Re: Seeking help on decreasing voltage & current for personal project

On Mon, 19 Jan 2009 17:38:34 -0800 (PST), Steve <dafella007@xxxxxxxxx>
wrote:

Thanks Paul,
I've spent the last couple of hours making a pack using 2 D cells.

How long should a full charged pack last?
Can you explain - why 2 D cells last longer than 2 AA cells - If both
produce 1.5 volts.
I'm not following

Thanks Again
Steve

On Jan 19, 3:52 pm, "Paul Hovnanian P.E." <p...@xxxxxxxxxxxxx> wrote:
Steve wrote:

All,
Please forgive me if this is in the wrong group.

I'm trying to make an external battery source for my Digital Camera
using mostly stuff I have laying around or can pickup locally here in
Missouri.

I own a Kodak ZD710 Digital Camera - I'm wanting to use a portable
external battery I bought from CompUSA when they closed the store in
my area several years ago.
The battery is "Initial RB-270 9V/5400 mAh" (http://www.initialdvd.com/
accessories.asp)
I used the battery a couple of days while travelling other than that
it's been in a drawer.

Looks like my Camera requires 3V / 2.5 Amps
I found this by looking up a compatible AC adapter on Ebay
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=200296871471&Categ...

Question is there some component I can send the output of the battery
through to drop the voltage and current to where I need them. 3V / 2.5
Amps

I wonder how much current the camera actually draws. The 2.5A is a
maximum number, which has a safety margin and does not reflect
continuous current draw.

You could use a linear regulator. But the efficiency could be pretty
poor. 2/3 of the battery capacity will be 'consumed' by the regulator.

From an efficiency standpoint, a switched mode buck converter or supply
would be your best bet. Somewhat more complex and a little more
expensive. But efficiencies in the 90%s are possible. So the battery
will last longer.

The simplest solution would be to swap your battery pack for a couple of
rechargeable NiMH cells. Two Ds connected in series should do the
trick.  

My goal is to have a lightweight portable external battery that last
longer than the AA batteries.

Thanks
Steve

--
Paul Hovnanian     mailto:P...@xxxxxxxxxxxxx
------------------------------------------------------------------
The more corrupt the state, the more numerous the laws. " - Tacitus- Hide quoted text -

- Show quoted text -

Really quite simple, the D size cell carries 4 to 5 times the energy
of an AA cell, thus should last 4 to 5 times as long.
.

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