Questions tagged [capacitance]

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

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104
votes
13answers
26k views

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 ...
39
votes
11answers
4k 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 ...
36
votes
4answers
16k views

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 ...
30
votes
1answer
5k 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 ...
27
votes
10answers
37k 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 ...
23
votes
2answers
37k 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 ...
21
votes
1answer
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. ...
21
votes
4answers
10k 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 ...
19
votes
4answers
5k 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?
18
votes
7answers
10k 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 ...
18
votes
3answers
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 ...
16
votes
3answers
10k 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 ...
14
votes
3answers
2k 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 ...
14
votes
3answers
1k 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 ...
13
votes
2answers
55k 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 ...
12
votes
4answers
2k 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 ...
12
votes
1answer
2k 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 ...
11
votes
3answers
760 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 ...
11
votes
2answers
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 ...
11
votes
2answers
2k 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 ...
10
votes
6answers
2k 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.
10
votes
5answers
69k 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?
10
votes
1answer
789 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 ...
9
votes
1answer
15k 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 ...
8
votes
4answers
1k 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 ...
8
votes
6answers
24k 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 ...
8
votes
3answers
2k 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 ...
8
votes
3answers
7k 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 ...
8
votes
3answers
882 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. ...
8
votes
2answers
10k 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) ...
8
votes
2answers
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 ...
8
votes
3answers
1k views

Will this approach accurately measure capacitance and infer spacing?

I am interested in any feedback or caveats regarding the following capacitance measurement method before I begin setting it up. For an experiment, I have come across the need to measure and track the ...
8
votes
1answer
1k 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 ...
8
votes
5answers
1k 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. ...
7
votes
3answers
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 ...
7
votes
2answers
1k views

Estimate capacitor parameters

I am thinking of making a capacitor, just for fun/for studying purposes. And I thought of the following exercise. In my local store, there exists rolls of polyethylene food film and aluminium foil. ...
7
votes
2answers
6k 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 ...
7
votes
5answers
2k views

Are there any non-ideal side-effects of putting capacitors in parallel to increase capacitance?

I want a 500uF capacitor. Theoretically, I should be able to place 5 100uF capacitors in parallel to achieve 500uF of capacitance. However, are there any side effects of practically implementing this?...
7
votes
4answers
5k 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 ...
7
votes
2answers
2k 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 ...
7
votes
1answer
1k views

What is this yellow capacitor?

I bought these big yellow capacitors from ebay, just to try them (only information present there: "10pcs Yellow feedthrough capacitors axial capacitors 100V 15UF"). Obviously, they are simple axial ...
7
votes
2answers
5k 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 ...
7
votes
3answers
6k views

If MOSFET is a voltage-controlled device, then why do we need to supply it with high current when using in an H-bridge?

I might be confusing myself, but from what I am reading so far, a BJT is a current-controlled device and a MOSFET is a voltage-controlled device, which to me implies that a MOSFET requires very low ...
7
votes
3answers
3k views

Is a human (or other) electrical signal absolutely necessary to activate a capacitive touchscreen?

I know this is the general wisdom, and that someone has asked a similar question here: How can a capacitive touch screen be triggered without human contact? However, I didn't quite understand the ...
7
votes
1answer
17k 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 ...
7
votes
1answer
370 views

Inductive vs. capacitive PCB layout

I've noticed that some high-speed switching PCB's (i.e. microwave) use a layout, where each net is maximized and the 'traces' are the non-copper. Is this to decrease capacitive reactance in the ...
6
votes
3answers
15k 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 (...
6
votes
7answers
5k views

Is a very large capacitor the same as a short circuit?

This is a theoretical question. Let's say that we have two black boxes, each with two terminals. One contain an infinity (or arbitrarily) large capacitor in series with a 1 ohm resistor and the other ...
6
votes
7answers
17k views

how a phase delay occurs in capacitors/inductors with visual images

Capacitors provide a phase delay between the current and voltage. Current leads the voltage by 90 degree. I was taught these only with the equations. But I want visual intuition, what happens in the ...
6
votes
4answers
29k views

Are too high capacitance capacitors “bad” for the circuit?

I am trying to learn basic circuitry and I've been looking into capacitors and their uses in different areas. When looking at capacitance several different sources say that circuits might ...

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