electrical calcs, low volts & useage ???

[steptoe]

In my attempts to identify unauthorised intruders and vandals I am settin' up video surveillance. I plan to use a garden cam mounted in a 100 x 100 metal post powered by a few sealed lead acid batteries I scored from recycle dudes.

Would like to know how to work out power calculations to know how long a battery is gonna last.

The wireless camera uses a power pack 240V and are rated at 7.5V 300mA.

output power CE<10mW/FCC <1mW

No 240V where I want to post the cam so going the batteries.

They are BB Battery BP5-12 (12V,5AH/20HR)

Also gonna need to reduce the output of these batteries to 9V or so, instruction says the camera can run for about 3hours on a 9V transistor battery.

Wonder how a 9V compares in AH rating to the fatty above.

Gonna plan to make a charge port so need to charge externally instead of pull garden ornament apart for each recharge.

Any help in calcs and just what resistors or diodes I need to cut power down will be appreciated

[steptoe]

400 to 565 mAH is found here

http://en.wikipedia.org/wiki/Nine-volt_battery

for the typical carbon 400

to the typical alkaline battery 565 mAH,

so, does 5AH mean 5000 mAH , and 565 is 0.565AH ?


So.... ???? one 5AH battery will last about nine times that of a alkaline 9V rated at 565mAH ? 3hrs x 9 = ~27 hours, so if this is correct, does dribbling the power down to 7.5 - 9V make power last longer again or it is used in the conversion process?

3 batteries shoved down the post may last 3 days , 3 hours at most, maybe I get more or solar recharger ??

Am I on correct track in my calcs guys ?

[El_Freddo]

No idea Jonno!! I've not had the real need nor the patience to work it out!

But I reckon the solar charger would be the go in this equation - maybe get a pond pump to pose as the user of this oversized solar panel... Otherwise they (those offenders who look for things like this) would be suss as to what this panel does unless you mount it far away enough...

Cheers

Bennie

[Brumby Kid]

That all looks complicated! A battery with 50 Amp hours, will last 50 hours if it has a 1 Amp draw, or 1 hour at a 50 amp draw. Etc
Hope it helps

Cheers Cam

[Gannon]

For getting 7.5v or 9v, you need one of these. Its designed for plugging into a cigarette lighter and powering various devices. Pretty cheap from shops like Jaycar or DSE


Reducing the voltage will have little effect on reducing the power used, but with the regulator set at 7.5v, it means the 12v battery can drain down to about 9v before it has an effect on whatever you are powering.

I agree with the small solar panel idea, a 5w panel should be enough to maintain you battery with the max 300mA x 7.5v = 2.25w, but more likely be less than 200mA, so thats 1.5w. I have a feeling that a panel of that size wont need a regulator to keep the battery topped up.

[fredsub]

what you need is a step-down converter to run the camera.
easiest is just give you this link
http://www.ebay.com.au/itm/LM2596-DC-DC ... 847wt_1397

i bought from that seller a few things, will no problem.

If you want an AGM battery to last, you should plan to not discharge it more
that 20% off full charge, however you would probably get about its specified
recharge cycles if you use down to 40% of charge.

so now your down to 2A/Hr useful use.

lets estimate the cam uses [email protected]=1.5W
Voltage conversion 80% efficient (if you use the one as linked above), so 1.8W.

so at 12V, using 0.15A, close enough to 0.2A.
so 2A/1Hr
0.2A/10Hr

I really think you should go for a 10A/Hr battery, what if you miss recharging it for one day?


hope that helps.

[steptoe]

this little project is starting to dry up the budget, especially if I go solar panel recharge! Thanks for the reminder Gannon, just happen to happen similar unit not in use, has a 7.5 V option, so that'll get a job

Also , thanks for the heads up the battery is not gonna perform to the end continually - usually discover these things after MK I

[steptoe]

That all looks complicated! A battery with 5 Amp hours, will last 5 hours if it has a 1 Amp draw, or 1 hour at a 5 amp draw. Etc
Hope it helps

Cheers Cam

Aw Cam, you could have simplified that for me down to my correction

so, if I have a 1/3 of an Amp draw a 5AH battery may last 3 x 5 = 15hrs ?

more batteries, a daylight switch maybe, a solar panel and a little white LED to give the post a less suss look !

[RSR 555]

I find the BF dog works to stop them

I really dont see the need to identify them.. the cops these days do sweet FA about it anyway... they just give you a report number and tell you to claim your insurance

Just better off putting that power to better use and increase the voltage.. to lets say about 500,000 volts !!! and stick it on the handles :D:D

[steptoe]

BFD's eat smelly chum, leave BF calling cards - like the one over the back fence - absolutely loves the artificial turf

Cops ? All the little angels have great parents !

Yeah, cattle prod myself when i forget , then I'd drop me keys in the dark

The motion detection software in the DVR is great, selectable area to use as a trigger so unit will only waste record time for motion detection from 5 - 60 seconds .

[RSR 555]

Yeah, cattle prod myself when i forget , then I'd drop me keys in the dark

hahahahaha.. I could just see you doing this too :D