12V power for remote video

[tfinch]

Hi,

I am an Ecologist (with little engineering / electrical experience). I am using a mini CCTV camera with a digitial video recorder to remotely monitor bird nestboxes. The DVR has a motion activated mode, and records everything to an SD card. The whole lot is wired up to a 12v battery.

I have done a couple of back-of the envelope calculations to a) estimate how long the battery should last and b) work out whether it would be feasible to install a small solar panel to keep the system running.

This is a bit out of my comfort zone, so forgive me. The 12V 24Ah battery should provide 288Wh of power? The manufacturers suggest that the CCTV camera and DVR consume 110mA and 150mA respectively, which sums to 260mA or 3.12W (at 12V). So, 288Wh divided by 3.12W means that the battery should last for 92 hours?

The DVR also has a sleep function, to switch off over night (when the birds aren't active). So assuming the setup is only running during daylight hours (I'm in the south of France, so the sun is usually shining), a 5W solar panel should be able to keep the battery topped-up (assuming I'm correct that the setup uses just 3.12W)

In reality the battery runs out after 4-8 hours, so my calculation has clearly gone wrong somewhere.

Thanks in advance for any assistance

 

[IRstuff]

> How do you know the battery was fully charged?

> Your assumption about the solar aspect is only partially correct. The amount of solar power varies as a function of the time of day, so you cannot expect 5W from a 5W panel during the entirety of the day. Additionally, the output power of the panel cannot be completely applied to the battery charging, due to inefficiencies in the system. I'd guess a panel that outputs 50W to 100W would be what's needed.

TTFN
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[tfinch]

Thanks for your reply,

I'm assuming that the battery is full charged, because the light on the charger goes from red (empty) to amber, then green. Although I suppose the assumption that the batteries will always be operating at 288Wh is not necessarily valid.

Interestingly, when I use a different DVR & camera (same model etc.) the same batteries last over 24h, so I think there may be a fault with the device which is causing it to draw more current than normal.

Thanks also for your advice regarding solar wattage

Tom