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Designing effective usage time from 12v car battery

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#1 kuankuan



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Posted 21 December 2017 - 03:00 AM

Why so few members in here, is it a technique place for camera? Why I feel nervous? :ph34r: I hope that I can't post an error where is not a suit place. I want to need a little power design help:

Background for question: I have a project I'm working on where I have measured that I will use approximately 14.4Ah over 24 hours. This is quite the load for a small timelapse setup where I need the camera clicking for 5 months. I need 24 hour power because once the camera turns off, it needs a human to press the power on button. I will have access to the site, but it won't be everyday access - most likely on the weekends.
 I'm looking at needing to go with a deep cycle marine battery and a 25w solar panel to keep this system powered on and the battery charged.

As an example, if I have a 40Ah 12v car battery, and I know my draw is 14.4Ah a day, then this battery can give me 2 days of usage?

However my project requires only 5v, and my 14.4Ah is calculated from 5v.

This is where my math breaks up, but if I convert the car battery 12v to 5v output, and draw 14.4Ah a day from it, does this mean I'll get approximately 4 days of usage?

Ultimately I'd like to hook a 25w solar panel to the battery to try and keep it charged, too.

Edit: adding a little info about my project. It may help with the design.

I'm an electronics rookie, I know enough to get me in trouble, but not enough to help fix it :)

I'm looking to setup a long-term timelapse camera. The enclosure will consist of 1 camera and 1 mobile broadband device. I'd like to use solar power to try and keep the unit operational.

Some brief details on my setup: The camera is a Canon ELPH 130 point and shoot which has firmware on it to take 1 photo every 10 minutes, between 6am and 6pm. When a photo is taken, it'll save it to an Eye-Fi SD Card. When the Eye-Fi receives a new photo, it'll connect to the MiFi and automatically upload it to the internet.

I've connected my Multimeter in-line with these devices to gauge their amp usage.

Here's my findings:

  • Camera: average current of 0.25a over 2 hours.
  • Mobile Broadband: average current of 0.35a over 2 hours.

Both devices showed various spikes - mainly when a photo was taken and uploaded. Then the current seemed to "settle down" back into the averages above.

The downside: I need these devices up 24 hours a day because if they lose power it requires human intervention to push a button to power them back on.

So here's my math:

  • Camera: 250mA x 24 hours a day = 6000mAh
  • Mobile Broadband: 350mA x 24 hours a day = 8400mAh
  • Totaling: 14400mAh battery required to keep this thing going for 24 hours.

One thought on the camera and current usage: The camera does not have a sleep function, so it's powered on all the time. It does have a power-reducing mode (LCD off), but that's about it. Perhaps I can connect some jumper wires to the power button to be able to control on/off without a human needing to press it?

Thanks all advice!

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