120V Ac ?

Control Boards, Controllers, Tethers, Ect.
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orangeltr456
Posts: 20
Joined: Jul 5th, 2013, 10:44 am

120V Ac ?

Post by orangeltr456 »

I have been having alot of trouble trying to run dc down a tether. I am tired of pumping o much power down the 12 AWG wire i am using and only getting 50-60% of it to the motors, the length of the tether is not something I can change. 150ft makes a 300ft round trip and dc will not travle that far with the current draw I have roughly 30 amps. I do not want to lug 4 batteries around to run 48v.

So I have come up with this
http://www.wikihow.com/Convert-a-Comput ... wer-Supply

120v ac run down the tether to a modified pc power supply. to provide about 22 amps of current at 12v, they also supply 3.3 and 5v which is perfect for logic and such

IN my final design I may end up using 2 to supply enough current for all my motors.

Anyone do this or know of any potential problems.

as long as there is no exposed wire to the water 120v ac is safer than 48v dc
Zaibach
Posts: 48
Joined: Aug 13th, 2013, 9:50 am

Re: 120V Ac ?

Post by Zaibach »

Uncertain as to if it will work but I have also been entertaining the same ideas.
The thing that gives me pause is that it seems to me that AC would be quite dangerous if there was a breach in the line.

They make low temp power cables that should stay flexible where normal extension cables would likely become too rigid to be useful. Of course drag could be troublesome. Then there is the issue if your cable breaks anywhere you don't want to keep pouring on the electricity, so some sort of fusing and ground fault system would undoubtedly be a good idea.

I have also been entertaining the idea of trying to use two Ethernet over Powerline modules I picked up to piggyback data on the AC. They seem to work well enough along normal wall sockets but I have no idea how they would take AC off a generator. I suspect additional line conditioning would be required.

Even if all that goes off without a hitch (and it probably won't) you will still likely want a battery with enough juice to get your ROV back to the surface if either power or data communications are lost.
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Rover
Posts: 108
Joined: Jul 18th, 2011, 10:23 pm
Location: Minnesota

Re: 120V Ac ?

Post by Rover »

We have been using a computer supply to power our rov in the lab and test tank with good results. On eBay you will find 12 power supplies made specifically to power LED lighting and are thinking about using one of them.
jsut210
Posts: 35
Joined: Aug 14th, 2013, 7:53 am
Location: Maryland

Re: 120V Ac ?

Post by jsut210 »

Yea I would agree that running high voltage AC could pose a safety issue if the line was broken. Also, I currently use an ATX supply as a bench supply (great setup btw) and I am also thinking that the power supplies are quite large. I'm not sure how big you are making your ROV but it's an awful big component to keep dry.
aquajack
Posts: 26
Joined: Mar 20th, 2012, 5:33 pm

Re: 120V Ac ?

Post by aquajack »

In theory that would work well, as many commercial rovs use upwards of 480 volts ac. This works well in the commercial market on a 5 million machine but on a home built system that much voltage sounds like a terrible idea. It is just to easy to slice a tether of debris and 120 vac is not something to toy around with. Instead try pumping 24 volts down using a dc/dc converter which is much safer and in the end you will get around 14 volts, as much as a freshly charged car battery.

http://www.newark.com/jsp/search/produc ... 0261|plid|
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orangeltr456
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Joined: Jul 5th, 2013, 10:44 am

Re: 120V Ac ?

Post by orangeltr456 »

120v ac run through a gfi (ground fault interrupter ) IS safer than dc. I dropped an extension cord into a bucket of water and no sparks bubbles or anything. gfi clicked expediently cutting power. plus with 120 ac i wont need batteries because I will be operating off of a large boat with generators on board.
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ROVER3D
Posts: 128
Joined: Nov 9th, 2012, 7:45 pm
Location: Wuppertal, Germany

Re: 120V Ac ?

Post by ROVER3D »

I can drive with my car more then 150mph. If there is noboby on my way ...
So you can operate with 120AC, if there is no fault on cable...

For using DC or AC over 60V you need to use a very strong and safety cable your ROV will not be able to push.
I don't think you will get a safety way to use it. Beware of using this voltage and somebody else will be damaged. THIS IS NOT THE RIGHT WAY!
So if there is a minimum possibility of any fault (and there will be) you are (in my country) not allowed to power it up, and thats the thing!

You need batterys because of building an rov which is able to push your tether!
rossrov
Posts: 383
Joined: Feb 28th, 2013, 5:01 pm
Location: Australia

Re: 120V Ac ?

Post by rossrov »

This one is what they call a "NO BRAINER". You really have to expect the unexpected in any situation that could pose a threat to life or limb. That includes failure of protection equipment, or faults in the design of the overall system. As pointed out by ROVER3D, a tether suitable for anything other than very low voltages would have to be armoured and properly engineered, making it thicker, so you have gained nothing unless you increase the size and cost of the ROV. On top of that you still need specialist designed protection systems in the way of leakage detection, isolation etc etc etc. An extension lead in a bucket of water is hardly an example of whether something would work or not. This is the sort of thing one would expect to see in some dodgy third-world mining operation.

Consider the safety of others, especially those unaware of the risks
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ROVER3D
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Joined: Nov 9th, 2012, 7:45 pm
Location: Wuppertal, Germany

Re: 120V Ac ?

Post by ROVER3D »

Thx rossrov!
I had this discussion several times in german forum, but you have to know we're using 230V AC. So there are also freaks who want to try it out, but never had worked with this voltages or simply don't think about the danger. But this is only the first step.

The next step is you build your solution and, as i know, you will see it doesn't works well because of less current. What you want to do this time?

I think you will try to take higher voltages...

This is nothing to discuss, this is only to accept! Never take more than 60VDC and 48VAC!
Ozzyboy
Posts: 10
Joined: Jun 19th, 2016, 12:03 pm

Re: 120V Ac ?

Post by Ozzyboy »

Hi, I realise this is an old thread, but still, when you start thinking about voltages and water, bear in mind everything everyone else has said as it's very valid, commercial rov's can send down 5000v but also use a tether that cost millions! There is actually a law requiring a licence to send voltage through cable in water and the threshold is around 24v and that is there for a reason I believe
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