Questions tagged [capacitance]

Capacitance is the ability of a body to store an electrical charge.

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105 votes
13 answers
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Measuring feline capacitance

When I pet my cat, and then touch her on the nose, I get a little shock. Sometimes, when she walks up to something, her nose sparks and she jumps back and puffs out. I was wondering how I might go ...
timthelion's user avatar
46 votes
11 answers
5k views

Is there a dual of the transformer?

Capacitors and inductors are duals of each other. A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?) Also, you can vary ...
endolith's user avatar
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38 votes
4 answers
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How do transposition towers in transmission lines work?

There're such things as transposition towers in power distribution powerlines. The idea is that for example you have three conductors running in parallel at the same height and the leftmost of them is ...
sharptooth's user avatar
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33 votes
10 answers
45k views

What are some reasons to connect capacitors in series?

Usually you either combine capacitors in parallel because you want to increase the total capacitance while fitting the components in a certain shape/position, or you just combine capacitors by buying ...
endolith's user avatar
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31 votes
1 answer
6k views

What effect does selecting the wrong load capacitance for a crystal have?

I've seen questions such as this one and this one that talk about selecting capacitors that, in series, match up as closely as possible to the load capacitance of the crystal. What effect does ...
Polynomial's user avatar
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23 votes
2 answers
40k views

How do I decide what capacitor to use in a circuit?

I am using a voltage regulator, and to get cleaner power, the datasheet recommends using a 0.33uF capacitor. However, it doesn't say what type it wants. Stupidly, I ...
Anonymous Penguin's user avatar
23 votes
4 answers
8k views

Capacitance between Earth and Moon

Is there a capacitance between the Earth and the Moon, and if there was enough potential difference, could a discharge strike occur?
skyler's user avatar
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22 votes
4 answers
16k views

Crystals and load capacitance

If a crystal has a rated load capacitance of 6 pF, is the right thing to do to put a 6 pF capacitor to GND on either leg of the crystal? I'm using it as the clock source (TOSC) for an XMEGA and it's ...
vicatcu's user avatar
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21 votes
1 answer
2k views

Capacitors with a "/" on schematic

I'm looking at a schematic for an old turntable that I am needing help on when viewing the capacitor values. All of the polarized caps will have 2 values written next to symbol i.e. ...
kernisme's user avatar
  • 211
20 votes
3 answers
3k views

Health risks of exposed contact to a capacitive sensor

I want to make a wearable metal trinket with the ATtiny85 chip acting as a capacitive sensor (with the same technique that this Arduino library uses), so it can detect when it's being worn. Are there ...
Edoardo's user avatar
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19 votes
7 answers
13k views

LC circuit, bigger L than C, or bigger C than L?

So if I want my LC circuit to resonate at 20MHz, I just use the formula, \$F=\frac{1} {2\pi\sqrt{LC}}\$. Using available inductor and capacitor values, there are lots of different possible ...
griffin175's user avatar
18 votes
4 answers
8k views

What does negative capacitance mean?

I see negative capacitance measuring electrolytic capacitor at high frequencies (40kHz). How should I interpret that? The device is LCR Meter Hantek 1832C. I failed to find anything about that in the ...
max5555's user avatar
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16 votes
3 answers
16k views

Crystal oscillator load capacitance, again

There's a lot of seemingly conflicting information regarding how the load capacitance for a parallel resonant crystal is calculated. Faced with a lot of problems in recent years with non-oscillation ...
PkP's user avatar
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16 votes
3 answers
11k views

How does a Theremin "antenna" work?

I always assumed that the shape of the antennas was important; a vertical monopole for pitch and a horizontal loop for volume, thinking that this minimized their interference with each other. But it ...
endolith's user avatar
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15 votes
3 answers
3k views

How can I measure gate capacitance?

Is there an effective way to directly measure the gate capacitance of a power MOSFET, like say the IRF530N? The way my circuit is behaving would indicate that the effective gate capacitance is ...
scanny's user avatar
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14 votes
9 answers
2k views

How do I measure the capacitance of a 0603 capacitor which is in the order of pF?

My multimeter does not have pF resolution and I am not able to find any tools which can measure a pF capacitance. My goal is to identify the capacitance of a 0603 capacitor that I have removed from a ...
dinoswords's user avatar
14 votes
2 answers
1k views

Why does the capacitance value of an MLCC (capacitor) increase after heating?

I have a general purpose MLCC capacitor design kit, which consists of capacitors of different values. I took a 2.2 µF (X5R, 16 V, +/- 20 %, -> this one) capacitor out of it and measured its ...
CatastrophicFailure's user avatar
14 votes
3 answers
2k views

How does capacitance depend on AC voltage?

I am aware of the dependence of some ceramic capacitors (e.g. X7R) capacitance on DC voltage. I assumed that if a high enough AC voltage is applied, capacitance changes in its rhythm causing ...
Hyp's user avatar
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14 votes
3 answers
2k views

Why need the capacitors be as close as possible to the device?

Just a simple question: what exactly stands behind the need for placing the capacitors as close as possible to the current consuming device's pins? Is that the inductance, resistance or maybe ...
eltomek's user avatar
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13 votes
4 answers
4k views

Why do we use two parallel capacitors in a voltage regulator circuit? [duplicate]

C1 and C2 are parallel capacitors and their total capacitance is 1000.1 uF. I think C1 is ...
Michael George's user avatar
13 votes
6 answers
83k views

Why does the distance between the plates of a capacitor affect its capacitance?

Why does the capacitance of a capacitor increase when its plates are closer in distance to each other?
awesomeguy's user avatar
13 votes
3 answers
915 views

How to select the resistance value for an Arduino capacitance meter

I'm working through examples for an Arduino capacitance meter and the ones I've seen give the known resistance of the RC circuit as 10 kilohm. It's my understanding that we could use "any" ...
Elizabeth Woodward's user avatar
13 votes
1 answer
3k views

Why must USB low-speed devices use a captive cable?

The USB 2.0 spec says: "A low-speed device is required to have a captive cable." However, I can't find a good explanation for why this is the case. I have seen hints towards two possible ...
Martin Geisse's user avatar
13 votes
2 answers
58k views

how to select capacitor values

I am trying to find information on formulas used to calculate capacitance required for a given circuit. Not a circuit in particular, just in general how to figure out what value should be used. I know ...
rob j loranger's user avatar
13 votes
3 answers
1k views

What capacitor(s) will be best replacement

Living and working in West Africa. We cannot purchase capacitors here, we can only beg (and pay) used parts from the workshops which rewind electrical motors. Our gray-water-pump is broken, the ...
Martin Zaske's user avatar
11 votes
5 answers
8k views

Self capacitance of an isolated object

A few times I've been reminded that an object can have self capacitance and it's just not registering with me how this can be so. I'm sure there's a good explanation. Here's the explanation I am ...
Andy aka's user avatar
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11 votes
2 answers
3k views

Are film capacitors affected by DC bias?

After looking around, I have found quite a few things about how DC bias reduces effective capacitance for a ceramic, or electrolytic capacitor, however nothing seems to talk about the effect on film ...
Puffafish's user avatar
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11 votes
2 answers
9k views

Noise (capacitance-related?) in serial signal

The "executive summary" pictures: I want to decode the serial signal coming out of my tablet's headphone jack. This is a somewhat weird "hack" that exists in a few phones and tablets: basically, if ...
ttsiodras's user avatar
  • 427
11 votes
2 answers
4k views

How do I size the coupling capacitance for a SEPIC converter?

The app notes I've seen for a SEPIC converter1 all tell me to size the coupling capacitor for ripple currents and voltages. I haven't seen one that tells me how to size the capacitance. Obviously ...
Stephen Collings's user avatar
10 votes
4 answers
3k views

If a diode has capacitance, why doesn't it block the circuit after some time?

It is well known that diodes have a depletion region, which in itself has some form of capacitance due to the presence of charges on its opposite sides. In RC circuits, the capacitor always acts as an ...
Wais Kamal's user avatar
10 votes
6 answers
3k views

Capacitive Sensing

Is there a way that I can make an Arduino or other Micro-controller detect a change in capacitance? I'm thinking of having a screen on my door that only turns on when you touch the metal door handle.
littlebirdceo's user avatar
10 votes
3 answers
11k views

Understanding capacitance in oscilloscope probe tip

I am trying to understand the capacitance and resistance in oscilloscope probe tip. In the above attached image, that 9Mohm resistance is used for that 1x and 10x setting that divides the input ...
user avatar
10 votes
2 answers
8k views

How is the electrical bus capacitance for I2C trace calculated?

i am trying to learn how to calculate the bus capacitance of an I2C tree with a master and multiple slaves. For example, in this document from TI, it shows how to calculate the value of the pull up ...
user1406716's user avatar
10 votes
1 answer
24k views

how to select capacitor for a crystal oscillator

Here is a 32 MHz crystal from one of TI's reference design The BOM list defines the crystal as ...
sven's user avatar
  • 738
10 votes
1 answer
876 views

Why do capacitors across my FETs minimize ringing/distortion?

I'm designing a 24V to 350V DC-DC Converter based on a H-Bridge. The power requirement is 500W and the circuit operates at 20KHz. The design works fairly well and I've achieved about 90% efficiency at ...
Saad's user avatar
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9 votes
7 answers
28k views

Why is charge the same on every capacitor in series?

Why is the amount of charge on every capacitor in series equal, regardless that capacitance values of capacitors are not the same? What really happens here so they are the same? simulate this circuit ...
Junior's user avatar
  • 1,019
9 votes
1 answer
19k views

How can capacitance values be determined from a cyclic voltammogram?

I am reading an article (Khomenko, Electrochimica Acta 2005, 50, 2499-2506) that investigates the capacitance of carbon-based electrodes for use in supercapacitors. In particular, they use cyclic ...
Andrew's user avatar
  • 175
8 votes
3 answers
21k views

Why did the capacitor blow up?

So my friend and I were working on this project which required capacitors. We needed to charge a capacitor with the following rating: 100microFarad, 400V. When we connected it to a 220V AC source (...
Kunal Pawar's user avatar
8 votes
7 answers
31k views

How to calculate equivalent capacitance to a battery?

I have a 1.25V 2Ah battery and I'm trying to calculate a equivalent capacitance with rated voltage of 2.7V for each of those batteries. This is what I did: Work of Battery = \$1.25V \cdot 2A \cdot ...
user36337's user avatar
8 votes
4 answers
3k views

Why do we have to discharge the capacitor before testing it in an LCR Meter?

LCR meters charge and discharge the capacitor to find out the capacity value (by using the time constant formula.) I wondering why a charged capacitor(even few volts) can damage the LCR meter? Why do ...
M.A.K's user avatar
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8 votes
3 answers
1k views

µ in the Middle of a Capacitor Rating

I'm looking at an electrolytic capacitor (and old blue, Philips one used in electronics classes) and am wondering why it is printed with 4µ7-M. I tried Googling, figuring that it was a common enough ...
Synetech's user avatar
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8 votes
3 answers
9k views

Capacitor Bank Rating

I need to know why capacitor banks are rated in KVAr rather than Farads? Suppose I have one capacitor bank of 10kVAr which is for a rated voltage of 400V. Will this bank provide the same reactive ...
Rahul Tungar's user avatar
8 votes
3 answers
1k views

Does someone have a non-textbook analogy to explain elements of a circuit?

I was wondering if someone could explain with analogies what inductors, capacitors, transistors, diodes, and op amps do? I understand the basic idea; I'm currently an Electrical Engineering student. ...
Kenny Truong's user avatar
8 votes
2 answers
2k views

Why are these capacitors treated as if they are in series? Why must the incoming and outgoing current in a battery always be equal?

A circuit with three capacitors and an open end at A: I am a high school student. I am very confused by this example. The circuit is open at end "A" as shown but still there would be some ...
Arun Bhardwaj's user avatar
8 votes
2 answers
12k views

Why does an ideal capacitor give rise to a rectangular cyclic voltammogram (CV)?

Many scientists are interested in developing supercapacitors, which have electrolyte rather than solid dielectric between the charged plates. In the field of electrochemistry, cyclic voltammetry (CV) ...
Andrew's user avatar
  • 175
8 votes
2 answers
1k views

Button debounce ringing

I have a circuit where I am using a tactile switch to pull 3.3v down to ground and investigating debouncing the button. My relevant part of the circuit is The 100nF cap does work here my signal has ...
Glenn Pierce's user avatar
8 votes
1 answer
398 views

How to estimate electrolytic capacitance from foil area

I opened a failed 1000 μF electrolytic capacitor. It contains 2 foils coiled with paper and some wet dielectric. With reasonable assumptions (to me), I can not derive marked capitance from this ...
philcolbourn's user avatar
8 votes
1 answer
2k views

Mimic human capacitance

In a video at Kickstarter a project called Tapcaps is mimicing human capacitance for triggering touches to a capacitive touch screen (the iPhone). At 0:45 in the video we can see a glimpse of the ...
runeb's user avatar
  • 181
8 votes
2 answers
252 views

Why the effect of a triphasic capacitor could be as twice as its rated kVar? *(check Update 1)*

Why the effect of a triphasic capacitor could be as twice as its rated kVar? Please check Update 1, since if its true, then I think my issues are solved. Intro This is a real life case of a client of ...
Joako's user avatar
  • 131
8 votes
5 answers
5k views

Simulate Earthing in LTSpice

I wan to simulate earthing or frame ground which is separate from circuit GND in LTSpice. I want to simulate line filter using Y capacitors C2 and C3 in the below image. See below image for clarity. ...
Vishal P's user avatar
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