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
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.
It does not apply to batteries because they are governed by different
differential equations. Their recharge can be approximated as as highly
non-linear capacitors, and because of this non-linearity can be shown
that they can be much more efficient than straight capacitors (mostly
because they maintain almost constant voltage).
Regards,
Evgenij
Even
> in very stressing conditions, such as advanced dielectric capacitors
> under high discharge rates (pulsed power systems, for example) you can
> get well over 90% of the energy back out of a capacitor. If you're
> losing energy in a capacitor, then the capacitor was poorly selected for
> the application- such as using an electrolytic cap at radio frequencies
> or higher.
>
> Batteries are indeed a different story, though. I agree that current
> hybrids are probably achieving well below 50%.
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