If I submerge a 12v 7ah sealed lead acid battery in freshwater will it cause any issues? Shock to people, fish, etc?

Thread Starter

travy641

Joined Apr 26, 2020
26
If I submerge a 12v 7ah sealed lead acid battery in freshwater will it cause any issues? Shock to people, fish, electronics in a sealed container, etc? The reason I ask is that I built an ROV, remote underwater vehicle, and have the battery on board, so it would be submerged. Thanks.
 

SamR

Joined Mar 19, 2019
2,126
Well, 2 obvious things come to mind, Voltage leakage due to contact with semiconductive water and integrity of sealing due to pressure. Pure water is an insulator, most water has dissolved minerals and is conductive. Water pressure increases rapidly with depth and may overcome the battery sealing barriers.
 

KeithWalker

Joined Jul 10, 2017
900
In freshwater it only takes 1.23 volts to start an electrolytic action. It will generate hydrogen and oxygen. If the water is deep enough, some of the gasses will dissolve before they get to the surface. The oxygen will corrode the positive battery terminal in time.
The voltage is not high enough to cause an electric shock to a person but fish will sense the electric field and avoid it because it will saturate their sensors.
Keith
 

Externet

Joined Nov 29, 2005
1,493
If it is truly sealed, (hermetic) will likely implode at a certain depth, leaking chemicals that may conduct between terminals and the above comment.
12V is a benign potential where shock is unlikely, but some feeling may occur.
 

Thread Starter

travy641

Joined Apr 26, 2020
26
In freshwater it only takes 1.23 volts to start an electrolytic action. It will generate hydrogen and oxygen. If the water is deep enough, some of the gasses will dissolve before they get to the surface. The oxygen will corrode the positive battery terminal in time.
The voltage is not high enough to cause an electric shock to a person but fish will sense the electric field and avoid it because it will saturate their sensors.
Keith
Good to know. Thanks for the information. I guess its probably safer to just put it in a waterproof case of some sort, attach it to the craft, drill holes for the pos and neg wires and then cover/fill with epoxy? Any suggestions on sealing the battery within a container, or if there is something already that I could put it in and it work how I want as far as wires coming out of the enclosure to connect to electronics? Thanks.
 

KeithWalker

Joined Jul 10, 2017
900
There are lots of submersible enclosures available but they are not cheep. When you choose one, make sure it will withstand at least 3 atmospheres of pressure (about 45 psi at 100 ft.).
Keith
 

SamR

Joined Mar 19, 2019
2,126
For freshwater, the pressure gain is ~ 1Atm/30' so @ 125' = ~4Atm @ 14.7psi/Atm = ~ 60psi fluid pressure. Quite a significant pressure.
 

Reloadron

Joined Jan 15, 2015
5,455
We just did an exercise in DPDT relays. :) So the battery is going for a swim. At a depth of 100 feet the pressure will be about 3 atmospheres or roughly 45 PSI. Based on your other thread I assume the battery will be in a water tight enclosure which is good to that depth, would that be correct? If that is true then the battery presents no problem and if that is not true I suggest you working on a solution which includes the battery inside a watertight enclosure.

Ron
 

Toughtool

Joined Aug 11, 2008
63
At a depth of 100 feet the pressure will be about 3 atmospheres or roughly 45 PSI
At this pressure and depth, a one square foot lid would have 4,363 pounds of pressure on it. That's more than my car weights. So if you can drive your car over it then you are OK. "The average new car weighed 3,221 pounds in 1987 but 4,009 pounds in 2010 (fromhttps://slate.com/business/2011/06/american-cars-are-getting-heavier-and-heavier-is-that-dangerous.html )"
 
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Thread Starter

travy641

Joined Apr 26, 2020
26
We just did an exercise in DPDT relays. :) So the battery is going for a swim. At a depth of 100 feet the pressure will be about 3 atmospheres or roughly 45 PSI. Based on your other thread I assume the battery will be in a water tight enclosure which is good to that depth, would that be correct? If that is true then the battery presents no problem and if that is not true I suggest you working on a solution which includes the battery inside a watertight enclosure.

Ron
Yes that is correct. I originally was going to leave the battery submerged without any enclosure, but something told me I better check first with someone who knows what they are talking about before I potentially put my self or others at risk. I am, however, having a bit of trouble finding a box relatively small in size that is completely waterproof. Should I look for any ole box that is ip67, ip68 rated? I found a site here https://www.polycase.com/techtalk/ip-rated-enclosures/polycase-ip68-rated-plastic-enclosures.html detailing the rating meaning. However, the boxes on this site are a bit oddly shaped and none seem to fit what I need in size? Thanks. This is the battery I am using, and here are the dimensions 5.9 x 2.5 x 3.7 inches.

https://www.amazon.com/gp/product/B003S1RQ2S/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1
 

SamR

Joined Mar 19, 2019
2,126
No, not a waterproof box, a pressure-proof box capable of withstanding more than 4 atmospheres of pressure. That pressure specification will, by its nature, be waterproof at that pressure. The same specification will have to adhere to for any through-hull fittings.

Edit: Note that Submersible in Electrical Classifications basically means covered in water in the bathtub. It does not mean watertight at various depths. You will need an outside pressure-rated vessel that can withstand pressure for 125' x 14.7psi/33' = ~55psi + 10% (minimum safety margin) = ~65psi minimum. Not just the box but any connector penetrations also. One way is to use stainless steel pressure tubing and fittings for wiring conduits. (~60% fill max) for sizing.
 
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Thread Starter

travy641

Joined Apr 26, 2020
26
No, not a waterproof box, a pressure-proof box capable of withstanding more than 4 atmospheres of pressure. That pressure specification will, by its nature, be waterproof at that pressure. The same specification will have to adhere to for any through-hull fittings.
Any idea where I can get a "pressure-proof" case? I found this pelican case, https://www.pelican.com/us/en/product/cases/protector/1120 it says it has an "Automatic Pressure Equalization Valve"? Would this be what I am looking for? Also, would I be able to use the "waterproof through-hole connector" with it? Thanks.
 

SamR

Joined Mar 19, 2019
2,126
Pelican does not make cases for that pressure. The valve is for use after the case degasses at 35 thousand plus feet in the unpressurized cargo hold of an airplane which when it lands the case is impossible to open because of the partial vacuum in it. No, the waterproof through-hole connects are not pressure rated. There is a difference between pressure vessels rated for outside and inside pressures. Also, any penetrations of a pressure vessel must be designed for pressure. You can't just punch a hole in a pressure vessel to make a connection to it.
 
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