Top Video again JW.. i used to install a lot of Auto transformers in rack equipment for CCTV systems going abroad, And we used Variac's to test +/- voltage tolerances on the said racks, a nice refresher course thanks.:-)
Brilliant stuff JW, this has resolved some points I was wondering about. I believe Network Rail now use autotransformers for the 25KVAC supply, I'm now beginning to see how that works.
Oh! John, I recall my instructor many years ago, when checking similar to your descriptions, always wear gloves. If theres a chance one will touch live mains you will!
+John Ward I think the existence of leakage-inductance and other ElectroMagnetic-voodoo is worthy of mention. In particular, when measuring the unloaded output of an isolating-transformer, you may well find the output voltage is higher than under some amount of load-applied... I suspect you see this more with smaller AC-plug-packs etc than larger transformers. Do you find, in practice, need to use a "Lo-Z" setting on meter (where available), or a 40w incandescent-lamp in parallel with the meter, or similar, when measuring some smaller transformer outputs? I believe, you don't see this effect when measuring with an auto-transformer/variac single-winding configuration as demonstrated in this particular video.
sbusweb - The unloaded secondary voltage vs. the full load secondary voltage is known as the transformer regulation. Typically the manufacturers add some extra windings to compensate for the voltage drop over the resistance of the copper wire when used at the maximum rated load current. The power loss due to this resistance is known as ‘copper losses’. The regulation of small cheap transformers can be fairly bad at 20% or worst. Whereas bigger higher quality transformers can be 10% or better. I’ve never investigated or researched the regulation of auto-transformers, so I don’t know the answer, but if I had to guess, I would say that they too must suffer from ‘copper losses’ and therefore have similar regulation. However, with a variac, as the ‘tapping’ is not fixed, it may not be as noticeable.
+John Ward A large-transformer issue you mentioned recently related to inrush-current, I have noticed this with variac and otherwise. This can be problematic when you want to run the transformer from a 16A radial, or a longer 5-amp extension-cord or similar. I think it would be highly-desirable to find a safe, sensible/convenient way to apply some inrush-limiting to that initial magnetizing-current on our variacs/chunky-transformers when re-casing them etc... I found my variac (same type as yours I believe) appears to work beautifully wired in series with one of those black "NTC thermisistors" (was often a black circular disc unit) taken from mains-input-side of a reasonable rating supply. This allows the variac to then work with only 5A mains-fuse, but I'm not sure the NTC-thermo would handle full rating of variac, 8A current max [applies to both input and output separately with brushes in good condition, etc.]. I found an older monitor PCB which used a slow-start circuit involving transistor or relay, too, let alone NTC-thermo approach. I've seen electronic Tridonic-ECO ballasts with active-PFC electronics and microcontroller soft-start dim-up-lamps etc etc.... SO:- Basically, from what I can see, to inrush-limit your big electromagnetic core you need either:- (1) a large NTC thermisistor (suitably rated) (2) or some kind of resistive-ballast, which gets "shorted out" by a relay that has a short startup time-delay (3) or some electronic voodoo (I'm thinking zero-crossing start-up and dimmer-like behaviour and all that) Any ideas? Seen this problem solved in practice on big transformers some other way without requiring high-rating D-curve-breakers hard-wired-supply and all-of-that? As above be nice to have chunky-transformers more adaptable to 5amp-fuse-feeds / B16 breakers and so-on without popping fuses/breakers on inrush...?
I've done some work on this exact problem. What you need is the NTC, but you also need a mains voltage time delay relay and contactor. The NC and common terminals of the contactor is wired in series with the transformer coil. The NTC is wired across the the NC and common terminals as well. The contactor coil is connected to neutral and the NO contact on the time delay relay. Active will be connected to the time delay relay common as well as to the power input. The time delay relay can be set to something around 0.5 seconds. The mains comes on, starts the time delay, passes through the NTC and energizes the transformer coil. The time delay then energizes the contactor coil which shunts the NTC out of the circuit.
Quicktest down and touching the terminals :P The neon was off after all :P You can also test now an modern appliance if it covers all voltages , say a power supply 100V ~240V
Great video JW. I remember Dad teaching me that lesson (just because it’s 12V doesn’t mean it’s 12V), as a five year old with a set of 20 Christmas lights, the globe says 12V, how can it have 240 on it, and the pretty coloured globes lit up when I connected them to my 6V battery. It was our first Christmas on the farm with mains power so it was the first time the string of lights got plugged in, naturally they didn’t work so I had to find the bad one, somehow I’m still alive with more than 40 years in the trade, love your channel it’s very interesting seeing the differences between here and the UK, I can’t believe you still use bare earths I certainly don’t understand why you are allowed to have single solid earths, they have never been allowed here in Aus, nothing less than 7 strands since the late 60’s and insulated since the mid 70’s.
@@elonmask50 Here in Germany it's prohibited to use stranded wires in the electrical installation, only permitted if the conductor size is 16mm² or above, then the strands are so big that you can't damage them so easy. The risk to decrease the conductor size during the stripping of the wire by damaging the strands is too high. But here the earth wire is completely insulated in the cable and it is always the same size as the other conductors. That's of course not the case for power cords or inside of appliances. These are fine stranded conductors.
Marcel Germann, wow that’s interesting, I am trying to imagine what it would be like trying to neatly terminate 10mm solid strands into anything, the largest solid strands we are allowed is 2.5mm, which still has a stranded earth, and generally that cable is only used by people trying to save money. I have had the pleasure of working with a number of European electricians but none of them ever mentioned the solid cables.
@@elonmask50 Requires some elbow grease...especially if you use 5x10mm² for a three phase connection. In most cases 5x10mm² is used to connect a fuse board. For most other appliances in the house 6mm² is enough, for example a 22 kW flow type water heater fused with 3x32A. There you need a cable with 4 conductors (L1, L2, L3 and PE). Neutral is not required because they run with 400V and the water heater is a purely resitive load and the load is balanced between the three phases. 5x2.5mm² for a kitchen cooker (and baking oven), fused with 3x16A (~11 kW). One big and one small cooking plate are connected to one of the lines, so they use L1 and L2. L3 is for the baking oven. The wiring for the kitchen cooker should be dimensioned big enough so you could fuse it with 3x20A if necessary. Three phase power is the standard here in Germany, everything that requires more than 4.6 kVA should be connected to the three phases.
Michael Harman - well, technically the earth or ‘CPC’ wires are not (supposed to be) bare. Inside the twin and earth cable, it is inside the outer PVC sheath. Inside terminal boxes, consumer units/fuse boxes, switches, ceiling roses, light fittings, socket outlets, fused connection units etc., etc., the earth / ‘CPC’ wire is supposed to be fitted with a green and yellow sleeve. Where separate earth wires are run, they are insulated cables. The voltage potential on an earth or ‘CPC’ wire is supposed to be at or close to ground potential anyway. So you could argue that it does not need to be insulated... As is always the case with these things, there is no ‘right’ answer, just different ideas in different countries.
Autotransformers are perfect in some applications, I have seen them used to step 600v that we use in Canada for commercial and industrial applications down to 460-480v to supply American devices.... Only problem with using an autotransformer as a step down is if the winding becomes open circuit the supplied voltage may appear across terminals marked for lower voltage.
Hello, great explanation! Would you please give me a help into an exercise that i'm trying to solve? A single-phase autotransformer rated at 40KVA supplies a lead impedance of 4
What is the equation if I just want to split a phase? I did the math but I am not sure about the windings. 5000 watts at 240V. I got 3000 turns when tapped for the neutral. 120v 0v 120v.
I had know idea that autotransformers existed. One thing that I don't understand is that isn't a transformer coil essentially a wire resistor? It would seem like a transformer would always draw a load even when there is no load connected. I don't know how the load changes when a load is connected to the transformer. What is the difference between an autotransformer and a voltage divider?
It does draw a small current even without any load. But it's limited by the fact that the magnetic field around the coil opposes the change of current within the coil. It does this by inducing an emf in the direction opposite of the current in the coil, so only the net current actually flows within the coil. This is called inductance.
When you put an AC current into a coil of wire, it creates a moving magnetic field. That moving magnetic field will create a voltage in any wires nearby. This includes the transformer primary coil, itself. The voltage "reflected" back from the magnetic field cancels out the primary voltage, so there is virtually nothing left to cause current to flow. There are losses in this process, so the reflection is not perfect; and also you need to have enough current flowing for you to get a magnetic field. So, you will get a current flowing in the primary even when there is no load, but it is small. Now, when you allow current to flow in the secondary - the AC current in the secondary coil produces a moving magnetic field - because the current and voltage in the secondary are "reflected" from the primary, this magnetic field is opposite and cancels out the primary current magnetic field. So, as you increase load on the secondary, you reduce the reflected magnetic field going back into the primary, and there is less cancellation of the voltage, so more primary current flows.
It's easiest to understand if you look at a 115V to 230V autotransformer... Lets say for convenience, that you wanted 230VA out. If it wasn't an autotransformer, you'd have a 115V/2A primary winding, a 230V/1A secondary winding and a core capable of 230VA. In autotransformer form, you'd have a 115V/1A primary, with a 115V/1A continuation on top of it, so it only needs half the capability, as half the output power comes from the input. In the reverse case, 230V to 115V, half the output current comes down through the top of the winding, and half comes up from the bottom. If you only want a small boost or buck to the mains voltage, the economy of an autotransformer is even greater
@@matthewday7565 I would also add to this that it's useful to remember when thinking about this that the energy always has to come from somewhere. And from that fact you then logically derive a conclusion about what happens within the windings of the transformer when it comes to voltage and current. Just remember you cant get energy out of nothing.
Robert Gaines - There is a very big difference between a resistor / resistive voltage divider and a transformer (any type). Any current flowing through a resistor causes heat to be generated. The coil of a transformer is made with good quality copper wire. Whereby the aim is to have as lower a resistance as is affordable and practical. We don’t want the copper wire to get hot or to consume power. The current flowing through the copper wire transformer winding (coil) is primarily generating a magnetic field (as described by others in other answers). But the copper wire will have a very small amount of resistance, hence there are some losses (known as ‘copper losses’).
WOW 20 white screen Thought it all gone wrong. 1:37 you say you get the current in the secondary winding? do you not mean voltage as you need a load for a current.
I know you love the regs and do everything by the book but can you PLEASE stop it with the 230v & 400v It's not 230-400 and it never has been, it's 240-415v or just over. I've got over 245v at my house and everywhere I've worked it's always been 240v or higher. My Variac's kick out over 280V, which is quite handy 😊
geoepi321975 - The amount of power transformer can transfer depends on the size and type of construction of the core and formers. The secondary winding voltage depends on the ratio of the number of wire turns compared to the primary. Both depend on the size (diameter) of the relevant wire used. So for a higher secondary voltage, in order to get more turns in, the wire diameter has to be smaller. It is the diameter size of the wire and the size and type of construction of the core and formers that determine the maximum safe current (safe, as in continuous rating, a higher current may be drawn for intermittent loads).
The core is made up of lamented thin slices of iron. The expanding and collapsing of the magnetic field causes those laminated slices to vibrate at 2x the frequency ( expand and collapse per cycle). Then the vibration transfers to the oil then to the tank then to air waves at 2 x the frequency.
John, you are usually so precise in your language, it is a shame that your imprecise terms here may cause confusion to novices. Conflating moving with changing is bad enough, but confusing the terms voltage and current is really beneath you. When the flux changes in the core, it induces a current in the winding. It does not induce a current. A current may flow because of the induced voltage across the load, and that current may contribute to changes in the core flux, but the changing flux does not induce current. V = L x di/dt.
Only because of resistivity losses in the coil and induced losses in transformer core caused by the changing magnetic field by things like eddy currents (cores are usually laminated to reduced the effects). If we could eliminate resistance (such as superconductors do) and the parasitic losses in the core then, in principle, if there was no load on the secondary, there would be no load on the primary either as the energy lost when creating the magnetic field is returned when it collapses during the AC cycle. It just acts like a perfect inductor. In switched-mode transformers, the frequency is much higher and the cores of the transformers are ferrite and those have much lower losses because there's less loss in wire and the transformer core.
gazzaka - As Steve Jones said, the only power used is due to the losses in the transformer. For a transformer with no secondary load, the majority will be ‘iron core’ losses. However, if you measure the input current, it may appear to be consuming more electricity. But of course, being an inductor, the voltage and current are not in phase.
It is misleading to say a transformer is 90%+ efficient, as that is in the best case. if the 200V primary draws 1 amp and my 12V secondary draws 1 mA then the efficiency is almost zero. if the secondary is open circuit it is 0% efficient or a waste of energy.
gazzaka - Transformer efficiency is normally given at full load. Using your argument, all internal combustion engine vehicles are 0% efficient when they are stopped at red traffic lights...
Buy a UPS marked 1800VA and find out later that it is rated at 900watts! I wouldn't use "VA" for any measurement because really it doesn't mean S#@%!! Dubious marketing...
UnrealVideoDuke - Buy an industrial switch or relay and you will find various ratings depending on if the load is resistive or inductive. In an electrical or electronics catalogue, and you will find that all power transformers are rated only in VA. If a load is inductive or has a poor power factor, the supply system has to provide a greater current than that indicated by any “Wattage” shown on any load (or in the documentation). In this case VA is NOT equal to Watts. As more current is required, the VA figure will be greater than any Wattage figure. Whereas if the load is resistive, then the power used is simply the voltage multiplied by the current (measured in Watts). In this case, VA = Watts.
14:10 I almost had a heart attack when you touch the 245 volt terminal with the Quicktest down.
@pmailkeey I think he was more reliant on the fact that he hadn't flicked the switch lol... Neon testers are evil ;-)
Me too! Its always the last thing i do closing the quick test!
Thanks for this, John. I no longer feel quite as mentally challenged!
Excellent tutorial/refresher.
Thanks for sharing.
Top Video again JW.. i used to install a lot of Auto transformers in rack equipment for CCTV systems going abroad, And we used Variac's to test +/- voltage tolerances on the said racks, a nice refresher course thanks.:-)
This is awesome John. I am just doing a paper on autotransformers and your videos have helped me so much.
Brilliant stuff JW, this has resolved some points I was wondering about. I believe Network Rail now use autotransformers for the 25KVAC supply, I'm now beginning to see how that works.
Great explanation John, as always!👍
Thanks for the brilliant explanation, I learned something from it.
Excellent as usual, keep them coming jw 👍
Thank you John. Learnt a lot.
Oh! John, I recall my instructor many years ago, when checking similar to your descriptions, always wear gloves. If theres a chance one will touch live mains you will!
First class explanation and easy to understand as with all off your videos the best A+++++++
very good lecture
Great video
Well done down at a level I can understand
+John Ward
I think the existence of leakage-inductance and other ElectroMagnetic-voodoo is worthy of mention.
In particular, when measuring the unloaded output of an isolating-transformer, you may well find the output voltage is higher than under some amount of load-applied... I suspect you see this more with smaller AC-plug-packs etc than larger transformers. Do you find, in practice, need to use a "Lo-Z" setting on meter (where available), or a 40w incandescent-lamp in parallel with the meter, or similar, when measuring some smaller transformer outputs?
I believe, you don't see this effect when measuring with an auto-transformer/variac single-winding configuration as demonstrated in this particular video.
sbusweb - The unloaded secondary voltage vs. the full load secondary voltage is known as the transformer regulation. Typically the manufacturers add some extra windings to compensate for the voltage drop over the resistance of the copper wire when used at the maximum rated load current. The power loss due to this resistance is known as ‘copper losses’. The regulation of small cheap transformers can be fairly bad at 20% or worst. Whereas bigger higher quality transformers can be 10% or better.
I’ve never investigated or researched the regulation of auto-transformers, so I don’t know the answer, but if I had to guess, I would say that they too must suffer from ‘copper losses’ and therefore have similar regulation. However, with a variac, as the ‘tapping’ is not fixed, it may not be as noticeable.
Good one.
thank you
Thanks you for informatio
Do you think I need a AFDD for my welding set?
+John Ward
A large-transformer issue you mentioned recently related to inrush-current, I have noticed this with variac and otherwise.
This can be problematic when you want to run the transformer from a 16A radial, or a longer 5-amp extension-cord or similar. I think it would be highly-desirable to find a safe, sensible/convenient way to apply some inrush-limiting to that initial magnetizing-current on our variacs/chunky-transformers when re-casing them etc...
I found my variac (same type as yours I believe) appears to work beautifully wired in series with one of those black "NTC thermisistors" (was often a black circular disc unit) taken from mains-input-side of a reasonable rating supply. This allows the variac to then work with only 5A mains-fuse, but I'm not sure the NTC-thermo would handle full rating of variac, 8A current max [applies to both input and output separately with brushes in good condition, etc.].
I found an older monitor PCB which used a slow-start circuit involving transistor or relay, too, let alone NTC-thermo approach. I've seen electronic Tridonic-ECO ballasts with active-PFC electronics and microcontroller soft-start dim-up-lamps etc etc.... SO:-
Basically, from what I can see, to inrush-limit your big electromagnetic core you need either:-
(1) a large NTC thermisistor (suitably rated)
(2) or some kind of resistive-ballast, which gets "shorted out" by a relay that has a short startup time-delay
(3) or some electronic voodoo (I'm thinking zero-crossing start-up and dimmer-like behaviour and all that)
Any ideas? Seen this problem solved in practice on big transformers some other way without requiring high-rating D-curve-breakers hard-wired-supply and all-of-that? As above be nice to have chunky-transformers more adaptable to 5amp-fuse-feeds / B16 breakers and so-on without popping fuses/breakers on inrush...?
I've done some work on this exact problem. What you need is the NTC, but you also need a mains voltage time delay relay and contactor. The NC and common terminals of the contactor is wired in series with the transformer coil. The NTC is wired across the the NC and common terminals as well. The contactor coil is connected to neutral and the NO contact on the time delay relay. Active will be connected to the time delay relay common as well as to the power input. The time delay relay can be set to something around 0.5 seconds. The mains comes on, starts the time delay, passes through the NTC and energizes the transformer coil. The time delay then energizes the contactor coil which shunts the NTC out of the circuit.
sbusweb - In industrial electrics the normal way is to use suitable fuses or MCBs that can handle the switch on surge.
Checl out Electroboom, he did a recent video on inrush current on induction motors. Worth a look.
Quicktest down and touching the terminals :P The neon was off after all :P You can also test now an modern appliance if it covers all voltages , say a power supply 100V ~240V
Thanks. !
Hiya John, can you do more electrical items refurbishment videos please. Keep the videos coming!
Great video JW. I remember Dad teaching me that lesson (just because it’s 12V doesn’t mean it’s 12V), as a five year old with a set of 20 Christmas lights, the globe says 12V, how can it have 240 on it, and the pretty coloured globes lit up when I connected them to my 6V battery.
It was our first Christmas on the farm with mains power so it was the first time the string of lights got plugged in, naturally they didn’t work so I had to find the bad one, somehow I’m still alive with more than 40 years in the trade, love your channel it’s very interesting seeing the differences between here and the UK, I can’t believe you still use bare earths I certainly don’t understand why you are allowed to have single solid earths, they have never been allowed here in Aus, nothing less than 7 strands since the late 60’s and insulated since the mid 70’s.
R-77, much harder to accidentally break all 7 strands and be left with no earth.
@@elonmask50 Here in Germany it's prohibited to use stranded wires in the electrical installation, only permitted if the conductor size is 16mm² or above, then the strands are so big that you can't damage them so easy. The risk to decrease the conductor size during the stripping of the wire by damaging the strands is too high. But here the earth wire is completely insulated in the cable and it is always the same size as the other conductors. That's of course not the case for power cords or inside of appliances. These are fine stranded conductors.
Marcel Germann, wow that’s interesting, I am trying to imagine what it would be like trying to neatly terminate 10mm solid strands into anything, the largest solid strands we are allowed is 2.5mm, which still has a stranded earth, and generally that cable is only used by people trying to save money.
I have had the pleasure of working with a number of European electricians but none of them ever mentioned the solid cables.
@@elonmask50 Requires some elbow grease...especially if you use 5x10mm² for a three phase connection. In most cases 5x10mm² is used to connect a fuse board. For most other appliances in the house 6mm² is enough, for example a 22 kW flow type water heater fused with 3x32A. There you need a cable with 4 conductors (L1, L2, L3 and PE). Neutral is not required because they run with 400V and the water heater is a purely resitive load and the load is balanced between the three phases. 5x2.5mm² for a kitchen cooker (and baking oven), fused with 3x16A (~11 kW). One big and one small cooking plate are connected to one of the lines, so they use L1 and L2. L3 is for the baking oven. The wiring for the kitchen cooker should be dimensioned big enough so you could fuse it with 3x20A if necessary.
Three phase power is the standard here in Germany, everything that requires more than 4.6 kVA should be connected to the three phases.
Michael Harman - well, technically the earth or ‘CPC’ wires are not (supposed to be) bare. Inside the twin and earth cable, it is inside the outer PVC sheath. Inside terminal boxes, consumer units/fuse boxes, switches, ceiling roses, light fittings, socket outlets, fused connection units etc., etc., the earth / ‘CPC’ wire is supposed to be fitted with a green and yellow sleeve. Where separate earth wires are run, they are insulated cables.
The voltage potential on an earth or ‘CPC’ wire is supposed to be at or close to ground potential anyway. So you could argue that it does not need to be insulated...
As is always the case with these things, there is no ‘right’ answer, just different ideas in different countries.
Autotransformers are perfect in some applications, I have seen them used to step 600v that we use in Canada for commercial and industrial applications down to 460-480v to supply American devices.... Only problem with using an autotransformer as a step down is if the winding becomes open circuit the supplied voltage may appear across terminals marked for lower voltage.
Hi John. Am I right in thinking that if there is a short along an autotransformer winding, the other taps beyond the short can become higher voltage?
Aryon Llewellyn - Depends where the short is and how the transformer is being used.
Hello, great explanation!
Would you please give me a help into an exercise that i'm trying to solve?
A single-phase autotransformer rated at 40KVA supplies a lead impedance of 4
What is the equation if I just want to split a phase? I did the math but I am not sure about the windings. 5000 watts at 240V. I got 3000 turns when tapped for the neutral. 120v 0v 120v.
..oh yeah, Hysteresis effect/loss is another thing with Transformers, fascinating subject :-) a bit deep lol..
I had know idea that autotransformers existed. One thing that I don't understand is that isn't a transformer coil essentially a wire resistor? It would seem like a transformer would always draw a load even when there is no load connected. I don't know how the load changes when a load is connected to the transformer. What is the difference between an autotransformer and a voltage divider?
It does draw a small current even without any load. But it's limited by the fact that the magnetic field around the coil opposes the change of current within the coil. It does this by inducing an emf in the direction opposite of the current in the coil, so only the net current actually flows within the coil. This is called inductance.
When you put an AC current into a coil of wire, it creates a moving magnetic field. That moving magnetic field will create a voltage in any wires nearby. This includes the transformer primary coil, itself. The voltage "reflected" back from the magnetic field cancels out the primary voltage, so there is virtually nothing left to cause current to flow.
There are losses in this process, so the reflection is not perfect; and also you need to have enough current flowing for you to get a magnetic field. So, you will get a current flowing in the primary even when there is no load, but it is small.
Now, when you allow current to flow in the secondary - the AC current in the secondary coil produces a moving magnetic field - because the current and voltage in the secondary are "reflected" from the primary, this magnetic field is opposite and cancels out the primary current magnetic field. So, as you increase load on the secondary, you reduce the reflected magnetic field going back into the primary, and there is less cancellation of the voltage, so more primary current flows.
It's easiest to understand if you look at a 115V to 230V autotransformer... Lets say for convenience, that you wanted 230VA out.
If it wasn't an autotransformer, you'd have a 115V/2A primary winding, a 230V/1A secondary winding and a core capable of 230VA.
In autotransformer form, you'd have a 115V/1A primary, with a 115V/1A continuation on top of it, so it only needs half the capability, as half the output power comes from the input.
In the reverse case, 230V to 115V, half the output current comes down through the top of the winding, and half comes up from the bottom.
If you only want a small boost or buck to the mains voltage, the economy of an autotransformer is even greater
@@matthewday7565 I would also add to this that it's useful to remember when thinking about this that the energy always has to come from somewhere. And from that fact you then logically derive a conclusion about what happens within the windings of the transformer when it comes to voltage and current. Just remember you cant get energy out of nothing.
Robert Gaines - There is a very big difference between a resistor / resistive voltage divider and a transformer (any type). Any current flowing through a resistor causes heat to be generated. The coil of a transformer is made with good quality copper wire. Whereby the aim is to have as lower a resistance as is affordable and practical. We don’t want the copper wire to get hot or to consume power. The current flowing through the copper wire transformer winding (coil) is primarily generating a magnetic field (as described by others in other answers). But the copper wire will have a very small amount of resistance, hence there are some losses (known as ‘copper losses’).
Hallo John, would You say "Transformers, More than meets the eye"?
I didn't think so :-)
Is an autotransformer how the 220/110v shaver sockets work?
No, those are an isolating transformer with the input and output totally separate.
WOW 20 white screen Thought it all gone wrong. 1:37 you say you get the current in the secondary winding? do you not mean voltage as you need a load for a current.
I know you love the regs and do everything by the book but can you PLEASE stop it with the 230v & 400v
It's not 230-400 and it never has been, it's 240-415v or just over. I've got over 245v at my house and everywhere I've worked it's always been 240v or higher.
My Variac's kick out over 280V, which is quite handy 😊
Do you have any material on Spotify?
I am in some of the podcasts in this series: open.spotify.com/show/0ycVX0yoFdyfljQfhl2yyk
@@jwflame Thanks
Why are Variacs rated in amps? Is it because the voltage isn't fixed?
Yes. The windings are only rated for a certain current, regardless of what the voltage is.
why is neutral always referred to 0 volts
How you calculate primary winding power sir ?
Do you mean VA or actual power?
@@Mark1024MAK I wonder how many turns the primary mast have and what thickness, sorry for this silly question i am arrogant in electricity
geoepi321975 - The amount of power transformer can transfer depends on the size and type of construction of the core and formers. The secondary winding voltage depends on the ratio of the number of wire turns compared to the primary. Both depend on the size (diameter) of the relevant wire used. So for a higher secondary voltage, in order to get more turns in, the wire diameter has to be smaller. It is the diameter size of the wire and the size and type of construction of the core and formers that determine the maximum safe current (safe, as in continuous rating, a higher current may be drawn for intermittent loads).
@@Mark1024MAK i see, i understand now thank you
Why does it hum?
Most of the losses are heat but some are magnetic, physically pulling the transformer components around slightly like a solenoid.
It is the INTENSE HUMMING OF EVIL! :-) or just magnetic 50Hz AC amplified through the iron core...the bigger the load, the bigger the hum :-)
The core is made up of lamented thin slices of iron. The expanding and collapsing of the magnetic field causes those laminated slices to vibrate at 2x the frequency ( expand and collapse per cycle). Then the vibration transfers to the oil then to the tank then to air waves at 2 x the frequency.
John, you are usually so precise in your language, it is a shame that your imprecise terms here may cause confusion to novices. Conflating moving with changing is bad enough, but confusing the terms voltage and current is really beneath you. When the flux changes in the core, it induces a current in the winding. It does not induce a current. A current may flow because of the induced voltage across the load, and that current may contribute to changes in the core flux, but the changing flux does not induce current. V = L x di/dt.
Oh the irony of your third sentence!
if there is no load on the secondary, the primary will still be using power....
Only because of resistivity losses in the coil and induced losses in transformer core caused by the changing magnetic field by things like eddy currents (cores are usually laminated to reduced the effects). If we could eliminate resistance (such as superconductors do) and the parasitic losses in the core then, in principle, if there was no load on the secondary, there would be no load on the primary either as the energy lost when creating the magnetic field is returned when it collapses during the AC cycle. It just acts like a perfect inductor.
In switched-mode transformers, the frequency is much higher and the cores of the transformers are ferrite and those have much lower losses because there's less loss in wire and the transformer core.
gazzaka - As Steve Jones said, the only power used is due to the losses in the transformer. For a transformer with no secondary load, the majority will be ‘iron core’ losses. However, if you measure the input current, it may appear to be consuming more electricity. But of course, being an inductor, the voltage and current are not in phase.
It is misleading to say a transformer is 90%+ efficient, as that is in the best case. if the 200V primary draws 1 amp and my 12V secondary draws 1 mA then the efficiency is almost zero. if the secondary is open circuit it is 0% efficient or a waste of energy.
gazzaka - Transformer efficiency is normally given at full load. Using your argument, all internal combustion engine vehicles are 0% efficient when they are stopped at red traffic lights...
@@Mark1024MAK That's right, and many stop the engine these days
You have autotransformers, but I’m wondering about the deceptitransformers...
Needs a capital V
Buy a UPS marked 1800VA and find out later that it is rated at 900watts! I wouldn't use "VA" for any measurement because really it doesn't mean S#@%!! Dubious marketing...
Yes, it does. Volt-Amps and Watts are not the same thing, but both have their correct usage
UnrealVideoDuke - Buy an industrial switch or relay and you will find various ratings depending on if the load is resistive or inductive.
In an electrical or electronics catalogue, and you will find that all power transformers are rated only in VA.
If a load is inductive or has a poor power factor, the supply system has to provide a greater current than that indicated by any “Wattage” shown on any load (or in the documentation). In this case VA is NOT equal to Watts. As more current is required, the VA figure will be greater than any Wattage figure.
Whereas if the load is resistive, then the power used is simply the voltage multiplied by the current (measured in Watts). In this case, VA = Watts.