Making a Current Transformer from Washers
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- เผยแพร่เมื่อ 18 มิ.ย. 2024
- This is a tutorial showing how to make an AC current sensing transformer out of a handful of steel washers.
We also do a deep-dive into the design of signal processing circuitry to make our washer transformer into a useful building block.
You can download the schematics here:
www.fernekes.com/2020/04/makin...
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It is amazing how well you convey the lessons learned from decades of experience!
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!
Oh that's what that thing is called. I've been calling them it a knitter.
Forbidden pineapple slice. I really love how you explain this. Really clear and concise. Thank you
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.
❤️❤️❤️❤️❤️❤️
Wire wrapping technique on washer was the best part of this video for me....
Thanks for sharing! The format of the video is amazing. I love all the details you added. I'm excited to watch the rest of your videos.
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.
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
You are amazing builder. Glad I stumbled upon your channel.
Great presentation and explanation. Thanks!
another excellent video with great explanations. nice job
Thank you Leo, this is a great job and a very interesting video.
Best electronic channel ever
Great videos. Wish I had found them earlier as you fill in a lot of practicle gaps in my knowledge
Looking forward for a new lessons. Those kind of videos are great for beginner. Subscribed
Excellent, keep them coming! Thanks
very instructive video - thanks!
Another fantastic video, thank you.
Thank you. This is very useful information.
I love those microchip opamps. Some even come with a built in divider for a virtual ground reference.
Amazing explation really learned a lot from it!
This project is very good!
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! 👍
Using the washers is an excellent idea for a low cost AC transformer. I will probably use this idea in a future project.
very useful bag!
Amazing knowledge Sir..
Nice explanation. It would be great if you could zoom in on each section of the schematic.
I might build one. Thank you.
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?
really useful!
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.
@@perwestermark8920 Why can't you overlap? I have all sorts of transformers with overlapping wires.
Oh no!. washers? Don't give China any ideas.
Super explanation on a very COoL mini project. Inspiring! Thank you.
Cool well done vid
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.
Really loved the video. Can you please help me with constructing a 'Rogowski coil'.
tres bien merci
Thank you.
God damn this is amazing!
This is fantastic. Any advice on selecting a burden resistor value? I'm using a 15:1 CT. Any tips greatly appreciated.
Look up the data sheet for the CT, they typically recommend a value.
You are a great
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.
Be careful with 'random' ferrite materials, those designed for RFI suppression are very lossy and not suitable.
I did a bit of weaving when I was a kid. Why did I never think of using a shuttle for winding toroids?... Nice one!
100% agree......love the idea.
I was today years old when I learned how to wind a transformer like that.
Just a layer of clear lacquer or paint is probably enough insulation to prevent eddy currents. Sometimes the oxides on the metal is enough.
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.
Probably just line frequency and a bit above.
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 Leo, quick question. Is it possible to supply power of opamps from secondary output of current transformer?
Not this one!
Leo, what are those tubes in the background?
Looks line something that blows air and makes ping-pong balls hover in the tubes. But I'm curious too.
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 .
I would be very grateful if you could explain the need for C1 and C5 capacitors, that's all i don't understand. Thanks 🙏
Those capacitors are there to reduce the bandwidth of the circuit, to limit the high frequency noise.
2:08 Was that 1A passing through the primary (red wire) ?
I think you're right. The meter is reading 100 microamps.
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.)
Because the output is referenced to the power supply ground. You cannot connect the two - they are at different voltages.
What's the difference between a current transformer and a normal transformer? I can't find anything online
its a one turn primary transformer, the wire passing through.
What is the value of your burden resistor you used here?
In the description, he has a link to a page with the schematics as a PDF download. On there, it's listed as "100"
Nice project very interesting. Where can I buy it ?
You can buy all the parts to build it yourself at digikey and other parts suppliers.
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,.
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
Yes- as long as you select the correct burden resistor value.
@@leosbagoftricks3732 thanks you sir. Cảm ơn ngài rất nhiều (´∩｡• ᵕ •｡∩`)
Sorry for stupid question, but can I use two lm358 instead? Need measure 50hz current.
No -it will not work with those opamps
The 0-5V output signal from a device powered by 5V means a need for rail-to-rail operation of the OpAmp.
can you simulate this current transformer into LTspice to get even more how to information? 😎 thanks
Hi dear, can we use LM324 instade of MCP6024, please reply i am waiting for.
Thanks in advance.
Santosh B.
No, the LM324 does not operate well near zero volts, it will give poor performance.
@@leosbagoftricks3732 ok thanks dear.👍👍
@@leosbagoftricks3732 oh I thought its operation was supposed to include inputs down to zero V.
@@ihateemael Read the data sheet for the LM324, the answer is "it sort of works down near ground"
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?
Ground is a deep subject. Virtual Ground can be anything you want it to be, chosen to give you the behavior you need.
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?
Always! I would always hire the guy that can show that they can actually build and work with real stuff over some guy with just good grades.
@@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!!
sir what is magnetic wire used to wound
Insulated #30 AWG copper magnet wire- standard material.
Parece interesante, lástima que no se le entienda nada, podría poner subtítulos en español?
1:10 mmmh... forbidden pineapple slice
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.
Can 90 degree phase shift be from ICE and ELI properties?
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!
How many ampere can we measure ?
Since he winded a100 turns on the sec it may be a 100:1 based on even the wire guage he used on da sec ofcos
@@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) )
@@arvindh13 It was the secondary coil he winded. The primary is the single power wire through the hole.
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.
Kewl...
It's missing a LED indicator!
I will use this ! I will call it the "Leo Torroid" BUT I will use electrical tape
Can this circuit measure DC current?
NO! it's a transformer, it relies on changing magnetic fields.
Thank You, Sir.. It will be amazing if You willing create one for us someday
I loved your vids
1 You didn't show us it working, how do we know it actually works?
2 Couldn't you use a bridge rectifier to change from AC to DC easier?
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.
And how did you then plan to measure currents that produces a voltage below the forward loss of your rectifyer diodes? 🤔
The whole point was to build a transformer using 3 washers and how to get a decent 5v out of it.
1:00 I'ts not a joke.
Ahh nothing like spending 17 days making and winding my own inductor to save 12 cents... just joking :)
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
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
Ah - so replacing a few Op-Amp with a microcontroller makes it less complicated? You just made it a different way complicated.
That is not matter thing is cheaper or expensive if you couple worlds most cheap op amp lm324 it will definitely work
Yes- but it will work BETTER with a better opamp - the LM324 is 46 years old, think about that for a second. Why not use better modern parts?
@@ihateemael This is TH-cam!
@@ihateemael because the fun of it was to make a working usable transformer out of 3 cent washers.
1:00 me when your mom
(no jokes please)
Not because you said so, because physics said so, or Mother Nature said so, or God said so, pick your deity.
"Just kinda because" -> "Dadsplaining". Works.
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.