storytellingelements, it was a rather fun and educationalexperience.So if you want to try out Brilliant for yourselfthen go to Brilliant dot org /GreatScott andsign up for free.And the first 200 people that sign up foran annual subscription through this link willalso get a 20% discount.First off you might be asking yourself: “Whybother with a current clamp when I can justadd a small resistor in series to my loadand probe the voltage drop across it in orderto not only visualize the current flow butalso easily being able to calculate the currentvalues by knowing the resistor value”.Now this current measuring method by usinga so called current shunt is pretty popular.The disadvantages of this method however arethat you will have to insert a current shuntinto each area where you want to measure thecurrent which can be a hassle.And of course there is a voltage drop acrossresistors which you can keep small by usinga super tiny resistance, but it will stillbe there to for example mess up your GND referencea bit.A current clamp on the other hand does notcome with such problems; so let's start investigatingmy old broken one.After taking it apart and having a closerlook at not only the clamp sensor part butalso the circuitry, I had some idea of whatwas going on.But let's start with the head which is basicallya split ferromagnetic core through which laterone wire from our load will go through.And if I wind a second imaginary wire aroundthe core then I think everyone should seethat we are dealing with a transformer here.If a current flows through our load wire thenit creates a magnetic field around it whichcreates a magnetic flux in the ferromagneticcore which thus induces a voltage into oursecondary winding which we can then measure.This is basically how such a commercial ACcurrent clamp functions.By taking it apart we can see the secondarywinding I talked about.And as a proof of our theory, I soldered asalvaged BNC connector wire to this currentclamp, connected it to the oscilloscope andled a wire through the current clamps ferritecore in order to display the AC current consumptionof a universal motor, which worked perfectlyfine, theory confirmed.The problem however is that as soon as wetry to measure a DC current with this setup,we get pretty much nothing on the oscilloscope.The problem is that while there still is amagnetic field and also a magnetic flux, itis not constantly changing anymore which isa requirement for inducing a voltage intothe secondary coil.That is why the AC/DC current clamp does noteven come with a secondary winding but insteadwith two small ICs.Now googling the labels of those ICs was prettyfruitless but since I am aware of lots ofother current sensors you can buy from theinternet, I was pretty sure that we were dealingwith a linear hall effect sensor.To show you what such an IC can do I got myown one, in this case the S49E.After soldering a 100nF capacitor betweenits supply voltage pins, I powered the ICwith 5V and had a look at its output pin onthe oscilloscope while bringing a magnet closeto it.As you can can see the IC varies its outputvoltage depending on how close I bring themagnet.That means this IC can show us how strongthe magnetic flux inside our core is and thereforetell us how much current is flowing.To test this I firstly desoldered the diodefrom the secondary coil and then removed asmall part of the ferrite material in orderto glue the hall effect sensor there throughthe help of two component adhesive.And after then adding a couple of wires aswell as some hot glue, my new DIY AC/DC currentclamp didn't look half bad.So I let a constant current of 1,2 and 3Aflow through its core while writing down theoutput voltages.And if we remove the offset voltage of 2.472Vthen we can see that we got a pretty linearrelation between those output values, Great!So what we need next in order to use thisDIY current clamp with an oscilloscope isa suitable circuit that gets rid of the offsetvoltage and amplifies the remaining linearsection of the sensor voltage.Now a schematic that I came across on theinternet quite often for such a task lookedsomething like this.And while we can adjust the offset voltagewith this trimmer and fine tune the amplificationfactor with this trimmer, this circuit isstill only suitable for a DC current clampand not an AC/DC current clamp.The reason is that as soon as a negative currentis flowing through the core, the sensor voltagedecreases beneath the offset voltage whichmeans the Op Amp would need to work in thenegative voltage area which due to a singlesupply voltage does not work.So my solution was to create a dual rail voltagewith a virtual GND.And while I know that such a voltage dividersolution can be quite terrible for such atask, it was pretty stable in my design.So here is my final schematic for my AC/DCcurrent clamp which I of course firstly testedon a breadboard; but let's just say that sucha delicate Op Amp circuit is not made fora breadboard.That is why I soldered all of the componentsonto a piece of perfboard and after around1 hour of soldering, I connected a 9V batteryfor power, the current clamp and the BNC connectorwire which I hooked up to the oscilloscope.After then fine tuning the offset voltageso that the output voltage is at GND leveland using a calibration current of 1A in orderto adjust the amplification so that I getaround 100mV for 1A, it was time for someproper testing in direct comparison with mycommercial clamp.As you can see measuring an AC current withmains frequency was no problem at all butwhile measuring the current consumption ofa PWM driven LED with variable frequency,I noticed some problems.As you can see at 250Hz both waveforms lookpretty similar but while increasing the frequency,the DIY waveform started to look uglier andat 3kHz it was pretty much unusable.Now at this point I thought the current clampwas the culprit which is why next I triedusing my circuit with the commercial clampcore as well as with another ferrite corewhich I pretty much only cut in half and withthose; the results were much more promisingbut still almost unusable with higher frequencies.I am not entirely sure where the problem liesbut it seems like my DIY version is not suitedfor higher frequency applications.But anyway if you combine my circuit withsome DIY clamp designs you can find on theinternet then the total cost of such a systemshould be around $15 while working prettydecently with DC and AC voltages that comewith a lower frequency.And the other negative aspects about my DIYsolution are that it takes a bit of time tomake and the calibration process can be abit cumbersome but other than that it is adecent alternative in certain situations whichis why for my both DIY and Buy are this timethe winner.With that being said, thanks for watching.As always don't forget to like, share, subscribeand hit the notification bell.Stay creative and I will see you next time.
