If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #54278
Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367
I have tried to charge one capacitor from another in various ways, mainly a crude switch or resistor. I have never seen even 50% energy efficiency in the transfer. Is there some kind of Joule efficiency limit in this type of charge transfer? Does anyone know of a way to get >50% direct transfer of energy between even two 'identical' caps?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Yes, but it's all about conservation of charge.
As a simple example, let C1 and C2 be identical 1 F capacitors sharing a ground terminal. Initial voltage are 1 and 0 volts. Charges (Q=CV) are 1 and 0 coulomb. Energies (E=CV*2/2) are 1/2 and 0 joule; total energy 1/2 joule.
As charge moves from C1 to C2, there's a point where each capacitor has 1/2 of the charge, at 1/2 volt. Energies are 1/8 joule per capacitor, 1/4 joule total. It's the minimum energy static state; we could leave the capacitors connected together.
If charge continues to move in the same direction, eventually all of it is on C2 and none on C1. We are back to the initial 1/2 joule of energy, all on C2. But it takes work to move charge from a lower to higher voltage.
We can move most (ideally, 100%) of the initial energy from C1 to C2 by making the connection through an inductor. Close the switch for just 1/2 cycle of the RLC (ideally, LC) resonant frequency. At mid-transfer, when the voltages are equal, the "missing" energy is stored in the inductor. How long would the whole transfer take with an ideal 1 henry inductor?
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
You have found the "Capacitor Paradoxon" (just google it) Half the energy is wasted inevitably in the ESR. (if there was no ESR the current would be infinite. thats impossible too, so dont even start a theoretical case without ESR) The way to go is to make the resistance imaginary as klugesmith stated by using an inductor (and i would like to add a diode to prevent oscillation).
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Signification wrote ...
I have tried to charge one capacitor from another in various ways, mainly a crude switch or resistor. I have never seen even 50% energy efficiency in the transfer. Is there some kind of Joule efficiency limit in this type of charge transfer? Does anyone know of a way to get >50% direct transfer of energy between even two 'identical' caps?
Yes, you can get very high efficiency.
In fact there's a name for this device, and there's probably several in your house right now: switch mode power supply
If you think about it, in a switch mode power supply after the rectifier there's a capacitor on the input and there a capacitor on the output, and the charge goes from one... to the other.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
DerAlbi wrote ...
You have found the "Capacitor Paradoxon" (just google it) Half the energy is wasted inevitably in the ESR. (if there was no ESR the current would be infinite. thats impossible too, so dont even start a theoretical case without ESR) The way to go is to make the resistance imaginary as klugesmith stated by using an inductor (and i would like to add a diode to prevent oscillation).
I can do a theoretical simulation with no series resistance and no problem at all. The current never gets infinite. I just add an inductor to the system.
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Bored Chemist: what simulation?? Does the current not go to infinite without the inductor? Or do you add the inductor to make the simulation run?? Very confusing statement. Are you just troling? I mean.. we all know that simlation programs have mechanism in place to resolve such situations. (like default ESR in LTSpice or a finite minimal time step)
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727
Ahahahaaa BigBad i hit a nerve. Dont bother, i was just trolling.. No need to defend yourself. It was a good example, no worries.. but this obvious flaw.. excuse me, i couldnt hold back
What would be really mean at this point would be mentioning that charge pumps can have a near 100%-efficiency with resistive switches only. Now your minds boggle!
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
CAPACITOR-TO-CAPACITOR CHARGING EFFICIENCY LIMITS
In an insulated power supply the charge does not really "go" from one to the other due to the lack of a path 
I mean.. we all know that simlation programs have mechanism in place to resolve such situations. (like default ESR in LTSpice or a finite minimal time step)
