33
votes
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How to calculate air gap in flyback transformer?
Power output and energy per switching cycle
An output of 265 volts at 5 mA is a power of 1.325 watts and this means that the energy that needs to be transfered each switching cycle is 1.325 W divided ...
- 473k
30
votes
Help with homemade electromagnet
20 AWG wire is about 33 mΩ/m, wikipedia so I'd estimate the resistance at around 3.3 Ω
Into that load, your 9 V batteries are acting as current sources, not voltage sources. You will get a better ...
- 174k
25
votes
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Why do most flyback converters / LED drivers operate under 100 kHz?
There are many reasons:
- Cost: This is probably the biggest reason. The lighting market is quite competitive. There are lots of Chinese players offering aggressively cheap prices. This forces the ...
- 38.5k
25
votes
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Why use aluminum wire in an (old) TV degaussing harness
In consumer electronics there is only one reason.
Price
Saving 10c each on a run of 100,000 devices saves $10,000
the degausing coil doesn't need to be compact or have to low skin-effect losses so ...
- 36.4k
23
votes
Accepted
Very small transformer powering a microwave oven
If you double-check your wiring diagram you will find that is NOT a transformer. That is a common mode choke to keep RFI from being transmitted out through the mains power cord.
There is no way (with ...
- 14.5k
23
votes
Why does a permanent, non-moving magnet, stuck to a long piece of metal generate a voltage?
You are not actually measuring anything about the circuit because the leads are plugged in incorrectly.
The negative black lead is stuck into multimeter current measurement input, and positive red ...
- 172k
23
votes
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How accurate is my phone's magnetometer?
So then I thought, "Perhaps the phone's magnetometer is just not designed for this range of magnetic field strength; It's really supposed to be just the a compass, and the earth's magnetic field ...
- 8,227
22
votes
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How does Ethernet magnetics work?
There are a few bad things that the system was designed to mitigate, one is ESD, noise and ground loops.
The first transformer (up down one) is an isolation transformer, it passes the high frequency ...
- 88.8k
20
votes
Very small transformer powering a microwave oven
As an amplification of Richard Crowley's answer, I'd do this in a comment but there is no way to include a circuit diagram. Your circuit actually looks like
simulate this circuit – Schematic ...
- 61k
18
votes
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Why does a permanent, non-moving magnet, stuck to a long piece of metal generate a voltage?
My guess is it's a Galvanic cell. One electrode is your metal strip (maybe nickel), the other is your magnet whatever it's made of (or coated). The electrolyte is probably sweat or saliva (you used ...
- 462
16
votes
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Does Shielding "Electrically" shield "Magnetically" too?
You would not be alone in this one. This is an often misunderstood phenomenon.
Static magnetic fields can not be shielded. They can be re-directed using ferrous materials but even those will not ...
- 47k
16
votes
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Sampled 100 Hz sinusoidal signal from Hall sensor shows 10 Hz sidelobes when sampled at 500 Hz
If the sensor is set to 500 Hz sampling, and you have a MCU timer also set to 500 Hz to read the results, this is never going to work, because nothing is ever exact, especially devices with internal ...
- 172k
15
votes
Accepted
Construction for a homogeneous field using permanent magnets
The magnetic field in the region between the arms would be relatively uniform in direction, but non-uniform in intensity. Below, I've attached an image of the field that I made using very simple ...
- 38.5k
15
votes
Why use aluminum wire in an (old) TV degaussing harness
Reasons for using aluminium wire in a CRT degaussing harness:
The lower electrical conductivity of aluminium (only 63% that of copper) would be good enough for the degaussing application.
The lower ...
- 19.2k
15
votes
Accepted
Why does this metallic magnetic core have so little core losses up until 100s of kHz?
Take a look at this cross section of a tape-wound core from https://www.magneticmetals.com/products-materials/tape-wound-toroidal-cores :
I have added the arrow to show the direction of the eddies ...
- 11.8k
14
votes
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Why do Rogowski coils work for measuring current?
A Rogowski coil is not a current transformer.
The current in the main conductor generates a magnetic field round itself. The Rogowski coil samples the field, generating a voltage as the field changes....
- 174k
14
votes
Accepted
What does this beautiful 8-winding magnetics do?
This could be part of an electron beam stigmator. A solenoid with an axial magnetic field can focus/defocus an electron beam. If you have 2nd order and higher astigmatism to correct, you need higher ...
- 23.4k
14
votes
How to design a 12V to <100mV 15A DC-DC converter?
Your requirements are quite close to the CPU VRM found on a PC motherboard, which outputs around 1V at huge current (50-100A). So you should be able to find the same parts, which are available and ...
- 81.9k
13
votes
Help with homemade electromagnet
"The Cool Magnet Man" provides an excellent tutorial on the practical aspects of the design and winding of your own electromagnets here
This is a summary of his procedure:
Before you can ...
- 2,956
12
votes
Accepted
Can I swap TX+ and TX- (and RX+ and RX- ) using ethernet magnetics?
As long as the RJ45 connector line pinout adheres to the standard, you shouldn't have any problems. The magnetics are a passive device, they don't care about RX + or RX-.
You can even get away with ...
- 7,705
12
votes
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How do I build an electromagnet?
I'm sorry, but you need to find a new project. Lifting a paper clip at 8 inches will require an extremely powerful magnet.
If you still want to see what you can make, you need to change your wire ...
- 61k
11
votes
Accepted
Does this experiment show that Kirchhoff's Law hold when there's a changing magnetic field involved in a circuit?
The lumped component models to which KVL is applied are just that--models. Like all models, they are only accurate to the extent that they represent the relevant characteristics of the system they ...
- 3,474
10
votes
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How can single phase induction motor's direction be reversed?
Typically reversing the fan motor is done like this, an SPDT switch changes which end of run capacitor is connected to the feed, and in doing so changes which winding sees the advanced signal.
...
- 36.4k
9
votes
Accepted
Is magnetic hysteresis present even with a DC bias?
By adding a DC bias, you are just shifting the hysteresis loop to another operating point. You are not eliminating it. The smaller the AC component of the current, the smaller the hysteresis loop and ...
- 2,992
9
votes
How do I build an electromagnet?
Here's an example electromagnet you can buy: ELECALL electromagnet.
The datasheet shows that the most powerful model (the ELE-P100/40) can run at 12 volts at 1 amp (12 Watts).
The lifting force at ...
- 191
9
votes
Accepted
What to connect to center-taps of Ethernet magnetics?
The basic way PoE works is there is a pair of transformers on each end.
On the end that sends power (PSE - Power Sourcing Equipment) the secondary of the transformers are center tapped and voltage is ...
- 27.9k
9
votes
Why does this metallic magnetic core have so little core losses up until 100s of kHz?
Vitroperm is not a metallic material, it's an nanocrystalline alloy (ultra fine grains of FeSi are embedded in Nb and Cu additives). Transformers made of this type of materials are commonly used in ...
- 1,616
8
votes
Accepted
What is the purpose of perpendicular "smaller" magnets in between the main magnets in a rotor of a motor? had never seen this before. Do they help?
This is more or less just transferred from Wikipedia, however:
As @HarrySvensson indicates, this is a Halbach array, apparently used to create a magnetic field that is stronger on one side than the ...
- 4,143
8
votes
Accepted
Should Ethernet MDI Pairs all be Length Matched (Inter-Pair) before going into magnetics?
There is no need to have the pair lengths balanced.
The standard for 1000base-T (IEEE Std 802.3-2008) states:
40.7.4.2 Link delay skew
The difference in propagation delay, or skew, between ...
- 3,104
Only top scored, non community-wiki answers of a minimum length are eligible