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87 votes

Why is the number 63 popular in electronics?

Using the table in @VoltageSpike's answer we can see that the standard values follow a ratiometric step increase from one value to the next. V Ratio to previous value 10 12.5 1.25 16 1.28 20 1.25 ...
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49 votes
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What type of glass fuse is this and what does the spring do?

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 ...
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  • 1,654
49 votes
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What causes a fuse to blow, the current or the power?

It's the watts dissipated in the fuse itself not the watts in the system. Therefore since the fuse has resistance (R) it's the current, which provides that power I^2*R. The voltage has nothing to do ...
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48 votes
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Does it matter if a fuse is connected to the negative or positive terminal of a battery?

[Should I] connect the fuse to the negative terminal of the battery since it's where the actual flow of electrons originate which is opposite to the conventional flow of current from the positive ...
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41 votes
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Can thin sections of copper traces be used as fuses?

It's certainly been done. Source It's a bit more of a crapshoot than a traditional fuse, like a printed spark gap, but can be done. The trace should not be exposed. An exposed trace will be subject ...
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  • 11.6k
41 votes

Why did my fuse blow after 3+ years of no problems?

Fuse Design Looking at this datasheet for fast 5x20mm fuses from ESKA, you find a table with "pre-arcing time limits" at the bottom. For a 500mA fuse, it states: ...
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  • 8,440
39 votes
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Why did my fuse not blow?

Even fast fuses don't respond immediately after the rated current is reached. Most fuses require a significant over current to fire almost instantly. This is an obvious requirement since its all about ...
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  • 9,809
39 votes

Why are multimeter batteries awkward to replace?

The internals of a well designed handheld multimeter are designed to contain any explosions that may occur from failing parts. Imagine the following situation: you're holding a meter in your hand, ...
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  • 19.7k
38 votes

Why do Americans use fuses and not differentials and breakers like Europeans do?

You are mistaken. There are houses in the US which use circuit breakers - I'd say most of them have circuit breakers rather than fuses. Houses in Europe aren't all modern and up to date, either. I ...
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  • 58.2k
37 votes

How to solder a 70 °C (158 °F) thermal / temperature fuse

This was a problem with transistors in the early days and standard advice was to use a pliers as a heat shunt close to the body of the component. Figure 1. Protecting a capacitor from overheating ...
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37 votes
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How to solder a 70 °C (158 °F) thermal / temperature fuse

I think those thermal fuses are normally connected using crimp terminals, rather than by soldering. Even with the heatsinks the other answers mention, it would be much too easy to damage the device ...
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34 votes
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What is the reason for a fuse next to a thermostat?

The fan doesn't produce heat, but if the fan never blows, the heating element might overheat and start a fire. Thermostats fail. Safety regulations generally work on a "single fault" principle. ...
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34 votes
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Why do Americans use fuses and not differentials and breakers like Europeans do?

Our breakers I would say almost all US homes have breakers. Even those with legacy fuse boxes have breakers between them and the service. There are six major types of service panel, and all 6 designs ...
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33 votes

Parallel MOSFETs

MOSFETs are a bit unusual, in that if you connect several of them in parallel, they share the load quite well. Essentially, when you turn on the transistor, each one will have a slightly different on-...
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32 votes
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Why did my fuse blow after 3+ years of no problems?

The rating of a fuse is the amount of current that it will carry indefinitely without blowing. In order to guarantee this, most fuses will not blow until the current rises to 2× or more of their ...
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32 votes
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Why do fuses have a maximum breaking capacity?

To elaborate a bit on the answer by Neil_UK... At a modest overload, the fuse wire will melt at its weakest point, and break the current. At a larger overload, an arc will form across the ends of ...
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27 votes
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Why do fuses burn at a specific current?

So if we have a 10A fuse, and it has some arbitrary resistance such as 100 ohms, ... This typical 10 A fuse has a resistance of 5 mΩ. So your guess was out by a factor of about 20,000. At 10 A ...
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  • 160k
27 votes

Suicidal ASUS power brick?

That's the power factor correction circuitry. The FET Q1 will be switching at high frequency so it won't short rectifed 300V to 0V as there are inductors in the path, most likely L4 is the boost ...
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26 votes

What type of glass fuse is this and what does the spring do?

BobT has it right - my answer serves only to add information. This class of fuse is commonly known as a "3AG" or "3AB" fuse. The Buss number would be AGC-20 (fast blow) or ABC-20 (Slow Blow). ...
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25 votes

Why do fuses have a maximum breaking capacity?

I don’t understand that if a small current can blow the fuse, why a bigger current can’t. A bigger current will indeed melt the fuse wire. The question is, what happens after that? If the fuse is ...
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  • 141k
24 votes

Can thin sections of copper traces be used as fuses?

I've done this in a real production design, and regretted it. "It seemed like a good idea at the time." I wanted to protect a backplane against a card being plugged in with a power-to-ground short in ...
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24 votes
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Will a fuse improve the safety of my non-isolated buck converter design?

Will a 500mA fuse after the 12-to-5V linear voltage regulator make the design safe against electric shock since the buck converter is non-isolated? No. A fuse does not protect against electric shock. ...
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  • 160k
24 votes

Why are multimeter batteries awkward to replace?

It's a safety thing: A multimeter needs to be safe to connect to the mains while holding in your hand, and there are stringent tests for this. One of the hardest to pass is that it must not spark to ...
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  • 7,158
24 votes
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What would it take to make a PS/2 keyboard interface hot-swap?

Somehow, un-plugging or plugging in a keyboard can cause a surge. I don't recall having these issues with serial ports (RS-232, Appletalk, etc), parallel ports, VGA, etc. These don't power the ...
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  • 59.1k
24 votes
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Can I put a 250 mA fuse in replacement of a 160 mA fuse?

Widening of protective envelope for any circuit is NOT good. the fuse is there to protect the circuit in case of overcurrent. Overcurrent does not mean shortcircuit, it means that the circuit is ...
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24 votes
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Suicidal ASUS power brick?

As the other answer points out this looks like active power factor correction. Power factor is the ratio of real power (short-term average rate of net energy transfer) divided by apparent power (RMS ...
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  • 19.3k
23 votes

Logic behind this fuse status indicator

Q1 and Q2 form a astable multivibrator which will output a square wave (12V, 0 V, 12 V, 0 V, ...) voltage via D2. If D1 wasn't there then that square wave would turn on/off Q3 and with that also the ...
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21 votes
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How To Know If a Fuse Will Work Properly?

I think maybe you misunderstand how a fuse behaves. A fuse doesn't instantly open when current meets the Ampere Rating. There is a minimum ...
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  • 13.4k
19 votes

Why do fuses burn at a specific current?

The conductor fails when it reaches a certain temperature. Because the fuse is in thermal contact with ambient, it can dissipate a certain amount of power before it blows. Your 10A fuse is designed ...
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  • 36.3k
19 votes
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What component may this be?

Those are thermal fuses. They break the connection permanently once a certain temperature is reached to protect devices from overheating and possibly causing fire.
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