Making a current transformer is a process that has been refined over many years. There are a few key things to keep in mind when making one, and these lessons have been learned the hard way. The first lesson is to use washers that have a consistent diameter. This will ensure that the current transformer has a consistent output. The second lesson is to make sure that there is enough space between the washers. If they are too close together, they will create an inductor, which will distort the output of the transformer. The third lesson is to make sure that the windings are evenly spaced. If they are not, it can create an imbalance in the current transformer and lead to inaccurate readings. Finally, it is important to make sure that all of the connections are tight and secure. A loose connection can cause electrical shorts and damage the current transformer.
I'm not crazy about using washers when much better cores are easily available from broken electronics, but I learned about using a winding shuttle from this video, and that will save me countless hours going forward. Thanks!
Would like to thank you for this wonderful work, I am working on a wireless mains monitoring device and wanted to build something similar for monitoring the a.c. mains, came across your video but I had LM324 available that is pin 2 pin similar with 6024, instead of 75k 1% used 82k that was readily available, it worked like a charm and fulfilled my requirements.
Really enjoyable video, its been years since i designed an analogue circuit that had to eliminate the diode forward drop, id almost forgotten the frustration and then the euphoria of solving it- great project, looking forward to watching some of your other videos
I really can't thank you enough for this video. You have solved all the problems that I anticipated - I have been thinking about how to solve this for days and was stuck on the Vf loss of the rectifier diode. But you solved it. I'm just getting started - I'm a software engineer by trade but I'm enjoying electronics *so* much! Thank you again! 👍
Definitely agree with your advice of using components that have really reliable and flexible behavior when getting started. The only thing missing from this video is some background on the AC side of things. How do we know to do 100 turns of wire on the washers? Also, what range of AC inputs will this circuit work with? Thanks for the cool video.
The process of making a current transformer (CT) is not difficult, but there are a few things that need to be done in order to make sure the transformer works properly. The first step is to wind 100 turns of wire around each of the washers. It is important to make sure the wire is tightly wound and does not overlap itself. Once the wire is wrapped around the washers, the next step is to solder the ends of the wire together. This will create a circuit that will allow electricity to flow through the transformer. Finally, the last step is to connect the CT to an electronic device and test it out.
You can use a multimeter to get an idea of the voltage you get from 10 turns and maybe 1A input current and then figure how many turns to ger a good output voltage for the intended inout current range. Just that you want the wiring evenly spaced so that will kind of put a limit on min/max number of windings that is reasonable to do - and then have the following Op-Amp step up the voltage further. As seen from the video, 100 turns seems to be about what fits for the inside of the washers - more turns and there would be overlapping wires.
When you need to measure a current and don't have a current transformer, there are a few ways to make one. One way is to use some common household items. For this example, we will use two washers. Take one of the washers and bend it into a loop. The hole in the middle of the washer should be facing downwards. Take the other washer and do the same thing, but make sure that the loops are facing in opposite directions (one clockwise and one counter-clockwise). Now, take some wire (preferably with insulation) and twist it around each of the loops a few times. Make sure that there is enough wire so that you can connect it to your voltmeter or other device.
Subscribed. Very nice video. It’s been decades since this old EE did anything with circuitry. Nice commentary on $2 op amp. Can you imagine the cost of building that from discrete components?
741 op-amp no working is due to the op-amp require negative voltage due to the constant current in the differential amplifier inside.. some old op-amp cant work at both input voltage close to the Vee, at least 4-5V above the Vee .
Love it. What they say: learn from other's mistakes because it is free. Your's could be costly. Saving a buck on an OpAmp (or anything else) could cost you days of stress. Cheers,.
Great video with a lot of useful tips. That wrapping tool for instance, would work perfectly for the ferrite type toroidal cores that I use somewhat frequently.
I thought virtual ground referred to a point in a circuit that is at 0V but is not connected to ground. Wouldn’t your set up just be like a floated DC operating point?
Hello Thank you for making this probe. I wanted to know how many Hz is the frequency response of this probe and how much current it senses as well as how much frequency it can operate.
It can't really handle very evil distorted currents with big crest factors since the AC->DC will fill the capacitor to the peak voltage and not care about the RMS value. But to some part, that transformer may help a bit working as a low-pass filter. Maybe I should build one and experiment a bit to see how much it's affected by either current with overtones or the extreme pulsed currents at voltage crests from equipment with just rectifier+capacitor, where all current is drawn at peak voltage to fill the capacitor and then the device lives on the capacitor until next crest. One way to get further is to use a microcontroller and not rectify but to instead sample the AC at 50-100 kHz (most microcontrollers have 10-12-bit ADC capable of such sampling rates). You get the resolution limit from the ADC and the crest factor limitation from the bandwidth the home-made transformer manages to handle.
Hello Im wondering one thing. Why didnt you use that virtual ground as the only shared ground of the entire system? In that case, you wouldn't need the diff amplifier stage. (I thought you used that diff amplifier to eliminate common mode interference btw.)
This is my last semester as an EE and was fortunate enough to obtain a job as an Electrical field coordinator but it is not what I want to do. Should I build up my resume with electronic projects and then keep applying?
@@leofernekes343 Your comment just motivated me to start applying what I’ve learned and build it. I plan on starting with simple ones like amplifiers, boost and bucks. Thank you!!
Awesome Video! I am attempting something similar but using a ferrite bead instead of washers. Is there any reason to use 30 AWG wire over thicker wire. I've been using 24 AWG wire to no avail and it is not quit as form fitting as the thinner wire.
The phase shift between the current and the output of the opamp will be caused by the transformer being a transformer, not because it's crappy. The output of the transformer will be the derivative of the input, no? EDIT: referring to 7:00
I have puzzled over this, a standard proper current transformer has negligible phase shift between the primary and secondary windings. My washer transformer has very low inductance, the reactance of the primary is probably lower than the 1 ohm burden resistor "seen' by the primary (100:1 turns ratio = 10,000:1 impedance ratio) which looks like 0.1 milliohms. Most of the current entering the primary is taken through the magnetization inductance, this is also why the output voltage is so low. It's a really terrible transformer.
@@leosbagoftricks3732 racking my brains over the phase shift cause. Are you saying current phase in primary and secondary coils should align? I think that's how it goes. But, a full 90 degree phase shift vs anything else is a little strange. you point out that channel 4 measurement was a current measurement. 6:58 The secondary measurement was a voltage that developed across the resistor due to current × ohms. and while the voltage and current are in phase with a resistor, there is 90 degree differences between current and voltage phase in an inductor.
When you measure the output from the CT are you using ingredients a CT probe attachment to measure it as a current or are you using a probe and measuring as a potential reference. I believe this would make a difference. A full 90 degree shift implies an entirely inducti e circuit with no capacitive or inductive elements involved. I work with transmission protective relaying and use and Arbiter phase angle meter to check secondary load angles from instrument transformers a d would use a CT or Amprobe like attachment to check the ant CT secondaries and a straight meter lead to check potentials against it. It's all about your point of reference though. Cool experiment!
hi sir. im come from vietnam, and my english is not so good :(( i have a CT Andeli MSQ-30 100/5A, can i use this circuit with my ct ? reply me soon . Thanks you
@@derrickpro4105 I guess it may be 5-10k, and did he wind a secondary?, he has it in his circuit, but i don''t see in the washer transformer? do u have any idea?
@@arvindh13 One can see he starts winding 100 turns at 1:22. At 2:05 he performs the first test of the transformer. And as you seen in the circuit, the washer transformer is symbolized by the current transformer in in the upper left of the diagram at 6:06.
The potentiometer at output is to calibrate Full scale reading. Output of transformer is AC volt; we can use a voltage divider for range settings. ( Nice video. I've been looking for similar circuit, and plan to use ferrite core, then measure directly from transformer output. Thank you for the video. (Y) )
The circuit is too complicated without much sense. You only need to build a current transformer that when rectifying and filtering about 5V or more for the maximum current that we want to measure. Then that output is the one we use. In order not to damage any circuit connected to that output, we connect a 5.1V zener in parallel. We don't need any op amp.
You have just made it so complicated,lm358 is enough. After current transformer we need small resistor after that we create 2,5v virtual ground using two 10k resistor and op-amp as follower after that we can amplify signal 100 times after that take signal to Arduino or any microcontroller for measuring peak and make some calculation so that we don't need all that diodes and 4op-amo you are using in your video
Lm741 ic was not working on your circuit because 741 ic is of dual supply and your circuit on single supply so dual supply op amp not works on single supply
Just in case anyone thinks that they could use a stack of washers as a kind of regular toroid transformer... There is a not so slight problem with using solid hunks of metal! It is called Hysteresis, and magnetic reflux, which cause heat, and power loss. These problems are both quite a bit smaller in regular toroid cores, due to the fact that both the iron type and the ferrite type of cores use materials that are composed of powdered items, which are glued into a solid form.
many thanks dear, great video,, i hope you can do something about the shunt resistor and an OP amp, to make a current monitor or current limiter, specially if we can read that current using a 7 segment display.
