My brother-in-law is buying an underwater camera for use with his marine biology studies.
Here are the electrical specs for the camera.
Input voltage 12 VDC
Power Consumption: 1.4 W
Cable: 30, 50, 100m (basically a really long cable with an RCA connection)
21 LED lights
Image Sensor: Color CCD
He's trying to understand the options that he has available for the Battery Kit.
He can choose from:
- 4.5 A Battery + charger
- 7 A Battery + charger
Why would he get one over the other? Is it actually paired up with the length of cable that is connected to the camera?
Doing some quick Math:
P = VI => I = P/V
I = 1.4 W / 12 V = .12 A.
So the camera doesn't really require that much amperage. So why would he choose the 7A Battery over the 4.5 A Battery b/c that seems more than adequate.
Best Answer
The misunderstanding is about the unts: the battery capacity is expressed in Ah, which means the number of Ampères that it can supply for an hour, or the number of hours fot which it can supply 1 A of current.
The cable hasn't a great influence on this, other than dissipate power due to its length. But at that low current, it shouldn't be an issue if it's big (and I bet it is!).
So, given that your current is .15 A (150 mA, rounded to the top ti be safe), the smaller battery should ideally be able to supply the camera for 4.5/.15 = 30 hours, if the values are correct. But probably the capacity will be a bit less and decrease with time, and the consumption may be higher, and you will have a slow leakage depleting the battery.
But for this scenario, 4.5 Ah seems to be enough, I guess (depending on how long he needs the camera on).
With the 7 Ah battery, the duration will be 7/.15 = 47 hours.