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Power over Tether for Fathom-S


(Mark Langille) #1

We have a client that is looking to run power over the tether for a drop cam project using the Fathom-S for the video transmission interface. As well would like to also power a GoPro camera.

As I’m not an electrical guru just looking for some general thoughts on this approach and if anyone has tried it. I know BR is working on a power over tether approach for the BlueROV2 so figured it was doable for this smaller application given the the low power an amp requirements.

Adding a BEC for th 5V GoPro power conversion is a non issue and the Fathom-S handles a wide voltage range from 7-20V.

Will be using the BR tether cable in 100M length.

Open to thoughts and suggestions.


(undersearobotics.com) #2

Your “enemy” when trying to send power down a long tether is voltage drop. Here’s a voltage drop calculator you can play with to see what sort of drop you’ll have at various voltages:

http://www.calculator.net/voltage-drop-calculator.html

Each wire is 26 awg, which is pretty tiny. For example, if you send 24 vdc / 0.5 amps down a single twisted pair, you’ll only have 10.6 vdc at the ROV. If you send 48 vdc / 0.5 amps you’ll get roughly 13.4 vdc at the ROV. And so on…


(Mark Langille) #3

Thanks yes that is our main concern even at these lower voltages, it is so much loss.
Pushing them to use an onboard battery but sometimes the client likes to go their own way :slight_smile:

Certainly are advantages of both approaches, nice having all power at the surface for easier management and having the camera system sealed, ie not needing to open to change batteries of make connections.


(undersearobotics.com) #4

I think this would be one case where using the Fathom-X might be the better way to go. By sending both control and video over a single twisted pair, that leaves the other 3 twisted pairs to be used for power. 3x 26 awg gives you considerably more copper to send power.


(Todd Sparkes) #5

Using even two twp would give you an acceptable voltage loss ratio. As Paul said three would be ideal…Your current draw is minimal so your only concern is voltage loses.


(Mark Langille) #6

Problem is no easy means to interface a GoPro with Fathom-X unless I’m missing something.
Need to use a camera other than the Pi in this case.

We don’t need control in this case, it’s a drop cam so we can bind the other 3 lines as only using 2 for video on Fantom-S.


(undersearobotics.com) #7

@schoonerlabs - Ok, now you lost me. :wink: Why are you using a GoPro with the Fathom-S in a drop camera? To preview in SD while you record in HD? Might it not be better to just use the Fathom-X with Raspberry Pi and HD camera instead? Or just a good SD camera with the Fathom-S?


(Mark Langille) #8

Because the GoPro is what they want to use :slight_smile:
Using Fathom-S also allows pretty much any camera to be used.

Yes it is SD but lot more flexibility over the Pi HD camera if needed. Allows you to frame what you are actually shooting. It also means not having to have a PC on the surface, just the Fathom-S and a monitor. No software to have to run etc.

It is for a school project so outside my control in terms of the needs.

We are planning to use the same setup for a secondary camera with the BlueROV2. Will allow us to run any camera system more easily, from the SD zoom cam module we have through to GH4, D800, etc.

I wish the Pi had an easy way to accept an alternate HD input for the feed. Until then the Fathom-S is the quickest and easiest solution.