Hot answers tagged

95

This is a bit complex. Basically, there are a number of limiting factors: The IO lines from the microcontroller (i.e. the analog and digital pins) have both an aggregate (e.g. total) current limit, and an per-pin limit: From the ATmega328P datasheet. However, depending on how you define the Arduino "Pins", this is not the entire story. The 5V pin of the ...


86

I think I may have the definite answer to this. This naming comes from a 1963 IEEE standard 255-1963 "Letter Symbols for Semiconductor Devices" (IEEE Std 255-1963). I'm an electronics history fanatic and this might be interesting to other (fanatic)s, so I'll make this answer a bit broader than necessary. First of all, the first letter capital V comes from ...


80

That's the Ukrsepro mark. It means the product has passed the certification of UkrSEPRO, the safety certification requirement symbol for trading in the Ukraine region. Scope of products covered by the above regulations include but not limited to the following: Information technology equipment Audio and video equipment Household and similar ...


75

100 µF is really pushing the limit for ceramic caps. If your voltages are low, as a few volts to 10 or maybe 20 volts, then paralleling multiple ceramics may be reasonable. High capacitance ceramic caps have their own set of advantages and disadvantages. The advantages are much lower equivalent series resistance and therefore much higher ripple ...


75

Most commercial IC circuits are isolated from the substrate material by a reverse-biased P-N junction (including CMOS parts). The substrate is usually tied to the voltage expected to be most negative. If it isn't, then that junction becomes forward biased and can conduct a great deal of current, melting metal or heating the junction to the point where it no ...


71

CPUs are not 'simple' by any stretch of the imagination. Because they have a few billion transistors, each one of which will have some small leakage at idle and has to charge and discharge gate and interconnect capacitance in other transistors when switching. Yes, each one draws a small current, but when you multiply that by the number of transistors, you ...


66

You are right in that power is the product of voltage and current. This would indicate any voltage x current combination would be fine, as long as it comes out to the desired power. However, back in the real world we have various realities that get in the way. The biggest problem is that at low voltage, the current needs to be high, and that high current ...


56

Take a simple example where the sums are trivial. I have a voltage that is on 50% of the time and off 50% of the time. It is 10V when it is on. The average voltage is thus 5V. If I connect a resistor of 1 ohm across it, it will dissipate 100W when it is on and 0W when it is off. The average power is thus 50W. Now leave the voltage on all the time but make ...


48

20 amp glass cartridge type slow blow. It has a thermal mass that generates a delay before the solder melts at the left hand end. The spring pulls the mass away from the wire, making sure the two conductors separate and stay separated.


46

While it may be true that distributors don't want to check every single part individually, in this case it is not down to laziness that the 0Ω resistor has a specified rated power of 125mW. As pointed out by @BumsikKim's answer, the datasheet for the series does in fact specify this rating - the distributor product page is correctly representing the ...


44

Congratulations for having the wit to know something was wrong! simulate this circuit – Schematic created using CircuitLab Figure 1. Parallel and series arrangements of batteries will have the same VAh rating. I will effectively have a battery of 20 V with a capacity of 2 Ah. That's the error. In parallel they can supply 1 A each for one hour. ...


41

Janka comes close, but there are are several more details. (Note, recalling from EE classes about 45 years ago.) On many high voltage lines there are arc electrodes at various points. When lightning strikes the line, the increased voltage causes an arc to form across the electrodes. This helps to dissipate the voltage of the lightning strike. But the ...


39

Anixter says: Even though copper has a long history as the material of choice for conducting electricity, aluminum has certain advantages that make it attractive for specific applications. Aluminum has 61 percent of the conductivity of copper, but has only 30 percent of the weight of copper. That means that a bare wire of aluminum weighs half as much ...


38

You should not be so hard on your professor. Much of the confusion newcomers to EE struggle with is that we talk about theoretical IDEAL circuits as part of the teaching process. In ideal circuits things often act rather contrary to your intuitive and experimental notions of how things actually work. Things like short circuits, transformers, diodes, and ...


38

Because UL 1741 does all the heavy lifting for you. That's what makes it "so easy". UL 1741 is a complicated spec for "grid-tie solar inverters". Aside from doing their usual inverter thing (itself no small matter), a 1741 inverter also senses the presence of the grid, and obviously syncs its output to the grid. A UL 1741 inverter is intentionally ...


36

USB-C will use the Power Delivery specification, a first connexion is done at 5V, then "negotiate" whether it can use a higher profile to charge. There are 5 profiles available : Profile 1 : 5V@2A Profile 2 : 5V@2A or 12V@1.5A Profile 3 : 5V@2A or 12V@3A Profile 4 : 5V@2A or 12V@3A or 20V@3A Profile 5 : 5V@2A or 12V@5A or 20V@5A There are 4 connection ...


35

Anyone who has a clue about how physical units works will of course realize that kWh/1000h means "1000 watt-hours per 1000 hours" which can be shortened to just W. But when it comes to lamps, the unit "W" is already used for the light output. Light bulbs which use more energy-efficient technologies than the classical incandescent light bulb often state ...


35

The problem assumes you understand something that is not clearly spelled out: the wires and the (unknown) load are in series. Therefore they share the current, not the voltage of the battery. That's the situation: simulate this circuit – Schematic created using CircuitLab As other have pointed out, the voltage drop across the wires is small given ...


34

For power to be average i must be average current, so I am surmising that the effective current is the average current. In short, average voltage x average current only equals average power when the voltage and current are DC quantities. Think about the following example: - If you applied 230 V AC from your utility power outlet to a heating element, it ...


33

10 years =~ 87650 hours. 1 uA drain will require 87.75 mAh in 10 years. With som shelf life degradation that's close enough to = 10 mAh / uA / year or = 100 mAh / uA / 10 years So your cited 163 mAh battery will supply 1.63 uA mean. Pushing technology, size and luck may get you to say 5 uA mean. There are 86400 seconds/day. There are 1440 minutes/...


33

@The Photon's answer is quite extensive, the only thing missing is, how electrical energy is now actually transferred. In a simple case where you just have some kind of ohmic load, it is exactly the same as for DC, just with switching polarities. If you want a picture, imagine a saw: It is pulled through the same block of wood, back and forth. The same ...


33

60A through a 0.01ohm resistance gives a 600mV drop. That is the voltage you need to use in the equation.


32

Lightning brownout procedure: When lightning hits an overhead power line, there is overvoltage at first, for about 100 milliseconds. This overvoltage creates an arc at a nearby pole. The arc works as a short circuit, so current from both sides of the overhead lines flows to the arcing pole. The voltage at other places of the grid dips because of the huge ...


32

You can get 8 kV rated (at several thousand amps) thyristors for use in HVDC converters. The gate is optically coupled for the obvious reasons and also because, when used in tandem on HVDC links, the gate driving speed differences between series connected thyristors is important and optical is a little bit more clear cut speed-wise: - Stack a few together ...


31

When you're looking at an AC source in isolation such as in your question, indeed there's no polarity and you can connect the wires either way round. When combining two or more AC sources in series or parallel, the relative phasing is very important.


30

I've built payloads for a dozen suborbital shots and one satellite. AC was never used. As our missions were not really long-duration interplanetary trips, we used commercially-available DC-DC converters built to aerospace standards. The satellite, I believe, is still functioning after about 6 or seven years. Converter frequencies were, I believe, about 550 ...


30

The voltage for the Hall–Héroult process is inconveniently low (and the current too high) for efficient parallel operation so they use a whole bunch of cells in series. From this source ("Studies on the Hall-Heroult Aluminum Electrowinning Process"): The optimum current density is around 1 A cm-2 with a total cell current of 150-300 kA and a cell ...


29

I haven't seen anybody else mention temperature. Perhaps you left the default 10 degree rise in the online calculator? That's pretty conservative. A 20 degree rise isn't that bad in a lot of situations. And if you aren't running the highest current continuously, it's quite possible even a higher temp rise would be acceptable, since it will have time to ...


29

Transformers are AC only. Running DC through a transformer basically gives you a heater. Critically, transformers work through the fact that a change in magnetic field induces a voltage in a wire. The critical portion is that the change is required. In an ignition coil, the change is created by simply connecting and disconnecting the ignition coil from ...


28

You are getting your terminology all muddled up. Firstly, V = Volts which is a measure of potential difference (voltage), not power. So saying "extra 7V of power" is incorrect. Secondly, the resistor doesn't "resist voltage", it resists the flow of current. Thirdly, a device doesn't "draw 2V from the battery", it draws a current from the battery. So lets go ...


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