# Battery capacity

Hi everyone, a question about the bluerov2 navigator electronics, not sure about it, I’m thinking about running the navigator and fathom x and rpi from two 11.1v 3s batteries in parallel, would this be enough and how long would it run for? Each battery is 3000mah, nothing else from these batteries, thanks for any help

Hi @Scottrov, welcome to the forum

This is a somewhat difficult question to answer, because the power draw for the Raspberry Pi depends on how much work it’s doing, as well as any other connected peripherals (e.g. camera, camera servo, Ping Sonar, pressure sensor).

From the technical details on the Navigator product page it has a typical draw of 150mA, and max draw of 200mA. The Fathom-X only has a max listed, as 2.5W (225mA @ 11.1V). Note that 5V switching regulators are ~90% efficient, which gets applied to the combined current of all the 5V electronics. Our Camera is specified as max 220mA.

If you assume the Raspberry Pi is under “normal load” then it would use ~1A. For rough estimates, the pressure sensor and camera servo are likely pretty negligible. Adding up what we’ve counted so far, that’s

\begin{align} P &\approx 5\cdot(0.200 + 0.220 + 1.000) / 0.9 + 2.5\\ &\approx 10.4\text{ W}\\ \rightarrow \text{runtime} &\approx 11.1\cdot 2\cdot 3.000 / 10.4\\ &\approx 6.4\text{ hours} \end{align}

Note that most of the power in a vehicle is generally drawn by the actuators (e.g. thrusters, lights, gripper, etc). If you’re not using any actuators that’s fine, although it’s a bit unusual to be using a Navigator then. If you are using some actuators then you’ll either need a larger battery for those, or power from the topside, otherwise their power will run out far before the supply for the control electronics.

Hi and thanks for reply, it’s a home build with mostly blue robotics parts, yes the 3s batteries are only supplying the control side, it’s a 12 thruster set up, with 4 of your 4s batteries, each powering 3 thrusters, still need to order some more bits, but coming along nicely so far

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