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T-fuse. Are they always required?

DEEP NNN

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I see T-fuses being mentioned in other threads and even in my own listed below.

I understand a T-fuse is a quick acting fuse inside a sand filled cartridge and that it prevents arcing after being blown. I don't understand why I would need a T-fuse for a 12V DC system with 100A output LFP batteries. I didn't think 12V was enough to create a sustained arc through a typical blown fuse.

I see DIY advocates saying "fuse to protect the wires" and the equipment will look after itself. So why T-fuses?

 
A single LFP cell has a short circuit potential ampacity of > 20,000 amps at 3.2 volts nominal.
A 12 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 12.8 volts nominal.
A 24 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 25.6 volts nominal.
A 48 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 51.2 volts nominal.
This fuse has the required breaking capacity to protect a 12 volt battery

This fuse has the required breaking capacity for 24 and 48 volt LFP batteries.
Bluesea calls breaking capacity interrupt capacity.
 
A single LFP cell has a short circuit potential ampacity of > 20,000 amps at 3.2 volts nominal.
A 12 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 12.8 volts nominal.
A 24 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 25.6 volts nominal.
A 48 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 51.2 volts nominal.
This fuse has the required breaking capacity to protect a 12 volt battery

This fuse has the required breaking capacity for 24 and 48 volt LFP batteries.
Bluesea calls breaking capacity interrupt capacity.
Thank you. I still don't understand how a 12V 100A battery can create >20,000A. I understand even less how one of its Cells could do it.
 
Thank you. I still don't understand how a 12V 100A battery can create >20,000A.
Is it necessary for you to understand or can you just take my word for it?
I understand even less how one of its Cells could do it.
There is a scary amount of energy in a cell.
The internal resistance of a 280ah prismatic cell is ~0.00015 ohms.
3.2 vots / .00015 ohms = 21,333.333333333 amps
The dead short ampacity of the battery is less than for a cell because of the resistance of the interconnects between the cells + the resistance of the BMS.

dcp3.gif
 
The often overlooked scary bit is on a dead short the cells will vent highly toxic electrolyte.
 
Is it necessary for you to understand or can you just take my word for it?

There is a scary amount of energy in a cell.
The internal resistance of a 280ah prismatic cell is ~0.00015 ohms.
3.2 vots / .00015 ohms = 21,333.333333333 amps
The dead short ampacity of the battery is less than for a cell because of the resistance of the interconnects between the cells + the resistance of the BMS.

dcp3.gif
Thanks. Okay, above my pay grade. Does this meet the requirement? 10,000 A/C
 
Wow, that looks like a re-branded bluesea fuse.
Even calls it an MRBF.
I suggest you use the genuine article just in case this is a cheap knockoff.
FYI, per your comment on trust. Yes, I can trust without understanding. It's a little difficult when everything and everyone is new and unknown. I gladly accept your information.
For now I'll assume this cheaper knock-off is good enough and hope it is.
 
The often overlooked scary bit is on a dead short the cells will vent highly toxic electrolyte.
How highly toxic?

Why go with the possible knock-off?
I'd have to research my research to figure that out. Price and availability. Blue sea seemed over priced or packaged, Gloso and South Bend each had something the other didn't and Photo-Top seemed a real stab in the dark.
I guessed.
 
How highly toxic?
I only passed high school chemistry by memorizing stuff which I promptly forgot after the final exam.
As someone who is not up on his chemistry, I would roughly characterize it as really bad.
I think we are talking about asphyxiating on your own dead lung endothelial cells.
Hopefully someone else can explain things better.
Blue sea seemed over priced or packaged, Gloso and South Bend each had something the other didn't and Photo-Top seemed a real stab in the dark.
I don't consider Blue sea fuses to be over-priced.
Over-current protection is not something to cut corners on.
 
DEEP NNN: I received an class T fuse from Amazon labeled South Bend Components. Your Canadian link helped see other products made by them by clicking on their name. Vehicle jacks and some gas related stuff as well as these fuses. It is also confusing because their is a company called South Bend that makes commercial kitchen appliances (that have fuses)

I am trying to get a better handle on South Bend Components to see if it is a recently available legit product or cheapo not a good idea product.
 
I only passed high school chemistry by memorizing stuff which I promptly forgot after the final exam.
As someone who is not up on his chemistry, I would roughly characterize it as really bad.
I think we are talking about asphyxiating on your own dead lung endothelial cells.
Hopefully someone else can explain things better.

I don't consider Blue sea fuses to be over-priced.
Over-current protection is not something to cut corners on.
If not for you more experienced hands, I'd probably completely rely on the equipment's fusing and relays. At least I'll be a couple of steps better than that.
 
DEEP NNN: I received an class T fuse from Amazon labeled South Bend Components. Your Canadian link helped see other products made by them by clicking on their name. Vehicle jacks and some gas related stuff as well as these fuses. It is also confusing because their is a company called South Bend that makes commercial kitchen appliances (that have fuses)

I am trying to get a better handle on South Bend Components to see if it is a recently available legit product or cheapo not a good idea product.
Interesting.
 
So far not good regarding South Bend Components.

I am unable to ask questions on Amazon site for that class t fuse; tried 3 times

Twice I wrote a review, first time I was rejected because I had questions in the review (because I could not ask a question in the designated area)

Second time I lowered the star rating and voiced concerns over the legitimacy of the product. No sign of that review and it has been more than 10 days.
 
So far not good regarding South Bend Components.

I am unable to ask questions on Amazon site for that class t fuse; tried 3 times

Twice I wrote a review, first time I was rejected because I had questions in the review (because I could not ask a question in the designated area)

Second time I lowered the star rating and voiced concerns over the legitimacy of the product. No sign of that review and it has been more than 10 days.
On a different note but similar result to yours, I asked on Amazon, WATTS247 and another vendor site, a question about wire size specification for the PV Circuit Breaker in a combiner box. No answers.
Amazing coincidence. South Bend Components just replied to my question on Amazon.
 
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A single LFP cell has a short circuit potential ampacity of > 20,000 amps at 3.2 volts nominal.
A 12 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 12.8 volts nominal.
A 24 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 25.6 volts nominal.
A 48 volt LFP battery has a short circuit potential ampacity of ~10,000 amps at 51.2 volts nominal.
This fuse has the required breaking capacity to protect a 12 volt battery

This fuse has the required breaking capacity for 24 and 48 volt LFP batteries.
Bluesea calls breaking capacity interrupt capacity.
What about the case where the BMS cuts off high current discharge? Epoch batteries say that in a short situation that there will be 500A for a few seconds before getting cutoff by their BMS. Can that be trusted in a dead short? Would a MRBF be okay in that situation?
 
What about the case where the BMS cuts off high current discharge? Epoch batteries say that in a short situation that there will be 500A for a few seconds before getting cutoff by their BMS. Can that be trusted in a dead short? Would a MRBF be okay in that situation?
I don't know the technical details but after stepping up from MRBF for my 24v system to Class T for my 48V I'd never want to go back to the MRBF. Yes the class Ts are salty but buy it once ( and a spare) and you'll likely never have to do it again. You'll also be quadruple checking all of your work because you don't want to blow that expensive fuse.
That reminds me I need to order spares and another block for my 3rd pack.
 
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