Power loss in cable

[onibnasir]

I would be supplying power to my ROV using LIPO batteries at the surface. I plan to design the ROV to goto 100 feet and use 14 AWG for powering the thrusters which are Rule Bilge pumps. Providing a supply of 24V which requires 1.5A, there is going to be a power drop across the power line. Would it help if i use a DC-DC converter for stepping up the voltage at the ROV?

[Rover]

Great question.

Yes you will have a voltage drop in your tether, but starting with 24 volts will cut the loss in half if you use a 24 volt to 12 volt DC to DC converter..... They use them on Semi's to run 12 volt appliances off of the 24 voltbattery system

I purchased our DC to DC conveter on eBay for approx 14 dollars...... looks like the photo below.

NOTE: although they rate it at 30 amps, it runs cooler in the 7 to 10 amp range with occasional higher bursts of current draw.

During our testing, I was pounding the power through it, adding additional load, pushing it harder then I typically would to see if it would take it, and it did get hot enough that it powered down until it cooled enough and came back on line 30 seconds later.


If you are going to consume 10 amps at the ROV, our testing has show that you will be drawing a little over 5 amps through the tether @ 24 volts.

Using a 110 foot tether at 24 DC with a 5 amp load on it, you will have a 2.75 volt loss, and should have 21.75 volts at the dc to dc convertor. Since it drops the voltage in half, you will have approx 10.8 vollts available to the ROV motors pulling 10 amps.

The actual voltage drop will vary depending on actual motor load.

The following info is based on 100 foot of tether in the water..... The other 10 feet of the 110 foot tether is topside out of the water.

This info is based on our testing of the fine strand bulk 14 gauge wire we purchased for .06 per foot at Axeman Surplus (St Paul MN)

100 foot long 14 gauge fine stranded wire = 1.79 pounds

So two 100 foot wires = 3.58 pounds

or .57 ounces per foot.

Plus you have to add in the 4 twisted pairs of cat 5 wire... (The outer sheathing has been removed to save weight)

You will be in the .61 to .63 ounce per foot of flotation you will need to add to your tether.

Be observant off all connections on the 24 volt tether...... Anytime you connect it to a small gauge wire you will induce additional voltage drop....... So try and keep the 24 volt tether 14 gauge all the way to the battery.

Jim

[bikerbones1968]

There is also another style DC to Dc converter (step up module) that I use. It has a completely adjustable/setable output voltage. I needed 30VDC for my LED lighting. I connected two 12V batteries in series actually 11.9V and 10.8V when I measured them. I adjusted the output to 30VDC. Later I connected the converter to a single 12V battery and the output remained constant at the 30VDC that I had it set to earlier. It can handle 10 amps

[Ian MacKenzie]

Where did you find the adjustable step up converter???
I want one!!!

[KR2_Diving]

Where did you find the adjustable step up converter???

Hey Ian,
I got mine off of Ebay.
Here is the link I posted a while back... might be able to dig a bit and find this on a ebay.com (vs .ca)

http://www.ebay.ca/sch/sis.html?_nkw=2x ... 1163929926