# Tag Info

## Hot answers tagged electrical

27

Here in North America, each house is fed from a single phase of the distribution system thru a step-down transformer. The secondary of that transformer is 240 V center tapped. All three lines go into your house. The center tap is earth grounded near where it enters the house. Ordinary 120 V circuits are between one of the ends and the center, which is ...

24

There are several reasons. 1) Soldermask is lossy, and different types of mask are differently lossy. So having no soldermask where the RF fields are gives the best transmission, and if your board is made by different fabs, the most repeatable transmission. 2) Line dimensions, which affect characteristic impedance, are critical. It's difficult to optically ...

23

If you want to convert the voltage to 5 volts, you should not use a resistance-voltage divider. That way you will indeed create 5 volts, but as soon as you apply a load the voltage will drop. Instead, you have two options in general to regulate voltage. The first option using a linear regulator, and the second option is using a switch-mode power supply. ...

20

You should always tie unused inputs to a valid logic level. That could be tied to GND or to the VDD voltage rail. Never leave unused inputs floating in that it can cause excessive power dissipation in that IC package and introduce extra noise into the voltage / GND rails. It is common practice to use a pullup or pulldown on the unused inputs on unused ...

20

"Cut the foam! Cut the foam!", she cried as she wriggled and squirmed in the styrofoam dishwasher packaging she got stuck in. "With what?", cried Bob as he scanned the kitchen for something suitable. "With a hot-wire styrofoam cutter, of coarse! You'll need about 50 cm and a couple of hundred watts.", said Alice. "There isn't one in the cupboard.", said ...

19

The two responses given have been from a North American members. I'll give a European perspective. In parts of Europe (I know for sure about Belgium, The Netherlands, Germany, France and the UK), they use a 230 V/400 V (230 V between line and neutral, 400 V between phases) three phase system. Most houses are provided only one of the ...

18

Before connecting a generator to the grid, they spin it up to more or less the right speed. Then they hook what is basically a voltmeter between a generator phase, and the corresponding line phase. They adjust the generator drive until the observed voltage is a) very slowly changing (frequency difference below some threshold) and b) drops below some low ...

18

In addition to the reasons given by Niel_UK, there is the matter of predictability and modeling. Soldermask is applied as a liquid. As such, its thickness may not be as well controlled and predicable as the thickness of the substrate and conductor layers. In addition, it may have an unpredictable profile - how does it "flow" in between the traces? All of ...

15

You're confusing an accurate number of cycles over a 24 hour period with very rigid instantaneous frequency control. That's not how it's done in most places. The frequency is maintained at around its nominal frequency by matching generation to load - all the time that the load is greater than the generation, the frequency will be (very) gradually falling, ...

15

With R4 and R6 being zero, this means they are essentially a short circuit. You should imagine the initial circuit to look like this: simulate this circuit – Schematic created using CircuitLab This now becomes much easier to visualise. however when I solved it I just took out the R3 and R5 so I got a different answer for the current flowing ...

15

A transistor on its own does not make it an amplifier. The transistor needs a circuit around it to do the actual (signal) amplification. Depending on the circuit a transistor can amplify current changes and/or voltage changes and that means power amplification. Power amplification means that you need a smaller power to control or output a larger power. In ...

14

Capacitor banks designed for power factor correction are rated in kVAr (kilo-volt-ampere reactive) because it's convenient. One will typically know the reactive power required by some load, then it's simply a matter of selecting a capacitor of the equal but negative reactive power to improve the power factor. Reactive power $Q$ for a purely reactive load (...

14

This all brings me to wonder, how much of what we use is calibrated to someone else's meter. And how many of those meters, are calibrated to yet someone else's.. and on and on. Seems like one big house of cards. and... Is there some sort of certification sticker one should look for when buying a meter or other equipment that indicates it is indeed ...

14

Yes, at the nano-meter scale you always run into an issue titled Electromigration. At the nano scale a conductor has to not only be rated for voltage drop but also for current density. To achieve sufficient reliability due to deterioration from electromigration.

14

That's a Chinese RoHS / recycling indication: Under RoHS 2, manufacturers must indicate dangerous chemicals inside on the outside. The number in the circle is an indication for the "Environment Friendly Use Period", the period in which it's safe the contained substances will not leak out. 10 in your circle means that it's pretty safe that for 10 years, no ...

14

The crux property that allows anything to act as an amplifier is that it can control a high power signal, using a low power input. In the case of a transistor, it's the fact that a low power base current or gate voltage can change a large collector or drain current. There's a whole host of other devices that can be used as amplifiers. One of the earliest ...

13

There is no math here; the notation "amplitude∠phase" is simply shorthand for "amplitude×sin (ωt + phase)", where the frequency ω is implicit (and fixed). It's just two ways of saying exactly the same thing.

12

It's the symbol for an adjustable transformer. See yourself:

11

Aside from the lossy nature, solder mask has a high dielectric constant relative to air and poorly controlled thickness, so the characteristic impedance will be harder to control with solder mask applied. Zo decreases by about 1 Ohm / mil of soldermask thickness. LPI solder mask affects Zo by about 2 ohms and dry film by as much as 7 ohms.

11

This is a 3-phase permanent magnet (PM) servomotor. Induction motors do not have permanent magnets, therefore it is a synchronous motor. If any two phase connections between the motor and controller are swapped, the motor will reverse. Since the controller can reverse the motor electronically, it may make no difference how the motor is wired during ...

10

With any CMOS logic IC, you MUST connect unused logic inputs to a known logic level. You may connect unused inputs to either High or Low, whicever is convenient (or whichever is necessary to make the part work as desired). An unconnected CMOS input may take on any level - if it sits at a "maybe" state, the input circuit will draw excessive current, and ...

10

The tip is not mounted correctly on the iron body! It is absolutely normal that a soldering iron becomes brownish due to oxidation around the heating element - which for such tips should be inside the sleeve. But it is outside! The iron also looks "unnaturally" long. When zooming in and looking into the slit, the iron body is not inserted completely into ...

9

It is a cable "strain relief*. These are designed to prevent the cable bending sharply where it enters the appliance otherwise the cores are likely to fracture internally or the insulation crack. Figure 1. A progressive strain relief The progressive strain relief gets thicker and more resistant to flexing the closer it gets to the point of entry into the ...

8

They use a Synchroscope. I have seen this done in power plant control rooms. https://en.wikipedia.org/wiki/Synchroscope

8

It depends on your location. China, India, EU, UK, NA, Africa, NZ, AU are different. Many of the 220Vac residences are only single phase. many with √3 * Vac for 2 of 3 phases. North America is generally split phase with center tap = Neutral like below with 120/240V 60Hz Others may be 1, 2 or 3 phases in various combinations with 120 phases. or any combo ...

8

another relay option. simulate this circuit – Schematic created using CircuitLab with appropriate choice of relay this layout could be used in the case where both switches are on different phases, but not all relays that can switch 240V are suided to that task.

8

It's very fruitful to compare inductors and capacitors. They are dual components. They both store energy. However, you have to remember to swap current and voltage, short circuit and open circuit, series and parallel. A capacitor 'tries to' keep its terminal voltage constant. If you try to change the voltage suddenly, it will demand a large current. '...

8

I will not give you the full solution, but the required non-trivial sidestep. You have got this far: C(A + B) + A'B = AC + BC + A'B = Now here is the sidestep. We know that (A+A') is 1, so we can do: = AC + (A + A')BC + A'B From here you will need to expand it and use the "OR absorption law" twice.

7

Wikipedia explains it fairly well in their article Utility Frequency: The induction motor was found to work well on frequencies around 50 to 60 Hz, but with the materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of ...

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