EVE 280ah 24v battery frame

[nebster]

Nebster, you are the only person I've seen trying to put an MRBF on a Cell, they are designed to go on a 3/8" Battery Terminal. These do not belong on the cell.

MRBF are worth the trade. They are safer than any longer wire, and they are ultra compact. In my application, every extra wire and junction and pigtail takes up precious space.

I've been using them on lithium cells for years now with no issues, so I think I'll keep right on going, thanks.

 

[Steve_S]

I've used MRBF's for a long time, am quite comfortable with them hence why I recomend them to people.
If you choose to Bodge it or do it right it is entirely your option & choice as it is all on you, the risk & expense should something go awry. Being the latest fashion of the 21st century, of course accept no responsibilty & blame others when things go wrong... but you have been advised, so.

If someone tells another to stand in a puddle of water barefoot & play with their live electrical panel, it's their choice to do it or not, the responsibility is on them, not those offering the suggestion to do it.

Existing this pointless thread now.
Have a Wonderfully Pleasant Day.

 

[Luthj]

Now that looks perfect. I wish I knew how to click around better on Mcmaster and find random stuff. "Show me everything cylindrical with an OD of 10mm and an ID of 6mm" would be a cool search feature, too.

They are pretty good if you start searching for generic terms. If I want something round, I search for tubing, bushings, rod, drilled rod, spacers etc.

As far as MRBF safety vs a short wire run. If you properly protect the unfused wire length, the risk is minimal. AYBC specs something like 18 inches unfused from the battery pack, but longer is necessary sometimes, just take all possible precautions to prevent shorts. For example most autos have no fusing between the battery and starter motor. Of course they use considerable wire protection and securing mechanisms.

Personally I wouldn't put a fuse directly on a cell in a high current application. The temperature risk in the cell could be 10-15F above the rest of the pack under continuous loads. Which might produce issues with balance.

 

[nebster]

I've used MRBF's for a long time, am quite comfortable with them hence why I recomend them to people.

Very cool.

If you choose to Bodge it or do it right it is entirely your option & choice as it is all on you, the risk & expense should something go awry. Being the latest fashion of the 21st century, of course accept no responsibilty & blame others when things go wrong... but you have been advised, so.

Thanks?

Existing this pointless thread now.
Have a Wonderfully Pleasant Day.

Thanks.

 

[nebster]

They are pretty good if you start searching for generic terms. If I want something round, I search for tubing, bushings, rod, drilled rod, spacers etc.

I'll have to improve my McMaster-fu; thanks.

As far as MRBF safety vs a short wire run. If you properly protect the unfused wire length, the risk is minimal. AYBC specs something like 18 inches unfused from the battery pack, but longer is necessary sometimes, just take all possible precautions to prevent shorts. For example most autos have no fusing between the battery and starter motor. Of course they use considerable wire protection and securing mechanisms.

Yeah, like usual, it's a tradeoff. (ABYC actually specifies 7 inches, btw.)

I have long runs, through multiple cabins and areas, between battery packs and the bus up point where they are all joined together. I'm not confident I have perfect wires, crimps, and for that matter clearance over time, in motion, for all of these wires. I also have children and pets living and sleeping above this system every day, and fire is our #1 risk.

On top of that, at the bus up point I have two 4/0 takeoffs, each also with a 300A MRBF fuse. I was concerned that those master fuses are also only rated to break 2kA current in a 48V design, and so each paralleled pack is separately fused at 100A in kind of a belt-and-suspenders approach. I figure in a catastrophic short that, even if the main fuses fail short themselves, probably the distributed current across the (now 9) packs is below 2000A and enough to start blowing all the small fuses in kind of a cascading way.

Really, I should be using a class T fuse in this application, but in the current design I don't have the space for one. I'm working on a bus bar redesign that might leave room for one, one day. But I'll still be keeping the MRBFs on the actual lithium strings with that change.

Personally I wouldn't put a fuse directly on a cell in a high current application. The temperature risk in the cell could be 10-15F above the rest of the pack under continuous loads. Which might produce issues with balance.

We had this debate in a thread recently, and I completely agree. At the same time as I don't advocate for running small bus bars to their table rating for heating reasons, here I am with the hottest part of my system (the fuse itself) sitting right near a cell terminal!

But, I had to make a trade, and the good news is that I'm rarely sourcing more than 30A through any one of these.

So far, cross fingers, I can't see any degradation on the seven cells that have fuses directly on them after 3 years. I've actually had one cell start to act up, but it was buried back in a string far away from the warmest point.

 

[Ampster]

I agree they dont belong on a cell, especially one with a 6mm stud. However you can add me to the list of people using one on a cell. After reading this post I ordered a 3/8" terminal and will be rewiring my 12 volt battery. I was never comfortable with the loose fit and the leverage that the pigtail and the MRBF created on the cell terminal.

This is my work around on how I avoided putting one of those MBRF Bussman Fuse holders directly on a 6 mm stud. the buss bar was one I got from Deligreen and drilled out one end to 3/8". It bent easily. The 3/8 stand off I found on Amazon for $5 and the other thing that worked out is now I can much more easily see the fuze and whether is is functioning.

 

[ZebraPainter]

This is my work around on how I avoided putting one of those MBRF Bussman Fuse holders directly on a 6 mm stud. the buss bar was one I got from Deligreen and drilled out one end to 3/8". It bent easily. The 3/8 stand off I found on Amazon for $5 and the other thing that worked out is now I can much more easily see the fuze and whether is is functioning. View attachment 23711

I like this. I’ve had my cells for a few weeks and just got into trying to understand hooking a big cable to an M6 grub screw. They supply extra bus bars so I’m going to do something like this. Thanks.

 

[DJSmiley]

This is my work around on how I avoided putting one of those MBRF Bussman Fuse holders directly on a 6 mm stud. the buss bar was one I got from Deligreen and drilled out one end to 3/8". It bent easily. The 3/8 stand off I found on Amazon for $5 and the other thing that worked out is now I can much more easily see the fuze and whether is is functioning. View attachment 23711

Nice done, but I'm not sure if this will work properly when a real short circuit occurs. The Littlefuse CF8 fuses have an interrupting rate of 2000A.
If you have a short near the terminals, the short current (especially with 280Ah LiFePO4) is likely to exceed this 2000A, so the fuse might just arc and continue to let current pass, instead of actually cutting of the power...

A class T fuse might be a better option, since those have a much higher interrupting rate. However, I haven't seen real-life tests with fuses and lithium short currents..
On paper, it will be exceeding many commonly used fuses interrupting rates, but in reality, wire gauge and connection resistance might lower the current so it might be (just) within specifications...

 

[Ampster]

Nice done, but I'm not sure if this will work properly when a real short circuit occurs.

That fuse is rated for 54 Volts. I am not sure what a "real short" is versus a lithium short or a plain vanilla over current event? That pack is 12 volts and a 75 Amp fuse opened on a surge from an inverter. I now use a 150 Amp fuse which is okay for my wire size.

 

[cinergi]

I'm guessing the "real short circuit" concern is with respect to the interrupt rating of the fuse - the ability of the fuse to actually interrupt the circuit (no DC arc'ing for example) under a short-circuit condition which is *extremely* high amperage in a LiFePO4 situation. Often you have to go with a Class T fuse to get proper protection with this chemistry.

Edit: which I see DJSmiley explained above; so I must be missing something about @Ampster 's question

 

[Ampster]

If you have a short near the terminals

I use the fuse to protect the wire. The only thing that I have seen near the terminals is a wrench dropped across the terminals. It did get red hot. Do you have an example?

 

[cinergi]

I'll take another stab at this ...
A fuse has at least 3 critical ratings: 1) Voltage, 2) over-current rating, 3) Interrupt rating. All 3 should be satisfied in a system design.

You're good on #1 - voltage.
It looks like you're good on #2 - over-current rating (e.g. a 150 amp fuse protecting a 4 AWG wire
However, #3 seems to be the most misunderstood problem which I only came to understand myself recently.
Just because a fuse will blow if you reach or somewhat exceed its over-current rating (150 in this case) does not mean it will properly blow and stop the flow of current if you literally short-circuit the circuit. The reason is due to the extremely high amperage that can happen in that situation with this battery chemistry. The fuse element will melt as it should, but that doesn't mean that an arc inside the fuse won't set up and continue to allow the current to flow. Or that the melted element inside the fuse sets up in a way that allows the current to flow through the melted remains.

My 48v 280Ah pack can do something like 16,000 amps under short circuit, and only a Class T fuse is rated for that level of interrupt. The fuse is 300 amps, but has something like a 200,000 amp interrupt. ANL, MRBF, etc are not rated for this. The others might happen to work, but it's not designed for it and could fail to interrupt the circuit and leave you with an unprotected system.

Hope that helps!

 

[Ampster]

Hope that helps

Yes it helps me understand a problem that I hope to never have with that 12 volt pack. On my 2P16S pack I may go to a class T fuse like I used on an EV conversion. I currently have a 125 Amp circuit breaker at the inverter and a 150 Amp MBRF at the pack. If I recall the Class T fuse was expensive and had some kind of arc suppressing powder inside. I have read about them in Tesla packs but don't recall seeing one in a Nissan Leaf pack I disassembled years ago.

I am thinking of reconfiguring my 2P16S pack and adding some more cells to make 16S3P parallel packs. In that case, a Class T fuse on the common negative buss would protect from that situation and each sub pack would have its own pack fuse or circuit breaker.

 

[Gazoo]

only a Class T fuse is rated for that level of interrupt.

So would one need a fast blow or slow blow fuse? Or would it matter?

 

[Dzl]

I believe the two types of fuse the ABYC rates for main battery circuit protection, (1) Class T, and (2) MRBF 'marine rated battery fuse'
Blue sea specifically recommends class T for lithium battery banks, and for use with inverters.

I believe Class T is relatively slow blowing: (I'm second guessing myself)

Here is the trip curve for MRBF, it looks fairly similar maybe a bit quicker:

Here are ANL and Mega trip curves for further context

 

[Ampster]

So would one need a fast blow or slow blow fuse? Or would it matter?

I would hope my breaker or the MBRF fuses went first but that would be a last resort in case it was a major short circuit and all the others

 

[Dzl]

Now I'm second guessing myself on whether Class T is slow or fast blowing or somewhere in the middle. I don't have enough context to feel confident.

 

[Gazoo]

Now I'm second guessing myself on whether Class T is slow or fast blowing or somewhere in the middle. I don't have enough context to feel confident.

They make both fast and slow blow.

 

[Dzl]

Yep, looks like I got it wrong:

From FusesUnlimited.com:

What is a UL Class T, Fuse? A Class T fuse is a fast acting, current limiting, fuse that is rated to interrupt a minimum of 200,000 amps.

Note: I'm pretty sure the 200,000A is a typo and should be 20,000A (not a typo)

From the Samlex Evo Manual:

To prevent occurrence of hazardous conditions under short circuit conditions, the fuse used in the battery circuit should limit the current (should be "Current Limiting Type"), blow in a very short time (should be Fast Blow Type) and at the same time, quench the arc in a safe manner. For this purpose, UL Class T fuse or equivalent should be used (As per UL Standard 248-15). This special purpose current limiting, very fast acting fuse will blow in less than 8 ms under short circuit conditions.

Marine Rated Battery Fuses, MRBF-xxx Series made by Cooper Bussmann may also be used. These fuses comply with ISO 8820-6 for road vehicles.

Magnum is slightly more ambiguous:

If a fuse is used as an overcurrent device, a Class-T type or equivalent is recommended. This fuse type is rated for DC operation, can handle high short-circuit currents, and has a time delay that allows for momentary current surges from the inverter without opening the fuse

Eaton (Bussmann):

Bussmann's Class T current-limiting, fast-acting fuses. Provides 10X better current limitation to help prevent equipment damage caused by short-circuit events. 200 kA Interrupting rating complies with NEC® Section 110.9 for today’s large capacity systems.

Best guess: while a Class-T fuse can may be able to be fast or slow acting, a UL 248-15 Class T fuse, is 'current limiting' and 'fast acting'.

 

[Gazoo]

Yep, looks like I got it wrong:

From FusesUnlimited.com:

Note: I'm pretty sure the 200,000A is a typo and should be 20,000A (not a typo)

From the Samlex Evo Manual:



Magnum is slightly more ambiguous:

Eaton (Bussmann):



Best guess, while a Class-T fuse can maybe be fast or slow acting, a UL 248-15 Class T fuse, is 'current limiting' and 'fast acting'.

Thanks for that. Question has been answered. I think fast acting Class T is the way to go or use the MRBF fuse Samlex recommends.