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# What is the current output of a capacitor? Answered

I want to make a circuit where a light is powered by a capacitor until it is discharged, and then powered by a battery until the capacitor is full again.

How long is it possible to power a light on a capacitor?

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## Discussions

Thats the highest there is at my local electronics store.

Sorry that is way too small.
For a long LED light time Use something like 2.2 Farad.

A

Look at the energy balance

E = CV^2/2

Energy used by an LED = IVt

Where I= LED current, V = LED volts/ capacitor volts and t=time

IVt=CV^2/2

t=CV/I

Its not accurate, because the real answer needs calculus, but its a start

Why ? I loved it when I learned it. If you're struggling, find Silvanus Thompson's book

thns. it is just that i did not have a good teacher.

You should to stay away from girl horses at night :-Þ

A

Sanity check: Why not power the light directly from the battery?

Batteries do not recharge forever :(
Ultra Caps will still be recharging when our descendents
have long forgotten us :-Þ

What capacitor?
Short answer: not long enough for you - use a rechargeable battery instead.

L

A friend I have makes a police flash light that charges an ultra capacitor
array to 63 VDC in less then 90 sec and provides full light output
for over 45 min.

A