On Board Batteries v. Powered Tether

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MNDeepROV
Posts: 34
Joined: May 12th, 2014, 3:46 am
Location: Minnesota

On Board Batteries v. Powered Tether

Post by MNDeepROV »

Hey all,

So I'm still working on my design plans and will start out with a smaller rov with 3-4 thrusters. However, I would eventually like the option to have up to eight and am trying to plan ahead. I'll use a controller for the expansion capability, but right now I need to decide on a power system before I can move forward with size of hull, thruster choice, etc.

My subject today is Lipo batteries v. a powered tether. I've never used Lipo's and have seen the discussion threads about serious voltage drop over a powered tether, from any given power source. One of our fun challenges! Lipo's obvisouly seem convenient for an easier/lighter tether, but perhaps has prolonged use limitations, along with charging and cost factor of extra batteries. I know some of you use a powered tether, but I couldn't see if any of the designs were for significant depths.

My target depth: 300'
Factors I am considering:
1. Time of ROV use with Lipo's v. a powered tether (could swap out batteries, but that means surfacing, and spending more money on extra batteries).
2. Weight of a tether that would affect control and potentially my thruster choice/needs.
3. Efficiency of thrusters overall for the two above mentioned factors (bilge v brushless...haven't decided which way to go for the first model, but might not want to buy brushed speed controllers and then have to buy brushless ones on top of that. Maybe they make a universal speed controller?).

I welcome any advice specifically relating to the detailed pro's and con's of Lipo's v. tether for my target depth. And, for those that do use a powered tether what kind of power and wire have you found effective for larger distances?

Things I don't have experience with:

1. How long the Lipos will last with say a 4 thruster system (I know this is dependent on amount of thruster use). Lipo's seem to come in many different sizes. An recommendations on power requirements/brands, etc?
2. Would it be better to use four different packs (one for each thruster) to isolate each to a specific thruster, or connect them in a way so that they all drain equally?
3. Details on high voltage powered tethers, wether 110 AC or 48 AC/DC. I understand there are obvious dangers for high volt AC, and an electricians knowledge is key, not to mention a variety of other factors!! I'm only researching at this point. I'm a safety nut, so if I can successfully use 12-48 v DC that's what I'd like to do.

Thanks to all!
MNDeepROV
Posts: 34
Joined: May 12th, 2014, 3:46 am
Location: Minnesota

Re: On Board Batteries v. Powered Tether

Post by MNDeepROV »

Note: I thought about moving this to the Control Systems and Tether thread...but also, as newbie thought maybe other would benefit from seeing it in this section. If you think I should move it, drop me a note.

Anyway, a night of sleep and much more reading (great posts spread all over this forum), I've got a better idea of what I'll need to do to start. Looks like until I really learn how to do a higher powered an AC/DC tether powered system, which includes knowing thruster power requirements for the heavier tether, I'll be using Lipos. Might be spendy, and limiting on time use, so I'm going to see ow many I can pack in to hit my goals.

I'd still be interested to hear some success stories from anyone who uses a powered tether at depth around 200-400 feet. I know there may be some slight hesitation to share everything because of safety issues (like when using AC) but perhaps some pointing to good resources is a start. Everything is always at our own risk...

I'm still pursuing the forum in greater depth, and if there is already some info out there on powered tethers I'll find it, or feel free to shoot me a link to the thread.

Thanks!
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TigerShark
Posts: 108
Joined: Jan 7th, 2014, 2:43 pm
Location: Washington State

Re: On Board Batteries v. Powered Tether

Post by TigerShark »

I am going to use a hybrid system with electronics powered over cat 5 tether and 2 3S (11.1V) 5000mA LiPolys. I'll be running 4 brushless thrusters total. I am feeding 32V down the tether now with 12V conversion onboard to power my arduino, camera etc.
MNDeepROV
Posts: 34
Joined: May 12th, 2014, 3:46 am
Location: Minnesota

Re: On Board Batteries v. Powered Tether

Post by MNDeepROV »

Thanks. I hadn't thought about a hybrid system before!

Just came across the following post too...cool concept. I have to research it and see if it's something I would apply.

viewtopic.php?f=9&t=1039&p=7267&hilit=w ... lipo#p7267
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