Questions tagged [transformer]
A transformer couples two or more AC signals through a magnetic field. Often used as galvanic isolation and to transform one AC voltage to another.
3,601
questions
75
votes
4
answers
108k
views
How is using a transformer for isolation safer than directly connecting to the power grid?
How is using a 1:1 transformer safer than using the mains straight off? Is it because you can limit the current coming from the transformer whereas straight from the mains its not current limited? I ...
- 8,418
67
votes
8
answers
43k
views
Why do we need an isolation transformer to connect an oscilloscope?
My professor always insists that I provide power to an oscilloscope thorough an isolation transformer. What is the necessity of this? What is the risk if I don't connect it?
- 1,585
62
votes
3
answers
10k
views
Is this video fake? I thought Tesla coils only worked on AC
This video shows a 9-volt battery connected to a wire as a primary.
The first reason I think this is fake is that he is powering a Tesla coil with 10 volts.
The second reason is that Tesla coils work ...
- 691
53
votes
6
answers
18k
views
Why do transformers use so many turns?
Transformers have hundreds of turns on both the secondary and primary winding, and as a result use very thin copper wires for each. But, why do they not just use fewer turns on each winding and get ...
- 663
46
votes
11
answers
5k
views
Is there a dual of the transformer?
Capacitors and inductors are duals of each other.
A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary ...
- 28.7k
41
votes
9
answers
11k
views
How can "purely" electrical circuits emit sound?
Moving membranes or piezoelectric materials obviously produce sound waves, but how can "purely" electrical circuits such as transformers or DCDC choppers (and others) often have an audible noise? Is ...
- 9,777
37
votes
7
answers
170k
views
Why does the USA use 110V and UK use 230-240V?
Why does the USA use 110V and UK use 230-240V? What are the advantages? Explain me with calculation. Why do they use different frequencies like 50Hz, 60Hz? What is the reason?
- 491
31
votes
4
answers
6k
views
How were four wires replaced with two wires in early telephones?
In this video, when A wanted to talk to B, a microphone was connected to a distant speaker using two wires (A → B).
When B talked to A, a copy of above was used in the other direction (B → A) using ...
- 1,120
26
votes
6
answers
4k
views
Why do high-voltage transformers need oil?
Someone told me that high-voltage transformers need oil because it prevents arcing. However, in terms of dielectric breakdown, isn't air the strongest?
I remember from classes in college that as the ...
- 857
23
votes
4
answers
8k
views
5 V home network
I'm planning on adding multiple IoT devices in my house, and I'm looking for an elegant solution to power them all. They'll all need 5 V, a small number of them (cameras) would draw up to 2 ...
23
votes
1
answer
3k
views
How does the switch on the back of older computer power supplies work to vary between 110 and 220 volt input?
There is a little switch on the back of older computer power supplies to select between 110 and 220 volt AC input. I imagine this switch enables/disables a 220 to 110 volt transformer. Or perhaps a ...
- 463
23
votes
4
answers
38k
views
What is the difference between a transformer and a coupled inductor?
Transformers and coupled inductors seem very similar. Is there a difference in construction? Or only in use?
This question asks something similar, but the answers don't address my question:
Coupled ...
- 17.5k
21
votes
2
answers
3k
views
Why do travel transformers have a setting for either 50W or 1600W?
I've noticed this "feature" on a number of travel-oriented voltage converters - they either are meant to be used for small 50W loads, OR for larger loads up to 1600W. But you can't run a ...
- 1,236
21
votes
3
answers
105k
views
How to transform 5 V into 12 V?
I would like to transform 5 V 500 mA (from USB power) into 12 V with a few cheap components.
Is this possible with the help of some generic parts (and not with the help of some expensive transformer, ...
- 619
20
votes
3
answers
8k
views
Can roles of primary and secondary windings be reversed?
Is there a practical reason that the roles of the primary and secondary of a simple single-phase transformer cannot be swapped?
Say you have a transformer (from the old vacuum tube days) that has ...
- 1,655
20
votes
2
answers
3k
views
Power supply - purpose of the capacitor on the side of the transformer before full bridge rectifier
I was wondering if someone can explain the purpose of the capacitor C1141 from the attached picture. I know that C1142 is a filter cap: that much is obvious to me. However, I can't seem to grasp the ...
- 301
20
votes
2
answers
13k
views
How do I use a transformer as an inductor?
Lp: Self inductance of the primary winding.
Ls: Self inductance of the secondary winding.
Lm: Mutual inductance between the primary and secondary windings.
Assume that I need an iron core inductor ...
- 14k
20
votes
3
answers
3k
views
How critical is winding a solenoid/electromagnet neatly?
We've all seen the expensive toroidal winding machines on YouTube, and manufactured solenoids are always so neat in construction - as in: Each winding is neatly packed to its previous, without ...
- 311
19
votes
7
answers
6k
views
Why don't three-phase transformers use toroidal cores?
When looking at different transformer core designs, three phased, I never see any core designed as a circle or torus.
Why is that so? Will it not work as well as the common B-shaped core?
- 317
19
votes
4
answers
11k
views
Why don't AC transformers burn up
I'm marginally familiar with the way that an AC transformer works. After viewing this question:
Why don't all motors burn up instantly?
It got me thinking about the same thing with AC ...
- 1,957
19
votes
8
answers
2k
views
What precisely is the numerical (or any) meaning of mutual inductance and, is it useful, representative (of something) or important?
When we consider two inductors that are magnetically coupled, we sometimes talk about mutual inductance. As an example, consider two inductors (such as 9 μH and 4 μH) that are 100% coupled and produce ...
- 1
19
votes
2
answers
40k
views
How does this mosquito zapper circuit work?
For the purpose of learning, I have tear down a small mosquito zapper racket.
I am now trying to understand how the circuit is working (which goal is to produce high voltage).
(yellow = resistor, ...
- 1,873
18
votes
2
answers
4k
views
How to calculate air gap in flyback transformer?
I’m designing (or at least trying to design) a flyback converter on LM3478. I chose the EFD20/10/7-3F3 core [1]. Using a PDF from Infineon [2] I calculated that I need a primary winding inductance of ...
- 411
18
votes
4
answers
13k
views
Cellphone charger has no transformer?
I opened up a really tiny mobile phone charger I have, to see how it is designed. The entire "charger" is integrated into a small 2-pin mains plug, 1 x 1.25 x 0.5 inch, that has an USB socket for the ...
- 592
18
votes
1
answer
12k
views
How do these new-fangled phone chargers achieve step-down?
There appear to be two kinds of power supply adapters in market.
The first/older kinds were such that they were reasonably heavy and had a small transformer inside the adapter itself. The newer ones ...
- 3,011
17
votes
4
answers
4k
views
I ripped the lead off this film capacitor by mistake - is it beyond repair?
As the title says, I accidentally ripped the lead off this film capacitor. It was the only one I had - am I out of luck, or can this be soldered back on? I've provided photos, including one under my ...
- 314
17
votes
2
answers
28k
views
What happens if I connect a transformer in reverse?
I was thinking the other day. A transformer is just two coils, right? There is no polarisation or anything else fancy? The ratio of the number of windings on the input to the number of windings to the ...
- 173
17
votes
3
answers
49k
views
Why does LTSpice say that my "Matrix is singular" for this ideal-transformer circuit?
I'm trying to do find the voltage over R1 in the following circuit, where L1/L2 is an ideal transformer. LTSpice complains that the "Matrix is singular". Why? I've tried to play around with lots of ...
- 307
17
votes
4
answers
4k
views
Is this a safe way to measure mains power on an oscilloscope?
I wanted to use my cheap battery powered single-channel oscilloscope or my Rigol 1054Z to see the 120V AC mains signal in my house. No particular reason, just curious.
I at least knew enough to not ...
- 181
16
votes
4
answers
80k
views
Why does a delta/wye transformer make 30 degrees phase shift ?
I'v heard that a delta/delta or Wye/Wye transformers do not make any phase shift. In delta/wye or wye/delta transformers, There is a 30 degrees phase shift between the primary and secondary coils. So, ...
- 3,782
16
votes
6
answers
2k
views
Can step down transformers malfunction in such a way that they become live?
I know a few things about electronics, but transformers are still an unknown for me. I know AC to DC converters use them to isolate live voltage from the DC output, or at least I think that's what ...
- 317
16
votes
3
answers
32k
views
Difference between current transformers and power transformers
In a current transformer, the primary current causes a magnetic field in the core, which in turn generates a current in the secondary. Fine.
How come then that a power transformer outputs a voltage,...
- 9,678
16
votes
3
answers
145k
views
What does 40VA rating for transformer mean?
I am working on a circuit for a home make home security system. I bought the following wall transformer to power my circuit. I was going to use with a 5VDC Linear voltage regulator to get 5 volts for ...
- 3,705
15
votes
5
answers
5k
views
Can a transformer work if the core is not circular?
I am trying to build a transformer to convert 12V AC power to 5V AC. Here is what I have right now:
I haven't adjusted the coil ratio yet but I tried it just to see if there would be any output and ...
- 305
15
votes
3
answers
2k
views
What is the purpose of transformers on the output side of a DC power suppply?
I have a PSU that plugs into 220-240V AC mains (L&N, no ground) and outputs 9V DC to a single barrel plug.
On the barrel plug side, just about 10cm before it, there's a little box on the cable ...
- 160
15
votes
4
answers
7k
views
What are the effective power limitations of the flyback converter topology, and why?
Looking at several different isolated converter topologies, flyback looks like it's the simplest at first glance. There's only one switch, so there's only one driver, which (all other things being ...
- 17.5k
14
votes
4
answers
3k
views
Does the number of turns in Turns Ratio matter in transformers?
Suppose we have two transformers with same turns ratio, \$N_2/N_1\$. First transformer \$A\$ is of \$100:10\$ and the second transformer \$B\$ is \$1000:100\$. Both have same turns ratio so both can ...
- 2,762
14
votes
3
answers
86k
views
Why do thunderstorms knock out power?
It isn't like lightning strikes the wires. And surely the whole apparatus is designed to be water-proof. So what is it that causes power outages during thunderstorms?
- 149
14
votes
2
answers
5k
views
What is the purpose of putting a capacitor on the primary side of a step-down transformer?
I'm looking at this design
For a split supply. I get that the thermistors are there to limit the inrush current, but I don't understand the purpose of C9 and how its value was chosen.
- 433
14
votes
2
answers
4k
views
Why does this isolation transformer have another transformer in it?
The isolation transformer I'm looking at: http://www.mouser.com/ds/2/336/HX1188NL-515471.pdf
My question is why is it there? Is it not enough to have just the transformer on the left?
- 1,177
14
votes
2
answers
2k
views
If I used the primary coil as an inductor, does the secondary coil affect it?
I've read this question. It's about how to obtain the maximum inductance from a transformer:
How do I use a transformer as an inductor?
Now, I would like to use the primary coil only as an inductor ...
- 3,782
14
votes
4
answers
19k
views
How are neon sign transformers built?
I'm aware that neon sign transformers (NSTs?) produce high voltage - up to 15 kV. But I cannot picture what's inside of one. Wikipedia seems to indicate that they may be a form of resonant transformer ...
- 265
14
votes
3
answers
6k
views
Why do underground cables "require a higher degree of reactive power compensation" than overhead lines?
I was reading a brag sheet for a certain company's giant transformers, and I came across this sentence:
Furthermore, in some regions, the existing over head lines are being replaced by underground ...
- 396
14
votes
3
answers
113k
views
How to determine which wire is which on a transformer?
Let's say I have a transformer with 3 coils. When primary coil is connected to 230V, two secondaries output 12V. Wires are color coded, but I don't know what colors stand for and there is no ...
- 23.3k
14
votes
1
answer
1k
views
What does a black bar across transformer symbol designate?
What does a black bar across a transformer symbol designate?
This appears in a power electronics context, and in particular in this case with substituting a DC transformer as an equivalent circuit ...
- 7,082
14
votes
3
answers
38k
views
What is a Class 2 Transformer
I need to replace a damaged 120V-12V transformer that is a European sourced Comelit Model 542012/A, also marked as "Class 2 Transformer" supplying power to a halogen table lamp. My question is what is ...
- 141
14
votes
6
answers
21k
views
Why isn't a transformer a short circuit?
I'm a newbie with electronic components and I never fully understood why transformers, while essentially being a short-circuit from a wire perspective, don't act like short circuits (i.e. they don't ...
- 271
13
votes
4
answers
2k
views
Why does this metallic magnetic core have so little core losses up until 100s of kHz?
I have a small signal transformer with values as in the below schematic (the simulate button works well to see the AC response). The values are measured and the simulated AC response agrees sort of ...
- 19.7k
13
votes
1
answer
2k
views
Are these transformers or giant capacitors?
I sometimes see these devices along power lines when I'm driving and was wondering what they were. They look just like the regular transformers that I see on top of electrical poles, but it seemed ...
- 357
12
votes
3
answers
12k
views
Why do laptops need larger transformers than mobile phones?
I was wondering why a laptop power adapter is so huge. Most laptops that I have seen use a ~19V power supply. Using transformer equation, and considering 100 turns in the primary(just an assumption), ...
- 293