Planning Submersible ROV

Hi guys, my son and I have been talking about making a submersible ROV for a while and now I feel confident I can research and read my way through it we've decided to give it a go.

So I've been reading up on the whole subject for a couple of days when I have chance, and one thing I've noticed is a lot of the information is pretty dated and a couple of questions I have I haven't found answers for yet. These are power and with the arduino part of the project so here we go.

I am going to be using 4x( if not 6 )12v Bilge pumps for thrusters, led light clusters and a camera of some sorts on board.

Control side of it going to house 12.1” LCD monitor, raspberry pi, 2.5” hard drive and probably other things.

Now the thing I'm stuck on at the moment is planning on how to power the system.

I would ideally like all the batteries on control side of the thing, and to keep it as light as possible to begin with (if we use it enough we can upgrade).
But I have read about voltage drop along wires after a distance and with me wanting a tether of around 100m I could do with a bit of advice on the matter.

Someone posted to use 2x 24v volt batteries to send 48v down the tether then use 12v converter on board.
Then I've read another that says to use a battery on board charged by the batteries on land.

If anyone fancies throwing their advice my way it would be greatly apreciated.

Thanks

Put the batteries on board. The voltage drop over a 100m cable will be extreme unless you can boost it to 100-1000V for transmission.

Underwater, weight is less of an issue. You just have to make the vehicle a bit bulkier to offset the weight of the batteries with some more flotation. But you save weight on the tether - that will outweigh your vehicle by several times over.

Sorry to bump an old thread, but just wondering about the suitability of using laptop batteries for this project??

Would it be feasible to use them out of their plastic housing and then using a suitable charger to charge them??

Also, I was planning on using 2 battery packs no matter what, as with the design I have I am using them as weight for stability and balance. If I use batteries that are a lower voltage than the 12v the motors and lights require, what solution is more desirable
a) using the batteries in serial and using a buck converter to come down to 12v or
2) using the batteries in parallel and using a boost converter to get up to 12v

The reason for that question is if the laptop batteries are suitable, the max voltage I can find in them is 11.1v, so was just wondering if there was a preferred way of doing it.

Thanks

Finding a "suitable charger" might be more difficult than you think. A laptop has some of the charger electronics built into the laptop and some in the power supply brick. Finding a simple charger with both components in one box might be difficult. You end up buying general-purpose chargers which can be expensive.

Are these old batteries that were used in laptops? Then they are half dead already. The life of a laptop is very harsh on a battery. That is why people will buy new batteries for their laptop after one or two years. The loss of capacity in the first year can easily be 50%.

If I was designing for a system with nominal-12V equipment, I would use a higher voltage and PWM controllers to reduce the effective voltage that the motors and lights see. For lights, a 12V buck converter may be appropriate but for motors, where you always want to control the speed and direction, you must have a PWM controller anyway. So long as the voltage is close - say 18V for 13.8V motors - then PWM will be reasonably efficient.

MorganS:
Finding a “suitable charger” …

I was just browsing what type of batteries were available, sizes and shapes, capacities and voltages. Just more daydreaming time. As the plan up to now is to suspend the batteries in mineral oil in tubes, long slim laptop batteries seemed an ideal solution shape and size wise.

Everything will be PWM so they will be safe.

Will have another look around.

Thanks again

So you now have to find out which batteries are affected by oil as a solvent, and deal with a
real messy construction. Is this to avoid having a pressure-resistant container? Why not use a
strong sealed tube to contain batteries?

Everything will be PWM so they will be safe.

I don't understand this - batteries are only safe if they have appropriate battery management.