Re: Best capacitor for back-up applications

Eeyore wrote:



Chris Jones wrote:

Eeyore wrote:
AJ wrote:
"Eeyore" wrote
AJ wrote:

I was just wondering what the best type of capacitor I should use
for a
back-up application (> 5uA). I am looking for something surface
mount around the 100-330uF range with a low profile and as cheap as
possible. Any
suggestions?

A coin cell ?


I would rather use a cap as I only need an hour or so of back-up time.

Well..... 330uF won't do it.

dV/dt = I/C = 5uA/330uF = 15mV/sec

In even 100 seconds, the voltage on the cap will have dropped by 1.5V.
So to get a reasonable voltage drop after an hour, you're probably
looking at ~ 33000uF. In other words nothing small.

Use a coin cell.

Or one of those super-capacitors that they put in VCRs for running the
clock
during power cuts. You can get them in values between 0.1 Farad and a
couple of Farads. They are usually cylindrical about 20mm or 3/4 inch
diameter and about 12mm high (half inch).

http://www.pollin.de/shop/shop.php?cf=detail.php&pg=OA==&a=NTc0OTg3OTk=&w=Nzk3OTk4&ts=0

That's hardly small is it ?

They're expensive too. A coin cell can be had for ~ 30c.

Graham

Well if you don't need a whole Farad, then it would be smaller. Whether it
is worthwhile probably depends on whether the power drain is such that
being rechargeable would be an advantage.

Chris



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Relevant Pages

  • Re: Best capacitor for back-up applications
    ... to get a reasonable voltage drop after an hour, ... Use a coin cell. ... You can get them in values between 0.1 Farad and a ... They are usually cylindrical about 20mm or 3/4 inch ...
    (sci.electronics.basics)
  • Re: Best capacitor for back-up applications
    ... I would rather use a cap as I only need an hour or so of back-up time. ... to get a reasonable voltage drop after an hour, ... You can get them in values between 0.1 Farad and a ... They are usually cylindrical about 20mm or 3/4 inch ...
    (sci.electronics.basics)
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