I am working on powering an ROV continuously over a long tether and would really appreciate input from anyone who has practical experience with this problem.
Specifically, I am interested in feedback on the following:
Power delivery voltage:
Has anyone successfully delivered continuous power over ~150 m tether using 230 VAC?
If so, how did you manage issues such as voltage drop, efficiency, and heat dissipation in the tether?
Alternatively, is it necessary or recommended to use higher voltage (e.g., 400 VAC or DC) to reduce losses and maintain stable supply over that length?
Power conversion on the ROV:
My ROV electronics require low voltage DC (e.g., 15 V).
Does anyone know of existing solutions, power conversion units, or so-called “power bottles” that can be mounted on the ROV to convert 230 VAC (or higher voltage) down to the required DC supply reliably?
Are there recommended products, suppliers, or manufacturers of these units?
Custom tether options:
Does anyone have experience with custom power tether solutions, or know vendors that provide specialized tethers optimized for power delivery (e.g., larger conductors, hybrid power + data lines, custom shielded assemblies) for ROV or subsea use?
Any first-hand experience, recommended suppliers, technical considerations (e.g., required cable gauge, connector standards, safety), and lessons learned would be incredibly helpful.
Hi @Henkedoodle -
Welcome to the forums!
This is a common topic - have you read some of the related threads?
Blue Robotics sells the Outland system for this application. Other vendors have solutions too!
The critical thing to remember is that AC (and DC) voltages, especially above ~30V, are INCREDIBLY dangerous! Any power over tether system needs to have proper fault-interruption circuits - using a household “GFI” is not enough - a line insulation monitor of some kind is typically used- I’ve tested with models from Bender. Vicor makes good DCDC power converters - I would avoid AC on the tether.
A simpler idea may be to keep your ROV battery power, but charge the battery at a low rate via a DC surface power supply. You still need to take care to keep the battery cells balanced, but this can be a lower budget solution that is not only safer, but cheaper to implement. The voltage drop calculator is relevant, as is this new guide!
Hello and welcome to the world of subsea robotics.
Just to reiterate what Tony mentioned: mixing electricity and water has risk. 12, 15, and 24V batteries are one thing, 48V isn’t too bad, but can be deadly under special circumstances, but 120V, 240V, and 400V can easily be fatal if the required safety features are not properly implemented. Remember “electricity wants to kill you!” I’ve worked on everything from 12V to 4,000V.
For these reasons, I would strongly recommend buying the power converter on the ROV, the surface power supply with appropriate safety features, and the high voltage tether and slip-ring as a set from a supplier such as Outland Technology or Poseidon Robotics. While you could make one a little cheaper yourself, it won’t be much cheaper if having the housings and heat sinks machined, ordering high voltage tether (usually minimum of several thousand dollars) and the few thousand dollars of safety equipment like isolated power supplies, line isolation monitors, and safety interlock circuity and high voltage DC contactors.
In answer to your questions:
Yes, you can get power across a 150m tether. We’ve done up to 250m tethers with 240VAC and over 1,000m using 400VDC. As Tony mentioned, check the voltage drop calculator to see how much power you’re going to loose in the tether and also be mindful you don’t want to overheat the conductors, especially when the tether is coiled on the reel, sitting in the sun, and there’s no cooling water.
There are a number of solutions out there, Outland being one of the best and most established, but we make similar products as well. Nearly all of them are based on parts from Vicor Power and these come in a few different flavors: Fixed output voltages (12, 14, 15, 24, and 48V). Note that the output voltage can be adjusted a small amount, but maximum power will be reduced. They also come in “fixed ratio” converters, which are much more powerful for the size, but the output voltage varies with the input voltage at the converter. These come in 8-12V, 17-24V, and 32-48V.
Standard solutions for Blue ROV power upgrade from Poseidon are:
-250VAC input with 8-12VDC output, 500-1,000W depending on tether lengeth
-400VDC input with 14VDC output, 1,200W
-400VDC input with 18VDC output (1,000W) + 24VDC output (200W) + gigabit fiber connection
While it is possible to run power over the standard Fathom Tether from Blue Robotics, Ohm’s Law limits how much power you can get down the tether, so pretty much everything we make at Poseidon from 500W to 2,000W is done over a tether with a single set of 19AWG power conductors and signals are run over a twisted pair of 26AWG conductors. For our 3,000W and 6,000W systems, we run larger tethers up to 2 sets of 16AWG wires. Many combinations can be used, but the standard Fathom reel slip-ring will not survive the high voltages, so the reel and connectors must be upgraded. We use both Linden Photonics, Inc out of Boston, MA, as well as UNIR Cable out of China, but South Bay, ROV Cable, Nexans, and many others are also excellent suppliers.
If you have a good amount of electrical experience and are determined to make your own, please feel free to reach out directly and we can point you in the right direction and would be happy to look over your design and offer pointers or identify potential hazards. It can also take a lot of time to tune the filter networks, without which the tether bandwidth may be very low due to noise, or there can be oscillations on the power converter that can cause it to fail or damage the ROV electronics.
Here’s a datasheet for our AC system we have successfully used to power Blue ROVs. It’s higher voltage than most, and the voltage can damage the Newton Gripper, so use caution, but it is one of the lower cost systems out there. If you want DC, the Outland might be a better option.
If you want 18VDC and a gigabit and aux 24V connection as well, we have our system for that know as SQUID.