Class T fuse mounting

[neoflyer]

I followed the advice of a van systems solar internet guru and installed a 250a MRBF fuse in a fuse holder directly to me positive terminal on a SOK 12v lithium battery bank. He said in light of the scarcity and prices of Class T fuses that would be acceptable. Since then another forum thread advises that MRBF fuses don’t have a high enough AIC for lithium use. Is that tru?

If I install a 250a Class T fuse connecting my 12v SOK battery bank a 4/0 positive cable directly or is a fuse block required? The battery bank is on a slide out tray so I don’t have a place to mount the fuse block.

 

[DIYrich]

I would install a wire from the Battery to the Class T Fuse block. The fuse is then installed in the block.

Class T Fuse Block with Insulating Cover - 225 to 400A - Blue Sea Systems

Allows use of Class T fuses for high speed circuit protection of electronic equipment and inverters.

www.bluesea.com

Note: I know of at least 2 different size Class T Blocks. Figure out your Class T size, and then buy the appropriate block.

There are mounting holes for the Class T Fuse. I don''t know what happens to the structural integrity of the fuse when it blows. You don't want a loose wire that can short against anything.

 

[curiouscarbon]

here is a table about AIC or how many amps certain fuses are expected to handle at a given voltage

Post in thread 'MRBF or class T'
https://diysolarforum.com/threads/mrbf-or-class-t.47659/post-606422

using a fuse block with class-T is strongly recommended to ensure cables don't move when it blows

 

[Aridom82]

There are mounting holes for the Class T Fuse. I don''t know what happens to the structural integrity of the fuse when it blows. You don't want a loose wire that can short against anything.

Class T fuses are rated for environments where there are flammable substances. I seriously doubt they come loose when they pop.

 

[JoeHam]

Class T fuses are rated for environments where there are flammable substances. I seriously doubt they come loose when they pop.

They make the fuse holder for a good reason and it seems beyond silly to buy the fuse and not the holder.

This has been thoroughly argued before though :

Class t fuse without holder

In one of the vids floating around, I saw a class t fuse, bolted to wire at each end, and the wire/bolt connection heat shrinked. That is, a fuse inline with no holder. I thought it was brilliant. Is there any downside other than the trouble of replacing if blown?

diysolarforum.com

 

[Supervstech]

Class T fuses are rated for environments where there are flammable substances. I seriously doubt they come loose when they pop.

It is a fiberglass body. The innards extinguish an arc, but failure certainly can cause the fuse to open. I’ve seen PLENTY of fuses sheared and blown open.

 

[Aridom82]

I’ve seen PLENTY of fuses sheared and blown open.

I wouldnt like to work at your place...
I was hoping myself not to have to buy the holder too. I am trying to fit a Tfuse in my prototype lifpo4 battery pack and the fuse holder is expensive and bulky af.

 

[42OhmsPA]

I wouldnt like to work at your place...
I was hoping myself not to have to buy the holder too. I am trying to fit a Tfuse in my prototype lifpo4 battery pack and the fuse holder is expensive and bulky af.

What is the percent of the cost of the fuse holder compared to the rest of your system?

 

[Aridom82]

What is the percent of the cost of the fuse holder compared to the rest of your system?

Compared to the battery pack prototype is 2,5% of the total price.
Compared to the battery pack prototype without the cells, just the holder is 10% of the expense

 

[Aridom82]

Is kind of a ripoff for a couple of tin plated copper pieces mounted on a plastic base with polycarbonate cover.

 

[42OhmsPA]

Compared to the battery pack prototype is 2,5% of the total price.
Compared to the battery pack prototype without the cells, just the holder is 10% of the expense

I can see why you're considering considering it expensive, I did too when I bought 2.
Look at it as cheap insurance and being a step ahead when the addiction takes full control and you substantially increase the size of your system.


On the topic of Class Ts - where is everyone finding the best deals on fuses and holders currently? (name brand not knockoff)

 

[Aridom82]

I am thinking of fitting it there, one side screwed directly onto the positive of the dc breaker, the other side screwed to the pla support with a piece of nylon rod as separator (pla is not temperature resistant).
I am finding the fuses and holders in online stores that sell equipment for boats. 50 eur the Tfuse, 60 eur the 110-200a holder.

 

[OffGridForGood]

I wanted to put the T-class directly into my 2P disconnect but not go, will not fit.
Did you test this configuration - ie does the T-class fit the 2P disconnect you picked? (and if so what model is that 2P breaker?)
{I have been getting my (Blue Sea) T-class fuses/holders from Fat Boy Boating Supplies in Etobicoke/Toronto.}

 

[Aridom82]

The 2p disconnect is this one, from aliexpress. I have measured it with a caliper and cad it myself. The Tfuse fits, it is a 175A one, 22mm wide and this dc breaker fits anything up to 24mm wide. Both holes are 8mm in diameter. If the Tfuse was more than 225 A then it wouldnt fit according to the drawings.

 

[Aridom82]

I it is too big i guess that you could bridge it with a piece of copper 2-3 mm thick. Depending on how many amps it needs to handle.

 

[OffGridForGood]

I see, in my case I was trying to put 300A Class T into a two pole 250A breaker - The class T is 25.4mm wide but the slot in my Tomzn 2P breaker is only 24mm.

For each rack battery I wanted to put a 125A Class T into a single pole 125A Tomzn breaker - the class T 125A fuse is 22mm wide (as you show) but the Tomzn breaker is only 17.5mm wide.

I should have looked at the DIHOOL breakers, they even look the same as the Tomzn, now I know they are not the same.
I didn't use bus bars, tight space, so I used short cable with ring terminals to move the class T fuse away from the breakers.

Thanks for the reply and dimensions @Aridom82

 

[neoflyer]

There are mounting holes for the Class T Fuse. I don''t know what happens to the structural integrity of the fuse when it blows. You don't want a loose wire that can short against anything.

Good point.
Thanks

 

[JRH]

Is kind of a ripoff for a couple of tin plated copper pieces mounted on a plastic base with polycarbonate cover.

I have seen many fires on expensive boats ( 50 thou thou and way up) due to the owner trying save a few bucks after he bought the boat and rigging a fuse improperly , poorly , no fuse, to small, wrong kind, loose bolts and wires, not having a proper protective cover , etc etc etc .
..fuses are the last place to try and save money…not cool.
They are not a rip off…it’s your life preserver if somthing bad happens.