Keeping the water off your Lifepo4 installation

[newhaul]

Originally Posted by 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.

Well there is the cost prospective my DIY 250ah lifepo4 bank cost me right at 600 including Bms And new battery monitor and shunt.

Definitely a difference in banks .

[CaptainRivet]

Originally Posted by Pete7

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

you don't need ventilation for the LFP. Inverter as a heating source should be installed not in the same compartment anyhow

[hjohnson]

Originally Posted by 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?

So my DIY LFP battery is lightly compressed and put inside a fiberglassed plywood open-top box. That box is fiberglassed to the hull under our pilot berth, and the bottom of the box sits about 3" up from the inside of the hull itself. The pilot berth itself is high enough that any water in there will drain into the bilge (or onto our cabinsole), so any water is transient.

The box itself was deliberately built with gaps at the bottom edge to allow any moisture in the box to drain out, and the cells themselves sit on plastic pool tile, which gets them about 1/4" above the box bottom, and not sitting on anything that can retain moisture. The gap is also used to run nylon webbing that holds the battery down.

That box is then capped off with a U-shaped plexiglass cover that makes it splash proof, but lets me see what's going on. (The plexiglass was salvaged from my local pub after they got rid of their covid barriers).

In the year since we've had this installation, there's never been a hint of moisture anywhere near the battery. Just before winter, we completely disassembled to see how it was faring, and it was all good.

[newhaul]

Originally Posted by hjohnson

So my DIY LFP battery is lightly compressed and put inside a fiberglassed plywood open-top box. That box is fiberglassed to the hull under our pilot berth, and the bottom of the box sits about 3" up from the inside of the hull itself. The pilot berth itself is high enough that any water in there will drain into the bilge (or onto our cabinsole), so any water is transient.

The box itself was deliberately built with gaps at the bottom edge to allow any moisture in the box to drain out, and the cells themselves sit on plastic pool tile, which gets them about 1/4" above the box bottom, and not sitting on anything that can retain moisture. The gap is also used to run nylon webbing that holds the battery down.

That box is then capped off with a U-shaped plexiglass cover that makes it splash proof, but lets me see what's going on. (The plexiglass was salvaged from my local pub after they got rid of their covid barriers).

In the year since we've had this installation, there's never been a hint of moisture anywhere near the battery. Just before winter, we completely disassembled to see how it was faring, and it was all good.

Pictures please your box sounds great .

[hjohnson]

Originally Posted by newhaul

Pictures please your box sounds great .

Some photos are visible here.

That's it before we added all the electrics, and finished off the box. The long sides are made from laminated 1/4" marine ply, the ends are 1/2" marine ply. The bottom of the box is about at the level of that cross-piece you see going along the hull to the left of the box. There's about a 2" gap on the right side of the box (under the lip) between the box and the side of the engine compartment, that we use as a cable chase.

The second photo is from when it was slightly more complete, as we were making cables and figuring out equipment placement and what not.

[newhaul]

Originally Posted by hjohnson

Some photos are visible here.

That's it before we added all the electrics, and finished off the box. The long sides are made from laminated 1/4" marine ply, the ends are 1/2" marine ply. The bottom of the box is about at the level of that cross-piece you see going along the hull to the left of the box. There's about a 2" gap on the right side of the box (under the lip) between the box and the side of the engine compartment, that we use as a cable chase.

The second photo is from when it was slightly more complete, as we were making cables and figuring out equipment placement and what not.

Nice thanks

[wholybee]

Originally Posted by CaptainRivet

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..

I think you must be mixing up Class-T fuses and ANL fuses. Class-T fuses have AIC of up to 200kA. ANL are in the range you say.

https://www.eaton.com/us/en-us/catal...s-t-fuses.html

[Chotu]

Originally Posted by newhaul

This is getting ridiculous

Completely agree!

How about making the boats themselves more safe so the batteries don't get splashed with water?

This seems to be such a non-problem. Why are so many people worried?

[newhaul]

Originally Posted by Chotu

Completely agree!

How about making the boats themselves more safe so the batteries don't get splashed with water?

This seems to be such a non-problem. Why are so many people worried?

Still waiting for spring breakup I suppose

[CaptainRivet]

Originally Posted by wholybee

I think you must be mixing up Class-T fuses and ANL fuses. Class-T fuses have AIC of up to 200kA. ANL are in the range you say.

https://www.eaton.com/us/en-us/catal...s-t-fuses.html

no i am not mixing them up. if you look at the datasheet the distance from one side of the fuse to the other is 0,84" or around 20mm but wait look at the drawing, its roughly a 3rd of 1/3 of 0,84" or 20mm thats metal free for a typical 200-400A class T. the 200kA rating is interrupting current inside of the fuse that is filled with gas and sand but not the outside incl. the fuse holder and a fuse consists of both facing the short circuit amps that is still present
With a shortened bank the first disconnect by the fuse class T or NH or ANL or whatever fuse from the installation will be much earlier at 1000-1500A but that doesn't stop the bank from producing in eg my case up to 16500A, its actually a slow build up that can take up to over a sec to reach the max current. The fuse is blown before and can withstand to interrupt 200kA but then the blown fuse gets arced over the very short distance between both sides of the fuse by the massive low DC high current, comparable to arc welding.

Now check how much amps you need of actually only 30" or 7mm will be arced through the air and well that depends on the air very humid, salty air 5000A, very dry sahara air around 9000A. thats pure physics.

That's the reason even 300V 63A NH00 fuses have an isolated ceramic body length of 5cm or 2" and the base is ceramic too. They are used for power grid eg trafo station and have to seperate both sides in a short 100% and eg a house or a hospital can potentially burn down by an arced short. A buddy of mine is a grid engeneer who told me that, his daily bread job.
And just a tip, you can buy NH fuses used, they sell them sometime in big packages for very cheap when a demolition company takes down factories. As long as the fuse has electric through put, the blow indicator is ok and the ceramic body is undamged it works fine. it pure silver plated 99,7% copper besides the ceramic body and if black or dirty polish it with silver polish for your silver cuttlery and the fuse is like new. the 630A fuse with holder and 5x500A replacement was 45Euro :-) used plus 10min and 4 Euro for some silver polish.
A hole box with 50NH fuses and 20 holders in different sizes, 80% never used as they were replacement parts was 70Euro. They actually never changed the last 20 years, only slightly the ratings but in areas that is not a concern for marine 12V-48V use.

[newhaul]

Originally Posted by CaptainRivet

no i am not mixing them up. if you look at the datasheet the distance from one side of the fuse to the other is 0,84" or around 20mm but wait look at the drawing, its roughly a 3rd of 1/3 of 0,84" or 20mm thats metal free for a typical 200-400A class T. the 200kA rating is the inside of the fuse that is filled with gas and sand, but not the outside of the fuse holder and a fuse consists of both.
With a shortened bank the first disconnect from the installation doesn't stop the bank from producing in eg my case up to 16500A, its actually a slow build up that can take up to over a sec to reach the max current. The fuse is blown before and can withstand there 200kA but then the blown fuse gets arced over the very short distance between both sides of the fuse by the massive low DC high current.

Now check how much amps you need of actually only 30" or 7mm will be arced through the air and well that depends on the air very humid, salty air 5000A, very dry sahara air around 9000A. thats pure physics.

That's the reason even 300V 63A NH00 fuses have an isolated ceramic body length of 5cm or 2" and the base is ceramic too. They are used for power grid eg trafo station and have to seperate both sides in a short 100%. A buddy of mine is a grid engeneer who told me that, his daily bread job.

Nice writeup but what does it do for us wrt possible seawater shorting of terminals ?

[CaptainRivet]

Originally Posted by Chotu

Completely agree!

How about making the boats themselves more safe so the batteries don't get splashed with water?

This seems to be such a non-problem. Why are so many people worried?

because in many boats the bank gets relocated from the hot engine room to a different cold location with LFP, often into salon or under the bed in the cabin low down in the hull (coldest part) not set up for a battery bank and needs appropriate modifications. And the question here is what is actually needed for a LFP bank and one of this is water protection (as in the bilge now, lowes point of the boat for many).

eg I sleep on top of my bank now. And well water and electricity is never a good combo so I would take care the same way for any type of house bank i relocate. And because the bank run my bilge pumps in case of water ingress I want them to run as long as possible, eg i have a high volume 230V pump per hull aditionally and the hole must be quite big that they can't cover that but for that my bank and inverter must be running and not getting a problem if i have 15cm water in the bilge.

And given the fact that eg a lead bank will create arround 2000A but eg my LFP could do 16500A in a bank short I take a bit more extra care and add security measures to prevent that.
Especially if I am already modifing the location/new battery compartment anyhow and the extra costs nearly no money/small extra effort to do so.

eg laminating the holes to bilge close was 10min extra work and maybe 2 Euro for mats and resin. needed to laminate the even floor in anyhow that carries and also secures the bank in position. Also the unisolated pipe of the aircon I will install in the owners cabin, that cools down the battery compartment additionally. I could route around or through and through was even shorter distance and instead of the typical plastic ducting pipe i just used an alu pipe i had lying around anyhow.

[CaptainRivet]

Originally Posted by newhaul

Nice writeup but what does it do for us wrt possible seawater shorting of terminals ?

salt water or actually any water is one reason for a shortened bank.

So when bank get shorted by salt water the main battery fuse disconnects the whole installation properly and not anywhere else a fire in the boat gets started because the high current is distributed and melting cables.

[donradcliffe]

Originally Posted by CaptainRivet

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

LFP batteries are short protected by the BMS. Until you show me a Youtube with that causing a problem, I'm not going to install ANY fuses.

[CaptainRivet]

Originally Posted by donradcliffe

LFP batteries are short protected by the BMS. Until you show me a Youtube with that causing a problem, I'm not going to install ANY fuses.

your BMS steers a relay or mosfets that prevents it from getting shortend by the battery cables on the input side. One protection you need but not the only one. But that relay or mosfet will melt close if the bank internally gets a short and faced with 10000A+, that the BMS cannot protect but a main battery fuse can.

well i have no youtube video but eg my buddy is a surveyor that lately inspected the leftover of a electric motorboat with shortend banks due to a water ingress. reason he found main Fuses where the lovely Megafuses ok speced for the battery cable but that got bridged and melted a lot other cables causing fire in the boat. Well the luck that this could be inspected is because fire brigade is 500m down the road of the habour. it would have also burned with AGMs...

put your bank in a bucket of water and it gets shortened. I don't try that but if you want feel free to do so and make a youtube video.
if you have prismatic cells with the thin blue insulation and that gets rubbed through due to constant vibrations on a boat you get a shortend bank. If you buy dropins from china, you don't know whats inside...
just 2 reasons and well there is no youtube video as the boat is burned to ground then.

Well for 50Euro i can prevent that and easly disconnect my whole bank when boat stored for longer periodes.to me a good investbut your boat, your decision.