# Tag Info

31

It is true that it's only the volume and the power fed to the winding that matters for magnetic field, in electromagnets and motors. Therefore, you could have a single turn winding. Unfortunately, a single turn would (generally) require a very high current and a very low voltage. This is true on the scales we tend to work at, and the values that physical ...

29

The core doesn't need to be circular, but it must be closed, otherwise the linked flux will be very low. Moreover, the fact that the pipe is empty doesn't improve the situation, since the flux is concentrated where there is higher permeability, i.e. in the core, but the net section of the core in your case is small. In fact most of the section of the coil ...

25

Glass is clean, dimensionally stable and very strong, doesn't outgas at the operating pressures in the interior of the capsule, won't react with the fill gas in the capsule, and doesn't soften under soldering temperatures. Here's a beautiful link.

23

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 currently-known technology) to make a mains-frequency transformer that small that handles as much current as a microwave oven draws. You have seen how big the ...

20

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 created using CircuitLab as far as the "transformer" is concerned. As stated, it's a common-mode filter which keeps the microwave from driving noise onto the ...

20

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 other brands (even the bigger European ones like Osram, Philips, etc.) to use "cheaper" components to keep themselves in the game. As an employee for one of those ...

16

Keep in mind that the type of ethernet that uses magnetics requires the transformer coupling in the spec. The transformers do some nice things for you, like completely decoupling common mode signals, providing significant voltage isolation, and in some cases projecting a different impedance to the electronics than what is natively on the cable. If your ...

15

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 block them. Electric fields on the other hand can be. Since an electric field is basically a voltage in space, they can not pass through a conductive plate that is ...

14

H is the driving force in coils and is ampere turns per metre where the metre part is the length of the magnetic circuit. In a transformer it's easy to determine this length because 99% of the flux is contained in the core. A coil with an air core is difficult as you might imagine. I think of B as a by-product of H and B is made bigger by the permeability ...

14

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 signals that represent the bits of ethernet, but rejects DC. The second transformer is a common mode choke, it blocks signals that are common to both terminals ...

13

I've tested many card with my 1.5Kg rare earth magnet, so I can bet that magnets have no effects on flash cards or USB pen drives :-)

13

It's possible to "turn a magnet off" without requiring continuous power in either position- simply shunt the field lines away from the open end. Here is an example of a magnet with an on-off switch: And here is how it works:

13

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. It is weakly coupled to the main conductor. As little, ideally no, current flows in the Rogowski coil, there is no effect back on the main conductor. Any ...

12

I doubt you'll be able to destroy your data with a magnet without opening the drive up. Inside of the drive are a pair of neodymium magnets (similarly strong to the ones you have, but just not as large), within centimeters of the platter. The drives are well shielded, so it is near (if not entirely) impossible to wipe them by waving a magnet around them. ...

12

The two are basically the same class of device, although each will have parameters optimized differently. The two names are to explain the different intended usage, which also gives you a quick guess of how some of the parameters may differ. Of course only the datasheets would tell you what the parameters are for sure. A transformer is specifically ...

12

You should not expect any problems, other than the same problem any piece of metal poses. The magnetic field does not mask or influence any GHz transmissions. TV, Radio, 60Hz power lines should not pose a problem either. Think of the magnet as 0Hz; a DC electromagnetic field that is stuck in the magnetic form, with zero electrical component.

12

What you're doing is possible, but I don't see how you're going to do it cheaply. .05 degrees (3 minutes of arc) implies a resolution of 7200 counts/rev, or the equivalent of 13 bits (8192). Worse, since you're trying to make a position loop, you'll need at least one extra bit of resolution, or a 14-bit system. The problem lies in the fact that your ...

12

There are a few reasons. Polarity Ćuk converters must always have opposite input and output polarity. This makes them somewhat inflexible and would prevent them from being used in any application that simply wanted to reduce/buck or raise/boost the input to output voltage. The only way a Ćuk converter could do what the buck converter you linked does is ...

11

Like Mark said it's the changes in polarization which is used to encode the data; a magnetic head won't see a static field. Until some years ago recording was longitudinal, which means the fields were horizontal. Growing hard disk capacities required a different way: perpendicular recording. The image shows that you can record bits closer together. ...

11

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 reflect. The simple loop of two resistors model does not represent the susceptibility of the conductive path that constitutes the circuit to induced EMF, ...

10

Not an expert on hard drives but its not really an "indentation" unless that has a different meaning in physics. The "disk" contains a huge number of magnetized regions (really its a ferrous thin film on the disk), when writing to the disk the polarization of these regions is changed by the write head. The actual data, the ones and zeros, is encoded into ...

10

For venerable floppies, this statement holds true. We placed a 99-cent magnet on a 3.5-inch floppy for a few seconds. The magnet stuck to the disk and ruined its data. Fortunately, most modern storage devices, such as SD and CompactFlash memory cards, are immune to magnetic fields. "There's nothing magnetic in flash memory, so [a magnet] won't do anything," ...

10

If someone will die or have their life ruined if the drive contents are discovered, you need a big enough magnet to pulverize the drive when forcefully dropped onto it. Multiple, judicious applications of a magnetized sledge-hammer should serve nicely. OTOH, if you just need to keep out the curious, a wipe and reformat should be more than adequate.

10

It will "work" in a sense, just as any other transformer, but as the flux circuit is only closed by magnetic field leakage from one end of the core to the other, its reluctance will be enormous, and therefore it'll be much less efficient than you would like. This is normally modelled as a "leakage inductance". Measure the primary inductance with the ...

10

You can use a mains transformer at lower frequency, but you have to lower the input voltage to keep it below saturation. At normal operating frequency the inductive reactance of the primary winding is sufficient to prevent the current from rising too high. At lower frequency the current has more time to rise so it goes higher and saturates the core, ...

10

Why can't I just have one big wire or threaded wire on a motor? No problem with this - check out the rotor on most induction motors: There is no insulation on the aluminium (squirrel) cage and it is, in effect, one shorted turn. What is it about having multiple coils that enables the magnetic field? A magnetic field is produced by current AND turns ...

9

You calculate the core flux with the equotion above, and the inductance takes the sum of all fluxes through each turn. The flux through each turn is the same and equal to core flux. The core flux is proportional to N, and the per-turn sum of flux is proportional to $N^2$. Another way to express this dependancy is to say: because of magnetic coupling ...

9

Think of a single turn inductor (left below) then, imagine that single turn split into two parallel wires that are wound very tightly so that they occupy virtually the same space (right below). The two parallel wires, for a given applied voltage, will each take half the current of the single turn inductor and, together they take the same current as the ...

9

No, the magnetic material doesn't need to form a closed loop, but that will allow you to make a smaller transformer for the same amount of power. The magnetic field lines will always be in a loop, the only question is whether you provide nice material for them to easily follow or not. However, the problem in your case is that you are using a conductive ...

8

In addition to what Shamtam said about how waving a magnet around the outside of the case could be ineffective, it can do damage to other things, especially if you do this while power is applied. A strong but changing magnetic field (like that caused by waving a strong magnet) will induce current and voltage in anything conductive that happens to be at the ...

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