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