Battery Selection

# Introduction

The T100 thruster can be powered off of any 6–16V power source, and the T200 off of 6–20V. This can be an AC power supply, lead acid (Pb) battery such as from a car, nickel metal hydride (NiMH) battery, or a lithium polymer (LiPo) battery. LiPo batteries are particularly light and energy dense while offering high performance with low voltage drop under load, making them the recommended choice for on board ROV power.

# LiPo Batteries

## Voltage

LiPo battery packs come in different voltages, in which each cell is nominally 3.7V. However, when fully charged a LiPo battery cell rests at 4.2V, and this must be taken into account when determining if your electronics will be able to handle your battery. Furthermore, LiPo batteries should not be discharged below an absolute bare minimum of 3.0V per cell, or permanent damage may occur. Recharging a battery well before this point is reached will ensure good performance and long life of the battery.

Battery Nominal Voltage Maximum Voltage Recommended Minimum Safe Voltage (3.4V per cell)
3s 11.1V 12.6V 10.2V
4s 14.8V 16.8V 13.6V
5s 18.5V 21.0V 17.0V

For maximum efficiency, the T100 should be run at 12V, and the T200 at 16V. A 11.1V 3s LiPo is recommended for the T100, and a 14.8V 4s LiPo for the T200, though the T100 can be safely run with a 4s pack and the T200 with a 5s pack. If you choose to do this, you will see slightly higher performance, but reduced efficiency than when running at the recommended voltages.

## Capacity

The capacity of a LiPo, or any battery, is in milliamp hours (mAh) or amp hours (Ah) and determines how much energy a battery stores. For example, a 5Ah battery would approximately be able to run a 5 amp device for 1 hour, or a 1 amp device for 5 hours.

## Discharge Rate

The discharge rate is a rating of how much current a battery can safely provide. This is a multiplier of battery capacity, for example a 20C 5Ah battery can safely drive 20 x 5 = 100 amps. Similarly, a 50C 7Ah battery can provide up to 50 x 7 = 350 amps. The burst C rating describes safe maximum current bursts, usually a duration of about 10 seconds. Higher C rated LiPos also have lower voltage drop under load, giving a boost in performance and more punch.

Running more thrusters off of a single battery will put a greater load on it, so you must use a battery rated high enough such that it will safely be able to power your entire ROV.

Maximum Current Draw Each 12V 16V 20V
T100 14.5A 21.5A N/A
T200 18A 25A 32A+

## LiPo Safety:

LiPo batteries have a high energy density and must be treated with the proper precautions. More information about LiPo batteries including their correct use and care can be found on the following webpages.

iCharger (information)

iCharger (Safety)

Horizon Hobby

Team Orion LiPo Battery Production Video

LiPo batteries can be bought at hobby shops and online through numerous vendors, including HobbyKing. We use HobbyKing’s Multistar, Turnigy, and Zippy brands of LiPo batteries for our testing.

# Batteries for the Blue ROV

## Battery Clearance

The Blue ROV electronics tray will accommodate batteries up to 230mm (9in) long. However, if basic ESCs are being used, the ESCs mounted to the bottom of the tray will reduce clearances. Past 125mm (4.9in), 5mm (0.2in) of the height available is taken up by the ESC wires. Beyond 155mm (6.1in), 10mm (0.4in) is taken up by the ESC itself.

Due to the round shape of the enclosure, the maximum width of a battery is determined by its height. There is 47.2mm (1.858in) of clearance between the bottom of the electronics tray and the inside of the tube. However, up to an additional 2.5mm (0.098in) of clearance can be found if a battery is squeezed in such that the top shelf of the elctronics tray contacts the tube.

You can use the following formula to determine whether a battery of a given height will fit its width in the enclosure:

Here “d” is the inner diameter of the enclosure, “h” the height of the battery, and “x” the distance the lower part of the electronics tray is from the center of the tube. If “width” is greater than or equal to the width of the battery whose height you input, then the battery will fit, at least in height and width.

For the Blue ROV, “d” is 50.8mm, and “x” is 3.6mm. If your battery is long enough to come up to the ESC wires or another obstruction on the bottom of the elctronics tray, add its height to “x”. Conversly, if you wish to allow the battery tray to be moved up by the battery, you can subtract up to 2.5mm from “x”.

Hobbyking’s battery finder tool is very useful in finding batteries that will fit the Blue ROV. Note that the “width” and “height” dimensions in the battery finder tool are the reverse from the varaibles in the above fit fomula.

## Example Batteries

These batteries will all fit the Blue ROV with basic ESCs, many of them have been used for our testing at Blue Robotics without any issues.

Battery Voltage Capacity Discharge Rate Max Constant Current Draw Cost**
Zippy 11.1V (3s) 6200mAh 40C 248A $42 Turnigy 11.1V (3s) 6000mAh 25C 150A$47
Turnigy 11.1V (3s) 5000mAh 20C 100A $22 Turnigy 14.8V (4s) 5000mAh 20C 100A$28
Zippy 14.8V (4s) 5000mAh 30C 150A $39 Multistar 14.8V (4s) 6600mAh 10C 66A$43
Multistar* 14.8V (4s) 10000mAh 10C 100A $59 Zippy 18.5V (5s) 4000mAh 40C 160A$36

*Fits by squeezing electronics tray up, maximum sized battery confirmed to (barely) fit the Blue ROV with basic ESCs. **Approximate, as of Novemember 2015.

# Battery Calculator

## (Beta, please double check results & report bugs!)

This calculator finds battery energy based on voltage and capacity ratings. It also estimates how long a battery will run a thruster at a specific throttle level.

(success) Enter voltage followed by unit. (e.g. "11.1 V")
(success) Enter capacity followed by unit. (e.g. "5000 mAh" or "10 Ah")

Battery Energy