constant power for dash cam using 12V 7.2Ah battery hardwired to back of lighter socket?

J

Jaranson

Guest
I know I read about something like this in this forum, but I can't seem to find it. :(

When my car had a security system installed, it came with a 12V 7.2Ah battery. It was hidden under an empty space inside the center console, right next to the gearshift. It is meant to provide back-up power to the security & vehicle anti-theft tracking system. It is isolated from the car's main battery.(i.e. only gets charged when the engine is on)

I was just thinking... these batteries are quite small and there is plenty of space behind the cigarette lighter socket to put another one it. I'll hardwire it to the wires powering the lighter socket, so it will get charged when the engine is on. Since my dash cam's USB adapter is plugged into this socket, it will get at least 12 to 24 hours
of power from the small battery. (no drain to the car's main battery, as the lighter socket gets no power when the engine is off) Edit: based on my dash cam's specs, my fuzzy math came up with 16.75 hours of running time, using this 12V 7.2Ah battery.

This way, the dash cam will essentially be recording on a 24-hour basis. Or is the a very bad idea?

I found out this exact same 12V 7.2Ah battery is also used by Verizon FiOS as back-power. Only $26 on Amazon.

https://www.amazon.com/gp/B007ZHAYL6
picture below show the size of the battery... the yellow one that the woman is pushing into the Verizon FiOS device.

41Dq%2B5-s11L._SS400_.jpg

512d8a7PjpL._SX385_.jpg
 
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The microSD card's flash memory can only be written/erased so many times before it starts to fail. You'll have to factor in the cost of replacing the microsSD card more often if you are letting it record 24/7.

Check out the DIY section for in depth power project suggestions. Some of the titles you read go much deeper than the initial question so have a good read into each post here:
http://dashcamtalk.com/forum/forums/diy-projects.31/
 
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Time for some math to help out understanding this...

The term, "8Ah" says that the battery will put out 1 amp for 8 hours before it's 100% dead. In theory that could also be 8 amps for 1 hour, but in reality batteries are NOT linear and do not work exactly like that. However to avoid making the problem too complex, let's just pretend that batteries are linear and the math works correctly.

We never want to take a battery to zero capacity because it's hard on the battery. Deep Cycle batteries can go much lower than regular batteries, but neither can go to zero. For the sake of understanding, assume that the battery can safely go to 50% capacity. Thus 8Ah would be taken to 4Ah. We'll also assume that the drain or rate of current consumption is 300mA (0.3A).

Capacity / Rate = Time

4Ah / 0.3A - 13.33 Hours

As you can see, the capacity is not enough for even overnight.

Time x Rate = Capacity

48 hours (2 days) x 0.3A = 14.4Ah; however because we need to double that to avoid going to zero, 28.8Ah and I hope this is a deep cycle battery.
 
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