Searching for: Mega fuse holder that bolts directly to battery terminal

[Vigilant24]

I thought I'd seen a Mega fuse holder that bolts directly to a battery terminal, but now I can't seem to find such a thing. The idea would be to bolt one end down using the the 5/8th inch battery terminal bolt, have the 300A fuse in there, connect the other end to my 2/0 cable to my inverter and be done. I'm guessing that just bolting the bare fuse itself in there (no holder) isn't a great idea (I'm >pretty sure< the fuses aren't built for those mechanical stresses, and 300A is something to take seriously). Adding another 2/0 cable just so I can bolt a fuse holder to a board seems it will just add more resistance (cable length, one more connection) for little added benefit.

Did I really see such a thing? Any tips/links/thoughts would be appreciated.

 

[SilverbackMP]

I haven’t seen one but here’s how I did it:



I know this is what you are trying to avoid, but throwing out ideas. Would be a hell of a lot easier with 2/0 than the 4/0 I used.

 

[Shimmy]

I thought I'd seen a Mega fuse holder that bolts directly to a battery terminal, but now I can't seem to find such a thing. .

Are you thinking of Marine Rated Battery Fuses? The holder mounts to the terminal. Low fault current interrupting though unfortunately.

Terminal Fuse Blocks - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com

 

[Vigilant24]

Are you thinking of Marine Rated Battery Fuses? The holder mounts to the terminal.

That wasn't what I (think) I saw, but it does look like it would do the trick. Paying $16+ per fuse isn't great but I sure hope I would need very many.

Low fault current interrupting though unfortunately.

? Sorry, I don't understand the terminology. They are available up to 300A, apparently.

 

[cs1234]

? Sorry, I don't understand the terminology. They are available up to 300A, apparently.

Low AIC most likely. The maximum amount it can stop before it just doesn't even work correctly essentially. Say it has a 2000 amp AIC and is rated at 300amps for it's normal blow rating.. anything above 2000 amps surging through it and all bets are off as to whether it safely does its job or creates a fire hazard. The speculation here on the forum is that lifepo4 batteries at 48v require 10,000 to 20,000 AIC .. the jury is still out.

 

[Ampster]

I have a 3P16S pack so I just extended the bus bar on the negative end that was supported by the three cells. The T Class fuse bolted to the bus bar and the other end to my cable. No need for a fuse holder. The T Class fuses are mechanically strong. Lol

 

[cs1234]

The T Class fuses are mechanically strong. Lol

They do look pretty sturdy. Aren't they filled with some sort of sand or something?

 

[Vigilant24]

Maybe I could go with something like this: LittleFuse 02981028HXFC, ? Its just like many other Mega Fuse
holders, but the cover allows cables/etc to come from any direction. And, they sell a little copper bus bar that works with it. I could bolt down the bus bar to the battery terminal and then the other end gets screwed down inside the fuse holder. Not optimum (the whole thing is cantalevered off the battery terminal), but at least any mechanical stresses from the cables should be taken by the fuse holder and not the Mega Fuse.

 

[Ampster]

Paying $16+ per fuse isn't great but I sure hope I would need very many.

My T Class fuse is my defense against a high amperage short. My circuit breaker and charge/discharge settings on both my inverter and BMS are my primary and secondary protections against over discharge. I view it as layers of risk management.

 

[Ampster]

They do look pretty sturdy. Aren't they filled with some sort of sand or something?

Yes to extinguish any src that might fuse a less capable fuse. If it breaks off the negative cable would just drop off and no risk of further shorts.Unlike the above one cure there is lots of open space below the fuse.

 

[Shimmy]

Sorry, I don't understand the terminology. They are available up to 300A, apparently.

Fuses are rated in terms of continuous current and maximum current they can reliably open under. LFP cells have a low internal resistance, so if you short positive and negative together they can produce very high currrents-- over 5,000A for a single string. (When you parallel strings it will increase proportionally, 10,000A for two, 15kA for three, and so on )

If you get a dead short on your battery, a MRBF can only open up to a maximum of 2,000A. More current than that and it cannot extinguish the arc internally.

 

[Vigilant24]

Fuses are rated in terms of continuous current and maximum current they can reliably open under. LFP cells have a low internal resistance, so if you short positive and negative together they can produce very high currrents-- over 5,000A for a single string. (When you parallel strings it will increase proportionally, 10,000A for two, 15kA for three, and so on )

If you get a dead short on your battery, a MRBF can only open up to a maximum of 2,000A. More current than that and it cannot extinguish the arc internally.

Ah, thanks.

My batteries are two 12V/110 AH flooded lead acid batteries in parallel. I'd >guess< these have more internal resistance than many of the lithium chemistries. OTOH, I have no BMS as another "safety" in case of a dead short.

The MRBF's appear to have an interrupt rating of 10,000A at 14VDC. Would that do the trick given my battery pack?

Thanks,
Mark

 

[cs1234]

Ah, thanks.

My batteries are two 12V/110 AH flooded lead acid batteries in parallel. I'd >guess< these have more internal resistance than many of the lithium chemistries. OTOH, I have no BMS as another "safety" in case of a dead short.

The MRBF's appear to be rated for 10,000A at 14VDC. Would that do the trick given my battery pack?

Thanks,
Mark

Sounds good to me.

 

[Shimmy]

Ah, thanks.

My batteries are two 12V/110 AH flooded lead acid batteries in parallel. I'd >guess< these have more internal resistance than many of the lithium chemistries. OTOH, I have no BMS as another "safety" in case of a dead short.

The MRBF's appear to have an interrupt rating of 10,000A at 14VDC. Would that do the trick given my battery pack?

Thanks,
Mark

MRBFs are perfect in your case.

 

[pekka8]

I'm also interested in this. For Eaton MRBF it says that you need to use a block: "Do not fuse directly to batter terminal, requires use of Marine Rated Fuse Blocks."

Could you use mega fuse directly in battery terminal if the attached cables are supported/tied somehow?

 

[Ampster]

Could you use mega fuse directly in battery terminal if the attached cables are supported/tied somehow?

I have a 3P16S pack so I made the busbar on the three negative posts longer so I could attach the cable or fuse to a separate hole on that bus bar. The bus bar is well supported by the three battery studs so there is no concern that the leverage of the fuse or battery lugs putting strain in terminal tops.

 

[mikefitz]

MRBF fuse with Blue sea holder,

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com

Mike

 

[Vigilant24]

I'm also interested in this. For Eaton MRBF it says that you need to use a block: "Do not fuse directly to batter terminal, requires use of Marine Rated Fuse Blocks."

You wouldn't need to use that expensive ($60+) surface mount fuse block, you can also get one of the ones that mounts directly (and compactly) diretly to the battery post. I like this style that allows 2 of the marine fuses, each protecting different circuti. I'll use one for my "big" inverter and one for my much smaller inverter. Approx $16.

 

[Vigilant24]

Could you use mega fuse directly in battery terminal if the attached cables are supported/tied somehow?

I don't think it would be a good idea to put any mechanical stress on the megafuse itself (heavy terminal wires twisting, etc). If using a megafuse, I think the approach I described in post 8 would work better: Buy a fuse holder and attach it to the battery terminal with a small connector bus bar (and they sell appropriate pieces that would work, as shown).

 

[pekka8]

MRBF fuse holder would be nice, but then have to stock different types. Or use more expensive MRBF everywhere. Could also be harder to find in case you run out.