37
votes
Capacitors with a "/" on schematic
It almost always denotes capacitance / voltage rating.
Capacitance in µF, voltage in VDC.
For example:
100/6.3 would be 100 µF, 6.3 VDC
22/10 would be 22 µF, 10 VDC
- 175k
32
votes
Why did the capacitor blow up?
Your 100uF 400V capacitors were undoubtedly low cost aluminum electrolytic capacitors rated only for use on a DC circuit. When you connect such capacitor to the AC mains you are alternately subjecting ...
- 57.5k
26
votes
Health risks of exposed contact to a capacitive sensor
Yes, there may be a risk for long term wear. If your electrodes have an ohmic contact with the patient, and they have a DC bias, and they are made of a reactive metal like copper, then you may be ...
- 38.3k
23
votes
Accepted
Crystal oscillator load capacitance, again
Is there a one true answer to the question? It all seems very
frustrating to me. Why doesn't an oscillator start?
A crystal oscillator will fail to start when the crystal and the capacitors ...
- 465k
23
votes
Accepted
Do batteries have capacitance?
The situation, particularly with lead acid batteries, is a little complicated. As the battery is charging the chemical reactions take time to penetrate through the depths of the plates.
This results ...
- 10.1k
20
votes
Accepted
How does capacitance depend on AC voltage?
This effect in Class 2 ferroelectric MLCC capacitors is due to hysteresis in polarization, as illustrated in this paper.
At low AC voltage the hysteresis causes an effective loss in capacitance.
This ...
- 407k
19
votes
Capacitor Bank Rating
Capacitor banks designed for power factor correction are rated in kVAr (kilo-volt-ampere reactive) because it's convenient. One will typically know the reactive power required by some load, then it's ...
- 57.6k
18
votes
Accepted
Why must USB low-speed devices use a captive cable?
The reason is, as in your first explanation, to prevent the accidental use of a low-speed cable with a full- or high-speed device.
Yes, you're technically correct that they could simply mandate that ...
- 5,836
18
votes
If a diode has capacitance, why doesn't it block the circuit after some time?
Here's a (somewhat simplified) model of a diode:
simulate this circuit – Schematic created using CircuitLab
AC can bypass the diode because of its capacitance, but there's a catch to it.
...
- 72.5k
18
votes
Accepted
What does the capacitance labels 1NF5 and 1UF2 mean on my SMD capacitor kit?
It means 1.5nF and 2.2uF. It's because printing a decimal point is unreliable since it's small so easy to rub off and easy to miss so they use the units instead.
For example in my resistor kit if they ...
- 56.9k
16
votes
Accepted
How to select the resistance value for an Arduino capacitance meter
It is usually desirable to maximize the resistance in order to be able measure relatively small capacitance values.
The ATmega328P datasheet says:
"The ADC is optimized for analog signals with ...
- 407k
16
votes
What does negative capacitance mean?
I see negative capacitance measuring electrolytic capacitor at high
frequencies (40kHz). How should I interpret that?
Negative capacitance can be regarded as inductance so, at high-ish frequencies it ...
- 465k
15
votes
Why does the capacitance value of an MLCC (capacitor) increase after heating?
X5R capacitors are not very stable but, did you read this in the data sheet you linked: -
If you didn't apply the regime of heat treatment then measurements are invalid. Class I capacitors don't need ...
- 465k
15
votes
Accepted
Why does the capacitance value of an MLCC (capacitor) increase after heating?
The topic turns out to be quite interesting - at least for me ...
Simply put, the cause of this phenomenon is the change in the structural properties of the dielectric over time. For class II ...
15
votes
How do I measure the capacitance of a 0603 capacitor which is in the order of pF?
If it is really a few pF, then you will need special equipment. If it is 30-100 pF, you can use an RC filter and measure the cutoff frequency. Adjust the frequency until the voltage out is 70%, or the ...
- 16.5k
14
votes
Is a very large capacitor the same as a short circuit?
Yes, your analysis is correct for a infinite capacitor.
However, anything less than that can be detected in arbitrarily short time. The problem is that the size of the signal to notice the ...
- 314k
14
votes
If a diode has capacitance, why doesn't it block the circuit after some time?
It does apply. However the capacitance is not in series with the junction, it is in parallel over the junction so only the junction conducts when the capacitance is fully charged.
- 159k
14
votes
Accepted
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 ...
- 20.3k
14
votes
Accepted
Is it possible to do water detection with a single electrode?
If all you need is to detect the presence of liquid, you could use an optical method instead. Then you don't need any electrical connecton at all to the liquid or the tank.
The principle is very ...
- 55k
14
votes
Accepted
100mF Tantalum Capacitor?
They used to use mF for microFarads before \$\mu\$F became the de facto standard.
The board shown looks new enough that it should use \$\mu\$F though, so it's probably someone just doing things the ...
- 25.1k
13
votes
Why did the capacitor blow up?
If it was a polarized capacitor, remember AC will be the wrong polarity half the time, so it will go boom.
If it was a non-polarized capacitor, at 50Hz its impedance is 1/(2πfC) so about 32 ohms, ...
- 79.5k
13
votes
Accepted
Understanding capacitance in oscilloscope probe tip
The capacitance in parallel with the 9 megohm resistor is the primary factor in determining the probe capacitance presented to the circuit being probed since, by design, most of the signal voltage (90%...
- 16.1k
12
votes
How to Derive Capacitive- and Inductive Reactance Formula
The phasor approach is the easiest imo. You simply let V and I become a phasor. Then you replace all of the differential operators by algebraic expressions.
Ive done the capacitor for you
.
Note: in ...
- 1,831
12
votes
Capacitor electron flow
A capacitor is made of two metallic plates separated by insulating material.
Correct.
During the charging of the capacitor electrons flow towards the opposite direction the battery's electric ...
- 177k
12
votes
Accepted
Estimate capacitor parameters
Capacitance is given by:
This is the formula applicable for free space or vacuum. If you are using a dielectric material between the plates, you multiply the resultant capacitance with the relative ...
- 8,361
12
votes
Accepted
Why do we have to discharge the capacitor before testing it in an LCR Meter?
Both of the meters in question use some means of charging the capacitor under test by driving it with a controlled current and measuring the time it take to go between two voltages. When you charge a ...
- 177k
12
votes
What does negative capacitance mean?
If you measure reactance at a single frequency, you can't distinguish between negative capacitance and positive inductance.
Basically, the meter is converting the imaginary part of the reactance ( Im(...
- 19.4k
11
votes
Accepted
In a parallel plate capacitor, how does placing a metal in between the plates reduce the capacitance?
In the case of the valve/tube, the purpose of the screen grid is to reduce the effect of the capacitance between the grid and anode.
The screen grid is not just a floating piece of metal, it's ...
- 169k
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 ...
- 56.9k
11
votes
Why are these capacitors treated as if they are in series? Why must the incoming and outgoing current in a battery always be equal?
Unless this circuit is being operated with a voltage source with frequency in the megahertz or more, there's not much point in analysing what happens to actual charges here.
You can rely on Kirchhoff'...
- 38.9k
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