Steve wrote:
> Evgenij Barsukov wrote:
>
>> Steve wrote:
>>
>>> John Bailey wrote:
>>>
>>>> Is that a fact and reason based answer or just a guess? A battery is
>>>> not as efficient as a capacitor and there is a theorem from sophomore
>>>> EE that "proves" no more than 1/2 the energy stored in a capacitor
can
>>>> be recovered.
>>>
>>>
>>> Maybe at some EE correspondence school in outer Elbonia, but not
>>> anywhere creditable. Most capacitors are nearly 100% efficient at low
>>> frequency and moderate charge/discharge rates, I have no idea where
>>> you came up with some "proof" that no more than half can be recovered.
>>
>>
>> Sorry man, it might not be obvious, but this effect is true, easily
>> provable based on the differential equation describing capacitor
>> discharge and known to every electric engineer:
>> http://www.smpstech.com/charge.htm
>
> But we're not talking about the first-year method of charging a
> capacitor from an ideal voltage source through a resistor are we? Nor
> are we talking about discharging through a resistor to a purely
> resistive load, are we?
I would not downplay the generality of this relation****p. It has
nothing to do with complexity of the system.
It generally applies to arbitrary systems that consists of (as many
as you want, and arbitary connected) resistors and capacitors, and
arbitrary path of discharge (e.g. it does not have to be constant
current).
As long as both capacitors and resistors are linear, you can not beat
this rule.
The only way to beat it is to add inductors to the mix, or to make
capacitors non-linear (e.g. batteries).
It is im****tant to understand this conceptually to avoid some
attempts to beat the rule by making some complex systems (but without
inductors), which would be a bit like trying to beat the Karnot's
efficiency law by using alcohol instead of water in a boiler.
Regards,
Evgenij
>
>>
>> As other people have stated earlier, this applies only for straight
>> linear capacitor / resistor systems without inductance.
>>
>> Switching systems with inductance is a different story and they can
>> be 90-95% efficient.
>
> EXACTLY my point when I made the first rebuttal!! There is no "theorem"
> that states with any sort of generality that "no more than 1/2 the
> energy stored in a capacitor can be recovered." In fact you can get
> nearly 100% out as heat, should that be your goal (as it often is in
> pulsed welding systems, for example). Period. End of story.
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