# Tag Info

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

### Why are the poles of the stator and rotor taken differently in the picture below?

Magnetic lines of flux follow a convention and that convention is that lines of flux (leaving the "core") flow from a north pole to a south pole (through the air): -
• 462k
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### What happens if the secondary of an ordinary transformer is left open?

The ideal transformer equation is: $\frac{V1}{V2} =\frac{I2}{I1}$ That's fine but then you go on to consider a non-ideal transformer: - Suppose the secondary is open (that means I2=0): it will ...
• 462k
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### Does coil winding impact current direction? (Lenz Law)

What would happen if the solenoid was wound the other way In the second picture, I've put your first picture winding (now in red) in series with the winding from the 2nd picture (black). There is no ...
• 462k
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### Placing a reed switch behind a metal plate

A steel plate is going to block most of the magnetic field of the magnet. There is no chance that a reed switch will work with the supplied magnet through 3mm of steel, but heroic efforts may be able ...
• 34.3k

### How does the length of a transformer's core affect its properties?

Some aspects are equivalent, some are different. Let's assume they are the same cross sectional area, and you want to make a transformer, perhaps a power transformer, operating from a fixed mains ...
• 168k

### What exactly carries energy in a transformer from primary to secondary?

The net (total) flux remains constant. When you allow a current to flow in the secondary, it creates its own flux in the core that partially cancels the flux originally produced by the primary. More ...
• 174k
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### Unregulated Push pull converter simulation (LTspice) and flux walking

You've got one MOSFET driven at about 60% and the other MOSFET driven about 40% duty cycle - that puts dc into your transformer and walks the flux. If anyone reads this focusses on the 2nd picture ...
• 462k

### Can I use rectified AC current to heat an object inside a induction coil?

What you are really trying to do is add DC bias current so that the coil current never has a zero crossing. This is misguided. The losses in the coil are basically entirely resistive, and will be a ...
• 29.4k
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### What impact does winding tightly versus loosely have on transformer performance?

See my answer here if you want the theory behind the words below: - Normally, the flux will tend to want to concentrate in the ferrite core because that will have, by far, the lower magnetic ...
• 462k
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### From a flux point of view, how can we explain that the equivalent inductance is half when identical inductors are connected in parallel?

There are many different ways you can characterize inductance, including several different was that could be called 'flux-oriented', so this is hardly the only way to look at this, but it is my ...
• 29k
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### How does balancing currents within a cable or conduit cancel its magnetic fields?

To start, currents are not the same as bar magnets (i.e. permanent magnetic dipoles). Consider a pair of conductors carrying equal-but-opposite conventional currents (red): By the right hand rule, we ...
• 20.1k
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### DC saturation current of a power transformer of a given VA rating

So the peak current used to find $B$ is $I=I_{RMS}\cdot \sqrt2$. No, that is not the case. The load current passing into the transformer primary and exiting on the secondary has nothing to do ...
• 462k
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### Why we use constant value of magnetic flux in transformers

Secondary load current $\times$ secondary turns is exactly cancelled by the load current flowing in the primary $\times$ primary turns hence, fluxes associated with the secondary load are ...
• 462k

### Why we use constant value of magnetic flux in transformers

Think of the transformer theoretical model (without parasitic elements): simulate this circuit – Schematic created using CircuitLab The ideal transformer (IDEAL TX above) has infinite ...
• 35.4k
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### Can a slanted magnetic field be created with this insulated stranded wire arrangement?

One trick you can try to get the rifling you desire is to put "rotating" stages between the linear stages. Effectively, you would have a motor stator in between the linear stages (look up 3-...
• 4,668
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### X-ray back-projection for conversion to hard-field magnetic induction tomography?

It turns out that it is possible to image slices through a metallic object such as an Aluminium coke can, using hard field magnetic induction tomography (MIT) Back Projection in x-ray tomography and ...
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### Calculation of magnetic field saturation inside coil core

Apart from the fact that you are probably misusing the length dimension of the ferrite, you are also miscalculating flux density quite badly (See further below). The length dimension for a ferrite ...
• 462k

### Power output of a transformer with many secondary coils, each coil of turn exactly equal to that of primary?

If all coils have the same number of turns, they will all (theoretically) have the same voltage - 100VAC in on any coil, and all others will output 100 VAC. The total current from all secondary coils ...
• 59.8k

### Why does the current in a transformer's primary coil change when a load is attached to the secondary coil?

A more basic physics explanation is simply that conservation of energy holds*, and you can only stuff so much energy into the magnetic field of a transformer. So if you're taking energy out of the ...
• 46.6k

### Where to purchase the iron core for an electromagnet?

The 1018 core is working just fine, doubling the field is exactly what's expected. The problem is the remaining air-gap in the magnetic circuit. Using the steel core inside the solenoid has more or ...
• 168k
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### Magnetic flux density in a point

It looks to me like you are calculating flux density: - Picture from here. So, use superposition. Note also that the external diameters of A and B are irrelevant to solve this.
• 462k

### Why does inductor core saturation depend on the temperature?

This is mostly a solid-state physics question, but, to boil this down to something that we can answer without going into finesse of core material physics: Magnetism happens when in a material, you can ...
• 95.6k

### DC saturation current of a power transformer of a given VA rating

Calculate it backwards instead. Say we have a transformer with Ae = 200 mm2, le = 240 mm, μr = 10k, and Bsat = 1.2 T. First, solve for turns:  N = \frac{ V_\textrm{rms} }{ 4.44 B_\textrm{sat} F A_e ...
• 37.5k
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• 37.5k
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### How do you calculate the VA of a toroidal transformer core?

The only relevant quantities are size of the toroid, the saturation field, the frequency, and permitted temperature of operation. Windings, permaeability, don't figure. The cross section of the iron,...
• 168k

### How does the length of a transformer's core affect its properties?

The length of the core is used for determining the magnetic field strength, H (measured in ampere turns per metre). The "per metre" part is the mean length ($l_e$) of the core shown below: - So, if ...
• 462k