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US Navy develops underwater wireless battery-charging tech

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Isn't this stuff more electric vehicle than phone sized?

Which I think has also been demonstrated, but is non trivial.

100s of Volts, 100s of Amps all taking place in fairly conductive sea water, rather than fairly well insulating air.

What could go wrong? Quite a lot.

That said getting and setting a standard could make it as ubiquitous as the 21" torpedo tube, which dates from pre WWI, yet is still in use.

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Joke

Re: Isn't this stuff more electric vehicle than phone sized?

don't worry, maker 'X' will have it (along with the kitchen sink) as a feature in the ********* by next April.

Leccy and seawater really don't go well together so the ******** will guarantee to make your hair stand on end.

[see icon]

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Re: Isn't this stuff more electric vehicle than phone sized?

Would need to know how advanced the charging systems are? I am presuming that they are state of the art LION batteries and not at all using NiCad batteries with limited charge capability. How much charge can they put into a battery quickly, so as to have fast recovery, fast charge and fast release?

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Re: Isn't this stuff more electric vehicle than phone sized?

Probably lead acid batteries because them plus some empty space is closer to the weight of water. The charge top-off and balancing takes hours but the bulk charging and discharging happens as fast as the electrolyte can mix.

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Boffin

I'd think Qi would work ok

minus some losses due to eddy currents in the salt water, Qi should be able to manage it

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Anonymous Coward

Re: I'd think Qi would work ok

Shame about horrible efficiency.

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Obligatory XKCD...

here

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Re: Obligatory XKCD...

Actually, in this case, considering they're practically the only customers, they can probably force this standard on the manufacturers...

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It's obvious ...

Base the new standard on a standard torpedo tube. Induce vehicle to enter open tube. Seal tube. Expel seawater. WD-40 spray (optional). Charge using standard contacts on hull. Disconnect. Flood tube and release vehicle.

You know it makes sense.

At least, for vehicles less than 20 inches diameter, or so. Bigger than that, you would need a very big plastic bag instead of the torpedo tube.

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From the headline I thought it was going to use chemistry based on sea water to charge itself. That would be impressive. Would solar panels on top and parking it a meter or so work too?

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Mushroom

Even in a sea of chemicals...

You need a power gradient.

So you would need something to react with the seawater, then to replenish this. Fish can do it, because they eat plankton etc. Plankton can do it, because they use photosynthesis. No closed systems. Those crabs/shrimp on thermal vents eat the bacteria that run of the vents.

So you have a few sources of power. Solar, or heat generation and even then you use the gradient difference to produce power.

So you could make a battery that "runs on seawater" but it would never recharge, just discharge slower.

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Re: Even in a sea of chemicals...

Crazy idea that definitely won't work, but could you use a Peltier device to extract energy from the difference between the depths of water?

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Re: Even in a sea of chemicals...

You would need a long cable to reach below the thermocline. But there are long-range autonomous 'gliders' that travel by sawtoothing up and down, changing buoyancy to do so. Very low power consumption. Navigation underwater isn't easy, so they pop-up now and again to see where they are.

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Re: Even in a sea of chemicals...

So you would need something to react with the seawater, then to replenish this.

The USN (and I'm sure others) did research a long time ago on batteries that used seawater as the electrolyte, in which case I'd assume the anode was sacrificed (and the cathode, eventually). Whilst you might assume that people have considered these, I suspect that the equipment suppliers use industrially available solutions based on lithium simply because that's what they can easily buy, and thus the USN have to recharge the things.

Perhaps a chemist could give us a view on the energy density and implied endurance of a seawater battery? If the endurance is a few hours, then there's no benefit over rechargeable sealed batteries, if you could get weeks out of it, then it becomes more interesting.

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Unhappy

"From the headline..going to use chemistry based on sea water to charge itself."

Actually there are torpedoes that use salt water for the electrolyte in the batteries.

They area attractive because you can pack more cells in for the same weight (no electrolyte to carry) and don't self discharge (no path between the plates until the sea water is let in) so long shelf life.

Unfortunately they are single shot and can't be recharged.

I guess they'd also go faster in the Red Sea.

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Anonymous Coward

Re: Even in a sea of chemicals...

Upvoting you lot for being so fine tuned to the tiny detail that there is a tiny gradient of power through the depths and that some fish use this to swim.

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Joke

Re: "From the headline..going to use chemistry based on sea water to charge itself."

"Unfortunately they are single shot and can't be recharged."

IIRC one sci-fi had re-useable torpedoes...

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Re: "From the headline..going to use chemistry based on sea water to charge itself."

Unfortunately they are single shot and can't be recharged.

In context that wouldn't matter. If the undersea drones that USN are thinking of could be powered by an ultra long-life seawater battery, then it doesn't matter that it periodically has to have the battery switched out - if the frequency of that is much lower than recharging a rechargeable battery.

The use in torpedoes implies relatively short operating life, and high power output if driving the motor, but whether that is endemic to seawater batteries I don't know.

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Anonymous Coward

Makes sense keeping it under water as you don't anything crashing into it.

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Charging station ?

The charging station needs a LARGE electrical energy capacity (or a permanent cable to an external generator).

In hostile waters, the charging station would probably need to be either a large drone to allow it to get to a suitable location or an air dropped disposable charger. As the drones to be charged have to find the charger, it will need to emit some signal (probably acoustic) that the drones can detect. The presence of the signal would however tell any enemy that there are drones working nearby and where the charger is.

In friendly waters, a grid connected charger or a towed charger (if too far from mains electricity) would be possible.

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Re: Charging station ?

From the article: Wayne Liu showed he was able to run a proof-of-concept with his mobile phone, protected in a plastic bag, charging on a pad.

This sounds as though it was effectively a very small degaussing coil, a technology that is now highly developed for the demagnetisation of ships' hulls.

Trouble is that to transfer enough power to charge a submersible's batteries the amount of "input" power required would require a surface or submarine vessel to generate it; obviously enough a surface vessel would be visible (security risk) although a submarine would not be.

However, in order to get enough power into the uncrewed drone the magnetic field needed would be large enough to be moderately easy to detect by a hostile power using its own submarines or uncrewed drones. At the risk of stating the obvious this would compromise the security of any submarine charging vessel.

The "torpedo tube" approach would appear to have a lot to offer; the technology to enable bits of hardware to mate in orbit is now routine so an underwater equivalent should not be beyond reach. Of course it depends - at least in part - on the relative sizes of the drones and the "mothership".

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Re: Charging station ?

You could have a wave action, tidal or ocean current generator for the charging station. Or a field of them. This technology existed in the 70's, it should be ready for this kind of application by now. Position the charging station in an optimal location for the generation of power, store it in batteries there, then when the UUV comes in it charges up. The charging station would be almost unnoticeable, having a very localized signal to get the UUV from "very close" to "properly aligned". Make it look natural to the area - rock, coral, or for outside a shipping harbor a discarded shipping container.

If you move the data away from the location physically - long cable, another UUV, etc - the charging station would be almost impossible to identify once deployed. If the UUV is detected have it not return to the station and then just deploy another UUV from a safe distance and you're back in operation.

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Anonymous Coward

Re: Charging station ? - Obvious Solution

The obvious solution is to use microwaves to transmit the energy.

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Re: Charging station ?

"Trouble is that to transfer enough power to charge a submersible's batteries the amount of "input" power required would require a surface or submarine vessel to generate it; obviously enough a surface vessel would be visible (security risk) although a submarine would not be"

You're overthinking it.

An inductive charger setup can be sealed against water ingress. Having to plug things in means connectors and other things which don't appreciate getting salt water in them.

This is about reliability, not stealth

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Coat

How is this still a thing?

I guess I just don't get what makes this a novel innovation. We've had wireless chargers for how many portable electronics devices now? So we amp it up to do a drone. Underwater. Okay, a little tougher, but same basic premise, no? Now, back when Nikola Tesla experimented with this kind of stuff, that was innovation. Today, can't we just take that wireless power is possible for granted and that doing it in stranger environments (like underwater) can be assumed to be possible with little effort?

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Re: How is this still a thing?

The point of this however is standardisation. They want to develop a standard that they'll impose on their vendors so that they don't end up with incompatible kits (so whatever form their charging stations take, they don't have to deploy 6 versions of them if they have 6 UUV vendors).

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Re: How is this still a thing?

With some advanced 3D printing technologies it is a matter of time before the navy can make these themselves with what ever power arrangements they can manage.

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Where's the advantage?

"But recharging batteries by either landing or docking with a surface ship to recharge “expose the warfighter and impose limitations on remote autonomous operations.”"

How exactly will recharging by docking with the underwater part of a surface ship help matters? This won't be broadcast power, but very short-range effectively contact-based charging same as the mobile charger used to inspire the idea. There are quite possibly benefits in being able to charge in the water without having to haul the thing out and break waterproof seals to plug it in (although wireless charging tends to be much slower so turnaround time probably wouldn't improve much), but it will still be subject to exactly the same exposure and limitations currently experienced when cuddling up to a ship or base station in order to charge.

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Re: Where's the advantage?

> How exactly will recharging by docking with the underwater part of a surface ship help matters?

Imagine the Bad Guys are watching from another ship, a plane, a spy satellite, or from the shore. If you pull the sub out of the water, the Bad Guys will see it. If your sub stays underwater and just comes close to the ship - or close to the charger on a long cable lowered by the ship - then they Bad Guys won't see it.

Maybe you're doing secret spy stuff and you want to hide the fact that you're using the sub at all, so you launch it when the Bad Guys aren't looking and keep it submerged. Or maybe if the sub is part of your defenses you don't want the Bad Guys to know when it's off-duty and recharging, because that would be a good time to attack.

Perhaps you just want to keep the sub in service as much as possible, and hauling it out to charge it takes time. Or perhaps it's bad weather so hauling it out stresses the sub and crane and is dangerous to the crew, so you don't want to risk it unless you really have to. Or perhaps it's very bad weather so hauling it out is impossible, but charging on a submerged charger with a long cable is possible.

Having said all that, I don't know why they're not just looking at underwater power connectors for wired charging, but I guess that's tricky too. Maybe they are looking at that too, and just chose to speak about the wireless one. Or maybe they've already looked and decided it's not practical.

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Re: Where's the advantage?

Back in the day (WW2 minature submarines) the ship had an access port under water to launch/retrieve. Similar principle to a diving bell.

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Re: Where's the advantage?

Maybe they are not just thinking about surface ships.

A SSBN that could host electric drones to patrol nearby and detect hostile ships/submarines would certainly be useful and a similar tech could also help hunter killers find their targets.

For surface ships having a school of drones looking for mines and submarines, or in the case of the USN, large tankers and freighters, would also be useful.

Automatic docking and charging means the drones would be able to patrols with minimal intervention by the crew.

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Coat

Simples

Just go to the nearest underwater Waitrose car park.

Mine is the waterproof one with the loyalty card in the pocket.->

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Why not simply replace a shark's brain with a computer and train it to do what you need?

Far easier than trying to rig up underwater charging

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I would have thought ...

That a plug and socket arrangement that could withstand immersion in salt water would be cheaper, smaller and less heavy than any system that can transfer the same amount of power wirelessly.

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GBE

Re: I would have thought ...

"a plug and socket arrangement that could withstand immersion in salt water"

That's far more difficult than you think it is. Seawater is really hard on many materials and is fairly conductive. It's hard enough designing a high-power plug and socket arrangement that works reliably and robustly in when there's a trained person there to carefully plug and unplug it in air. An autonomously operated plug/socket submersed in seawater is a nightmare.

Some sort of near-field inductive charging system sounds way easier to me...

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