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Scam? Does having this capacitor wired as shown provide any surge protection?

All I find is this giant capacitor. Is this literally a capacitor with a switch that turns on a light? Would this capacitor provide any surge protection in either direction? Wondering if it might ...
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38 votes

Scam? Does having this capacitor wired as shown provide any surge protection?

A pretty thorough debunking of these ‘power saving’ devices can be found here: http://www.nlcpr.com/Deceptions1.php Besides this, the box appears to be shoddily made and has no safety approvals. You ...
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28 votes
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Why do travel transformers have a setting for either 50W or 1600W?

There are two options- an autotransformer and a triac phase control with a fixed setting to yield the correct RMS voltage for appliances such as hair dryers which are more-or-less resistive loads. The ...
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26 votes

How can a reed switch be used for high current applications?

Don't use the reed switch directly. Use the reed switch to switch the coil of a larger relay. Alternatively, use the reed switch to switch the gate of a FET large enough to handle to load current.
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25 votes

Why does the resistance of a space heater decrease as it gets hot?

Silicon carbide and similar IR heating elements are semiconductors and have a negative temperature coefficient. Image from here
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20 votes
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Cable standard for data and power

USB Type C, properly configured, can provide up to 100W and also a means to connect a serial device using the basic DP/DM pair. More here: How does a USB C port provide the power to charge laptops? ...
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  • 40.9k
20 votes

Why does the resistance of a space heater decrease as it gets hot?

PTC materials are prone to spot-overheating. Part of the wire gets hot, so the resistance increases, so more power is lost there, so it gets hotter, and the rest of the wire gets colder, and ... the ...
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  • 4,114
20 votes

How can the same radio signal be received by 100s of receivers without any loss in it?

... without any loss in it ... First, physics says there must be some loss, because energy is received at the antenna and is available to be consumed by the receiver. ... be received by 100s of ...
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  • 37.6k
20 votes

How can a reed switch be used for high current applications?

For long-term reliability, a 60 A load requires relay contacts rated for at least 100 A. The coil current for such a contactor almost certainly is greater than the reed switch rating. There are at ...
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19 votes
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What is the reason for these utility poles with a 6-sided hole in the middle for conductors

It appears the reason for these pylons is due to limited right-of-way (ROW) when the line was built. There was only a 50ft wide strip through which the line was allowed to be built on, so a narrow ...
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18 votes
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What may happen if I leave out bypass capacitors?

You can't predict what will happen if there is insufficient decoupling. You can get any manner of glitches, hiccups, errors, and latch-ups and it may be the same one every time, or a different one ...
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17 votes
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Is the bigger wire section always better from the electrical point of view?

Is there any case or application where using a wider cable section is worse? Yes, it may create the wrong characteristic impedance. Here I'm thinking cable (as per your question) and coaxial cable ...
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  • 388k
16 votes

Why does switching cause power dissipation?

Consider a MOSFET switching. Switching is a transient event, so losses are not usually modeled as "power". Each switching action dissipates a bit of energy. Then you multiply this by the ...
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  • 61.3k
15 votes

What makes barrel connectors good at carrying high power?

Current is all about contact surface area. For example this random high current barrel connector from the internet has plenty of metal fingers on both electrodes to make a solid contact. Cheaper ones ...
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15 votes
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Guess power from board?

The device marked as "U3" is a LM2940 voltage regulator which, without a schematic or seeing the back of the board, I am going to assume is connected to the input. The input voltage range ...
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  • 7,590
15 votes
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Can different manufacturers have same part number for a transistor?

Manufacturers, in general, can use whatever name they want, even if the characteristics or even functions vary. If they are members of some organization such as JEDEC they may have agreed upon some ...
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14 votes
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Can I increase the output capacitance of a DCDC beyond the specified maximum?

For a detailed discussion, see this excellent TI application report but gross simplification: the regulator relies on a feedback loop of which the output capacitor is a part. Values that are too high ...
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  • 7,590
14 votes

Does an EEPROM consume power only during the transition edges or during entire read/write cycle?

Here is an example write current waveform from the NXH5104 4 Mbit Serial SPI EEPROM datasheet. In the table of 'Static characteristics' the average write supply current with 4 sectors active and 5 ...
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14 votes
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Windmills generate electricity by the spinning blades. Why can't EV vehicles recharge their batteries from their spinning wheels? Is that too hard?

They do. It's called regenerative braking. The only time you can practically recover energy from the wheels is during braking. Taking energy from them slows them down. If you do it while they are ...
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  • 5,015
14 votes

Why do power supplies get less efficient at high load?

At higher loads conduction losses get higher. Power increases as the square of current, so the copper traces, on resistances of the FETs, and resistance of the inductors will contribute to higher ...
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  • 20.3k
13 votes

What load resistance will result in maximum power transfer - Art of Electronics

It may be worth slogging through the exact math to illustrate what's happening here. Assuming a source resistor \$R_S\$ and a load resistor \$R_L\$ the current through both resistors will simply be $$...
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  • 1,885
13 votes
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How to shunt 1500 joules when voltage exceeds 75 VDC

It seems perfectly feasible to dump the load into a 1 kW wirewound resistor using a mosfet. Example resistor: Vishay p/n FSE100022ER500KE This is a 1 kW wirewound resistor rated for 10x overload for 5 ...
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  • 25.2k
12 votes

Cable standard for data and power

Don't. (Or don't yet.) From your comments on answers, you describe yourself as "new to electronics" and you are unaware even of the ability of different wire gauges to carry current safely. ...
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  • 5,759
12 votes

How can the same radio signal be received by 100s of receivers without any loss in it?

You're right ... but Let's put some numbers to this. 3 mV (70dBuV) is a good strong signal into an FM receiver, on the 300 ohm (dipole antenna) input. That is a current of 10uA or a power of 30nW, so ...
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  • 66.1k
12 votes

What may happen if I leave out bypass capacitors?

These capacitors smooth the output voltage of the internal linear regulator that powers the logic circuitry. Without these capacitors the voltage will glitch whenever there is a change in current draw ...
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11 votes
Accepted

If I don't need USB power what should I do?

VBUS is used as a signal that tells the device that a host is present. For a self-powered device, VBUS sensing is mandatory. And the host and device must share GND. You need to connect all four ...
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  • 14.9k
11 votes

Can I increase the output capacitance of a DCDC beyond the specified maximum?

One reason is startup inrush current. If it's too high the regulator shuts down and can enter a cycle of repeatedly trying to starting up and shutting down. I think stability might be another one and ...
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  • 48.2k
11 votes
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Is this an acceptable way to create +/-5V from +/-12V?

No. What you're calling "-5 V" would actually be +5 volts with respect to the -12 volt rail, i.e. -7 volts. And it would only be able to source current into a load returned to a lower ...
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  • 20.3k
11 votes

I built a DIY DC-DC buck regulator. It's getting extremely hot. Why?

The 10 μH inductor is unsuitably low in inductance. Since you know output current, output voltage, input voltage, and switching frequency, you can plug the values into the formula given in the ...
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  • 92.1k
10 votes
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A 9 kW heater has an efficiency of 85%. How much power is lost over 4 hours use?

Is it a trick question? First, power is an instantaneous measurement. Power x time is energy. Second, it is a heater. How can it be only 85% efficient? What happens to the other 15%? Is it "...
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