Power via 48v Tether

[derelicte]

don't think about it in amps, think in watts. a 400w inverter can deliver almost 3x the power as the 150w solution in the first post.

if you have 3 12v thrusters on the rov, you really only need about 15-20w (4 - 5a each) + power for cameras, controller, etc.

[krigsmaskin]

the loss of voltage is minimal (110 to 106V is 3.5% or something)


in theory power is constant between the too voltage levels.

400W / 106V = 4A <--> 400W / 12V = 33A

This is only in theory, but 4amps of 110VAC would-be able to feed a hungry 110VAC to 12VDC power supply

50% increase yes and no.
Yes if you want the same ground connection as topside.
No if u dont. if u use a metal frame on your ROV as ground. if you use this option be sure to switch off all power before the rov exits the ocean. then its grounded any more=)

[anagama]

Yes if you want the same ground connection as topside.
No if u dont. if u use a metal frame on your ROV as ground. if you use this option be sure to switch off all power before the rov exits the ocean. then its grounded any more=)

That's an interesting idea and I'm getting pretty interested in the AC route. I note that the seabotix ROVs use AC:

Input Voltage: 100-130 VAC or 200-240 VAC
Power Requirement: 1,000 Watts maximum
Safety: Isolated input power, circuit breaker, line insulation monitor, leak detector. Meets and exceeds "Code of Practice for the Safe Use of Electricity in Water"
http://www.seabotix.com/products/lbv150-4.htm (see "specifications")


I do have concerns with galvanic action eating away at the metal below the waterline from stray current, though I do have fresh zincs on. Of more concern -- I really don't want to be electrocuting marine life.

Anyway, I found a PDF of that "Code of Practice ..." -- I'm going to have study it. Here's the link:
http://www.imca-int.com/documents/divis ... CAR015.pdf

---
Edit: Seabotix manuals: http://www.seabotix.com/service_support/manuals.htm
from the LBV150 model (smallest):
Input power is rectified inside the Surface Power Supply becoming 360 VDC for transmission via the tether to the LBV. At the LBV, the 360 VDC is converted to 28 VDC inside the Vehicle Power Supply (VPS).

[krigsmaskin]

Normally saltwater is an excellent conductor, so I think it can serv as ground connection for your rov.

The best is to use a 3rd wire as ground connection.

To be safe buy a pair of automatic fuses a couple of amps higher than your maximum need of amps.



Helge

[glot]

Higher the voltage, the lower the current. If you use an inverter ( they are getting cheap now) you need to allow for starting current of the motors, not just the rated running current. Also, you can get cheap 600w petrol gensets. Small and quiet. Because it is a floating system electrically wise, you need to get between both active and neutral to get an electric shock. Also, fit an RCD at the point of supply incase one of the conductors on the line side of the RCD somehow gets to earth ( a breakdown in the inverter or gen set for example) and the system is no longer fully floating.DC has lower cable losses than AC but then you need DC rated switches etc. There's all sorts of mains voltage rated equipment out there to scrounge for thrusters etc.
You need to still keep electrical connections dry to avoid excessive galvonic action ( ie, electrolosys) no matter what valtage you choose.

[anagama]

I've decided to go the AC topside, DC ROV route. When I get everything set up, I'll post back regarding how it works.

I'm going to try out the cheapest AC/DC powersupply I could find:
http://www.SuntekStore.com/dc-12v-12-5a ... rmer-.html

$20, free shipping, 12V, 12.5A, 150W. If it works, it will be a good deal. If it doesn't, not a big loss.

[Unorthodox]

can you really use the water as a ground?

[SoakedinVancouver]

salt water? For communication, probably, for power, I wouldn't count on it!

[Rover]

Salt water at 20 degC and a salinity of 35g salt per kg water has approx 0.2089 ohm per meter.

If you place two probes 1 meter apart in seawater under the stated conditions, the resistance will be 0.2089 ohm, according to the calculation and published conductance data.

Now add in the resistance of an ROV at 20 or 30 meters, and it becomes to high to be usable.

-Jim