Lipo Battery's at depths?

[TwistedElvis]

Has anyone seen a problem with Lipo Battery's with deep depths?
Just wondering about safe depth's and whats the deepest you have gone with Lipos?

[fluxno]

lipos must have a watertight and pressureproof container. lipo packs does not withstand any pressure. pressurizing them can make them short-circuit and explode.
put them in a container, and your good to go.

[martinw]

I know of Lithium Polymer batteries tested to over 3500psi and they worked fine throughout the test and afterwards.

Not in water of course, in oil :!:

They're even sold in pressure compensated oil filled housings ...... see below.

http://www.bluefinrobotics.com/assets/D ... -Sheet.pdf

Martin

[fluxno]

note that i was thinking of normal RC plane/car/boat lipo batteries.

regarding the link to the subsea batteries; they state that its "internaly pressure compensated" i'm not sure what they mean with that. i work with alot of pressure compensated enclosures at work, but they have a piston or hose to equalize the pressure on the inside and outside. there could be several pressure barriers in this cells we dont know about.

for the home builder of an rov i would say that a pressure vessel is the way to go for lipo batteries, and also other batteries.

[martinw]

http://www.o-vations.com/marinetech/pre ... sings.html

I would humbly disagree on your last point, I myself intend using lithium polmer batteries in an oil filled pressure compensated housing at pressure on my hobby ROV.

It is THE major advantage of lithium polymer batteries, RC plane/car/boat or otherwise as far as I can see.

There are risks with both one atmosphere enclosures and oil filled pressure compensated housings relating to putting batteries in them and I wouldn't want to underplay those risks but I'm not sure one is better than the other.

For example a one atmosphere pressure vessel could potentially turn into a bomb if a battery goes bad inside it and degasses

Just my humble opinion of course but I think LiPo batteries will revolutionise underwater vehicles because of this pressure tolerant property

Martin

[fluxno]

http://www.o-vations.com/marinetech/pre ... sings.html

I would humbly disagree on your last point, I myself intend using lithium polmer batteries in an oil filled pressure compensated housing at pressure on my hobby ROV.

It is THE major advantage of lithium polymer batteries, RC plane/car/boat or otherwise as far as I can see.

There are risks with both one atmosphere enclosures and oil filled pressure compensated housings relating to putting batteries in them and I wouldn't want to underplay those risks but I'm not sure one is better than the other.

For example a one atmosphere pressure vessel could potentially turn into a bomb if a battery goes bad inside it and degasses

Just my humble opinion of course but I think LiPo batteries will revolutionise underwater vehicles because of this pressure tolerant property

Martin

i'm familiar with the difference between a pressure vessel and a pressure compensated vessel. i've worked with subsea equipment for 7years.
after reading this article i got more knowlegde about the bluefin batteries buildup: http://www.batterypoweronline.com/image ... botics.pdf
i read that they use special cells from specific vendors, to make sure they dont have any air inside and can withstand the pressure.
The thing is that when you pressure compensate, the components inside the vessel must withstand the pressure. there can be no air or pockets without oil or solid mass. If the battery cells do contain material that are compressable under pressure, the water-depth-pressure WILL affect and crush it.
think of a ping-pong ball inside a oilfilled enclosure thats compensated with a piston or hose. to simulate external pressure, you compress the hose or push in the piston. The oil will not compress. where will the pressure force go? it will implode the ping-pong ball. the same would happen to a battery thats not completly solid. the ping-pong ball is equal to an airbubble/pocket in the battery.


This report is done by some norwegian scientists(i found it by googling) and they pressure test lithium (ion i think) batteries because of a failure on a battery pack on an PIG that exploded because pressure came inside the vessel, and compressed the cells so they exploded, and then damaging the container. http://www.ffi.no/no/Publikasjoner/Docu ... essure.pdf

I will admit that my statement for the homeuser should have specified a very important aspect you point out: very much, definitly have a form for safety function for gassing on batteries. This can be done by several ways. a one-way valve for hydraulics(0.2Bar or something like that), low quality bolt for stretch to vent out pressure(need alot of calculation) or a syringe/piston that can pop out when the pressure increase.

A safeguard for pressure compensated system is also a one-way valve that opens over the maximum pressure for the hose, or when the piston/compensator is a maximum position.

All pressure vessels are potential bombs if they have leakage of water at great depths, the water often comes into the container, but not out; therefore the pressure are kept inside the container when its brought to the surface. and could be dangerous when then opening it. At work we have a special bleedplug that can vent out inside pressure, before opening the container.

i stand at my opinion that one can just use pressure vessels for normal DIY available batteries, and not pressure compensate. but have a safety function.

[KR2_Diving]

I will admit that my statement for the homeuser should have specified a very important aspect you point out: very much, definitly have a form for safety function for gassing on batteries. This can be done by several ways. a one-way valve for hydraulics(0.2Bar or something like that), low quality bolt for stretch to vent out pressure(need alot of calculation) or a syringe/piston that can pop out when the pressure increase.

A safeguard for pressure compensated system is also a one-way valve that opens over the maximum pressure for the hose, or when the piston/compensator is a maximum position.

Hello Fluxno,
Thank you for all the great details!

Would you have any links or pics that you might be able to include that show the pressure release valves that you are recommending? I have a hunch I know what you mean, but a quick link would confirm!

Many Thanks!

Ryan
"KR2_Diving"

[fluxno]

something like this: http://www.snap-titequickdisconnects.co ... index.html
some types can be delivered with different springs for releasing on diffrent pressures.
make sure you get a zero leakage valve, some of the valves can leak slightly, and you dont want that on an rov.

[KR2_Diving]

perfect! Thanks for the link!

[fluxno]

no problemo