Viewer Questions: Transformers with a Scope to look at Spiky Currents,

In previous videos we used shunt resistors and voltages dividers to look at harmonics in current and voltage waveforms. For 220V, 230V, and 240V applications, this approach may not be suitable if there are two live wires or a live and neutral without a reliably polarized power plug. In this video we look at how to examine currents with strong harmonic content from electronic power supplies using current transformers approaches. Spoiler: its amazing how well transformers do even with higher harmonic or frequency content, even plain old filament transformers.
.-----------------------------------------------------------------------------------------------------------------------------------
Many thanks to Tesmen for supporting this channel by providing me with the
Tesmen Hound-200 EMF Detector #tesmen
It is available from:
tesmen.com/
US: www.amazon.com...
CA: www.amazon.ca/...
DE: www.amazon.de/...
FR: www.amazon.fr/...
IT: www.amazon.it/...
ES: www.amazon.es/...
UK: www.amazon.co....
DISCOUNT CODES10% off code for all of their product listings: THGMR8V2The discount code expiration date is: 2024/12/31.
.-----------------------------------------------------------------------------------------------------------------------------------
Many thanks to Kaiweets for supporting this channel by providing me with the
KAIWEETS Thermal Imaging Camera KTI-W02 #thermalcamera #thermalimaging #kaiweets
It is available from:
Amazon US: www.amazon.com...
Amazon UK: www.amazon.co....
Amazon DE: www.amazon.de/...
Kaiweets kaiweets.com/c...
DISCOUNT CODES15% off code: EMV15(Available sitewide at Kaiweets.com and it never expires.)
Buy from official webstore: kaiweets.com/p...
More offerings from Kaiweets: kaiweets.com/c...

[@ThriftyToolShed]

Excellent information as always! Transformers are amazing, and the isolation they can do for us is so helpful. They isolate so well that many people use them with GFCI protected outlets and never realize that the output of the transformer is no longer under the GFCI protection. I mention that because I was thinking about how many people were badly hurt or killed several years ago using microwave transformers and etching wet wood for Lichtinburg or fracking. Many of those people handling high voltage and burning wet wood with no idea that they were galvanically isolated and the GFCI can not pick up the ground fault current if it happened on the high voltage side.

[@ElectromagneticVideos]

I read about those microwave transformer disasters a few years ago. I guess there were some KZbin howto videos that people were following as you pointed out without sufficient understanding. The HV section of those transformers really scare me - more than enough voltage to puncture a lot of insulation, skin, and use moisture as a conductor, and more than enough current to cause severe burns or a fatality.

[@ThriftyToolShed]

@ElectromagneticVideos It's scary to think about how bad that can turn out! Especially without the proper knowledge on top of that.

[@WOFFY-qc9te]

One Tuber on a live stream making "Art" and things did not go well, sadly his audience witnessed something they will not forget. Big Clive repeatedly tried to get a video out to show how dangerous it is but YT take them down. Thrifty, many people doing radio restoration are not using an isolation PSU, not very good with the old hot chassis.

[@WOFFY-qc9te]

@@ElectromagneticVideos As for Current Transformers without Burden resistors I have seen a few of those cooking whilst "Service Tech's " isolate loggers duering tests. The voltages can be rather spicy. I think Medi "Elctroboom" had a close call with a microwave TX, not just spicy volts but DC with a capacitor.

[@ElectromagneticVideos]

@WOFFY-qc9te That sounds horrifying. I have repeatedly tried to suggest that whenever one one is doing something that could be electrically dangerous, one has to carefully evaluate the risk - and how faults/bad things might happen, and the chooses the best for or protection - isolation transformers, GFCI/RCD etc. Those hot chassis TVS and radio are really dangerous if not handled properly. They were really common in Canada and the US. Not so if they were common 220-240V countries. Also am an advocate for using a properly position dead mans switch for appropriate situations (such as when I was demoing HV power transmission for example).

[@retrozmachine1189]

I needed to look at the AC output of an inverter I had just finished repairing and didn't have a proper HV differential probe handy so I used an old modem transformer and was quite surprised at how much of the residual (inverter manufacturer skimped on the output filtering) 20kHz made it through.

[@ElectromagneticVideos]

I presume since you were expecting few harmonics it was supposed to be a true sine wave inverter? I was amazed at the Variable Frequency Drive I was experimenting with a while ago - PWM modulation but almost no filtering!

[@retrozmachine1189]

@@ElectromagneticVideos It was a sinewave output model but there was quite a bit of 20kHz PWM making it through the output inductor. It really was undersized for the 2kW rating of the inverter, to the point where the lacquer on the winding had discoloured due to the heat produced.

[@nlb9611]

Dr Jones i have a question i am a lowly mechanical engineer 😅. For 2 gensets both exactly the same, both producing the same active power , but one have a PF of 1 and the other having a PF of 0.8, will both generators still use the same amount of fuel? Id assome so since active power represents the actual mechanical work being done. If this is true why then do power companies charge for reactive power?

[@ElectromagneticVideos]

I wouldn't exactly call mech eng lowly - from turbines to stresses in material to the mechanical part of robotics and electric cars - all amazing stuff. One of these days I want to do some videos about the different types of engineering! Yes, both generators will use the same amount of fuel. Your example is the perfect setup for explaining that: Its the active or real power that results in the average forces that oppose rotation in the generator and result in the generator having to burn more fuel to keep the speed constant. The reactive power will have a pulsating push-pull effect on the rotation of the generator as the power flows to the load and then back as the AC cycle proceeds and repeats, but the push pull will average out to zero so will not impeded the rotation of the generator rotor and not need more fuel being burned to compensate. So as you put it. if "active (or real) power represents the actual mechanical work " why do the electric companies care? The total current on the AC wires (ie grid) is increased when reactive power is add to the mix. So for a big induction motor that uses 100A times 600V of real power to do whatever its supposed to do, the current draw may be more like 150A with e the extra current being from the sum of the (100A) real and reactive currents corresponding to the real and reactive power. So the power co now has to size cables, transformers, and generator windings 50% larger than they would need to be to carry the now larger total current. And, since most cables today are not superconductors, they all have some small resistance and the power lost due to current flowing though a wire (=low value resistor) is I squared R (ie I times I times R) we now have transmission loses in the grid transmission lines of 150 squared R as opposed to 100 squared R for the numbers in the example. So in this example, the transmission losses are about double what they would have been if the power was purely real. In the grand scheme of things, maybe that means 4% of the power is lost in the transmission lines as opposed to 2% so the electric co has to up the voltage a bit and supply 2% more power to compensate. Not a lot, but over megawatts or gigawatts on the grid it starts having real value. So that's why they charge - there are infrastructure costs and a small increase in power generation associated with increased transmission losses. The cost is enough that factories with big induction motors find it worthwhile to install capacitor banks or "synchronous condensers" - free running synchronous motors - to provide the reactive power and reduce the surcharge the power co makes them pay for reactive power. Hope that was understandable!

[@pendarischneider]

An extra feature might be to use an op-amps to present the signals to the outside world. I know this adds a need for a power supply and makes this more of a project. I am proposing two op-amp circuits with adjustable gain (for the calibration). These will isolate the measurement voltages produced at the transformers from the influence of any external load. Also the output signals become low impedance source, so less likely to pick up stray RFI. And these play nicely with the high impedance oscilloscope probes. Overall this could become a box approaching the higher end instrumentation standards.

[@ElectromagneticVideos]

That would be an excellent way to take things to the next level for all the reasons you describe. Wouldn't be hard to make a little op-amp PCB to do that. If you did that, you might also be able to use some good quality high bandwidth 600 Ohm audio transformers on the outputs to provide the isolation and use a shunt resistor for the current sense to try and get as wide a bandwidth as possible - beyond that of a CT or other transformer not intended for higher audio frequencies.

[@t1d100]

👍👍👍👍👍

[@ElectromagneticVideos]

Thanks!

[@stevenspmd]

A video covering the how and why of isolation transformers, grounding and ground loops might be interesting. I think most videos covering the topics are at least 8 years old. The history of grounding is interesting; when it started, only the pole was grounded and not appliances so people were getting zapped!

[@ElectromagneticVideos]

I'll put that on the list. Isolation transformers and ground loops - are you thinking of places like TV studios etc with audio hum problem? History of grounding - I dont know much about that sounds like something very interesting to look into .

[@stevenspmd]

@@ElectromagneticVideos Understanding/recognizing danger; its a rabbit hole but its always good to understand the "why". How do they teach that in school?

[@stevenspmd]

One video I really liked was "The Basics of Electrical Grounding" from tjwiltube

[@stevenspmd]

One video I really liked was "The Basics of Electrical Grounding" by tjwiltube

[@ElectromagneticVideos]

@@stevenspmd I'd actually be interested to find out what is being taught in school these days in terms of real hands on safety. When I was an EE/CE student, one course was "Machines" - essentially AC/DC motors, generators, transformed etc. The lab had dozens of 10 to 20hp machines with voltages up to 600V. As far as I known, nobody ever got hurt, but here was a wall of shame that had various the remains meters etc on display that had been vaporized as a reminder to everyone to be careful. That lab is now gone - machines are now fractional horsepower lab machines in plexiglass boxes. Not the same learning experience.

[@gregwmanning]

Thanks for another Transformer Video, if possible could you please demonstrate the trimming with variable resistors or a voltage divider of the voltage and current transformers to give a 10:1 (or 20:1) output? Is it possible to use a transformer winding as a choke along with the larger electrolytic capacitor in the filtering circuit of a linear power supply?. And which winding would be preferred primary or secondary? And what do you do with the unused winding(s), leave open circuit or install a burden resistor? Thanks again

[@ElectromagneticVideos]

OK, I'll put it on my (growing)list of things to do! Yes - you can use a transformer winding as a choke or inductor - actually that all transformer winding are! But transformers are often operated with the peaks of the AC cycle being around the saturation level of the BH magnetic curve. That adds nonlinarities and reduces the incremential inductance. So generally for a good filter, measure the AC RMS current into a transformer winding when operating as a transformer with no load attached. Limit your DC current to around that or less for good performance. You can use the inverse of the voltage ratio to figure the equivalent current for other windings without testing them. It makes no difference which winding you use - so long as the current is appropriate as above, pick the highest voltage winding (=highest inductance) than meets the current requirement. . NOTE Be sure to keep the unused winding terminals/wires insulated and away from fingers - the can develop HV spikes depending on the pulsating form of the DC on the winding you are using. As implied above, leave the unused windings open - they serve no purpose in this sort of application. Adding a resistor will lower the Q of the circuit and make the inductor less effective as a filter. Hope that helps!

[@SoundsLikeOdie]

Very interesting. I have been trying to make current transformers. The ones available here have gone up in price exponentially and are no longer practical for my automation projects. They surprisingly difficult to make. The only cores that work even slightly are toroidal ferrite cores with copper windings. I cant understand why something so simple can be so expensive. I used to get them for about $2 and now they are closer to $5. At that price I can buy a Chinese current meter with display anbd a Current transformer. If you know of a simple easy to DIY current transformer or equivalent I would be interested.

[@ElectromagneticVideos]

I suspect the main reason for high prices is supply and demand, and that they are manufactured in much smaller quantities than power transformers. The best thing I can suggest is find a small power transformer that has some space around its coil. Then you can put at turn of wire around the coil as your high current winding. To find out the turns ratio, measure the voltage of one turn when the transformer is powered normally, and the turns ratio will equal the ratio of voltages and will be the inverse of the current ratio. And choose a burden resistor for the HV side that will keep the voltage there well below the voltage that winding was rated for. Good luck!

[@SoundsLikeOdie]

@@ElectromagneticVideos Thank you. We are on the same page. I have been digging through my junk pile and trying different ferrite cores (I assume thats the same as a powder core). So far none are as good as a actual CT.

[@ElectromagneticVideos]

@ There are different types of ferrite cores, but thats typically aimed at RF characteristics. Have you looked on Aliexpress? They have lots of cheap CTs. You couldnt use them for anything that needs to be certified, but might be fine for occasional use lab equipment or experimenting.

[@LendzuLocuks]

69 counterclockwise => 17 clockwise 2 end of clockwise 3 end of clockwise and counterclockwise 4 both ends 5 sort of end of counterclockwise... ⏳

[@pwkoert6594]

Ah, filament transformer... it's not a type of transformer but a transformer for filament. of vacuum tubes... that makes it a 6.3 v with a few amps... ( for the people that don't know..8-)

[@ElectromagneticVideos]

I should have perhaps just called it a small power transformer to avoid confusion.

[@pwkoert6594]

in 240v AC 'land' you would use a transformer that gives 24 volt in 'normal operation' often a 'doorbell' transformer would do,

[@ElectromagneticVideos]

@ Makes sense - that would give about 1/10th the input V so makes conversion of and multiply by 10. For what its worth - for things like doorbells and HVAC, we (in 120V land) use 240V as well.

[@pwkoert6594]

@@ElectromagneticVideos Everyone has blind spots, just here to assist 8-) (and learn...)

[@pwkoert6594]

@@ElectromagneticVideos I am familiar with US power, but when I used it there was no 3rd pin, thus no polarity... I have 'played' with a few tube-amplifiers, I type my first comment before I could read it on screen. Saw an article about this subject years a go, they used 2 small transformers 1 to power the measuring electronics and 1 with a minimal load to measure from. As mentioned by you, a much safer way to get the same result with minimal distortion. I was always warned about connecting an oscilloscope to mains power.