Questions tagged [capacitance]

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

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3 answers
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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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22 votes
4 answers
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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 ...
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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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3 votes
1 answer
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Large photodiode capacitance

I'm working with an avalanche photodiode with a 320 pF capacitance. What exactly are the downsides of suc a photodiode with large capacitance values? I assume they would be slower due to the narrower ...
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1 vote
1 answer
3k views

Miller's Theorem - Input Capacitance

Please see attached image. I've become confused if the answer to this question, which uses Miller's Theorem is correct as it should not be a minus, rather it should be a plus. Please see my working ...
Arsenal123's user avatar
2 votes
1 answer
5k views

LTSpice capacitance dependend on voltage source

I am looking for a way to change the value of a capacitance dependent on the voltage source of the circuit. How do I create a voltage dependent capacitor in LT spice? Edit: Two capacitances in a row ...
soderhans'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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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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1 vote
1 answer
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Capacitor Voltage Rating

How to find the voltage rating of a capacitor after knowing the capacitance value. Example, For a power supply, If the input voltage is 60V and output is 5V. The input capacitor(C1) value is 100uf ...
Heknath's user avatar
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105 votes
13 answers
27k 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 ...
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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7 votes
3 answers
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Reading very low capacitances with Arduino

I'm trying to measure the capacitance of a very low capacitance sensor (two parallel plates across a block of foam). This is a self-produced force sensor; I'm trying to eventually use some of the work ...
David Pfeffer's user avatar
7 votes
3 answers
4k 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 ...
zakgottlieb's user avatar
5 votes
2 answers
10k views

How to measure capacitance without LC meter?

I would like to use capacitors salvaged from old electronics, but I currently don't have an LC meter. What would be some really simple circuits, that would convert capacitance to something I can ...
nana's user avatar
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2 votes
3 answers
669 views

Flashing LED circuits

How does the current flow through this circuit and thus how do the components work together to cause the flashing LED? I know the basics in that the current first charges the capacitor which ...
Lisa Ban 's user avatar
2 votes
2 answers
7k views

3 phase motor running on single phase using steinmetz delta connection

How do 3 phase motors manage to run on single phase power using the Steinmetz delta connection with a single capacitor? I thought capacitors only shift the phase angle upto 90 degrees, whereas 120 ...
Amit Hasan Arpon's user avatar
0 votes
2 answers
3k views

What will increase output volume (dB) on a Piezo Transducer?

I need to achieve 110dB at 25khz from a Piezo Transducer. According to the datasheet, the resonant frequency of the Piezo is 25khz and at 10 vrms it will produce 110dB. I will be using an ...
Curtis's user avatar
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0 votes
1 answer
464 views

Capacitors and capacitance

this time I'd like to ask a few questions about capacitors, all noob questions again; What's a better idea, having one capacitor at 5x farads or five capacitors at x farads each? I want to get a ...
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38 votes
4 answers
19k 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 ...
sharptooth'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
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
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 ...
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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 ...
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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 ...
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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
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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
5 votes
4 answers
11k views

Balancing resistor values for series capacitors

I just wanted to confirm my rough calculations are correct in selecting balancing resistors for two capacitors in series. Here are the specifications: two 10,000uF capacitors with 500V rating in ...
Cobi Yu's user avatar
  • 51
5 votes
5 answers
18k views

How to Derive Capacitive- and Inductive Reactance Formula

I've been searching around the internet to find out how to derive the reactance formula for capacitors and inductors. But I couldn't really find anything, so I thought why not make a post about it. ...
MrMongoloid's user avatar
5 votes
2 answers
1k views

How do I choose the correct capacitors to use with my Crystal?

I am looking at using this crystal for a new circuit design. It will provide the main oscillator for my PIC application. Here is the part on digikey. The datasheet indicates that it has a load ...
PICyourBrain's user avatar
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4 votes
2 answers
3k views

Capacitive moisture sensor not quite working

I have spent the past few days trying to reverse engineer a capacitive moisture sensor I ordered from eBay a while ago. The particular one I received looks like this: What fascinated me about this ...
Alexander Richter's user avatar
4 votes
2 answers
7k views

Why does a DRAM cell necessarily contain a capacitor?

From some other dynamic logic structures I know that the parasitic capacitances at the nodes(gate to drain/source, drain/source to bulk capacitors) can be used to keep charge on them. Why is there an ...
packt's user avatar
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3 votes
1 answer
1k views

Wrong load capacitance for 20 MHz, 20 pf crystal

I am new to microcontroller development, and I wanted to try running the MSP430f5529 off of an external crystal of 20 MHz that requires 20 pF of capacitance. I read on the datasheet that the pins can ...
Ashwin Gupta's user avatar
3 votes
1 answer
2k views

Calculate capacitance value and voltage rating in the event of ESD pulses

I have a input power filter circuit. It has ESD protection capacitors which help to protect the downstream circuit from ESD pulses. ESD Capacitors Specifications : C0001, C0002, C0003, C0004 = 47nF, ...
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3 votes
1 answer
8k views

How to take Time Measurements using LT Spice

I've been fooling around with LT spice .MEAS feature for a while now and I just can't seem to determine how to take the time measurements I need for an assignment. I can look at the time values on ...
Cody Richards's user avatar
2 votes
2 answers
3k views

Using an Arduino to measure wire capacitance

I wanted to use an Arduino as a capacitance measurement device for a coaxial wire. I started at measuring the wire capacitance using digital multi-meter UT58B. I turned the knob to 2 nF and then ...
disoderly's user avatar
1 vote
1 answer
730 views

How do I deal with different XTAL pin capacitance when selecting XTAL and load capacitors

I'm trying to select a 32kHz crystal and appropriate load capacitors for Atmega48A MCU. Atmega48A specifies different capacitances for Xtal1 and Xtal2 pins: 18pF for Xtal1 8pF for Xtal2 The ...
miceuz's user avatar
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1 vote
1 answer
4k views

Have I damaged my multimeter by applying voltage in resistance mode?

I have an VC97 digital multimeter. In resistance mode, I applied the multimeter leads to a battery with a 4.2V charge. I did this twice, and also did so in capacitance mode. I didn't notice any ...
Kat C.'s user avatar
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1 vote
2 answers
3k views

Electrolytic Capacitor Voltage Rating vs capacitance

I have always believed that it was ok to replace a capacitor with a slightly higher voltage rated one. eg 16v with 25v.Going higher than this would risk the capacitance value being out at the working ...
BenG's user avatar
  • 594
0 votes
1 answer
375 views

Temperature Coefficient of Capacitance

How can I find the Temperature Coefficient of Capacitance of the following capacitor series: http://www.cde.com/resources/catalogs/TAS.pdf
Dimitar K. Nikolov's user avatar
0 votes
2 answers
3k views

Resistors and capacitors calculation for 555 timer circuit

I am new to electronics and I want to try an experiment. I want to use a 555 timer to create an automatic food dispenser for my aquarium (something like opening a small door when the timer has ...
Rakesh's user avatar
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0 votes
1 answer
137 views

Should I add Capacitance on Switched High Side

Following from this question, which remains open... if I've got a microcontroller switching the high-side power to a sub-system, using a circuit like this: ... should I add bulk and/or decoupling ...
vicatcu's user avatar
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-3 votes
1 answer
233 views

At what capacitance and voltage are capacitors harmful? [closed]

I'm currently building a taser from scratch and would like to know which capacitor to use.
user72685's user avatar
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
  • 309
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
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
  • 7,102
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
  • 931
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
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