Power via 48v Tether

[anagama]

I'm still trying to figure out how I want to power the ROV I'll be building. I'm concerned about having batteries on board for a number of reasons. I also plan a 200' tether because my underwater camera already has a 200' cord, but I don't want to be dragging around a massive power cable.

I'm wondering what people think about running 16 gauge wire at 48V. I can plug into the 12V house batteries in my cockpit so my runtime would be awesome. I found these cheap DC-DC converters ($75 combined):

12V -> 48V: http://www.current-logic.com/shop/index ... cts_id=149
48V -> 12V: http://www.current-logic.com/shop/index ... cts_id=151

This voltage drop calculator says I should have 43V at 3A at the end of 200 feet, which should just give me 120W for 4x2.5A 12v thrusters.

I like this idea a bit more than onboard batteries, but I've never tried anything like it -- are there pitfalls I'm missing?

[SoakedinVancouver]

Better arcing capabilities, 4 times the charge time, 4 times the expense...

This said, it is a better way, because, as you say, the cable loss is less "costly". Cars are supposed to be getting 42V DC system "in the future", and one of the numerous problems was determined to be the ratings of the connectors, as in unplug a 42 VDC live connector and see how much molten copper you get off these connector's fingers. And it's gonna cost you a fuse.

Right, don't forget to get DC rated fuse, good for 50+ DC volts. Check the price of a 10A Neozed...

[derelicte]

slightly ot, but the 42v car system is dead.

http://en.wikipedia.org/wiki/42-volt_electrical_system
http://www.popularmechanics.com/cars/news/4226979
http://www.eetimes.com/design/analog-de ... -42V-auto-

[derelicte]

no reason it won't work. just don't forget the fuses!

[krigsmaskin]

sorry mate's if this is a rookie qestion
why not use AC 110 or 230?
Only bad thing with AC as I see it is the power source topside.
It's expensive to buy a inverter 12/24V DC to AC. But a cheep gasoline powered generator would to the trick.
And a AC to DC power supply for the rov is easy, cheap and smal.

[steve918]

Also be careful with the amp ratings on the step-up you posted. The step-down was 10A, but the step-up is only rated for 3A which is less than most single bilge pump motors pull under load. If you are running 3 pumps then 12A+ is not out of the question.

[anagama]

Also be careful with the amp ratings on the step-up you posted. The step-down was 10A, but the step-up is only rated for 3A which is less than most single bilge pump motors pull under load. If you are running 3 pumps then 12A+ is not out of the question.

I was wondering about this but sort of assumed there was some magic involved in the conversion such that by sending down 148 watts (48V*3A) [edit: bad math obviously! ], I'd be able to get back 120 watts (12V * 10A). What you're saying is that such magic doesn't happen -- if that's so, it's back to batteries.

[anagama]

Better arcing capabilities, 4 times the charge time, 4 times the expense...

I'm not sure I understand this. I would just use the house the bank on my boat (comprised of two 90amp deep cycle batteries) -- it's charged by the engine and shore power when at the dock.

[derelicte]

that is 3a at 48v (150w).

that plan should work fine.

[anagama]

sorry mate's if this is a rookie qestion
why not use AC 110 or 230?
Only bad thing with AC as I see it is the power source topside.
It's expensive to buy a inverter 12/24V DC to AC. But a cheep gasoline powered generator would to the trick.
And a AC to DC power supply for the rov is easy, cheap and smal.

A 4-500 watt inverter is pretty cheap, but I know even less about AC than I do about DC. The wire calculator I linked to above said I could get 106V AC at the end of 200' on 16gauge wire, but a 400W inverter is going to have less than 4A.

Would this be feasible? Would it be safer than 48V DC?

(Edit: hmmm ... I'd need three wires for AC right? that's a 50% increase in cable weight)