Current Transformers - How They Work

A look at current transformers, how they are used and how they operate differently from power transformers. We see what happens when the burden resistor is removed and also measure the current needed to drive the core into saturation. We also take a apart a GFCI receptacle to see its tiny current sense transformer and also a clamp on ammeter to see its transformer is put together.

[@tsbrownie]

Another very informative video. Thank you. Editing suggestion, give yourself about 1/2 second of "silence" at the start of the clip before you start. KZbin often starts playing the clip before it opens up from the suggested video screen. Look forward to the next.

[@ElectromagneticVideos]

THANK YOU!!!!! I had no idea that was happening! I will definitely do that from now on - I can see how annoying it would be to start viewing a video with someone in the middle of a word.

[@ThriftyToolShed]

Excellent video, thanks!

[@ElectromagneticVideos]

Thanks! Much appreciated!

[@davidmoore1303]

Awesome video, loved it

[@ElectromagneticVideos]

Thank you so much! I really appreciate that!

[@TimPerfetto]

Correct me if I'm wrong but I don't know of any other channel that discusses these topics. Thank you very much appreciated

[@ElectromagneticVideos]

Hi Tim, with so much on KZbin these days I wouldn't dare say there isn't anything like it but perhaps the mix of stuff is a bit unique. What I am trying to do with this channel is to connect practical and real things to the fundamental underlying theories while still keeping it understandable to a range of audiences. I glad you liked it. I see you have just started putting up videos - just subscribed - I have never seen the "Manhatten" style of doing PCBs before. Looking forward to your future videos!

[@user-ix1tq1ec9w]

excellent content, thanks

[@ElectromagneticVideos]

Thank you! I appreciate your comment!

[@garbo8962]

Years ago the place I was working at had a lot of amp meters to show how much load was on equipment. Was lucky to have a large meter repair shop that stocked up to 600 amp current transformers. All of them provided a 5 amp output. A 100 amp current transformer or " Donut " would have a 20 to 1 output. Meter shop had various size 0 to 5 amp meters where they would relabel meter face to read the amps. Large hospital that I retired from had expensive 400 to 1600 amp rack in 480 volt circuit breakers that had a display to read amps & voltage on each phase. I have a 10 to 1 donut (50 amps ) along with a nice panel meter that I am going yo install on my central AC unit. Great vidio.

[@ElectromagneticVideos]

That really interesting! Never thought about it but it makes sense they would have to have different meter scales so that what is shown would be the current being measured. I have actually been thinking about setting up some a couple of current transformers to monitor and log my house's input currents. I'm going to have to talk to a neighbor who is an electrician to find out what is permitted by code in terms of placing current transformers in a residential breaker panel.

[@BTW...]

​@@ElectromagneticVideos Interesting well expressed video, mate. Are you aware of DC metering CT's too? it's probably for a different video on Instrumentation works. Most of my working career involved CT use... just about every Distribution SwBoard have them.... yeah, 50 years of em. Mostly HV heavy Industrial generation/transmission, AC/DC protection/distribution... down to commercial/domestic. I feel sorry for you, living with the Nth Americana standards... 240Vper phase here in Aus. Hey, in domestic to heavy industrial instal' level... the Secondary windings always suffer high voltage insulation breakdown going open circuit/no load... sometimes dramatically and very costly. That voltage spike across S1 and S2 gets into the high kV range... even with 240/415V systems. The windings flashover burn, rendered useless. The first thing they taught me was... Identify P1 side of the CT, installed towards Line.. never Load. 2. ALWAYS short circuit the Secondary at the CT before disconnecting ANY field wiring, (never work on Live anyway) 3. ALWAYS use a 'ring' type crimp/wire terminal at the CT and Meter, that cant disconnect if loosened (Open circuit), and 4. ALWAYS use 2.5mm CSA for secondary wiring, minimum. 5. ALWAYS Earth/Ground the S2 circuit wiring at the CT, having 2 wires in the one lug for S2... not Earthed at Metering device. That's high quality and safety Standards, mostly found in Industry. In typical use, the burden resistors are located in the analogue meter case... never at the CT in a Swboard or yard. As noted there.. CTs come in many different ratios, and physical sizes. But importantly, you match and scale the Instrument to CT ratio and according to max Primary circuit current. The two old large Industrial CTs you have there are intended for placing in a Busbar circuit, far lest likely cables. Most of my work has been placing Busbars through CT's.. LOL Imagine 3x 125mm x 10mm Cu bar phase with a 10mm gap between bars.. so thats 125 x 50mm conductor passing through a CT.. or even a single 25 x 6.5 solid Cu Bar link bolted in. The real High Voltage CTs look very different, after all, they need to maintain HV flashover clearance between primary and secondary circuits... say at 220kV, it's a significant air gap or track distance. A real safety issue. Residential install is no problem.. after all, they are used in revenue metering everywhere. A Split core CT that clips around the Active conductor/s will do. These are used with some wireless Resident user level Energy Watch Metering devices. Common here and Govt subsidized.. promoting consumption awareness. They are made to be quick and very easy install. Never install private CT's prior to revenue metering. Never mess with stuff prior to Main Switch anyway! It's high kA fault level capacity.. a real blast... one flash ya ash. An after Main Switch is best install location for your CT. That way you can easily switch off supply, disconnect load cable, and pass through a non-split core CT, and reconnect... it's a too easy job. Make sure you always have the P1 side, often marked with a white dot of the CT, facing towards the supply, not load, especially if you have 3phase metering. and of course... here in Australia., only licensed, qualified people can do such electric works. ..but DIY... sigh... like folks you are teaching new knowledge.. do so at own risk, or better not at all.

[@ElectromagneticVideos]

@@BTW... One of the best thing about doing this channel has been heairng from people like yourself BTW who have amazing knowledge and experiance in one thing or another. And youre really got me intrigued - how on earth does "DC metering CT" work? It is really something like a hall sensor pretending to be a CT? Or some sort of clever arangement where DC satures an AC energized coil? Did a google search but didnt turn up anything useful. Do you by any chance have a link to a spec sheet? Australia! One of the nicest places I have ever visited! Spent a month in a camper van (thats caravan to you) exploring up the east coast and back down a bit inland at the edge of the outback.

[@lalogarcia6686]

great video!!!

[@ElectromagneticVideos]

Thanks!

[@anoimo9013]

as probably commented before, typical handheld ammeter clamps contain hall sensors, hence don't need sense coils and burden resistors. Naturally the magnetic material should be as unsaturable possible for the reasons very well explained in the video

[@ElectromagneticVideos]

I thought it was only the ones that did DC (as well as AC) that had hall sensors. Maybe hall sensors are cheaper now than a coil?

[@DaveEtchells]

FWIW, I also think that it’s only the DC-capable clamp meters that have hall-effect sensors in them.

[@knoxpruett1889]

Excellent video!!! It explains the function for basic users AND the Engineers like me.

[@ElectromagneticVideos]

Thank You - I really appreciate that! That's what I'm trying to aim for. I'm a Engineer too by the way!

[@Sparky-ww5re]

While on the subject of transformers, it would be cool to see a video on how they are wired together to produce certain voltages for certain applications, for example, we have our typical 120/240 single phase, or sometimes called split phase because of the center tap on the secondary, then we have 120/208Y, 277/480Y and 347/600Y (very uncommon in the USA) and finally delta connected systems, which includes ungrounded delta, corner grounded delta, high leg delta, open delta and open high leg delta. I've never seen it with my own two eyes, but it is possible to have a 240/480V delta three phase, with a high leg 415V to ground. Essentially the 120/240V with 208V high leg, but with the voltage double, this system is so rare, that the electrician I'm working alongside who has been in the trade for 43 years, only ran into this once in the early 1990s about 30 years ago in an old woodworking plant in Northern Kentucky, the large motors for the equipment ran off 480 volts, another set of transformers provided 120 volts for the office equipment, and 240 volts from two of the phases to neutral, powered the metal halide high bay lighting.

[@ElectromagneticVideos]

You know, a video on why three phase and the one on three phase transformers might be really neat. I do have an ancient three phase 220V synchronous machine that I scrounged years ago. Maybe next summer when its warm outside I should see if I can get it going. and use it to generate some good quality three-phase from the single phase I have at home. I have always found those three phase transformer configurations are interesting. And to add to your list - a Scott-T - have you ever seen one of those? Are they ever used? I remember being so intrigued by them in the machines class I took years ago and the idea of two phase 90 degree phase shift power was so interesting and different! Also have always been intrigued how the various Delta and Y combination suppress or increase harmonics. I wonder how they react to the harmonics from electronic power supplies? Since i have a stack of those toroid transformers I certainly have enough to demo and test various 3 phase configurations. Thanks for the comment - loads of interesting things to play with - have a great evening!

[@Sparky-ww5re]

@@ElectromagneticVideos I've heard of Scott T transformers but never understood the purpose or how they are hooked up. As for two phase, yes I've heard of 3 wire and 5 wire, and sort of have a grasp of the concept. Apparently in the 1890s - early 1900s, electric motors often ran on this system, and unless you happen to be working in Philadelphia or at least certain parts of Philadelphia, you will never have to worry about working with two phase. As for old two phase motors, one might question whether they are almost identical in construction to the capacitor start motors commonly used today, minus the capacitor of course, since the capacitor shifts the phase 90° to allow for starting.

[@ElectromagneticVideos]

@@Sparky-ww5re As I recall - and its been a long time - one purpose of a Scott T transformer was to be a three phase transformer with only two cores - I'm guessing with better results than a delta missing one leg. For motors - as you said similar to capacitor start - actually capacitor run without the capacitor. I think I read somewhere that way back it was hard to make capacitors big enough so maybe that was the alternative. I'm going to have to dig up my old notebook from machines class - believe it or not I saved a number of notebooks from the best courses I took and machines was one of the best. 5 wire? I going to have to look that up! Sp Philadelphia has two phase today? Wow - that interesting - a remnant from the past. I read somewhere that some parts of NY have 120V DC supplied to some old buildings for things like their old elevator systems - back from the Edison days. Over here in Ontario, we had a 25Hz antique AC system that was from Niagara Falls and powered some old heavy industry plants that didnt want to change. I think it got shut down in the last recession when those users shut down their plants.

[@Sparky-ww5re]

@@ElectromagneticVideos oh wow, 25hz, now that's what you call antique. Not sure if it's in use today, but I remember reading that 25 hz was once very common for electric railways, and it was also more efficient to use with rotary converters to produce DC from AC, when both systems co existed, and before mercury arc rectifiers were perfected and widely used. As for 120VDC in NYC, didn't know it was still in use, although I remember reading that in the 1950s or '60s DC was still being supplied to one of the college campuses, and students who were newly enrolled would plug their phonograph players, hair dryers etc. in their dorm rooms and burn them up, because the motors required AC. I Think because some of the elevators used DC motors, and also 25 hz was a comprise between DC and 60 hz, which became increasingly common after 1900 to 1910ish. Before that many frequencies were used, 133Hz was a commonly used frequency in the late 1880s until around the turn of the 20th century, since it reduced the flicker rate for the carbon arc lamps used in street lighting as well as large retail stores, factories and theaters, and to a much lesser extent, incandescent lighting.

[@ElectromagneticVideos]

@@Sparky-ww5re Apparently 25Hz reached up to Quebec before WWII - my dad told me how the lights flickered from the 25Hz when they first got electricity when his was a kid. One of my Profs from university (now long retired) recently told me he remembered seeing 25Hz flickering lights somewhere west of Toronto in the late 40s or early 50s. I just stumbled on this : www.lifebynumbers.ca/history/the-rise-and-fall-of-25-cycle-hz-electricity-in-ontario/ I'll bet those kids at the college with DC werent happy! I wonder what the wall switches were like for the DC systems - DC arcs don't extinguish as easily as AC. Here's some DC trivial for you: There is one relatively recent all new 120V DC installation - the International Space Station. I presume they must have real good DC Arc fault breaker on it to catch any dangerous arcs. Heres another one for you - 16.7 Hz on European raillways : en.wikipedia.org/wiki/15_kV_AC_railway_electrification Its conversations like this where I wish we we re close buy- would be fun to chat about all these things!

[@scottthomas3792]

Years ago, I had a clamp on dc ammeter meant to test the current draw if a automotive starter. It was about the size and shape of a Mason jar lid, and went from 0 to 100 amps. I got it at a yard sale for a dollar...it was old, but hadn't been used much. It didn't have the round clamp over the wire sensor like typical ammeters , but two clips, sort of like a large fuse holder...you clamped it to the starter cable. No idea how accurate it was. It provided some useful information...informal tests on warm weather and cold weather current consumption of starters... I had a cheap clamp on ammeter at my last job, and it held up quite well....

[@ElectromagneticVideos]

Sometimes yard sale things are a steal! I wonder if the clips held some sort of magnetic field sensor at a hopefully fairly accurate radius from the center of the wire? Its amazing how cheap things have gotten these days - the DC clamp on ammeter that I have used in some of the videos cost about $60Cdn, so less than $50US. Certainly not the same accuracy or durability of a more expensive one, but as a home workshop tool it cant be beat.

[@86Ivar]

Very good explanation of such a mystical device.

[@ElectromagneticVideos]

Thanks! I It is a bit mystical - so similar to a regular transformer but in a sense its how its used (essentially being shorted) that makes it so different.

[@qwertyuiop2895]

Not very good. Over-complicated explanation. And device is very simple, nothing "mystical" really.

[@MichaelCowden]

I have a nice Fluke clamp CT for diagnosis of HVAC and appliances at home, and my house has 350 amp electric service. The entrance cable runs through a big CT to feed the electric meter, which means I can't use a meter socket surge protector. I had never taken apart a GFCI outlet before, so that was very interesting and it makes perfect sense to me how it works now. I'm curious about the flat top sine wave you mentioned was caused by power supplies in the house. Is there any way other than a power reformer device to clean up that phenomenon and maintain a sinusoidal wave?

[@ElectromagneticVideos]

350 Amp service - wow! But great to have - I'm looking at converting to electric heat and my 200A service will be cutting it close (100A for the boiler). I think the problem about trying to clean up the flattened waveform in a bulk way is the huge amount of power involved - ie to one way or another push up the peak or depress everything else - probably a combination of the two and at the same time have to allow 350A to flow in your case with minimal resistive losses. I suspect the long term solution is better power factor correction / harmonic reduction in all the switching power supplies we now use. I think its beginning to be required in some places. Maybe we need to start to measure the current harmonics at the power meters and billing extra for that to get peoples attention.

[@MichaelCowden]

@@ElectromagneticVideos Thank you for that explanation. I know that commercial electric service does bill incorporating power factor but residential does not. An E.E. friend of mine told me about giant PFC systems that some companies use to straighten things out again just to save money on their power bills. Hopefully they don't start charging residential customers because I think almost everything in my house has motors or switch mode power supplies except the linear PS for my ham radio gear. 😀

[@ElectromagneticVideos]

@@MichaelCowden Your friend is probably referring to en.wikipedia.org/wiki/Synchronous_condenser typically used when plants have huge induction motors. Our houses are nothing compared to that! To be clear, each of us contributes only a little to the AC waveform issues - I'm certainly not the cause of 99% of the droop in the AC on my line. But a hundreds houses each adding 1% adds up!

[@86Ivar]

Thank you! ❤

[@ElectromagneticVideos]

Your welcome!

[@retrozmachine1189]

It might be interesting to do some experiments of the performance of CTs when there is a DC component to the current flowing through it, and also for different frequency in general instead of just 50/60Hz. There are significant implications for the performance of GFCIs (RCDs). It doesn't take all that much DC to significantly derate (ie make it worse) the trip current of an RCD. With a little more DC the device will not trip at all. This is why countries are moving to require RCDs that can handle a DC component in the waveform as well as a general DC bias as well as frequencies other than 50/60Hz passing through. Add arc detection into the mix and the price of these protection devices gets quite high.

[@ElectromagneticVideos]

I didnt know about the DC issue with GFCIs but makes total sense - interesting! Funny thing is I have been assembling the components of a tester to measure the exact trip current of GFCIs to see if there are differences between manufacturers. Using a load that pulls DC - maybe a incandescent bulb in series with a diode to magnetize the transformer core will be an interesting addition to that. Higher frequencies - I wonder if the harmonic frequencies from electronic power supplier drawing current in peaks messes them up? Yeah - the costs of those things are getting crazy and I think unreasonable based on the cost of the mass produced components used in the them. I wonder if its the risk/insurance cost that if such a device fails and a house burns down they could be a huge payout?

[@retrozmachine1189]

@@ElectromagneticVideos Even the cheap AFDDs from Asia come at a hefty premium, and there's no insurance there that's for sure. A basic RCD can be done with no semiconductors at all. A more responsive one with only simple components. Once we get to the point where we are observing the actual waveform and looking for distortions of it we are into the world of software development and that quickly adds to the cost. It's still hard to accept that an AC class RCD is $20 while an AFDD is $200.

[@ElectromagneticVideos]

@@retrozmachine1189 Can you make a RCD that's sensitive enough without semiconductors? A low current relay attached to the current transformer that triggers the tripping solenoid? Would seem way more long lived to be than a semiconductor one! Software development and signal processing - sadly I spend so much time on that these days - its the smarts in everything. I would still have thought the SW costs divided by millions of breakers would still be minimal. I do know that there are patents on the arc-fault detection methods so that might be part of the price gouging.

[@retrozmachine1189]

@@ElectromagneticVideos Originally RCDs (aka ELCB in Australia early on) etc were just the CT direct into the trip coil. They worked but the addition of a bit of electronics greatly improved their performance, particularly the trip time. Despite being thought of as relatively recent things since they started being required in many households, RCDs have been around since the late 1950s. Production of RCDs started in Australia in the early 1980s.

[@ElectromagneticVideos]

@@retrozmachine1189 Interesting! I had no idea they were available so long ago! I'm trying to think when I first saw one - probably sometime in the 1990s. Don't know if I ever mentioned it to you - a bit over ten years ago spent 2 months on vacation in Australia - you have a fabulous country!!!!!!!!

[@BjornV78]

Hi, i know this is a older video, but i have question. if you use a big enough iron core, would a selfmade 1 : 1 ratio CT work ? Like 1 turn primary and 1 turn secundary, or 10 turns primary and 10 turns secundary ? Only for high currents i presume ?

[@ElectromagneticVideos]

I'm always happy when an old video gets looked at! Yes - it would work! But the issue you may run into is the the limited voltage you can get out of your 1 turn to 1 turn secondary. With an ideal zero Ohm current detector attached to your secondary, that would not be a problem, but with the slightest resistance, the voltage would go up and it would become more of a potential transformer and the core might end up saturating. So 10 turn to 10 turn might be better if you want a that 1:1 ratio. Should work with low currents as well depending on your ability to measure them. I did do an examp of 1 turn :1 turn transformers here in the Electromagnetic Chain video kzbin.info/www/bejne/gJO1faKNr62Je6M Take a look if you haven't seen it - it is a potential transformer but it is 1:1 done a number of times. Hope that helps!

[@BjornV78]

@@ElectromagneticVideos , thank you for the quick reply. I'm building a isolation transformer project with 500VA isolation transformer (240V), build in dim bulb current limiter with small G9 halogen bulbs, a 500VA variac and a own design of electronic circuit breaker. For the electronic circuit breaker part i'm using a DIY current transformer, by converting a step down transformer 240V to 12V, with the 12V coil removed, and replaced by a few turns. Normally for such a circuit the output of the CT delivers very small voltages and small currents, and those get amplified with a OPamp. But in my case i use a higher value of burden, and instead of a resistor, i use a bi-polar capacitor rated for high voltage, this secundary voltage/current gets then feeded into a 1000V/1A bridge rectifier and with a 1Mohm potentiometer into a transistor Darlington to amplify it and have a 0 to 12V output that controls the trip circuit (trip circuit contains a few optocouplers and beefy Triac). The problem that i run into is that i want to measure currents between lets say 30mA minimum and 3A to 4A maximum, without any capacitor, i have just enough voltage after the bridge rectifier left over, to steer the Darlington configuration, then after a certain amount of primary current i need to add a 1µF capacitor as burden, but this 1uF is only useable to again a certain current level before i need to add again 1uF capacitor. In short, in the low part i can get away without any burden, and at the high end, i need to 2uF as burden. I'm now looking to get all more linear and if possible only use 1 capacitor from low to high. In a few tests last week, i have blown up twice a 0,1uF smoothing cap behind the bridge rectifier. The first one was a 50V version, the second one was a X2 cap, rated for 250V :-) So my idea was now to use a step down transformer, like a 240 to 12V or 6V type, and remove both coils, and make a 1 to 1 ratio with let say 10 turns on each side. I use 1.2 mm magnet wire from a 7A DC choke, which can handle the 3 to 4A primary current. I bought different types of CT with different ratios, but only this DIY version gives me enough voltage on the secundary side to use without any OPamp. I like to use 1 burden value over the entire range, but if not possible, i need to make a circuit that automatically switch to a extra burden value with a relay, like some lineair bench powersupplies with transformers with multiple taps work. I like to avoid that extra circuit if possible. Thanks in advance for your time. Grtz

[@ElectromagneticVideos]

@@BjornV78 I think - and its a bit hard to visualize from a written circuit description - the that issue you are having may be due to the use of a rectifier after the burden, which means the voltage drop across the diodes starts having and increasingly detrimental effect for lower currents and burden voltages, resulting in a very non-linear output that makes it perform poorly for low currents. My thought: attach the bridge rectifier to to the transformer secondary (with enough turns to produce way more voltage than the 1.2V rectifier drop at the lowest current you wish to measure. Now use a restive burden on the DC side and the DC voltage should be very linear in relation to the AC current. If I misunderstood, email me a circuit diagram (pdf or image) and I'll take a look and see if I can be of more help!

[@BjornV78]

@@ElectromagneticVideos , i have the rectifier on the secundary side, and the burden capacitor before the rectifier. In my first version of this circuit, i used a 5V Zenerdiode on the DC side that act like a burden, and i though everything worked great, but then discovered at a certain primary current level, the DC voltage starts to clip, and the extra current is no longer detected because everything kept at the 5V zenervoltage. I was looking for a email, but did not seen a emailadress under info, or maybe i have overlook it. Grtz

[@BjornV78]

@@ElectromagneticVideos , just found your emailadress and send you a email. Big thanks. Grtz

[@davesage9190]

How do you choose the correct value of burden resistor to give an output voltage exactly proportional to the input current. Is it by trial and error measuring the input current and output voltage across the burden resistor? Suppose you don't have an amp clamp to measure the input current.

[@ElectromagneticVideos]

I believe virtually all current transformers specify the value somewhere in their data sheets. Presumably the manufactures recommended one would give the best linear results. Without that info, as you said, you would have to measure and experiment!

[@davesage9190]

@@ElectromagneticVideos Thanks

[@BTW...]

You match the Instrument to the CT ratio you are using. The instrument contains the correct burden load. There are common manufacturing / engineering industry burden Standards, which will be marked on the CT nameplate or manufacturers data sheets. In practice, you don't select a resistor or install at the CT, like shown here in video. Typical CT metering wiring would be 2 heavy gauge wires (to minimise voltage drop) wires directly connected to an analogue meter (containing the resistive load to suit the movement) or a monitoring instrument that presents as the 'burden' load. To calibrate your metering instrument requires a 'calibrated reference Standard instrument' i.e. clamp meter or of kinds. If you order the correctly scaled instrument to suit CT ratio and burden, you get a manufacturer calibrated instrument, meter or whateva ya wanna call it. 2 wires.. simple. but never allow CT Secondary to go open circuit under any circumstance, if there is a wire/cable passing through Primary (hole)... energised or not.

[@ElectromagneticVideos]

@@BTW... Thanks for that informative post! really appreciate it BTW!

[@Graham_Wideman]

Not sure any of the existing replies are quite explicit enough. A current transformer's specs tells you the current ratio, like "100:1", and also lists some idea of the max current it can handle. So that tells you what output current to expect for what input current. Next you pick a load (shunt) resistor that you connect across the output winding, let's say 1 ohm. By ohm's law, if you then see 1V across that resistor, that means 1A in the secondary winding, so, with 100:1 ratio, that corresponds to 100A in the primary winding. Of course, since this is a measurement application,we are concerned with how linearly the output current corresponds to input current, and this varies a little according to the range of output voltage produced, or equivalently, the load resistor. Comprehensive specs for current transformers will provide a plot of [percent deviation from exactly linear] versus [input current], and multiple such curves for different load resistor values. Generally you want as small a load resistor as possible while still able to measure its voltage to sufficient resolution, as this reduces the burden voltage seen on the primary (ie: the voltage drop experienced by the primary current you're trying to measure but not disrupt.) A smaller resistor also reduces heat dissipation, and any effect that might have on the precise resistor value.

[@pixelpatter01]

Would it be best if the burden resistor matched the resistance of the coil?

[@ElectromagneticVideos]

Hmm - I don't think so, unless just by chance the resistance of the coil was the correct value of the burden resistor. You may be thinking of something common in amplifiers where the idea is to match source and load resistance to maximize power transfer. In the case of CTs, its really linearity between the primary and secondary currents thats trying to be achieved, so keeping the core out of saturation is key and best achieved with a burden resistor in the range of what is recommended by the manufacturer. Hope that helps!

[@newmonengineering]

If i want to wind my own transformer to plug into the wall, what math do I need to do to make sure it doesn't burn up or blow a fuse? There must be some formula that tells me how many windings I need of a certain size wire without it melting right?

[@ElectromagneticVideos]

Its actually a bunch of compromises that determines things so unfortunately one size fits all type formula. Your right about wire size - its needs to be big enough to handle your desired current, and you need enough turns to limit the magnetization current to some small fraction of your desired operating current. The size of wire and number of turns somewhat sets how big the core has to be for that to fit, but the size and geometry of the core determines the number of turns so there is some back and forth. Generally the practical way to do it is look for a transformer of about the power you want and get a similar size core. Then using the BH curve and the various equations I glossed over in this and previous videos, you can estimate the number of turns, and confirm that by winding a few turns and measuring voltage and current and adjust accordingly. Here's and article how to do it: www.electronicdesign.com/power-management/article/21800646/build-your-own-transformer

[@cynic256]

you should test a string of 12 or 14 gauge MC cable to see if it contains the flames and smoke

[@jvon3885]

I'm working on a battery I get a volt reading out of it and yet it won't light up an led. Why? I can get 1.v on the meter. I'm a complete newbie to electronics but want to become an electrical engineer someday.

[@retrozmachine1189]

LEDs are current oriented more than voltage oriented. LEDs require a certain voltage across them before they produce significant amounts of light too. Once they reach a certain voltage (the forward voltage) they will try to clamp the voltage there so current rapidly skyrockets. The voltage they require is different for different colour LEDs due to the different materials used in their construction. This is not colours produced by phosphors, rather the LED itself - unchangeable red, green, blue etc. Your 1V cell may simply not produce enough voltage to cause the colour LED you are using to light up and it may not be able to supply much current too. 1mA at the right voltage should be visible, although dim. A LED with more voltage across it than its forward voltage must have a current limiting resistor or a current limited power supply to keep things under control otherwise ... dead LED.

[@ElectromagneticVideos]

Well if its a 1V its very likely the minimum operational voltage of the LED is higher than that - often in the 2 or even 3V range. And whats the battery's max output current? Needs to be enough for whatever LED you are using? Also be sure to use a resistor in series with the LED to limit the current so you don't burn the LED out...

[@jayduffy7615]

To add to the great information that others have left, I will also say that LEDs are Light Emmiting Diodes. Which means that they will allow power to flow in one direction and not the other. Diodes work in this way. So check to make sure that your polarity from the battery to the LED is correct. Best of luck to you with your goals of being an electrical engineer!

[@ElectromagneticVideos]

@@jayduffy7615 Great point - somehow I competently failed to mention that. Hopefully our friend who asked the question gets his project going!

[@chadhiggins8397]

Those transformers don't look current at all, they look quite old. 🤣🤣🤣

[@ElectromagneticVideos]

The two big ones are antiques! The rest are modern....

[@qwertyuiop2895]

"Cut to the chase" next time. 1. Low number of turns (most of the time incomplete 1) on one side and many turns on other side = "ignition coil". No need for B-H curves to explain this. So current transformer may act like ignition coil and damage the insulation. Critical in real applications like power station measurement on high voltage side. You can damage the equipment and/or shock the personnel. 2. That's why you never use/manipulate current transformer with open terminals (low amps side). This is the very basic rule. 3. I've never seen "burden resistors" on classic current transformer (they are designed to work with amp meters, so this is natural "resistance"). Common thing is a permanently installed switch or piece of wire to short the transformer when not used (or for maintenance purpose, when you have to disconnect the amp-meters, live).

[@86Ivar]

No need for this type of comment thank you.

[@Graham_Wideman]

Yeah that's a bit abrasive. And you have point number 1 a bit off. If the current transformer has a "single turn", that turn is exactly 1 turn, even though it appears to be just a wire passing through the "donut hole". That is still 1 turn because the complete effect comes from not just the wire through the hole, but from the entire circuit, which of course has to be a complete loop no matter how large, otherwise current will not flow.

[@BjornV78]

1. Low number of turns (most of the time incomplete 1) on one side and many turns on other side = "ignition coil" No it's not !!! A ignition coil works with DC !!! The high voltage (and spark) occurs after the DC current has cut off from the primary, then due the collapsing magnetic field on the primary, a high voltage is induced on the secundary. Also a ignition coil has more then 1 turn on the primary (low voltage side) otherwise you have a death short. Back in the old days socalled ignition points (a switch with a capacitor in parallel over the contacts) were used to interrupt the primary current, this "switch" was located in the bottom of the distributor (Delco). In the later versions a Hall effect sensor was used to steer the moment of the energizing of the primary coil inside the ignition coil. There are also versions that use a current transformer arround 1 of the sparkplug cables (useally on cilinder 1 or 4) to detect when the spark was applied. In the modern ignition systems is still DC used, but has a ignition coil with Mosfet driver in 1 package on top of the sparkplug without any sparkplug cables in between.

[@robr4662]

I understood everything until you started showing the calculus equations.

[@ElectromagneticVideos]

Sorry that the math messed it up for you!

[@robr4662]

@@ElectromagneticVideos no need to be sorry it was a good video. It just shows my lack of knowledge in math.

[@ElectromagneticVideos]

@@robr4662 I glad you liked the rest of it. I am trying to give a bit of background as to where it all comes from but not too much. I should perhaps invite viewers to skip the math section if it isn't for them

[@nutgone100]

Please don’t say “irregardless”, it’s not a proper word, it’s a nonsense word. I usually stop watching a video as soon as I hear it, it’s often a good indicator that whoever said it doesn’t know what they’re talking about. The word is simply “regardless”. Otherwise a pretty good video.

[@mrkattm]

You are being very loose with your language. A current transformer converts the current trough the core to a voltage. The purpose of the burden resistor is to provide a place to drop the voltage induced to be measures (you are measuring a "voltage drop"). When you removed the low valued "burden resistore" you still had a high value burden resistor attached from your meter and your scope (they are high impedance devices 1 meg ohm or more), ie you can't measure it until you put a load or a "burden" on the circuit, that is why it is called a burden resistor, again you are meausing a voltage drop.

[@resenddelete6820]

no this guy has it all all all wrong, they work by snapping your fingers and they TURN on by magic :)

[@ElectromagneticVideos]

I knew I left something out - magic is definitely how they work :)

[@ovidius2000]

mightBeInteresting,IfTheTalkingWhouldNotBeSoSlowAt2xSpeed.

[@xNYCMarc]

@5:46 "irregardless"? Seriously? Ugh.

[@Graham_Wideman]

But is it flammable or inflammable?