2
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ Will this battery be used for all components on the platform? \$\endgroup\$ – sptrks May 2 '12 at 6:03
  • \$\begingroup\$ I'm in no way endorsing this product...but here's the link. theimportsworld.com/nauncasytide.html This bundle comes with the camera and a USB connection Kit...assuming that you will connect your computer. Perhaps @sptrks is hitting the nail on the head that the Battery Kit is also used for other devices. \$\endgroup\$ – milesmeow May 2 '12 at 6:10
1
\$\begingroup\$

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.

\$\endgroup\$
  • \$\begingroup\$ I had a feeling that it was also a mislabeled option. That would make a lot more sense. Thanks @clabacchio \$\endgroup\$ – milesmeow May 2 '12 at 6:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.