Can my $15 DIY AC/DC Current Clamp keep up with a commercial one? || DIY or Buy

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 for example designing switched mode power supplies 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. Like the name switched mode power supply implies, we are working with switched voltages and also currents. So needless to say using a multimeter to check those values does not make much sense. Instead we need an oscilloscope with a normal probe to check the voltages and like I said before a current clamp in order to show the current waveforms. Now I was quite happy with this current clamp model since it is acceptably precise and its price is also reasonable when you compare it to other models on the market. And I said was because I actually managed to destroy one of those clamps and the one I was showing you up until now was the replacement. Not sure how I did it but I messed something up on the battery input and now the whole circuit is dead. And since I needed a new current clamp immediately, I ordered a replacement but later while examining the old busted clamp I started to realize how simple this tool actually is and whether it would have made sense to DIY a solution instead of buying a new one. So in this episode of DIY or Buy I will show you how we can create our own DIY version which offered some rather unexpected challenges. And in the the we will be able to determine whether it makes sense to DIY such a tool or whether we should stick to the commercial solution instead. Let's get started! This video is sponsored by Brilliant which is a website and app that I would describe as an interactive storyteller where you can learn all about math, science and computer science. I was having a look at a few different courses from them and I have to say that in combination with all the interactive puzzles and storytelling elements, it was a rather fun and educational experience. So if you want to try out Brilliant for yourself then go to Brilliant dot org /GreatScott and sign up for free. And the first 200 people that sign up for an annual subscription through this link will also get a 20% discount. First off you might be asking yourself: “Why bother with a current clamp when I can just add a small resistor in series to my load and probe the voltage drop across it in order to not only visualize the current flow but also easily being able to calculate the current values by knowing the resistor value”. Now this current measuring method by using a so called current shunt is pretty popular. The disadvantages of this method however are that you will have to insert a current shunt into each area where you want to measure the current which can be a hassle. And of course there is a voltage drop across resistors which you can keep small by using a super tiny resistance, but it will still be there to for example mess up your GND reference a bit. A current clamp on the other hand does not come with such problems; so let's start investigating my old broken one. After taking it apart and having a closer look at not only the clamp sensor part but also the circuitry, I had some idea of what was going on. But let's start with the head which is basically a split ferromagnetic core through which later one wire from our load will go through. And if I wind a second imaginary wire around the core then I think everyone should see that we are dealing with a transformer here. If a current flows through our load wire then it creates a magnetic field around it which creates a magnetic flux in the ferromagnetic core which thus induces a voltage into our secondary winding which we can then measure. This is basically how such a commercial AC current clamp functions. By taking it apart we can see the secondary winding I talked about. And as a proof of our theory, I soldered a salvaged BNC connector wire to this current clamp, connected it to the oscilloscope and led a wire through the current clamps ferrite core in order to display the AC current consumption of a universal motor, which worked perfectly fine, theory confirmed. The problem however is that as soon as we try to measure a DC current with this setup, we get pretty much nothing on the oscilloscope. The problem is that while there still is a magnetic field and also a magnetic flux, it is not constantly changing anymore which is a requirement for inducing a voltage into the secondary coil. That is why the AC/DC current clamp does not even come with a secondary winding but instead with two small ICs. Now googling the labels of those ICs was pretty fruitless but since I am aware of lots of other current sensors you can buy from the internet, I was pretty sure that we were dealing with a linear hall effect sensor. To show you what such an IC can do I got my own one, in this case the S49E. After 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. As you can can see the IC varies its output voltage depending on how close I bring the magnet. That means this IC can show us how strong the magnetic flux inside our core is and therefore tell us how much current is flowing. To test this I firstly desoldered the diode from the secondary coil and then removed a small part of the ferrite material in order to glue the hall effect sensor there through the help of two component adhesive. And after then adding a couple of wires as well as some hot glue, my new DIY AC/DC current clamp didn't look half bad. So I let a constant current of 1,2 and 3A flow through its core while writing down the output voltages. And if we remove the offset voltage of 2.472V then we can 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. Now a schematic that I came across on the internet quite often for such a task looked something like this. And 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. And while I know that such a voltage divider solution can be quite terrible for such a task, it was pretty stable in my design. So here is my final schematic for my AC/DC current clamp which I of course firstly tested on a breadboard; but let's just say that such a delicate Op Amp circuit is not made for a breadboard. That is why I soldered all of the components onto a piece of perfboard and after around 1 hour of soldering, I connected a 9V battery for power, the current clamp and the BNC connector wire which I hooked up to the oscilloscope. After then fine tuning the offset voltage so that the output voltage is at GND level and using a calibration current of 1A in order to adjust the amplification so that I get around 100mV for 1A, it was time for some proper testing in direct comparison with my commercial clamp. As you can see measuring an AC current with mains frequency was no problem at all but while measuring the current consumption of a PWM driven LED with variable frequency, I noticed some problems. As you can see at 250Hz both waveforms look pretty similar but while increasing the frequency, the DIY waveform started to look uglier and at 3kHz it was pretty much unusable. Now at this point I thought the current clamp was the culprit which is why next I tried using my circuit with the commercial clamp core as well as with another ferrite core which I pretty much only cut in half and with those; the results were much more promising but still almost unusable with higher frequencies. I am not entirely sure where the problem lies but it seems like my DIY version is not suited for higher frequency applications. But anyway if you combine my circuit with some DIY clamp designs you can find on the internet then the total cost of such a system should be around $15 while working pretty decently with DC and AC voltages that come with a lower frequency. And the other negative aspects about my DIY solution are that it 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. With that being said, thanks for watching. As always don't forget to like, share, subscribe and hit the notification bell. Stay creative and I will see you next time.

Channel: GreatScott!

Views: 173,782

Keywords: current, clamp, probe, oscilloscope, voltage, waveform, ac, dc, wave, form, alternating, direct, diy, or, buy, do, it, yourself, project, guide, beginner, beginners, compare, make, weekend, opamp, operational, amplifier, sensor, hall, effect, linear, s49e, 49e, magnet, magnetic, field, flux, density, change, comparison, reverse, engineer, vs, switched, mode, power, supply, motor, frequency, offset, gnd, virtual, dual, rail, greatscott, greatscott!, electronic, electronics, led, pulse, schematic, ferrite, core, ferromagnetic

Id: ohQF79cMODw

Length: 11min 24sec (684 seconds)

Published: Sun Jul 04 2021