my question is about big capacitor and it's parasitic inductance.

xljin2006 · Apr 4, 2023

we know big capacitor has two big plates of two electrodes. it's said capacitor has parasitic inductance because the plates are curled tight. my question is: how this can make parasitic inductance?how the electrons flow on the plate while the capacitor is changing or discharging?and the next question is more important: why the parasitic inductance is seriesly connected to the capacitor?

xljin2006 · Apr 7, 2023

danadak said:
A discussion of L in parallel plates :

https://apps.dtic.mil/sti/pdfs/ADA448001.pdf

Regards, Dana.

Tony Stewart said:
When the plates of a capacitor are curled tightly, it creates a coil-like structure that can introduce parasitic inductance into the capacitor. This is because any current flowing through the capacitor must also flow through the coiled structure of the plates, which causes a magnetic field to be generated around the plates. This magnetic field, in turn, induces a voltage across the plates that opposes the flow of current, just like in an inductor.

The inductance introduced by the coiled structure of...

danadak · Apr 4, 2023

A discussion of L in parallel plates :

https://apps.dtic.mil/sti/pdfs/ADA448001.pdf

Regards, Dana.

Tony Stewart · Apr 4, 2023

danadak has posted an interesting article on the diffusion of armour-piercing weapons that travel at such high kinetic energy they easily penetrate. Using low inductance capacitor discharge of insulated transformer-like laminations with low inductance allows rapid fusion discharge to spread the energy and enhance the armour protection.

That example might over-reach the simplicity of your question.

The inductance of a square conductor is constant regardless of the size or area.

The equations for L depends on a logarithm ratio ln(l:w) and other geometry of the conductor ( flat, round, cube) wire, cables, plates and PCB traces. Try free software for Windows. namely, PCB Toolkit V8.23 to compute L with different l:w ratios or any other online L calculator.

Tony Stewart · Apr 4, 2023

When the plates of a capacitor are curled tightly, it creates a coil-like structure that can introduce parasitic inductance into the capacitor. This is because any current flowing through the capacitor must also flow through the coiled structure of the plates, which causes a magnetic field to be generated around the plates. This magnetic field, in turn, induces a voltage across the plates that opposes the flow of current, just like in an inductor.

The inductance introduced by the coiled structure of the capacitor plates is called parasitic inductance because it is not intentionally designed into the capacitor, but rather is an unwanted effect that arises due to the physical construction of the capacitor. Parasitic inductance can be problematic in some circuits, particularly in high-frequency applications, because it can limit the capacitor's ability to respond quickly to changes in voltage or current.

To reduce the parasitic inductance of a capacitor, manufacturers may use various techniques, such as using plates with a larger surface area or spacing the plates farther apart. Additionally, specialized capacitor designs, such as the multilayer ceramic capacitor (MLCC), can also be used to minimize parasitic inductance and improve the high-frequency performance of the capacitor.

Tony Stewart · Apr 4, 2023

if a wire or trace has an ESL of 0.5 nH/mm you can estimate the effects on a leaded capacitor wire measuring the series LC resonant frequency.. This also depends on the capacitor construction as series or coiled layers add inductance and parallel layers divide inductance.

unclejed613 · Apr 5, 2023

one thing to keep in mind, is that you have TWO closely spaced plates, and the current in one plate is traveling in the opposite direction of the current of the other plate. therefore most of the magnetic effects of one plate are cancelled by that of the other plate. so the effective series inductance of a large electrolytic capacitor is much smaller than you would expect. there are "audiophools" that will spend upwards of $500.00 for large capacitors to couple the output of their single-ended Class A amplifiers to their speakers because the vendor calls them "low inductance capacitors", when all they really are is rebranded off-the-shelf caps.

frederic_adriane · Apr 7, 2023

xljin2006 said:
we know big capacitor has two big plates of two electrodes. it's said capacitor has parasitic inductance because the plates are curled tight. my question is: how this can make parasitic inductance?how the electrons flow on the plate while the capacitor is changing or discharging?and the next question is more important: why the parasitic inductance is seriesly connected to the capacitor?

Parasitic inductance is an unwanted inductance effect that is unavoidably present in all real electronic devices.

xljin2006 · Apr 7, 2023

danadak said:
A discussion of L in parallel plates :

https://apps.dtic.mil/sti/pdfs/ADA448001.pdf

Regards, Dana.

Tony Stewart said:
When the plates of a capacitor are curled tightly, it creates a coil-like structure that can introduce parasitic inductance into the capacitor. This is because any current flowing through the capacitor must also flow through the coiled structure of the plates, which causes a magnetic field to be generated around the plates. This magnetic field, in turn, induces a voltage across the plates that opposes the flow of current, just like in an inductor.

The inductance introduced by the coiled structure of the capacitor plates is called parasitic inductance because it is not intentionally designed into the capacitor, but rather is an unwanted effect that arises due to the physical construction of the capacitor. Parasitic inductance can be problematic in some circuits, particularly in high-frequency applications, because it can limit the capacitor's ability to respond quickly to changes in voltage or current.

To reduce the parasitic inductance of a capacitor, manufacturers may use various techniques, such as using plates with a larger surface area or spacing the plates farther apart. Additionally, specialized capacitor designs, such as the multilayer ceramic capacitor (MLCC), can also be used to minimize parasitic inductance and improve the high-frequency performance of the capacitor.

thank you so much!

xljin2006 · Apr 8, 2023

Tony Stewart said:
When the plates of a capacitor are curled tightly, it creates a coil-like structure that can introduce parasitic inductance into the capacitor. This is because any current flowing through the capacitor must also flow through the coiled structure of the plates, which causes a magnetic field to be generated around the plates. This magnetic field, in turn, induces a voltage across the plates that opposes the flow of current, just like in an inductor.

I still can't imagine why the capacitor and the parasitic inductance are considered to be seriesly connected.

Tony Stewart · Apr 8, 2023

xljin2006 said:
I still can't imagine why the capacitor and the parasitic inductance are considered to be seriesly connected.

---||---- if the ESL was in parallel, that would short-circuit the Cap at DC, so it is always in series with "conductors" while Caps are "insulators" and ESR occurs at those two "interfaces".

xljin2006 · Apr 8, 2023

Tony Stewart said:
---||---- if the ESL was in parallel, that would short-circuit the Cap at DC, so it is always in series with "conductors" while Caps are "insulators" and ESR occurs at those two "interfaces".

sorry do you mean the ESL is conductor and Caps are insulators?

xljin2006 · Apr 8, 2023

Tony Stewart said:
---||---- if the ESL was in parallel, that would short-circuit the Cap at DC, so it is always in series with "conductors" while Caps are "insulators" and ESR occurs at those two "interfaces".

that's a good explaination,but it's better to explain straight to the curled plates and the current of ESL and the capacitor. thx.

Tony Stewart · Apr 9, 2023

xljin2006 said:
that's a good explanation,but it's better to explain straight to the curled plates and the current of ESL and the capacitor. thx.

The difference in path length where return fluxes do not cancel out from close proximity creates the ESL inductance. Mainly it is just the electrodes or wires or traces and not inside the cylindrical or MLCC layer.

xljin2006 · Apr 19, 2023

what do you mean how creates the ESL inductance? sorry English is not my mother language.

xljin2006 · Apr 19, 2023

Tony Stewart said:
Mainly it is just the electrodes or wires or traces and not inside the cylindrical or MLCC layer.

the inductance is not inside of the curled plates?

Tony Stewart · Apr 19, 2023

- all conductors have resistance and inductance per unit length often called Effective Series Resistance in insulators or DC resistance in conductors and Effective Series Inductance(L) which depends on length/diameter ratio.

When conductors are paired close together e.g. twisted pairs or parallel plates flat or curved, the forward and return inductance tends to cancel most of the flux with opposite fields.

rjenkinsgb · Apr 19, 2023

xljin2006 said:
the inductance is not inside of the curled plates?

The rolled plates are often offset so each reaches one end of the roll, and the whole thing is joined together at the end.

Otherwise, the resistance of the film making up the roll would be in series with much of the capacitance.

Or, the connecting electrodes are set half way along the total film length, to minimise the residual film resistance.

Either way, the inductance is also largely cancelled out as current either does not flow "around" the roll, or flows in both directions.

xljin2006 · Apr 19, 2023

I'm in a mess.

xljin2006 · Apr 20, 2023

rjenkinsgb said:
The rolled plates are often offset so each reaches one end of the roll, and the whole thing is joined together at the end.

Otherwise, the resistance of the film making up the roll would be in series with much of the capacitance.

Or, the connecting electrodes are set half way along the total film length, to minimise the residual film resistance.

Either way, the inductance is also largely cancelled out as current either does not flow "around" the roll, or flows in both directions.

what puzzled me is that capacitor charging current is the same to inductance current, so why they are series and not parallel?

rjenkinsgb · Apr 20, 2023

xljin2006 said:
what puzzled me is that capacitor charging current is the same to inductance current, so why they are series and not parallel?

Because the ARE in series!

Current is the same at all points in a series circuit.

With a parallel configuration, each parallel part can have different currents.
(Plus, an inductor has a permanent current path; the capacitor woudl be shorted out).

my question is about big capacitor and it's parasitic inductance.

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