Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

super capacitor

raman00084

Full Member level 6
Joined
Nov 29, 2010
Messages
350
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,298
Activity points
3,930
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

Advanced Member level 5
Joined
Sep 22, 2008
Messages
7,677
Helped
568
Reputation
1,139
Reaction score
543
Trophy points
1,393
Location
cambridge
Activity points
76,860
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

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
13,890
Helped
2,757
Reputation
5,512
Reaction score
2,665
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
103,639
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.
 

    raman00084

    points: 2
    Helpful Answer Positive Rating

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
18,943
Helped
4,215
Reputation
8,433
Reaction score
4,160
Trophy points
113
Activity points
124,543
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

Advanced Member level 5
Joined
Mar 4, 2008
Messages
7,140
Helped
2,091
Reputation
4,186
Reaction score
1,938
Trophy points
1,393
Location
USA
Activity points
57,287
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?
 

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top