canister light idea

[FallenMatt]

just got this idea passing through my head:

why not just fill the canister with non-conducting fluid? no air means equalized pressure means you don't have to have super strong canister walls.

and i guess it would make it also more leak-proof.

i don't know, just an idea.. anybody tried it ?

[jonnythan]

FallenMatt once bubbled...
just got this idea passing through my head:

why not just fill the canister with non-conducting fluid? no air means equalized pressure means you don't have to have super strong canister walls.

and i guess it would make it also more leak-proof.

i don't know, just an idea.. anybody tried it ?

Few things come to mind..


Non-conducting fluid is expensive and/or messy.

You'd need to have some handy all the time just in case.

It'd be hard to spot leaks.

Would ruin the buoyancy characteristics of any canister.

Strong walls are good for getting banged up and supporting a heavy battery, not just water pressure.

Charging would be a PITA.

[Fetch]

Sounds like a cool idea, the only question being the liquid to use. I've read reports of some computer overclockers who got a hold of some 3M liquid that was non-conductive and safe for electronics, but it was apparently horribly expensive stuff.

Also, I'd imagine you'd always have a little gas, at least, in the canister. In which case you'd have a roving bubble moving along :) not sure about the stress implications of that, tho ;)

jeff

[Scubaroo]

I'm with jonnythan on this one - trying to solve a non-existant problem (canisters imploding at depth) with a solution (pun intended) that introduces it's own problems.

How would you charge the battery?

The two methods I know of for canister construction are machining, and injection molding - if you're machining the canister, you're already starting off with excess material you have to machine away, so it's probably less work to leave a thicker wall in place, and if you're molding, you have complete control over the thickness of the walls during design, and the cost of additional raw materials for a thicker wall is probably minor compared to the overall cost of mold setup and the rest of the canister. You'd save maybe a few bucks on a several hundred dollar light, and then have to pay for the liquid.

[FallenMatt]

that was a specific situation. Overcloccers need a fluid with a high temperature capacity/transfer to use it for cooling. That's why it is such an expensive thing.
But just to fill a canister ? i would think mineral oil that you can buy in any pharmacy would be enough for this use.

about bouyancy characteristics: you could just add a piece of styrofoam or something like that inside.

you could also have a strong outer "shield" that is not necessairly watertigh and internal soft container (plastic bottle) with battery. This way all the remaining air in the battery compartment could still get squeezed to equalize pressure.

the cool thing about this that you would end up with a canister light rated to thousands of feet of depth :) how cool is that ?

(yes, i know you still have to deal with the lighthead that contains air.)


Fetch once bubbled...
Sounds like a cool idea, the only question being the liquid to use. I've read reports of some computer overclockers who got a hold of some 3M liquid that was non-conductive and safe for electronics, but it was apparently horribly expensive stuff.

Also, I'd imagine you'd always have a little gas, at least, in the canister. In which case you'd have a roving bubble moving along :) not sure about the stress implications of that, tho ;)

jeff

[FallenMatt]

well sure, you can look at it that way too :-)

but also: no o-rings do deal with, less stress on the canister, probably could survive bigger beating that a normal canister (you add the stress of the pressure to the stress of an impact and that can be a mighty force)

I've read in "caverns measureless to man" that Sheck Exley was using such custom made light canister on his dive past 800 feet....



Scubaroo once bubbled...
I'm with jonnythan on this one - trying to solve a non-existant problem (canisters imploding at depth) with a solution (pun intended) that introduces it's own problems.

[j-valve]

If you want to put liquid in the canister, why use it at all? The battery is made of ABS (canister) and it is filled with liquid (acid) so solder some leads for your wire to the terminals, lots of eposy on the termials and VOILA- insta canister :)

[jonnythan]

FallenMatt once bubbled...
well sure, you can look at it that way too :-)

but also: no o-rings do deal with, less stress on the canister, probably could survive bigger beating that a normal canister (you add the stress of the pressure to the stress of an impact and that can be a mighty force)

I've read in "caverns measureless to man" that Sheck Exley was using such custom made light canister on his dive past 800 feet....




Why no O-rings? Fill the thing with oil, you need to seal it in there somehow. It sounds incredibly complicated for something that is essentially a pipe with one end epoxied and the other end fitted with an O-ring. Styrofoam would compress under pressure, leaving you with almost the same pressure gradient as before. Dual layer canisters? Bull donkey, a battery sitting inside an air filled canister seems to be working fine, and you don't end up with something that's 8 pounds negative on your right hip.

J-valve's idea works fine for an SLA battery - but again, you're dealing with a very negative hunk of stuff on your hip. To balance that out, you need to create some buoyancy on the canister.. what's the best way? Trap some air in there, and do it with a sealed canister. If you really need to eliminate the pressure differential, duct tape a miniaturized BC bladder onto the battery and give it an inflation hose..

[FallenMatt]

:hehe:

[jtsmith]

Okay...I can shed some light on this. :)

You use mineral oil. I fill my light head and it helps disperse the heat (Flash Point > 420F)....in fact, I can run my light out of water as long as I need and then jump right.

I also fill my canister up too. My canister is small and uses NimH batteries so it only adds 1/2 pound to the weight since there wasn't much air to begin with.

My light is all homemade so I was concerned with leaking, especially with $40 worth of NimH batteries that would be corroded to hell if they got wet. So I sealed it the best I could and then filled it with Mineral Oil. I drain the oil at the end of the year and I usually find about a teaspoon or less of salt water.

Charging is easy. I have charging wires coiled up in the bottom so I just pop my end cap off and grab the wires and charge it. NimH batteries don't vent so there is no problem for the batteries....just make sure that you don't quick charge or overcharge because you risk popping the vent on the battery and ruining it. The oil doesn't ruin the batteries in this case because they would dry out after that vent pops anyway.


Now, all this said, I would not recommend using sealed lead acid for this. Sealed lead acid batteries have rubber caps on their vent holes that allow pressure to escape but not go in. Under pressure they do have air in them and the oil will be forced inside. This doesn't ruin the battery but does shorten the life I've found. I got about a year out of my lead acids using the mineral oil method. Considering how cheap they are, that's not all that bad.

Another tip, my lead acid canister is 6" round so when you fill it with oil it does add 2 to 3 pounds of weight. I always strap a 2" PVC tube sealed with air in it on the side of the canister to balance out the weight.

Mineral oil is a little more messy, but it reduces the failure rate to nothing.

Note** Mineral oil will basically allow you to use any electronic device underwater. I do quite a few night dives and got tired of the weenie strobe lights you can't see in low vis, so I place a high power strobe light (75 Watt) into a mason jar of Mineral oil and hang it on the line.

~JT
http://ecra.emeraldcoastboating.net

[jtsmith]

I have tried J-valve's idea of just sealing a lead acid battery and it doesn't work.

First off, a regular SLA battery has vent caps and the only way to seal them is to cover them with a potting compound of some kind. I tried this and basically had a square block of rubber with 2 wires coming out.

It worked fine for about 3 dives and then it got to where it wouldn't charge near as well or last near as long. I soon noticed a bulge in the side and found a large air bubble growing. It eventually caused the potting compound to crack and then water got in the battery.....it was toast at that point.


From further research I found that SLA batteries do discharge a small amount of gas even if you charge them gently and do not overcharge.

Another failed canister was a completely sealed one that I made just had charging terminals on the outside. This was my first canister and it eventually blew the switch boot off to outgas. I later added a vent plug for charging and found that this design works really well. The only limitation is that you can't use high power bulbs or heat became a problem.

~JT
http://ecra.emeraldcoastboating.net