20' DC power cable to surface power supply


Gday all,

I need to use my 2.7OpenROV in 10’ of water for an extended amount of time…8 hours. It will be running back and forth on a wire carrying an outboard camera to follow a water sport. It will be running pretty hard for 15 mins at a time then have 5 mins to “cool” down. Then back to work. Every hour it will be able to rest for 10 minutes. #1…will it do it? If so, just wondering if anyone can recommend how big of a supply to go with.

Any help appreciated!




It will do it, but it’s by no means a simple task. The only reason I’m suggesting it’s possible is because you’re not going too deep. The longer the cable run the more difficult it becomes. Is changing multiple sets of batteries an option for you? It’s probably the easier option.

The ROV uses between 0.5A and 0.8A just to run the computers, With each motor using up to 10A. So you’re probably looking at least a 20-30A 12V DC supply. A linear supply with voltage tracking would be a lot better than a switchmode, as the noise from a high current switchmode could interfere with the ROV or the network.

You will need a big chunky cable to handle the current without getting a massive voltage drop too. About 8-10 AWG would probably be okay. But this will also introduce drag on your ROV and make it much less maneuverable.

Are you planning to run the ROV just from the DC supply? or run it with the batteries on board as well and use a charge controller? Have you used the IMU wires or spare wires on your 2.7? You will need to use more than 1 pair of the wires potted thru the end-cap to handle the current. I would suggest using all the spare wires you have available.



I realize this is a bit late to the table but if you are able to run a higher voltage on the tether you can use smaller wire. 30A @ 12V is 360W but so is 7.8A @ 48V and the size of wire is related mostly to amperage. If you put a DC/DC converter to take 48V in to 12V out you can use smaller wire.

Wire sizing chart for a 2% loss says 12v @ 30A over 20’ needs #2 but 48v @ 8A only needs #14 or maybe #16.

You also indicate the duty cycle is 10min out of 60min so if you can use an on board battery for your peak loads during the 10min running time and re-charge for 50min. 30A for 10min would only requite 6A for 50min to recover. 12v @ 6A = 72W = 48V @ 1.5A. Again if I am reading them right the tables suggest #16 wire for 1.5A over 20’ with a 2-3% power loss.



Usually, the cable loss of ROV can be accepted by 30%, but pay attention to the heat accumulation of the cable wrapped around the cable shaft.
The higher voltage corresponds to a finer buoyant cable, which reduces the power loss of the cable while the ROV is moving. It is recommended that if the cable supply voltage is not less than 100V, the small size is not recommended for more than 500V, otherwise the insulation of the slip ring and water tight head is a problem.