Possible power problems

[Fraz]

Was looking at the Nikon P5000 page Pete posted and it says something
along the lines of "can take about 250 photo's on a single charge of
Nikon EN-EL5" that battery is a 11mAh battery, which boils down to
about 4.4 mAh per shot. Multiply that by the about 3000 photo's the
memory will allow us to take and you get 13200mAh or 13.2 Ah. That is
per camera, multiply by 3 to get 39.6 Ah. That right there is a scary
number considering the current D-cell batteries are rated at 7.75 Ah.

On the brighter side I was looking at Saft's website (the company that
make those batteries) and found this

http://lpsu-.googlegroups.com/web/LS_33600_LM.pdf

HUGE amp-hour increase just the recommended continuous current is
pretty low and would most likely limit the rate we could take pictures
(no idea what the current draw of each camera will be, but Im guessing
a capacitor will be a good idea). Here is the good news. The Nikon
battery looks to be a 3.7v pack, each of these cells is 3.6v so we
could power the cameras with a single cell. Each cell can supply
250mAh continuous power, and 17 Ah total power. need a total of about
3 cells to power the cameras, just the cameras, to get full use of
memory on board. Total cells to power that total weight comes in at
9.6 oz for the camera power and a max current draw of about 0.75A
question is can you power 3 cameras taking pictures at a reasonable
rate with that?

Kinda wrote this as i was figuring it out, looking at it Im not sure
if its possible to get the current down low enough for that battery,
and even if it is if we would want to stay awake as long as it would
run if we did :P Hopefully Pete has a few tricks to hack the camera
and lower the power consumption to help out here (turn off the LCD Im
guessing will help a lot)

Brian

[pete....@epi.epson.com]

Hola Sir,
Check the calculation you've got at the top... unless I'm missing
something, if you divide 11 by 250, you get 0.044 not 4.4. That makes
the total draw you'd need 0.396Ah instead of 39.6. I believe that the
LCD can be turned off as a camera setting on this one (major bonus),
and we won't be using a flash or the focusing motors (another camera
setting). The calculation that they do for 250 images on a battery is
done for a certain percentage of shots with flash, and also all with
auto-focus on, so it'll probably draw a little less than 0.044mAh per
shot. You might've found a better battery either way though - it'd be
worth looking into some more.
-pete-

[Fraz]

yah, supposed to be 1100mAh or 1.1Ah. my zero key doesn't work too
good sometimes.

The battery is rated higher, but it cant supply a very good sustained
current. I think the current we will need to sustain will be too much
and will end up driving the performance of the battery right down to
where the current batteries are at, or lower. Worst case it just
wouldn't supply the current and components would start shutting down.

Also the current draw to achieve the 17Ah was 5mA which is a joke of
low. However at 250mA they are supposed to be rated at 8.5Ah.
Marginally higher than the current batteries with a slight weight
increase too.

Guess it all depends on what our constant power draw is.

Brian

PS
Can you edit your previous posts? I cant find an edit button anywhere.

[m...@cecs.pdx.edu]

Just a note about the costs of these batteries...i'm finding $19.00
apiece and $17.00 if i buy more than 30. ($15.00 ea for the LO26SX)
This is ok if we only need 3 per launch of something i guess, it is
also okay if we can just striaght substitue normal alkalines for
routing grade school student launches, but it sounds like a spendy
solution over time.

mark

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