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Power supply options


(Austin) #1

What do you recommend as the best power source for multiple thrusters?

 

I would like to use a surface power source like a car battery or maybe even a power supply. Any suggestions would be grateful.

 

Thanks.


(Rusty) #2

Hey Austin,

There are lots of options for the power supply. The main concern is finding something that can supply enough current for multiple thrusters.

We've used the thrusters with DC power supplies, lithium polymer batteries, and lead acid batteries.

Here are some suggestions:

Power Supplies: Most DC power supplies don't the necessary current output to run the thrusters. You need at least 12.5 amps per thrusters. We used them for our lab testing because we run the thrusters constantly, but they aren't really cost effective otherwise.

Lithium Polymer: Lipos will work great. I'd suggest looking at HobbyKing.com for lipo batteries. They generally have a "C" rating (like "25C") that describes their output rate as a multiple of their capacity. For example, a 1000 mAh battery with a 25C rating would be able to output 1000 mA x 25 = 25,000 mA = 25 amps.

Lead Acid: Lead acid also works well and is affordable but heavy. We use a lead acid battery on our SolarSurfer because it's robust and reliable. Discharge rates for lead-acid batteries are a little more complicated something like a car battery can handle a few thrusters fine.


(Austin) #3

Rusty,

Thanks for the quick reply and suggestions.

My goal is to use a 12v 55 amp hr. marine battery at the surface to cut down on the weight and power my thrusters while using an on-board micro-controller for the ESC’s.

I’m just not sure the best way to power all 4 thrusters without having to run an additional 8 wires through my tether cable from the surface.

Is there some sort of power distribution circuit that you know of that could handle the necessary current?

 

Thanks for your help!


(Rusty) #4

Hey Austin,

Make sure your battery can handle "deep cycle" use where it is fully charged, then fully discharged. Many batteries that are meant for starting car or boat engines can handle being fully discharged and can get damaged.

It's difficult to transfer power through a tether because of power losses in the tether at low voltages (Power loss = current^2 * tether resistance). The only ways to avoid this are to have use short tether, a thick cable with low resistance, or to transfer the power at high voltage (and low current). The last one is difficult and expensive. Some commercial ROVs operate at voltages as high as 3000V to minimize losses in the tether.

If your ROV won't draw too much current, the power losses will be minimal and you could send power down through a thick tether wire. Otherwise, I would actually recommend using lithium-polymer batteries onboard the vehicle and only transmitting data and video through the tether.

This is definitely a barrier for low-cost ROVs. Hopefully there will be a better solution in the future.

Rusty


(Ron Ginger) #5

I am thinking about using a common orange extension cord for the tether, They are cheap and you can get 100ft or even 200ft. I have not tested the buoyancy yet, but I could add some foam floats along the line if needed. I am going to use the OpenRov electronics concept with the Home link power on Ethernet modules. Is it reasonable to consider 120VAC on the tether with a power supply on board?

I only want to be able to go down in the harbor, maybe 30ft deep max. I will operate from my boat so I can run an inverter for the 120vac

 


(Rusty) #6

Ron,

I'm sure at 30 ft the extension cord will work well. The buoyancy shouldn't matter too much at that length either. The OpenROV homeplug modules work great for the tether. It's definitely possible to send 120 VAC down the tether to an onboard power supply but I would be very careful obviously. That's a lot of voltage and power in the water.

If you do send power at 120VAC, you could probably use a much thinner cable and worry less about buoyancy.

Do you think you would directly power the thrusters from the onboard power supply or would there be a battery down there also? Power supplies for high currents are big and bulky generally.

Rusty


(Jim Forbes) #7

We’ve done pretty well with a higher voltage surface power system using lead acid batteries. It helps if you have the onboard electronics for the speed controllers set to run on 24 or 48 v, but the electronics can be a bit complicated. I’m hoping to get my brother to work on a version of ROVotron for brushless motors. It works great for brushed motors, with a 50-100 ft tether, the tether only needs to be about 16 gauge on a 48v system, and having a few volts of voltage drop doesn’t hurt performance noticeably, like it would at 12v.

 


(Rusty) #8

Jim,

The T100s are designed to operate around 12V, so unfortunately, they won’t work well at 24V or 48V. The higher voltage would definitely help with power loss. It should be possible to design the thrusters for higher voltages with a different winding scheme, but it would definitely take some work.

Rusty