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So I was thinking about building a deep water camera housing. The housing would be filled with a non-conductive fluid to counter the pressure at depth.

Although fluids like purified water or propylene glycol (anti-freeze mixtures) are stated to be non-conductive, they become ionized when in contact with metals and plastics, thus gradually conducting electricity again. There are ion-exchange resin products that are supposed to keep the fluids de-ionized though. Source: https://www.electronics-cooling.com/2015/12/tech-brief-low-electrical-conductivity-liquid-coolants-for-electronics-cooling/#

So while the electronics might survive being emerged in liquids for a day, what about the 3V lithium batteries that power the camera? Do you expect this thing blowing up in my face in any case, or is there a possiblity that this might work?

user3002097
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    Some interesting info: Exposure of lithium batteries to external hydrostatic pressure: https://www.ffi.no/no/Publikasjoner/Documents/Exposure%20of%20lithium%20batteries%20to%20external%20hydrostatic%20pressure.pdf – user3002097 Mar 16 '18 at 15:43
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    Transparent mineral oil is also a choice. – Janka Mar 16 '18 at 15:45
  • And mineral oil is a LOT cheaper – crj11 Mar 16 '18 at 15:53
  • Thanks, but mineral oil would burn the place to ashes if the lithium battery ignites, no? – user3002097 Mar 16 '18 at 15:54
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    @user3002097 where would the oxygen come from for combustion if it's underwater? And [propylene glycol is flammable](http://www.sciencelab.com/msds.php?msdsId=9927239) – Chris H Mar 16 '18 at 15:58
  • That Samsung Note 7 phone compressed its lithium cells a bit. –  Mar 16 '18 at 16:14
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    Thanks a lot for the clarification, I will take this into account. I'm concerned about the stuff going off on the surface, like in the back of my car when travelling to the lake. – user3002097 Mar 16 '18 at 16:15
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    How deep is "deep" for you? 10m? 100m? more? Depending on the answer it might be more practical to build an air-filled spherical steel chamber with a window for the lenses. – LorenzoDonati4Ukraine-OnStrike Mar 16 '18 at 17:17
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    @user3002097 What's your rationale for using lithium chemistry? Would you consider batteries with a more docile chemistry? – Nick Alexeev Mar 16 '18 at 17:25
  • google `liquid immersion cooling` – jsotola Mar 16 '18 at 19:06
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    "to counter the pressure" doesn't make a lot of sense. Filling your enclosure with some fluid may prevent leaks (as there's no empty space to leak into), but will do nothing to prevent everything inside the enclosure from being subjected to this pressure. I've build electronics to work at 100m+ depths and they were housed in steel cylinders filled with transformer oil. Any parts with any potential to be 'squished' were avoided. – brhans Mar 17 '18 at 02:36
  • 100m+ is the goal. Lithium because thats what the consumer grade electronics comes with out of the box, I would consider a replacement battery though if the lithium ones don't work out. – user3002097 Mar 18 '18 at 07:32

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My recommendation would be;

Lithium Sulfuryl Chloride (Li/SO2CL2)
or Lithium Thionyl Chloride (Li/SOCL2) cells
- only in a Stainless Steel case
- with the unit sealed in Aflas 7182B polymer O-rings.

Criteria; highest energy density with a flat voltage in the strongest high pressure proof case sealed resistant to aggressive chemicals, caustics, high pH, high pressure.

LiPo cells rupture explosions have been well documented under high pressure

Tony Stewart EE75
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