diy solar

diy solar

Boating with LiFePo4-safety

Bluedog225

Bluedog225

Texas
Joined
Nov 18, 2019
Messages
2,959
Good morning,

I was thinking about taking one of my LiFePo 12v 100 ah batteries on the small sailboat (or kayak) for some multi-day camping. It occurred to me that I ought to check on what happens in the event of a capsize. If completely submerged in salt water, I’m guessing that the battery shorts and melts. And if splashed it would burn off the water causing the short so damage might be limited.

Does this sound right?

However, the primary purpose of this question is what happens to someone in the water with a submerged battery? Say 1-2 feet away. Are you ok because you are not in between the terminals? Or are you SOL in the general neighborhood?

Thanks
 
Sorry to be "that guy" but it is LiFePO4 (Lithium Iron Phosphate), not LiFePo (Lithium Iron Polonium). :)

I don't have an answer to your question but I'm curious about the answer.
 
Bluedog225 said:
Good morning,

I was thinking about taking one of my LiFePo 12v 100 ah batteries on the small sailboat (or kayak) for some multi-day camping. It occurred to me that I ought to check on what happens in the event of a capsize. If completely submerged in salt water, I’m guessing that the battery shorts and melts. And if splashed it would burn off the water causing the short so damage might be limited.

Does this sound right?

However, the primary purpose of this question is what happens to someone in the water with a submerged battery? Say 1-2 feet away. Are you ok because you are not in between the terminals? Or are you SOL in the general neighborhood?

Thanks
Click to expand...
The battery terminals are fare away to being shorted with salt water. If the battery box is water proof you probably fine - maybe some (expected) oxidisation on the terminals.
You are safe with a submerged 12V battery, 12V is low voltage and not dangerous.
 
Thanks for the response. I have a hard time understanding how it would not arc through salt water given the high discharge capability of lifepo4. Eg. 100ah at 12v discharged over 60 seconds.
 
Salt water is around 20 ohms - cm (In full ocean salinity). So if the terminals are 10 cm apart and the current conducted over an area 10x10 cm then 2 ohms. So at 13 volts => 6.5 amps. won’t arc, will kill battery. I suspect any water intrusion thru the case will quickly corrode everything inside beyond repair.

edited based on fega72 correction
 
Last edited:
Thanks for the detail. Would this mean I don’t need the T-Class fuses I bought? If the BMS will shut down a short?

edit-The issue I’m struggling with is I’m told that high-discharge lifepo4 can arc across an air gap to the degree that special breakers, switches, and fuses are needed. I would guess that air is a better insulator than salt water.
 
Last edited:
I can't confirm or deny your source's assertion about LiFePO4 specifically arcing but can maybe clear up the terminology.

An "arc" occurs when a strong electric field causes a non conductive medium (like air) to break down into plasma, which then acts as a current carrying conduit through the air to allow current flow between two conductors that are not in contact. Voltages are often high, but currents generally are fairly low.

It is NOT high current flow through an already conductive medium. By definition, if something is normally conductive then an arc cannot occur. The current flow through salt water is just like current passing through a copper wire, not an arc through air.
 
codfish said:
Salt water is around .2 ohms per meter (In full ocean salinity). So if the terminals are 1/10 m apart, then .02 ohms. So at 13 volts => 650 amps. The BMS should see this as a short and shut down, but it would not arc. I suspect any water intrusion thru the case will quickly corrode everything inside beyond repair.
Click to expand...
It is NOT 0.2 ohm per meter! It is 0.2 ohm meter! Let's see it in ohm centimeter:
Water-Resistivity-Typical-Values-.jpg
 
Whatever. Can't you just put in in something like a small ice-box? Or a dry-bag? And tie it to the boat so it doesn't sink?
 
fega72 said:
It is NOT 0.2 ohm per meter! It is 0.2 ohm meter! Let's see it in ohm centimeter:
View attachment 77362
Click to expand...
Thank you, I read the table too fast. But saltwater immersion and BMS electronics is a near certain short term death of the BMS. The various bus bar and wire connections will take longer, but will probably require replacement within months. Aluminum cases of the cells will also pit.
 
codfish said:
Thank you, I read the table too fast. But saltwater immersion and BMS electronics is a near certain short term death of the BMS. The various bus bar and wire connections will take longer, but will probably require replacement within months. Aluminum cases of the cells will also pit.
Click to expand...
Yes, it will destroy the BMS very quickly if the battery (or the case/box) is not marine grade.
 
Agreed. My primary worry is not the battery. For example, I think the battle borns are sealed up pretty good.

My concern is being in the water in close quarters with a fully charged lifepo4 battery. If touching the terminals with sweaty hands is unwise, I would think there is a danger here. Trying to understand it better.
 
Bluedog225 said:
Agreed. My primary worry is not the battery. For example, I think the battle borns are sealed up pretty good.

My concern is being in the water in close quarters with a fully charged lifepo4 battery. If touching the terminals with sweaty hands is unwise, I would think there is a danger here. Trying to understand it better.
Click to expand...
No danger there, if you are using one 12V battery or the battery bank is 12V.
 
I do appreciate all the input. I can’t get past the idea that getting into a bathtub of salt water with a battery is unwise. (chuckle).
 
Bluedog225 said:
I do appreciate all the input. I can’t get past the idea that getting into a bathtub of salt water with a battery is unwise. (chuckle).
Click to expand...
One of the interesting things about electricity and water is that salt makes it much less likely to hurt you.

Fresh water is dangerous because it is somewhat conductive, but not as conductive as your body with all those electrolytes. So the water gets the electricity to your body, then it all decides to flow through the least resistive path - you.

Salt water on the other hand is about the same conductivity as your blood, and your skin is a decent insulator. So it has no reason to concentrate itself through your body. Of course an electric eel proves that you can get shocked, but it's still better than freshwater.
 
You can kill a battery with salt water or fresh water .
A 12V battery can not kill you if you submerging it in water.
12V is not enough force to push enough current trough your body to kill you.
 
Honestly... what is this?
Are you all trying to win the McIlroy Award? (for The Most Gratuitous and Fruitless Discussion in an Online Forum - any reference to the Rory Award not-so-coincidental ;·)

For one thing, any power source you put into the sea, the current will discharge between the poles, so unless you have any body parts right between them, even an arc won't touch you.

For another, as stated, if you take a battery kayaking, it's not too difficult to waterproof it enough to withstand a capsize.
So, since this is not in the Humour section - and even there, it would be a bit... - can everyone just stop shooting themselves in the feet (any reference to Guy Ritchie...)
 
You must log in or register to reply here.
Back
Top