LFP Battery and Battery Bank Fusing

[SteveK]

If it's from the published E-13, then yes. But the primary AIC info is in E-11 and has been around for a very long time.

The only mention of lithium in E11 is note 2 under Table 3B. I have edited my post to include this.

 

[tpbrady]

While the boating world is behind the solar and EV world it’s miles ahead of the RV world. I have yet to find a fused house bank except in my own trailer.

Tom

 

[SteveK]

2022 E-13 LITHIUM ION BATTERIES is 13 pages and is mainly Lithium Ion and not specific to LFP or LifePO4 definitions. Maybe the wording in 2025 revision will be more clear.

BTW, I have downloaded E11 & E13 and all mentioned other standards for free. Therefore I take back saying ABYC should share the info with the public freely.

 

[SteveK]

11.10.1.2 MAIN BATTERY OVERCURRENT PROTECTION
11.10.1.2.1 Overcurrent protection devices when installed as the main battery overcurrent protection device shall meet the requirements of E-11.10.1.6 or E-11.10.1.7
11.10.1.2.2 For batteries or battery banks with a rating of 2200 CCA or 500 amp hours or less, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating according to TABLE 3B
11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating as follows:
11.10.1.2.3.1 at least as great as the battery manufacturer’s short circuit rating,
or
11.10.1.2.3.2 20 kA at 125 VDC or higher, if a battery manufacturer’s short circuit rating exceeds 10 kA.
NOTE: For batteries in series/parallel configurations the short circuit current of the battery bank is calculated by adding the short circuit current values of the batteries connected in parallel, and the short circuit rating of the batteries connected in series is not added for this calculation (e.g., six 6 VDC batteries
are connected in series/parallel to create 12 VDC battery bank; if short circuit rating of a single battery equals 2400 A, the total calculated short circuit rating of the battery bank equals 7200 A).
11.10.1.2.4 Fuses, when used as main battery overcurrent protection, shall meet the ampere interrupting capacity (AIC) rating as stated in TABLE 3B
EXCEPTION: Fuses less than or equal to 30 amps in 12 V systems, 15 amps in 24 V systems, and 12 amps in 32 V systems.

 

[BDofMSP]

... It also sucks that pretty much nobody specified the short circuit current for their batteries, and as a result nearly all LFP batteries are also technically non-compliant. ...

So for the Epoch batteries that have gotten so much attention here, they say "Max Discharge Peak Current Amps: 500A (30 Seconds) , 1300A (1 Second)"

I assume that the 1300A doesn't qualify as a "short circuit current" rating?

 

[twistedtree]

So for the Epoch batteries that have gotten so much attention here, they say "Max Discharge Peak Current Amps: 500A (30 Seconds) , 1300A (1 Second)"

I assume that the 1300A doesn't qualify as a "short circuit current" rating?

No, and that opens up a whole other can of worms about just what is meant by the short circuit current when you have an internal BMS. I don't recall off hand whether language made it into the upcoming E-13, but the intent is that it's the short circuit current without any intervention by a BMS. It's a fault condition, and you have to assume a non-functional BMS.

 

[tpbrady]

No, and that opens up a whole other can of worms about just what is meant by the short circuit current when you have an internal BMS. I don't recall off hand whether language made it into the upcoming E-13, but the intent is that it's the short circuit current without any intervention by a BMS. It's a fault condition, and you have to assume a non-functional BMS.

Once opened a can of worms will only fit into a larger can. We are applying our standards to a Chinese product where standards are different if they exist at all.

 

[SteveK]

short circuit on my 100Ah batteries is => 500A and the BMS shuts down.
As TT said, what is the short circuit amps if the BMS does not shut down.

 

[luna]

With SteveK's inclusion of Note 2 to Table 3B, you cannot use the table for LFP batteries and what it appears that we are left with is the guidance that LFP "may require significantly higher AIC ratings." Not especially informative or comforting.

Unless there is some other text in the Standards, it appears that LFP batteries did not get the attention that they require with respect to AIC. Perhaps that helped drive the current upgrade to the Standards.

In the new, yet to be finalized version of E-11 we are told that we need a fuse with an AIC rating equal to 5000 Amps for every 100 Ah of battery capacity. I have a lot of confidence that the working minds of the ABYC E-11 Committee got it right.

If so, and Table 3B remains unchanged as it only applies to lead, the inclusion of LFP in the AIC requirements in a meaningful way has a huge effect on the fuses.

Think about it, a lead acid battery bank of 500 Ah requires a fuse with an AIC of only 5,000 Amps. The same 500 Ah battery bank using LFP requires a fuse with an AIC of 25,000 Amps. That's a 5 fold increase. This must be serious.

Those with LFP banks >200 Ah and only MRBF or similarly rated fuse may well be best served with a fuse upgrade.

 

[RobertLeatch]

Just circling back to solution mode, does something like this at the battery post (with then 2 wires to the common buzz bar) allow the required AIC rating to be split between each fuse?. For example, battery needs 15000A, each fuse has 10000A so a catastrophic short circut flows across both fuses and in spec.

 

[Delta Riverat]

All of the current in a LiFePO4 battery flows through the BMS. Otherwise it couldn't shut the battery down. So the "on" resistance of the power fets also adds to the internal resistance. Transistors can blow either open or closed, but there is still resistance even if closed. In order to get 10,000 amps on 12.7 volts you would need a resistance (total circuit) of less than 1.3 milliohms.

I just can't see that ever happening.

 

[luna]

If there are 2 fuses, are there 2 conductors? If so, is it possible that the external short is on only one conductor?

Even if there is only one conductor as you made a bus bar that connects it and the 2 fuses together, (a piece of copper plate with 3 holes in it) how do you propose to ensure that the current through both fuses is equal?

There are better/safer solutions.

 

[Marco Flamingo]

There are better/safer solutions.

And, oddly enough, often cheaper. It is interesting watching how folks are trying to make MRFB fuses the solution when limited to an AIC of 10k. I have them on the batteries for my 16' runabout with lead batteries. But they simply aren't the solution for a bank of LFP. The MRFB shown above is $67 and isn't likely to do whats needed.

Class T is sometimes close enough for a bank of LFP. Cost? I don't remember exactly, but IIRC they are somewhere around $75 and might do the job. They do make Class T with a 50K AIC, although for even more $$$$..

The solution I found was MCCB. DC breakers with a 50K AIC. True, most are made in China. But good ol American companies like Bussmann also sell them. And Eaton (which actually owns Bussmann). Don't tell anybody, but Eaton manufactures in China.

Right now, it takes some research to figure out better/safe/less expensive solutions. Lots easier to go with the common, costly, and close enough fuse.

 

[ksanders]

And, oddly enough, often cheaper. It is interesting watching how folks are trying to make MRFB fuses the solution when limited to an AIC of 10k. I have them on the batteries for my 16' runabout with lead batteries. But they simply aren't the solution for a bank of LFP. The MRFB shown above is $67 and isn't likely to do whats needed.

Class T is sometimes close enough for a bank of LFP. Cost? I don't remember exactly, but IIRC they are somewhere around $75 and might do the job. They do make Class T with a 50K AIC, although for even more $$$$..

The solution I found was MCCB. DC breakers with a 50K AIC. True, most are made in China. But good ol American companies like Bussmann also sell them. And Eaton (which actually owns Bussmann). Don't tell anybody, but Eaton manufactures in China.

Right now, it takes some research to figure out better/safe/less expensive solutions. Lots easier to go with the common, costly, and close enough fuse.

I like the MBRF. I like the idea, and as new standards are developed that require a higher AIC the MBRF market will develop higher capacity devices.

A MBRF protects at the source, rule #1 in the protection engineering world.

A MBRF minimizes extra cables by the very nature of it's design.

Right now today the Blue Seas MBRF is fully compliant with the published ABYC standards.

This is not a "second class" protection device. It does the job and it does it well.

 

[twistedtree]

All of the current in a LiFePO4 battery flows through the BMS. Otherwise it couldn't shut the battery down. So the "on" resistance of the power fets also adds to the internal resistance. Transistors can blow either open or closed, but there is still resistance even if closed. In order to get 10,000 amps on 12.7 volts you would need a resistance (total circuit) of less than 1.3 milliohms.

I just can't see that ever happening.

Maybe. The problem is that there is little to no hard data on this. My understanding is that FETs fail closed. And shortly after they vaporize, which results in a lot of people saying they fail open. Well, I suppose that’s right, eventually…. I suppose everything eventually fails open, with varying amounts of smoke and flames….

 

[Delta Riverat]

I agree and that's why I use them. Am I worried? No.

And after they vaporize (along with the fuse) there will be even a bigger air gap to quench the arc -

 

[Frosty]

So for the Epoch batteries that have gotten so much attention here, they say "Max Discharge Peak Current Amps: 500A (30 Seconds) , 1300A (1 Second)"

I assume that the 1300A doesn't qualify as a "short circuit current" rating?

That's the rating for how much you can "pull" from the battery with a load you want to power (on purpose, not via a short). The 30 seconds or 1 second means you can take that much power for a load, but only for shorter duration. There will usually also be a continuous load spec, obviously for fewer amps (since it can be continuous).

I like the MBRF.

A MBRF protects at the source, rule #1 in the protection engineering world.

This is not a "second class" protection device. It does the job and it does it well.

100% agreed! They are compact and tidy, and there is no unfused wire between the battery and the fuse. BUT, with LFP batteries, sadly, unless you have batteries of about 180ah or less apiece, their AIC rating is too small.

That's what got me. I have a 200ah battery and that is RIGHT ON THE EDGE. Hence I went Class T. I was able to keep the wire length very short between the battery and the Class T.... but those MRBF's are sweet.

@Marco Flamingo I quite like those MCCB's you researched and found. I remember that Lithionics 320ah battery (the one they have with an internal BMS) could come with a breaker that looked a lot like that. (You could also buy it without, but IIRC they said having it was part of their UL rating.) I didn't end up going with Lithionics so never had the breaker in hand. I do remember seeing that it required you to make/buy a special mounting. I think maybe it had to be mounted lying on its side? But don't quote me on that as I went in another mfgr. direction awhile ago.

 

[Marco Flamingo]

I think maybe it had to be mounted lying on its side?

The arc suppression chamber works best in a certain orientation. Remember the creepy electrical arc in the background of the mad scientist's laboratoratory? It arcs upwards (hence the name), based in part on the heat of the plasma. That arc, if generated inside a MCCB, rises into a chamber that immediately snuffs it out. So orientation is important.

As to MRBF fuses being ABYC aproved, absolutely not. MRBF fuses might be ABYC approved if apropriately used given the fuse's limitations (which for LFP batteries is quite limited). Class T is often the next step up. Still not ABYC approved in every application.

There is really no reason to believe that MRBF fuses will improve in the future such that they will have a 500A rating or a 20k AIC. There is only so much that can be done in a space the size of a sugar cube. Can a fuse that size have a rare earth magnet arc suppression chamber? No. How about a thermo-magnetic interrupt? No. If such electronic wizardry was possible, why not make the little ANG fuses 400A and 20k AIC? Turns out Bussmann knows that it can't be done.* Same with BlueSeas MRBF series topping out at 300A and 10K AIC. Size matters.

* Turns out some of those little ANG fuses have a 10,000 amp interupt rating, but only for 125V AC. AC is easy.

 

[ksanders]

The arc suppression chamber works best in a certain orientation. Remember the creepy electrical arc in the background of the mad scientist's laboratoratory? It arcs upwards (hence the name), based in part on the heat of the plasma. That arc, if generated inside a MCCB, rises into a chamber that immediately snuffs it out. So orientation is important.

As to MRBF fuses being ABYC aproved, absolutely not. MRBF fuses might be ABYC approved if apropriately used given the fuse's limitations (which for LFP batteries is quite limited). Class T is often the next step up. Still not ABYC approved in every application.

There is really no reason to believe that MRBF fuses will improve in the future such that they will have a 500A rating or a 20k AIC. There is only so much that can be done in a space the size of a sugar cube. Can a fuse that size have a rare earth magnet arc suppression chamber? No. How about a thermo-magnetic interrupt? No. If such electronic wizardry was possible, why not make the little ANG fuses 400A and 20k AIC? Turns out Bussmann knows that it can't be done.* Same with BlueSeas MRBF series topping out at 300A and 10K AIC. Size matters.

* Turns out some of those little ANG fuses have a 10,000 amp interupt rating, but only for 125V AC. AC is easy.

So I keep asking for a current ABYC publication that specifies a higher than 10,000 AIC rating for the largest LiFeP04 battery on the market today which is 460 AH.

Nobody has produced one. Yes there are proposed standards out there, but Proposed is not a standard, it is just as the name implies proposed for the future.

do you have different data substantiating your post?

 

[SteveK]

So I keep asking for a current ABYC publication that specifies a higher than 10,000 AIC rating for the largest LiFeP04 battery on the market today which is 460 AH.

Nobody has produced one. Yes there are proposed standards out there, but Proposed is not a standard, it is just as the name implies proposed for the future.

do you have different data substantiating your post?

These batteries contain a 500 amp fuse under the cover of the battery, just before the positive post of the battery. The fuse Epoch uses is from the EV market and carries an amp interrupt capability (AIC) of 50,000 amps. That rating means that with up to 50,000 amps flowing through the fuse, it will still successfully trip to an open and safe condition.

 

[ksanders]

These batteries contain a 500 amp fuse under the cover of the battery, just before the positive post of the battery. The fuse Epoch uses is from the EV market and carries an amp interrupt capability (AIC) of 50,000 amps. That rating means that with up to 50,000 amps flowing through the fuse, it will still successfully trip to an open and safe condition.
View attachment 163480

so this entire discussion is moot because at least the EPOCH batteries have an internal fuse?

Hmmm...

 

[SteveK]

CFriend fuse in the Epoch 460

 

[Iggy]

I am using 200A MBRF fuses on all 4 of my batteries. I am thinking of making them smaller. Plus a 400A T fuse for the whole bank. Each battery is rated, 150A max continues discharge and 200A max charge. My charger/Inverter only puts out 120A charging to all four batteries.

The way I look at it, and 4 years ago the MBYC standards where not clear on Li banks. on install. It also gets confusing, if your not a lawyer. Roughly my boat pulls about 40A when running. Worst case, lets say 120A. So I would rather go with smaller fuses, than what the bank or battery is truly rated for.

Cable size is another factor in all this, but. This all gets confusing and gives me a headache trying to read this whole thread or the topic. So I based the fuses more on the load then what the batteries can be rated for. In other words. Small fuses = more protection in my mind. Maybe I am wrong?

 

[CharlieO.]

I am using 200A MBRF fuses on all 4 of my batteries. I am thinking of making them smaller. Plus a 400A T fuse for the whole bank. Each battery is rated, 150A max continues discharge and 200A max charge. My charger/charger inverter only puts out 120A charging to all four batteries.

The way I look at it, and 4 years ago the MBYC standards where not clear on Li banks. on install. It also gets confusing, if your not a lawyer. Roughly my boat pulls about 40A when running. Worst case, lets say 120A. So I would rather go with smaller fuses, than what the bank or battery is truly rated for.

Cable size is another factor in all this, but. This all gets confusing and gives me a headache trying to read this whole thread or the topic. So I based the fuses more on the load then what the batteries can be rated for. In other words. Small fuses = more protection in my mind. Maybe I am wrong?

Yes, I've been trying to follow along also. Based on this thread I think I would like to change out to the MBRF fuses on my batteries, I have 2 - 100a batteries and I've been trying to decipher which size fuses I should install. Actually, I only have one battery right now but will be adding a second one.

I was also wondering if I should be sizing the fuse based on the potential battery output or based upon my projected load plus a healthy margin? We are not a power-hungry boat.

 

[luna]

Post deleted

 

[J.T kearney]

Yes, I've been trying to follow along also. Based on this thread I think I would like to change out to the MBRF fuses on my batteries, I have 2 - 100a batteries and I've been trying to decipher which size fuses I should install. Actually, I only have one battery right now but will be adding a second one.

I was also wondering if I should be sizing the fuse based on the potential battery output or based upon my projected load plus a healthy margin? We are not a power-hungry boat.

Charlie O
My 100 amp Epochs (4) batteries are set up with a MRBF (10000 AIC) 125 amp fuses on each battery. 2/0 cables to buss bar, then to a 250 amp class T fuse. Minimal electrical needs on boat at this time with small solar array (400 watt bi facial panels)install this spring.
From what I've been reading your fuse is to protect your cabling.
Cheers J.T.

 

[luna]

I'll try that again.

Based only on the information found in this Thread, I would agree with your statement shown below if we are dealing with certain lead batteries, but not any type of LFP battery.

Right now today the Blue Seas MBRF is fully compliant with the published ABYC standards.

I also have my doubts about someone providing what you have asked here.

So I keep asking for a current ABYC publication that specifies a higher than 10,000 AIC rating for the largest LiFeP04 battery on the market today which is 460 AH.

Nobody has produced one.

The reasoning for both of my positions is the same.
E-11's Table 3B, Note 2 clearly states that the table is not applicable for use with LFP batteries.

Unless there is something else in the current Standard that addresses this exclusion of LFP, we may be left with no guidance on LFP's AIC requirements.

 

[SteveK]

I am using 200A MBRF fuses on all 4 of my batteries. I am thinking of making them smaller. Plus a 400A T fuse for the whole bank. Each battery is rated, 150A max continues discharge and 200A max charge. My charger/Inverter only puts out 120A charging to all four batteries.

The way I look at it, and 4 years ago the MBYC standards where not clear on Li banks. on install. It also gets confusing, if your not a lawyer. Roughly my boat pulls about 40A when running. Worst case, lets say 120A. So I would rather go with smaller fuses, than what the bank or battery is truly rated for.

Cable size is another factor in all this, but. This all gets confusing and gives me a headache trying to read this whole thread or the topic. So I based the fuses more on the load then what the batteries can be rated for. In other words. Small fuses = more protection in my mind. Maybe I am wrong?

Do you have 4-200Ah batteries for a total of 800Ah?

 

[ksanders]

So...

We all need to understand something. When you examine a installation standard, IE the NEC for land based or the AYBC for marine based systems, you take a snapshot in time. You examine the current standard at the time of the installation, and you make your installation compliant with that standard. You do not need to predict the future, you need to install your equipment today, using todays standards.

Another very important concept is protection at the source. Remember that any fault occurring behind your protective device will not be in your zone of protection. People tend to not think about this on parallel battery installations, and almost all LiFeP04 installations are parallel batteries, IE parallel current sources.

Imagine for a moment that one of your batteries shorts internally and starts drawing current from the adjacent batteries. Your fuse on the buss bar is not going to clear that fault. Now you have a runaway situation and all the problems that can create, like fire. This is the case for protection at the battery terminal.

The next concept is multilevel protection. The Best example of this I can think of is a parallel bank with each battery being protected, and then a larger fuse in series with the load. This makes for two zones of protection. The first is from the batteries to the buss bar, including the batteries. The protective device for this is the battery terminal fuses. The next zone of protection is from the buss bar fuse out to the loads.

The idea is if there is a fault downstream of the larger fuse then it's that fuses job to clear the fault. If that fuse fails for any reason the battery terminal fuses are the backup.

This is how your utility power grid is protected. The lines going out to your neighborhood are each protected by a distribution breaker in the substation. There is another breaker on the transformer that provides backup, and yet another breaker on the transmission line feeding the substation. This creates a overlapping protection scheme.

 

[SteveK]

@ksanders
But the BMS is supposed to shut down when you description occurs. That should isolate the offending battery from the others.
Yes a lot of new possibilities from lead