Need assistance selecting a battery 1

[bbaca]

Hi,

I need a battery that can provide 11.3W at 12VDC for less than a second, and it only needs to be used once. It will be used on a sattelite, so it needs to be able to survive the trip. Also size and mass area a huge factor, we are working on only a 4"x8" board and it is nearly full.

Any suggestions? I was thinking watch battery, but I doubt I can get the power I need from it.

 

[BJC]

Whats it for?
Sounds like a detenator to me.

 

[gse1]

Could you supply a little more information, what will the 11.3W at 12V trigger?, what is the birds power bus system rated for?, what are the specs., and standards you are required to meet?, what power system did the project systems engineer, approve for your assembly.

 

[alehman]

How about a capacitor?
Theoretically speaking,
E = 0.5CV^2
C = (2 * 11.3W * 1s / 12V^2 ) = 0.16F

 

[IRstuff]

A typical watch battery such as a CR2025 has a short circuit current of only about 350mA. Likewise, a 357A. The only way out would be to use the battery with a boost regulator to charge a capacitor and rapidly discharge the capacitor.

Aleham's value needs to be increased by about a factor of 3 for a 2V droop. However, you'd need a capacitor with very low ESR, otherwise, you'll need a higher voltage to accommodate the series resistance. A single AAA has a short circuit current in excess of 1 A, so a charging circuit built around a AAA cell would charge up in a relatively short time, but you'll need a minimum of 15x boost.



TTFN

 

[jghrist]

How about a super capacitor in conjunction with a battery? See

http://www.spectrum.ieee.org/WEBONLY/publicfeature/jan05/0105wcap.html

 

[bbaca]

The power is needed to open a sealed door once the satellite is in orbit. It will piggyback with another satellite (hence its small size), and we will draw power from the mother satellite. We can use no more than 1A at 12VDC, and our computers need more than .7W so we are looking for an alternate method of providing the power.

Thanks for the ultracapacitor idea, we thought capacitor but I guess whoever looked into it, didn't find anything.

 

[Laplacian]

One additional parameter that needs to be considered regarding use of batteries for this application is temperature. Batteries struggle to deliver rated current barely below freezing.

Is this for an explosive fastener?

 

[bbaca]

I have been told it is a frangibolt (sp?). Basically it heats a special bolt until it snaps off.

The super capacitor looks really promising. Does anybody know if they are space rated? And how can I tell if they are capable of putting out the current I need?

Also, an update, I was informed at todays meeting the requirements are now known exactly. They are 1A at 28VDC for 15 seconds. (By my calculations I'll need just over a farad).

 

[IRstuff]

Whoa... You're allowing the voltage to droop down to 12 V with a couple of volts for IR drop? That's not what you stated last. This would also be inconsistent with the frangibolt spec I found:

http://www.tiniaerospace.com/fbfc2-16-31sr2.html

Based on that, you'd need to maintain 28V continuously for the time required.



TTFN

 

[IRstuff]

Oh, btw... supercapacitors seem to be typically like:

http://www.coiltronics.com/products_supercapacitors.asp

http://www.avxcorp.com/docs/catalogs/bestcap.pdf

The higher voltage ones are significantly lower capacitance:

http://www.evanscap.com/THQA2-FSpec.PDF

Although, there's this one:

http://www.tavrima.com/pub01a.html,

oops, it weighs 35 kg!!

TTFN