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Interested in some experimental power+data tether?


(Richard) #1

Hi All
I’ve been looking into trying out a DIY power+data tether solution for my BR2. I’ve gotten some quotes from some cable manufacturers for a neutral buoyancy, 150kg breaking strength tether with a twisted pair of 26awg wires for the data along with a pair of 18awg wires for power. The prices I’ve gotten were around $3 a meter, so something like 350m would be around or a little over $1,000. There’s a decent price break for getting 1,000m, so I was wondering if anybody else here might be interested in going in on this with me. I’m not 100% sure this will work (I don’t think DC power going down the tether will mess with the data lines, but you never know until you try…) but I’m pretty confident it will. So with that “no guarantees” caveat, anybody want to roll the dice with me?
-Richard


(k.deboer) #2

Hi Richard,

I had some very good results running high voltage DC down to the BR2. I used a 120 VAC to 320 VDC converter (brick). I used the BR Fathom tether, using 2-pairs for the DC power. (Pair-pair voltage rating is ok for that voltage) At the vehicle end, I used a short 2" enclosure to house two paralleled 30 Amp, 12VDC DC-DC converters, with the biggest capacitor on the high voltage side that fit. (a few custom inductors were required to be wound in order to build the R-L circuitry for the parallel the DC_DC converters) I dared not to put a connector on this tether at the vehicle-end due to the high voltage.

Ultimately, I ended up abandoning the power down the tether, as I ended up needing the tether pairs for options I added to the vehicle. The BR battery pack has provided all I’ve needed since.


(GONZALO) #3

Hello Richard, I am interested in trying with the power+data tether. What is the price for 1,000 meters?


(Karstein ) #4

Hello Richard.
i am interested but only need 100-150m.

Karstein


(Richard) #5

Thanks for your interest @Turoey and @gsantamarina. If we got 1,500 meters (1k for Gonzalo, 150 for Karstein, 350 for me) the cost should be $3.30 per meter plus $200 shipping to Los Angeles (where I live). Shipping to you other guys would be TBD. 1k meters weighs about 110kg, FYI. This quote was pre-tariff-insanity, so may be higher now, I will check again to confirm. I should also point out again that I don’t expect this to work beyond 350 meters or so with standard BR Fathom X interfaces and DC power, and can’t be sure it will work at all.


(Matt) #6

Something to think about … you can always inject data over power. Meaning you could use all your existing fathom tether pairs for power and just run data on it at the same time.
Limited in terms of lengths but still an option if someone was keen. Not really a lot of work likely required as would all be off the shelf gear.


#7

I am currently refurbishing the following commercial ROV Bleeper Pro : image http://www.praesentis.com/eng/bproi_car_tec.htm .

It came equipped with 24VDC Tether and it is working good alongside CANBUS (control) and PAL (video streaming) over a cat5 cable. I will switch to ethernet and Ardusub Plattform.


(Morten) #8

Hi! Please also add me for 200m. What will be the delivery time? Can we also start sharing the configuration and other parts needed?


(Richard) #9

Hi All
I’m glad to see a bunch of other people interested in this idea!
Production time will be about 10 days from the time they get paid, shipment by sea to LA will be similar once it’s on board which may take a few extra days. So I would say about a month.
As for the other parts needed-- At the surface I’ll be using a benchtop DC power supply I picked up on on eBay. It can do 120vdc up to 4.5 amps. For the vehicle, I got a Vicor step-down DC power converter designed for an input of roughly 72 volts (it can handle anything from 50 to 100+) stepping down to 15, boostable to 16.5, but it is limited to no more than about 250 watts of output. I’m still not sure how I will implement current sharing between the battery and this DC supply… if anyone has any ideas I would love to hear them.
I do appreciate @BayDynamics 's point about running data over power, and that’s exactly what the Fathom-X interface parts were designed to do, but I think they were intended for AC power and perhaps don’t work so well with DC. I know BR has done some experiments of that sort and wasn’t totally happy with what they found. Maybe I (or someone) could get an electrical supply place to loan me/them two spools of 1,000 feet of 18 or 16awg wire and we could do some tests… if we could do without the twisted pair that ought to make the tether a bit cheaper and thinner, in fact it might even be a ready-made thing we could just buy!


Battery charger on sub?
(Matt) #10

You might want to show everyone the cable drawing before proceeding. Designing a tether is no trivial task and you may be over simplifying things here.
You need to make sure you got your specs right for the power and data your sending to ensure you wont get interference, shielding and the way its shielded are important. Total data drop needs considering as over a 200m length you may not be able to handle enough data to be of use with power in the same cable.

Make sure its appropriate for the job in the water as well, eg you will need kevlar strands and water blocking compound to start on the practical side. The jacket is important as typical foam coverings have a tendancy to get heavier with use and stop being neutral. Types of copper strands need factoring to meet flexibility criteria and minimum bend radius is important to not damage strands and stretch insulation causing possible drop in insulation properties. This can cause possible shorts in your tether at any length, worst case scenario you get a short half way and end up loosing your tether because its not long enough anymore after the repair.
Overall size is also important as it will effect your drag friction in the water cause possible reduction of manoeuvrability in the water.

Just some points there really to make sure the cable manufacturer you choose is not just making you what you ask for instead of making you what you actually need.


(Karstein ) #11

Then I have rebuilt my seabotix tether. and it looks like it’s enough with this one. then I withdraw from this purchase. Sorry.