Ecosystem Electronics Lab

Power System

These ROVs were designed to be used by inexperienced children near salt water, so electrical safety was the primary consideration. We therefore limited our power source to a single low voltage battery. To achieve adequate power at modest cost under this design constraint, we opted to use a 12 volt, 12 amp-hour, absorbent glass mat (AGM), sealed, valve-regulated, lead-acid battery. This battery powers every aspect of the ROV, both on the surface and below the water line.

The diagram below provides an overview of all the circuitry in the Catalina ROV System. You can see that all of the power is derived from the single 12 volt battery located at far left in the diagram.

Overview of Catalina ROV Circuitry. The blue boxes, together with the heavy red and black arrows in the diagram, represent the power distribution system. “E-Box” stands for the splash-proof Electronics Box, which houses most of the electronic components of the system and is mounted on the Pilot’s Console.

This photo above shows an example of one of the 12 volt, 12 amp-hour absorbent glass mat, non-spillable, lead-acid batteries used to power the Catalina ROVs. These batteries, commonly used for emergency lighting systems, uninterruptable power supplies for computer systems, wheelchairs, and other applications are widely available from a variety of manufacturers.

Electrical power is conducted from the battery to the electronics box (pictured below mounted on the Pilot’s Console), by a red and black pair of 14 AWG speaker wire.

The photo above is a view looking down into the electronics box with the clear plastic cover of the box removed. Most of the red and black wires are involved in power distribution, with red being positive DC voltages (mostly +12V, some +5V) and black being ground (zero volts). The main power from the battery enters the box through a tiny hole center of the back wall, just to the right of the big, bright, blue LED. From there it goes to a large “barrier strip” or “terminal block” consisting of rows of screws that provide a convenient way to connect the power and ground wires from other parts of the circuitry.

The red and black insulations hues serve as a color code to reduce the chance of reversing the battery polarity. Red goes to the positive (+) terminal of the battery, and black goes to the negative (-) terminal. We stripped the ends of the wires and crimped on 1/4" female spade disconnects to fit the battery’s F2 terminals.

This photo shows a close-up of one of the spade connectors used to connect the power wires to the battery terminals.

Once inside the electronics box, the red (positive) lead of the power cord goes through a 20 amp automotive blade fuse in an in-line fuse holder. This fuse is an important safety feature to reduce the risk of fire in the event of an electrical short somewhere in the system. (These batteries are low voltage, but they are still capable of delivering enough current to make things very hot and potentially start a fire. )

A close-up of the 20 Amp automotive blade fuse inside its in-line holder.

Immediately after the fuse, the power line goes to the main power switch, a rocker switch located on the left outside surface of the electronics box.

From the other side of the switch, it goes to a barrier strip with pairs of of electrically-connected screw terminals that provide a convenient way to distribute the +12 volt DC power to the various electrical subsystems. One of these subsystems is just a big blue LED that lights up whenever the main power switch is turned on to let the pilot know that power is flowing to the circuitry.

A picture of the barrier strip used to interconnect the main power wires. Four pairs of screws at the far end are used to interconnect all the red wires, which carry +12 Volts. The four pairs of screws in the foreground interconnect the black ground wires, which return the electrical current to the battery.

Most of these subsystems can (and do) run directly off the 12 volts from the battery; however, the TV monitor and the GoPro camera used on this ROV each require a different voltage and therefore require an adapter of sorts.

The TV monitor is a small screen designed to be used in combination with a small TV camera mounted on the back of a recreational vehicle or other large vehicle to supplement the rear-view mirror, so the driver can see more clearly what is directly behind the vehicle while backing up. It therefore comes with a convenient power adapter box (with its own fuse and filtering) designed to connect to a standard 12 volt car battery. We simply hooked that adapter box to the 12 volts coming from our Pilot’s Console battery.

This photo shows the little black box that came with the TV monitor. It allows the TV monitor to be powered directly off a 12-volt supply. It also contains its own separate fuse for the TV monitor.

The GoPro camera has an on-board battery that can be recharged though the camera’s USB port, which supplies 5 volts; however, that USB port (or the corresponding wires accessible through the 30-pin GoPro bus socket located on the back of the camera) can also be used to power the camera directly from a +5 volt DC source. We therefore use a 5 volt DC-to-DC converter to convert some of our 12 volt supply to 5 volt, which we then send down the tether to power the GoPro camera from the main 12 volt battery. WARNING: Do not connect 12 volts directly to the GoPro, or you will probably kill the camera!

The photo above shows a close-up of the DC-to-DC converter we used to drop the 12 volt battery voltage down to a safe 5 volts to power the GoPro camera externally. The red and black wire entering the converter at lower left in the photo supply the 12 volt power to the converter. The yellow and black wires carry the 5 volt output, which is sent down the tether to the camera. We tried some 1-amp USB car chargers initially, but we experienced frequent failures with those, so we switched to these converters, which have a higher (3A) current rating. So far they have worked well.

All of the return current from the various subsystems comes back to the battery through other screws in the barrier strip, which is used as a ground bus. The black wire from the battery connects to this bus.

Some of the other details of the electrical box and the control system, including how the TReX motor controllers use joystick signals to route battery power to the motors, are described on the page that deals with the control system.

A final note about the power system and the tether: One limitation of using a low voltage power source rather than a high-voltage source is that a significant fraction of the available power is lost to resistive heating in the tether wires. This loss can be reduced by using thicker wires, but that results in a thicker, heavier, stiffer tether. The losses can also be reduced by using a shorter tether, but that limits maximum depth and maneuverability. Our tether represents a compromise; it uses 16 AWG speaker wire in 15 meter (50 foot) lengths to transmit power to the thruster motors.