super capacitor

[raman00084]

I am having a 24v smps with 3 amps current rating. If power is off i need a backup time of 5 sec with 1 amps current rating.
what capacitor can i add any circuit available kindly help.

 

[treez]

its i = C.dv/dt

If you want to keep voltage at 24V whilst 1A is delivered, then you may need an extra SMPS to do this for you aswell.

 

[BradtheRad]

For a crude estimate, use the RC time constant. Your load calculates as 24 ohms (24V divided by 1A). Suppose you choose 1 Farad for your backup capacitor. Then your RC time constant is 24 seconds. Voltage drops 63 percent in that time by definition.

Therefore in 5 seconds it drops about 13 percent. If your circuit continues to operate then a 1F capacitor is satisfactory. Or else 2F lets voltage drop 6 percent in 5 seconds. Etc.

 

[KlausST]

Hi,

Or calculate the energy.

Generally a capacitor will immediately drop voltage .... the drop rate V/t is proportional to current.
Thus it's impossible for a capacitor to keep voltage constant (24V) when you draw current.

Currently we see just "24V", no valid range in voltage or %.
You urgently need to decide this to find a suitable solution.

Klaus

 

[dick_freebird]

It might be that you'd be better off with a battery
(capable of >1A discharge). Supercapacitors are
not especially cheap, but simple. Many modern
batteries are not overcharge-tolerant and so
would need charge control and a capable
switch (could be just diodes, if you're lucky).

If you architected your supply around the need
for hold-up, could be easier - line to battery is
one section, pretty common charger design with
enough upside current to handle the
through-load-current when line is up, and then
battery to output as a regular ol' buck?