Keeping the water off your Lifepo4 installation

[Fuss]

It didn’t matter so much in the past, there’s a storm, the water came in, the batteries got wet, well, they are in the bilge so what do you expect. Or maybe the water came in from below. Well, we can’t plan for everything but now, not getting the battery installation wet is really important.

Did you think about this?

I put the Lifepo4s in the original battery box which is waterproof from the bottom and sides, but not from the top.
I’m making a top that is very splashproof.
That means that if I was to spray it from above with the hose on sprinkler then hopefully no water goes inside.

Any comments?

[Pete7]

I have drop in batteries and a completely dry bilge, so not a problem.

However, I can see that a DIY build with aluminium cased cells and a BMS could be a problem. I would be tempted to do a soft cover perhaps from an old dinghy material held in place with a band of velcro all the way around over the top of the box.

Pete

[Fuss]

I also have a shunt that has a circuit board now, the old one didn’t, so this also needs some protection, but good point about the drop ins.
I’ve got Switches and fuses down there, it all became very complicated. The old installation had no fuses, just a big 500a switch close to the battery. Now there’s more batteries each with its own switch and T fuse etc.

[Pete7]

Whilst our batteries are safe from splashes, we have an inverter, fuse box and MPPT also in the same location along with a flooded lead acid battery. I have to accept that if we get more than a foot of water in the boat in a seaway most of it will be toast. On a 31ft yacht there isn't really anywhere else to put it all, oh and a foot of water is probably 2 tonnes through the boat. Might have other things to worry about

Different for Jedi, he can probably re-purpose one of the crew cabins

[CaptainRivet]

Originally Posted by Pete7

I have drop in batteries and a completely dry bilge, so not a problem.

However, I can see that a DIY build with aluminium cased cells and a BMS could be a problem. I would be tempted to do a soft cover perhaps from an old dinghy material held in place with a band of velcro all the way around over the top of the box.

Pete

DIY Make your case from PVC board and acrylic top with a seal, then they are as watertide as drop ins. Also keeps salty moisture out so your busbars and connectors don't oxidize over time.
2nd isolate the battery cabinet from the bilge so if you get any water into bilge that doesn't reach the bank. Mine faces to stern to the watertide bulkhead, to bow i laminated in a seperator to hull and bilge under my bed seperating it watertide to bilge and hull. Then i laminated in a plain floor piece that sits about 15cm above floor where the bank is on, floor got a seperate bilge pump. So bank cabinet has its own seperated bilge.
Top of cabinet is fibre glass too and the lid is sealed with rubberised foam making it 95% watertide.
So first water needs to stand 65cm high in the hull till it goes over the whole box and then water will slightly drip in which the bilge pump should handle. At 80cm waterlevel it will reach the main cabling with the inverters...well if hull stands 80cm full off water its liferaft time anyhow...

[CaptainRivet]

Originally Posted by Pete7

I have drop in batteries and a completely dry bilge, so not a problem.

However, I can see that a DIY build with aluminium cased cells and a BMS could be a problem. I would be tempted to do a soft cover perhaps from an old dinghy material held in place with a band of velcro all the way around over the top of the box.

Pete

A completly dry bilge isn't dry anymore if eg a seacock leaks or fails...
Bank cabinet must be completly isolated from the bilge.

[CaptainRivet]

Originally Posted by Fuss

I also have a shunt that has a circuit board now, the old one didn’t, so this also needs some protection, but good point about the drop ins.
I’ve got Switches and fuses down there, it all became very complicated. The old installation had no fuses, just a big 500a switch close to the battery. Now there’s more batteries each with its own switch and T fuse etc.

A class T fuse is a very bad LFP bank fuse, its fast reacting, not what you want because
A) a short high peak will trip the fuse that won't be harm for the bank. So unnecessary blackout
B) you cannot use your house as emergency starter as class T will trip class T fast acting.
C)so you cannot use peak capacity of your bank.

But main issue is its physically to small to handle the light bow in a shortend LFP means light bow bridges the fuse making it useless. that lightbow will be created by the 5000A+x current a shorted LFP bank produces...
Highly suggest to use NH fuses, they can withstand 20000A (NH00) till 50000A (NH4) and are cheaper then class T. Yes they are bulky but safe and create the smallest voltage drop of all fuses in same rating. They are slow reacting, so a till c is also no problem.

[newhaul]

This is getting ridiculous. Lifepo4 are much safer in saltwater than any lead acid based chemistry. What happens when the acid comes into contact with seawater? It produces chlorine gas. Lifepo4 will just short out and stop working . A but of splash won't hurt either. But if either is under water we'll you have much bigger issues than keep battery dry. Use common sense .
BTW my DIY bank is in a normally dry compartment under the port sea berth. I sleep stud.
They ( Lifepo4) should not be in the engine spaces anyway. Heat is an enemy of longevity.

[s/v Jedi]

Originally Posted by Pete7

Different for Jedi, he can probably re-purpose one of the crew cabins

Mine are actually inside my keel and I always have some condensation or even rainwater collecting there that my pump can’t get
Never a problem though.

Originally Posted by CaptainRivet

A class T fuse is a very bad LFP bank fuse, its fast reacting, not what you want because

Again we are in complete disagreement and I actually think this claim is radical because a class T fuse is the #1 choice for LFP for the entire marine industry. I have attached the proof that completely discredits your statement. You do this on purpose to get me out, right?

Originally Posted by newhaul

This is getting ridiculous. Lifepo4 are much safer in saltwater than any lead acid based chemistry. What happens when the acid comes into contact with seawater? It produces chlorine gas. Lifepo4 will just short out and stop working . A but of splash won't hurt either. But if either is under water we'll you have much bigger issues than keep battery dry. Use common sense .
BTW my DIY bank is in a normally dry compartment under the port sea berth. I sleep stud.
They ( Lifepo4) should not be in the engine spaces anyway. Heat is an enemy of longevity.

I do recommend a battery box that is waterproof on all sides except the top and to make it as high as will fit. This will limit the problem to sinking boats only, where it doesn’t really matter anymore

[SailingHarmonie]

Originally Posted by newhaul

This is getting ridiculous. Lifepo4 are much safer in saltwater than any lead acid based chemistry. What happens when the acid comes into contact with seawater? It produces chlorine gas.

From a practical matter, it makes little difference, but as someone who actually understands chemistry, this old wives tale is like fingers on a blackboard. I hope your understanding of LiFePO4 safety is better than your understanding of FLA battery chemistry.

There is no balanced chemical equation from mixing H2SO4 and NaCl that produces Cl2 gas. It doesn’t happen. No matter what you learned from watching old movies about WWII submarines!

The actual reaction is:

H2SO4 + NaCl —> NaHSO4 + HCl

Much of the HCl (hydrochloride acid) actually stays in solution and doesn’t poison the air around, depending on how much water is around, although an open container of it is certainly more noxious than sulfuric acid.

[CaptainRivet]

Originally Posted by s/v Jedi

Mine are actually inside my keel and I always have some condensation or even rainwater collecting there that my pump can’t get
Never a problem though.



Again we are in complete disagreement and I actually think this claim is radical because a class T fuse is the #1 choice for LFP for the entire marine industry. I have attached the proof that completely discredits your statement. You do this on purpose to get me out, right?

In this case not. First look at industry standard they don't even put a main battery! bank fuse into the LFP system. The main fuse that present is rated according to and protecting the main battery cable! but NOT the LFP bank itself. And that main cable is chosen for the amps thats expected to be drawn from system. Thats it, nobody cares actually about the enormous current arising if the LFP bank gets shorted.

Simply calculate:

[SailingPNW]

From a battery perspective drop in LiPO4 batteries won't be any worse then any other type when dealing with water, as like AGM batteries or even lead acid they are essentially sealed so only the battery terminals will get wet. You shouldn't have enough water in the bilge to cause a problem.

In a worst case scenario where your boat is sinking the LiPO4 batteries should be safer as the BMS will shut down the battery.

I would probably avoid a DIY battery though, while in reality if made properly in a good box they should be fine, with the potential additional impact to getting insurance, and with the availability of reasonably priced good drop in batteries, it just doesn't make sense to add the extra hassle.

[CaptainRivet]

Originally Posted by s/v Jedi

Mine are actually inside my keel and I always have some condensation or even rainwater collecting there that my pump can’t get
Never a problem though.



Again we are in complete disagreement and I actually think this claim is radical because a class T fuse is the #1 choice for LFP for the entire marine industry. I have attached the proof that completely discredits your statement. You do this on purpose to get me out, right?

In this case not. over 20years ago in my car stero times I burned a car down due to a class-T beimg lightbow bridged in a bank shortage...welll we learning by doing, no docs around and the bats where from scraped military vehicles...


First look at industry standard they don't even put a main battery! bank fuse into the LFP system. The main fuse that is present in the industry standard is rated according to and protecting the main battery cable! but NOT the LFP bank itself. And that main cable is chosen for the amps thats expected to be drawn from system. Thats it, nobody cares actually about the enormous current arising if the LFP bank gets shorted.
2nd class T is widely used in US but hardly in europe.
Why do they use it: it very small so easy to locate and install.

Well and being restricted in size they are only avaliable in fast acting.

regarding starter engine&house with class T.
typical setup 70sqmm cable, so class T has 200A. A starter of 3000W at 12V needs typically 200-250A constant but startup surge is 300-500% in worst case. so take middle 200A fuse according to your table 300% at 1 sek is 600A, starter at 200Ax400%=800A so fuse blows...a slow acting cable fuse not.

But back to topic bank fuse:

Simply calculate the short curcuit current of your LFP bank:
I take mine 16 cells, 272AH, internal resistance 0,12mohm, voltage per cell when full (worst case) 3,65V. restistance of busbars connecting cells 16mohm.

the formula to do this:
(number of cell x cell voltage) / ((number of cells x internal resistance) + (resistance of connecting busbar) = short curcuit current


(16x0,012mohm)/((16x0,012mohm)+16mohm)=58V/(0,192mOhm+16mohm)=58V/0,00352ohm=16477,27 A hupsi :-)


This means my main battery bank(!) fuse must withstand 16477A or it gets bridge by lightbow in a short and is basically useless.
A typical main battery fuse class T 300A for a 95 or 120sqmm cable has a spec of 5000A till 9000A, depending on brand. So it will be bridged means its not appropriate as main LFP bank battery fuse. NH is...



The ratings for class T fuses are 5000-9000A depending on brand, well its simple physics. The current must travel the distance from one side of the fuse to the other through the air. Class T being small it is 10-20mm max distance and in salty humid environment to bridge that is around 5000A...means rating of 9000A is labratory setting with very dry clean air but not in marine...



So well yes a main battery fuse simple doesn't exist in todays industry standard, it is captainRivet standard to put in a main battery fuse additional as first fuse directly at the busbar of battery.
I always use NH fuses made for grid stations 24/365 use, heavly controlled and highest quality plus super cheap.

being 1120AH bank with 1 C const and 2C peak and having 15mm x 10mm copper busbars the max this bank should do is 0.5C constant = 650A, clostest is 630A NH3 or NH4.
I need 16500A short cuicuit so NH3 630A does the job. 2nd advantage it is aLso good the 630A will blow at around 2000A after 30sec and 2C of bank is 2240A means it also protects the bank against peak overload. And 3rd advantage the NH fuse acts also as isolation switch, simply pull it with the puller that is always located next to it. you actually don't need the puller, it has an isolateded ceramic body and with 12 or 24V you can always pull it savely without any harm to you. saves additional connection for an additional battery switch means resistance and point of failures. And well try to find a 630A rated switch...very expensive

[Pete7]

Originally Posted by CaptainRivet

A completly dry bilge isn't dry anymore if eg a seacock leaks or fails...
Bank cabinet must be completly isolated from the bilge.

That would be possible but quite a bit of work. Then problem then is the ventilation for the LFP and more importantly the inverter, isn't going to work. At present the bilges provide cool dry air at sea water temperature.

Pete

[newhaul]

Originally Posted by SailingHarmonie

From a practical matter, it makes little difference, but as someone who actually understands chemistry, this old wives tale is like fingers on a blackboard. I hope your understanding of LiFePO4 safety is better than your understanding of FLA battery chemistry.

There is no balanced chemical equation from mixing H2SO4 and NaCl that produces Cl2 gas. It doesn’t happen. No matter what you learned from watching old movies about WWII submarines!

The actual reaction is:

H2SO4 + NaCl —> NaHSO4 + HCl

Much of the HCl (hydrochloride acid) actually stays in solution and doesn’t poison the air around, depending on how much water is around, although an open container of it is certainly more noxious than sulfuric acid.

I am or was a us navy gas free engineer so I do have a clue what I'm speaking of and it's actually the shorting of the terminals that breaks the chloride ion attraction to the sodium ions releasing the chlorine gas .

Has nothing to do with wives or tales it is a scientific fact.

Was posting that above for dramatic effect on how ridiculous the debate on battery safety has become .