12v Battery enclosure

[Travis]

Any suggestions for battery enclosure? I am running a 12v 7ah lead acid sealed battery on board so I have full power. However, after consulting an electronics forum for wether it was safe to submerge battery in water they recommended I put it in an enclosure. Any ideas on what kind of enclosure to use? Here is the forum and now im a bit confused.

https://forum.allaboutcircuits.com/thre ... st-1507199

[Oddmar]

Before my ROV walked off i had my 12vdc 10kma SLA batteries in a 8" diameter, 4' long aluminum pipe from OnlineMetals.com.

If you aren't going TOO deep you could build an aluminum box and stack them inside, then seal the lid with silicone. Build internal baffles for better support. But the box shape would crush at any serious depth.

[bigbadbob]

If you put SLA's in a sealed box you could fill it with oil to prevent crushing.
but SLA's can vent hydrogen so better to put them in a crush-proof tube but you must have a blow off valve to vent excess pressure or you can end up with it "VENTING VIOLENTLY" (I hate to use the word "exploding")
I've seen first hand the results of a battery "venting with flame" in an AUV. not pretty but at least it had a blow off valve.

[Travis]

This was same post as below; however, it will not let me delete this post.

[Travis]

If you put SLA's in a sealed box you could fill it with oil to prevent crushing.
but SLA's can vent hydrogen so better to put them in a crush-proof tube but you must have a blow off valve to vent excess pressure or you can end up with it "VENTING VIOLENTLY" (I hate to use the word "exploding")
I've seen first hand the results of a battery "venting with flame" in an AUV. not pretty but at least it had a blow off valve.

Here is my ROV. Any ideas on how to incorporate something to fit the spot where the battery is without rebuilding? On the electronics forum, they asked if I thought of hooking two smaller lipo batteries up in parallel and sticking them in the tubes. If I went this route I could eliminate the large battery altogether and run multiple smaller batteries in parallel to allow for the "ah" of the original 12v battery. Any thoughts on this approach? Also, I plan to only go a max of 125ft, but will likely not go above 60 - 70 feet often as there are not many lakes near me with a depth greater than 60 feet. The two outer pipes are 3 inches and the center electronics tube is 4 inches. I tried sliding the battery in the 4-inch tube, but the tube is just a hair shy of being able to slide in. This is also my very first ROV, and I am an over-thinker, so I'm just consulting some advice on it. Thanks.

[bigbadbob]

Yes, if you use lippos in tubes you should be fine, I'd still use blow off valves though.
Lippos will be way lighter too and you won't need so much buoyancy if you're not trying to float a lead acid battery.
Best if you can remove the lippos for charging but that may present a sealing problem so If you charge them in the tubes I'd definitely have blow off valves/pressure relief valves/whatever you want to call them.
Personally I don't like putting batteries underwater I like to have them top-side.
but my rov is small and light and doesn't take much power so power transmission down the tether is not a problem if you use 48v or more. higher voltage means less current in the tether. but I digress... you asked about batteries.

[Oddmar]

I like both.

Batteries in the ROV to power everything, and to prevent crashing the electronics/ autopilot when the motors draw high amps when thrusting.

Power down the tether to recharge batteries for long dives.

On Bob's comment of "LiPo's are lighter too", i prefer heavy batteries, heavier everything really. The lighter you make the ROV the more it will get tossed around by tether drag, currents, etc, making getting good video difficult. Also if you eventually put a manipulator (grabber) on the ROV it's nice to have a nice heavy stable ROV when trying to grab onto things.

The downside of making it heavier is that, out of the water, gravity is not your friend...lol.